2002-08-12 Martin Baulig <martin@gnome.org>

[mono.git] / mcs / mcs / ecore.cs

//
// ecore.cs: Core of the Expression representation for the intermediate tree.
//
// Author:
//   Miguel de Icaza (miguel@ximian.com)
//
// (C) 2001 Ximian, Inc.
//
//

namespace Mono.CSharp {
        using System;
        using System.Collections;
        using System.Diagnostics;
        using System.Reflection;
        using System.Reflection.Emit;
        using System.Text;

        /// <remarks>
        ///   The ExprClass class contains the is used to pass the 
        ///   classification of an expression (value, variable, namespace,
        ///   type, method group, property access, event access, indexer access,
        ///   nothing).
        /// </remarks>
        public enum ExprClass : byte {
                Invalid,
                
                Value,
                Variable,
                Namespace,
                Type,
                MethodGroup,
                PropertyAccess,
                EventAccess,
                IndexerAccess,
                Nothing, 
        }

        /// <remarks>
        ///   This is used to tell Resolve in which types of expressions we're
        ///   interested.
        /// </remarks>
        [Flags]
        public enum ResolveFlags {
                // Returns Value, Variable, PropertyAccess, EventAccess or IndexerAccess.
                VariableOrValue         = 1,

                // Returns a type expression.
                Type                    = 2,

                // Returns a method group.
                MethodGroup             = 4,

                // Allows SimpleNames to be returned.
                // This is used by MemberAccess to construct long names that can not be
                // partially resolved (namespace-qualified names for example).
                SimpleName              = 8,

                // Mask of all the expression class flags.
                MaskExprClass           = 15,

                // Disable control flow analysis while resolving the expression.
                // This is used when resolving the instance expression of a field expression.
                DisableFlowAnalysis     = 16
        }

        //
        // This is just as a hint to AddressOf of what will be done with the
        // address.
        [Flags]
        public enum AddressOp {
                Store = 1,
                Load  = 2,
                LoadStore = 3
        };
        
        /// <summary>
        ///   This interface is implemented by variables
        /// </summary>
        public interface IMemoryLocation {
                /// <summary>
                ///   The AddressOf method should generate code that loads
                ///   the address of the object and leaves it on the stack.
                ///
                ///   The `mode' argument is used to notify the expression
                ///   of whether this will be used to read from the address or
                ///   write to the address.
                ///
                ///   This is just a hint that can be used to provide good error
                ///   reporting, and should have no other side effects. 
                /// </summary>
                void AddressOf (EmitContext ec, AddressOp mode);
        }

        /// <summary>
        ///   This interface is implemented by variables
        /// </summary>
        public interface IVariable {
                /// <summary>
                ///   Checks whether the variable has already been assigned at
                ///   the current position of the method's control flow and
                ///   reports an appropriate error message if not.
                ///
                ///   If the variable is a struct, then this call checks whether
                ///   all of its fields (including all private ones) have been
                ///   assigned.
                /// </summary>
                bool IsAssigned (EmitContext ec, Location loc);

                /// <summary>
                ///   Checks whether field `name' in this struct has been assigned.
                /// </summary>
                bool IsFieldAssigned (EmitContext ec, string name, Location loc);

                /// <summary>
                ///   Tells the flow analysis code that the variable has already
                ///   been assigned at the current code position.
                ///
                ///   If the variable is a struct, this call marks all its fields
                ///   (including private fields) as being assigned.
                /// </summary>
                void SetAssigned (EmitContext ec);

                /// <summary>
                ///   Tells the flow analysis code that field `name' in this struct
                ///   has already been assigned atthe current code position.
                /// </summary>
                void SetFieldAssigned (EmitContext ec, string name);
        }

        /// <summary>
        ///   This interface denotes an expression which evaluates to a member
        ///   of a struct or a class.
        /// </summary>
        public interface IMemberExpr
        {
                /// <summary>
                ///   The name of this member.
                /// </summary>
                string Name {
                        get;
                }

                /// <summary>
                ///   Whether this is an instance member.
                /// </summary>
                bool IsInstance {
                        get;
                }

                /// <summary>
                ///   Whether this is a static member.
                /// </summary>
                bool IsStatic {
                        get;
                }

                /// <summary>
                ///   The instance expression associated with this member, if it's a
                ///   non-static member.
                /// </summary>
                Expression InstanceExpression {
                        get; set;
                }
        }

        /// <summary>
        ///   Expression which resolves to a type.
        /// </summary>
        public interface ITypeExpression
        {
                /// <summary>
                ///   Resolve the expression, but only lookup types.
                /// </summary>
                Expression DoResolveType (EmitContext ec);
        }

        /// <remarks>
        ///   Base class for expressions
        /// </remarks>
        public abstract class Expression {
                public ExprClass eclass;
                protected Type type;
                protected Location loc;
                
                public Type Type {
                        get {
                                return type;
                        }

                        set {
                                type = value;
                        }
                }

                public Location Location {
                        get {
                                return loc;
                        }
                }

                /// <summary>
                ///   Utility wrapper routine for Error, just to beautify the code
                /// </summary>
                public void Error (int error, string s)
                {
                        if (!Location.IsNull (loc))
                                Report.Error (error, loc, s);
                        else
                                Report.Error (error, s);
                }

                /// <summary>
                ///   Utility wrapper routine for Warning, just to beautify the code
                /// </summary>
                public void Warning (int warning, string s)
                {
                        if (!Location.IsNull (loc))
                                Report.Warning (warning, loc, s);
                        else
                                Report.Warning (warning, s);
                }

                /// <summary>
                ///   Utility wrapper routine for Warning, only prints the warning if
                ///   warnings of level `level' are enabled.
                /// </summary>
                public void Warning (int warning, int level, string s)
                {
                        if (level <= RootContext.WarningLevel)
                                Warning (warning, s);
                }

                static public void Error_CannotConvertType (Location loc, Type source, Type target)
                {
                        Report.Error (30, loc, "Cannot convert type '" +
                                      TypeManager.CSharpName (source) + "' to '" +
                                      TypeManager.CSharpName (target) + "'");
                }

                /// <summary>
                ///   Performs semantic analysis on the Expression
                /// </summary>
                ///
                /// <remarks>
                ///   The Resolve method is invoked to perform the semantic analysis
                ///   on the node.
                ///
                ///   The return value is an expression (it can be the
                ///   same expression in some cases) or a new
                ///   expression that better represents this node.
                ///   
                ///   For example, optimizations of Unary (LiteralInt)
                ///   would return a new LiteralInt with a negated
                ///   value.
                ///   
                ///   If there is an error during semantic analysis,
                ///   then an error should be reported (using Report)
                ///   and a null value should be returned.
                ///   
                ///   There are two side effects expected from calling
                ///   Resolve(): the the field variable "eclass" should
                ///   be set to any value of the enumeration
                ///   `ExprClass' and the type variable should be set
                ///   to a valid type (this is the type of the
                ///   expression).
                /// </remarks>
                public abstract Expression DoResolve (EmitContext ec);

                public virtual Expression DoResolveLValue (EmitContext ec, Expression right_side)
                {
                        return DoResolve (ec);
                }
                
                /// <summary>
                ///   Resolves an expression and performs semantic analysis on it.
                /// </summary>
                ///
                /// <remarks>
                ///   Currently Resolve wraps DoResolve to perform sanity
                ///   checking and assertion checking on what we expect from Resolve.
                /// </remarks>
                public Expression Resolve (EmitContext ec, ResolveFlags flags)
                {
                        // Are we doing a types-only search ?
                        if ((flags & ResolveFlags.MaskExprClass) == ResolveFlags.Type) {
                                ITypeExpression type_expr = this as ITypeExpression;

                                if (type_expr == null)
                                        return null;

                                return type_expr.DoResolveType (ec);
                        }

                        bool old_do_flow_analysis = ec.DoFlowAnalysis;
                        if ((flags & ResolveFlags.DisableFlowAnalysis) != 0)
                                ec.DoFlowAnalysis = false;

                        Expression e;
                        if (this is SimpleName)
                                e = ((SimpleName) this).DoResolveAllowStatic (ec);
                        else 
                                e = DoResolve (ec);

                        ec.DoFlowAnalysis = old_do_flow_analysis;

                        if (e == null)
                                return null;

                        if (e is SimpleName){
                                SimpleName s = (SimpleName) e;

                                if ((flags & ResolveFlags.SimpleName) == 0) {
                                        Report.Error (
                                                103, loc,
                                                "The name `" + s.Name + "' could not be found in `" +
                                                ec.DeclSpace.Name + "'");
                                        return null;
                                }

                                return s;
                        }

                        if ((e is TypeExpr) || (e is ComposedCast)) {
                                if ((flags & ResolveFlags.Type) == 0) {
                                        e.Error118 (flags);
                                        return null;
                                }

                                return e;
                        }

                        switch (e.eclass) {
                        case ExprClass.Type:
                                if ((flags & ResolveFlags.VariableOrValue) == 0) {
                                        e.Error118 (flags);
                                        return null;
                                }
                                break;

                        case ExprClass.MethodGroup:
                                if ((flags & ResolveFlags.MethodGroup) == 0) {
                                        ((MethodGroupExpr) e).ReportUsageError ();
                                        return null;
                                }
                                break;

                        case ExprClass.Value:
                        case ExprClass.Variable:
                        case ExprClass.PropertyAccess:
                        case ExprClass.EventAccess:
                        case ExprClass.IndexerAccess:
                                if ((flags & ResolveFlags.VariableOrValue) == 0) {
                                        e.Error118 (flags);
                                        return null;
                                }
                                break;

                        default:
                                throw new Exception ("Expression " + e.GetType () +
                                                     " ExprClass is Invalid after resolve");
                        }

                        if (e.type == null)
                                throw new Exception (
                                        "Expression " + e.GetType () +
                                        " did not set its type after Resolve\n" +
                                        "called from: " + this.GetType ());

                        return e;
                }

                /// <summary>
                ///   Resolves an expression and performs semantic analysis on it.
                /// </summary>
                public Expression Resolve (EmitContext ec)
                {
                        return Resolve (ec, ResolveFlags.VariableOrValue);
                }

                /// <summary>
                ///   Resolves an expression for LValue assignment
                /// </summary>
                ///
                /// <remarks>
                ///   Currently ResolveLValue wraps DoResolveLValue to perform sanity
                ///   checking and assertion checking on what we expect from Resolve
                /// </remarks>
                public Expression ResolveLValue (EmitContext ec, Expression right_side)
                {
                        Expression e = DoResolveLValue (ec, right_side);

                        if (e != null){
                                if (e is SimpleName){
                                        SimpleName s = (SimpleName) e;

                                        Report.Error (
                                                103, loc,
                                                "The name `" + s.Name + "' could not be found in `" +
                                                ec.DeclSpace.Name + "'");
                                        return null;
                                }

                                if (e.eclass == ExprClass.Invalid)
                                        throw new Exception ("Expression " + e +
                                                             " ExprClass is Invalid after resolve");

                                if (e.eclass == ExprClass.MethodGroup) {
                                        ((MethodGroupExpr) e).ReportUsageError ();
                                        return null;
                                }

                                if (e.type == null)
                                        throw new Exception ("Expression " + e +
                                                             " did not set its type after Resolve");
                        }

                        return e;
                }
                
                /// <summary>
                ///   Emits the code for the expression
                /// </summary>
                ///
                /// <remarks>
                ///   The Emit method is invoked to generate the code
                ///   for the expression.  
                /// </remarks>
                public abstract void Emit (EmitContext ec);

                /// <summary>
                ///   Protected constructor.  Only derivate types should
                ///   be able to be created
                /// </summary>

                protected Expression ()
                {
                        eclass = ExprClass.Invalid;
                        type = null;
                }

                /// <summary>
                ///   Returns a literalized version of a literal FieldInfo
                /// </summary>
                ///
                /// <remarks>
                ///   The possible return values are:
                ///      IntConstant, UIntConstant
                ///      LongLiteral, ULongConstant
                ///      FloatConstant, DoubleConstant
                ///      StringConstant
                ///
                ///   The value returned is already resolved.
                /// </remarks>
                public static Constant Constantify (object v, Type t)
                {
                        if (t == TypeManager.int32_type)
                                return new IntConstant ((int) v);
                        else if (t == TypeManager.uint32_type)
                                return new UIntConstant ((uint) v);
                        else if (t == TypeManager.int64_type)
                                return new LongConstant ((long) v);
                        else if (t == TypeManager.uint64_type)
                                return new ULongConstant ((ulong) v);
                        else if (t == TypeManager.float_type)
                                return new FloatConstant ((float) v);
                        else if (t == TypeManager.double_type)
                                return new DoubleConstant ((double) v);
                        else if (t == TypeManager.string_type)
                                return new StringConstant ((string) v);
                        else if (t == TypeManager.short_type)
                                return new ShortConstant ((short)v);
                        else if (t == TypeManager.ushort_type)
                                return new UShortConstant ((ushort)v);
                        else if (t == TypeManager.sbyte_type)
                                return new SByteConstant (((sbyte)v));
                        else if (t == TypeManager.byte_type)
                                return new ByteConstant ((byte)v);
                        else if (t == TypeManager.char_type)
                                return new CharConstant ((char)v);
                        else if (t == TypeManager.bool_type)
                                return new BoolConstant ((bool) v);
                        else if (TypeManager.IsEnumType (t)){
                                Constant e = Constantify (v, TypeManager.TypeToCoreType (v.GetType ()));

                                return new EnumConstant (e, t);
                        } else
                                throw new Exception ("Unknown type for constant (" + t +
                                                     "), details: " + v);
                }

                /// <summary>
                ///   Returns a fully formed expression after a MemberLookup
                /// </summary>
                public static Expression ExprClassFromMemberInfo (EmitContext ec, MemberInfo mi, Location loc)
                {
                        if (mi is EventInfo)
                                return new EventExpr ((EventInfo) mi, loc);
                        else if (mi is FieldInfo)
                                return new FieldExpr ((FieldInfo) mi, loc);
                        else if (mi is PropertyInfo)
                                return new PropertyExpr ((PropertyInfo) mi, loc);
                        else if (mi is Type){
                                return new TypeExpr ((System.Type) mi, loc);
                        }

                        return null;
                }

                //
                // FIXME: Probably implement a cache for (t,name,current_access_set)?
                //
                // This code could use some optimizations, but we need to do some
                // measurements.  For example, we could use a delegate to `flag' when
                // something can not any longer be a method-group (because it is something
                // else).
                //
                // Return values:
                //     If the return value is an Array, then it is an array of
                //     MethodBases
                //   
                //     If the return value is an MemberInfo, it is anything, but a Method
                //
                //     null on error.
                //
                // FIXME: When calling MemberLookup inside an `Invocation', we should pass
                // the arguments here and have MemberLookup return only the methods that
                // match the argument count/type, unlike we are doing now (we delay this
                // decision).
                //
                // This is so we can catch correctly attempts to invoke instance methods
                // from a static body (scan for error 120 in ResolveSimpleName).
                //
                //
                // FIXME: Potential optimization, have a static ArrayList
                //

                public static Expression MemberLookup (EmitContext ec, Type t, string name,
                                                       MemberTypes mt, BindingFlags bf, Location loc)
                {
                        return MemberLookup (ec, ec.ContainerType, t, name, mt, bf, loc);
                }

                public static Expression MemberLookup (EmitContext ec, Type invocation_type, Type t,
                                                       string name, MemberTypes mt, BindingFlags bf,
                                                       Location loc)
                {
                        MemberInfo [] mi = TypeManager.MemberLookup (invocation_type, t, mt, bf, name);

                        if (mi == null)
                                return null;

                        int count = mi.Length;

                        if (count > 1)
                                return new MethodGroupExpr (mi, loc);

                        if (mi [0] is MethodBase)
                                return new MethodGroupExpr (mi, loc);

                        return ExprClassFromMemberInfo (ec, mi [0], loc);
                }

                public const MemberTypes AllMemberTypes =
                        MemberTypes.Constructor |
                        MemberTypes.Event       |
                        MemberTypes.Field       |
                        MemberTypes.Method      |
                        MemberTypes.NestedType  |
                        MemberTypes.Property;
                
                public const BindingFlags AllBindingFlags =
                        BindingFlags.Public |
                        BindingFlags.Static |
                        BindingFlags.Instance;

                public static Expression MemberLookup (EmitContext ec, Type t, string name, Location loc)
                {
                        return MemberLookup (ec, ec.ContainerType, t, name,
                                             AllMemberTypes, AllBindingFlags, loc);
                }

                public static Expression MethodLookup (EmitContext ec, Type t, string name, Location loc)
                {
                        return MemberLookup (ec, ec.ContainerType, t, name,
                                             MemberTypes.Method, AllBindingFlags, loc);
                }

                /// <summary>
                ///   This is a wrapper for MemberLookup that is not used to "probe", but
                ///   to find a final definition.  If the final definition is not found, we
                ///   look for private members and display a useful debugging message if we
                ///   find it.
                /// </summary>
                public static Expression MemberLookupFinal (EmitContext ec, Type t, string name, 
                                                            Location loc)
                {
                        return MemberLookupFinal (ec, t, name, MemberTypes.Method, AllBindingFlags, loc);
                }

                public static Expression MemberLookupFinal (EmitContext ec, Type t, string name,
                                                            MemberTypes mt, BindingFlags bf, Location loc)
                {
                        Expression e;

                        int errors = Report.Errors;

                        e = MemberLookup (ec, ec.ContainerType, t, name, mt, bf, loc);

                        if (e != null)
                                return e;

                        // Error has already been reported.
                        if (errors < Report.Errors)
                                return null;
                        
                        e = MemberLookup (ec, t, name, AllMemberTypes,
                                          AllBindingFlags | BindingFlags.NonPublic, loc);
                        if (e == null){
                                Report.Error (
                                        117, loc, "`" + t + "' does not contain a definition " +
                                        "for `" + name + "'");
                        } else {
                                Report.Error (
                                        122, loc, "`" + t + "." + name +
                                        "' is inaccessible due to its protection level");
                        }
                        
                        return null;
                }

                static public MemberInfo GetFieldFromEvent (EventExpr event_expr)
                {
                        EventInfo ei = event_expr.EventInfo;

                        return TypeManager.GetPrivateFieldOfEvent (ei);
                }
                
                static EmptyExpression MyEmptyExpr;
                static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
                {
                        Type expr_type = expr.Type;

                        if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
                                // if we are a method group, emit a warning

                                expr.Emit (null);
                        }
                        
                        if (target_type == TypeManager.object_type) {
                                //
                                // A pointer type cannot be converted to object
                                // 
                                if (expr_type.IsPointer)
                                        return null;

                                if (expr_type.IsValueType)
                                        return new BoxedCast (expr);
                                if (expr_type.IsClass || expr_type.IsInterface)
                                        return new EmptyCast (expr, target_type);
                        } else if (expr_type.IsSubclassOf (target_type)) {
                                return new EmptyCast (expr, target_type);
                        } else {

                                // This code is kind of mirrored inside StandardConversionExists
                                // with the small distinction that we only probe there
                                //
                                // Always ensure that the code here and there is in sync
                                
                                // from the null type to any reference-type.
                                if (expr is NullLiteral && !target_type.IsValueType)
                                        return new EmptyCast (expr, target_type);

                                // from any class-type S to any interface-type T.
                                if (expr_type.IsClass && target_type.IsInterface) {
                                        if (TypeManager.ImplementsInterface (expr_type, target_type))
                                                return new EmptyCast (expr, target_type);
                                        else
                                                return null;
                                }

                                // from any interface type S to interface-type T.
                                if (expr_type.IsInterface && target_type.IsInterface) {

                                        if (TypeManager.ImplementsInterface (expr_type, target_type))
                                                return new EmptyCast (expr, target_type);
                                        else
                                                return null;
                                }
                                
                                // from an array-type S to an array-type of type T
                                if (expr_type.IsArray && target_type.IsArray) {
                                        if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {

                                                Type expr_element_type = expr_type.GetElementType ();

                                                if (MyEmptyExpr == null)
                                                        MyEmptyExpr = new EmptyExpression ();
                                                
                                                MyEmptyExpr.SetType (expr_element_type);
                                                Type target_element_type = target_type.GetElementType ();

                                                if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
                                                        if (StandardConversionExists (MyEmptyExpr,
                                                                                      target_element_type))
                                                                return new EmptyCast (expr, target_type);
                                        }
                                }
                                
                                
                                // from an array-type to System.Array
                                if (expr_type.IsArray && target_type == TypeManager.array_type)
                                        return new EmptyCast (expr, target_type);
                                
                                // from any delegate type to System.Delegate
                                if (expr_type.IsSubclassOf (TypeManager.delegate_type) &&
                                    target_type == TypeManager.delegate_type)
                                        return new EmptyCast (expr, target_type);
                                        
                                // from any array-type or delegate type into System.ICloneable.
                                if (expr_type.IsArray || expr_type.IsSubclassOf (TypeManager.delegate_type))
                                        if (target_type == TypeManager.icloneable_type)
                                                return new EmptyCast (expr, target_type);
                                
                                return null;

                        }
                        
                        return null;
                }

                /// <summary>
                ///   Handles expressions like this: decimal d; d = 1;
                ///   and changes them into: decimal d; d = new System.Decimal (1);
                /// </summary>
                static Expression InternalTypeConstructor (EmitContext ec, Expression expr, Type target)
                {
                        ArrayList args = new ArrayList ();

                        args.Add (new Argument (expr, Argument.AType.Expression));

                        Expression ne = new New (new TypeExpr (target, Location.Null), args, Location.Null);

                        return ne.Resolve (ec);
                }

                /// <summary>
                ///   Implicit Numeric Conversions.
                ///
                ///   expr is the expression to convert, returns a new expression of type
                ///   target_type or null if an implicit conversion is not possible.
                /// </summary>
                static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
                                                                    Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
                        
                        //
                        // Attempt to do the implicit constant expression conversions

                        if (expr is IntConstant){
                                Expression e;
                                
                                e = TryImplicitIntConversion (target_type, (IntConstant) expr);

                                if (e != null)
                                        return e;
                        } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
                                //
                                // Try the implicit constant expression conversion
                                // from long to ulong, instead of a nice routine,
                                // we just inline it
                                //
                                long v = ((LongConstant) expr).Value;
                                if (v > 0)
                                        return new ULongConstant ((ulong) v);
                        }

                        //
                        // If we have an enumeration, extract the underlying type,
                        // use this during the comparission, but wrap around the original
                        // target_type
                        //
                        Type real_target_type = target_type;

                        if (TypeManager.IsEnumType (real_target_type))
                                real_target_type = TypeManager.EnumToUnderlying (real_target_type);

                        if (expr_type == real_target_type)
                                return new EmptyCast (expr, target_type);
                        
                        if (expr_type == TypeManager.sbyte_type){
                                //
                                // From sbyte to short, int, long, float, double.
                                //
                                if (real_target_type == TypeManager.int32_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (real_target_type == TypeManager.short_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.byte_type){
                                //
                                // From byte to short, ushort, int, uint, long, ulong, float, double
                                // 
                                if ((real_target_type == TypeManager.short_type) ||
                                    (real_target_type == TypeManager.ushort_type) ||
                                    (real_target_type == TypeManager.int32_type) ||
                                    (real_target_type == TypeManager.uint32_type))
                                        return new EmptyCast (expr, target_type);

                                if (real_target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.short_type){
                                //
                                // From short to int, long, float, double
                                // 
                                if (real_target_type == TypeManager.int32_type)
                                        return new EmptyCast (expr, target_type);
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.ushort_type){
                                //
                                // From ushort to int, uint, long, ulong, float, double
                                //
                                if (real_target_type == TypeManager.uint32_type)
                                        return new EmptyCast (expr, target_type);

                                if (real_target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (real_target_type == TypeManager.int32_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.int32_type){
                                //
                                // From int to long, float, double
                                //
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.uint32_type){
                                //
                                // From uint to long, ulong, float, double
                                //
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (real_target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R4);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.int64_type){
                                //
                                // From long/ulong to float, double
                                //
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);     
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.uint64_type){
                                //
                                // From ulong to float, double
                                //
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R4);        
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.char_type){
                                //
                                // From char to ushort, int, uint, long, ulong, float, double
                                // 
                                if ((real_target_type == TypeManager.ushort_type) ||
                                    (real_target_type == TypeManager.int32_type) ||
                                    (real_target_type == TypeManager.uint32_type))
                                        return new EmptyCast (expr, target_type);
                                if (real_target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.float_type){
                                //
                                // float to double
                                //
                                if (real_target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                        }

                        return null;
                }

                //
                // Tests whether an implicit reference conversion exists between expr_type
                // and target_type
                //
                public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
                {
                        Type expr_type = expr.Type;
                        
                        //
                        // This is the boxed case.
                        //
                        if (target_type == TypeManager.object_type) {
                                if ((expr_type.IsClass) ||
                                    (expr_type.IsValueType) ||
                                    (expr_type.IsInterface))
                                        return true;
                                
                        } else if (expr_type.IsSubclassOf (target_type)) {
                                return true;
                                
                        } else {
                                // Please remember that all code below actually comes
                                // from ImplicitReferenceConversion so make sure code remains in sync
                                
                                // from any class-type S to any interface-type T.
                                if (expr_type.IsClass && target_type.IsInterface) {
                                        if (TypeManager.ImplementsInterface (expr_type, target_type))
                                                return true;
                                }
                                
                                // from any interface type S to interface-type T.
                                if (expr_type.IsInterface && target_type.IsInterface)
                                        if (TypeManager.ImplementsInterface (expr_type, target_type))
                                                return true;
                                
                                // from an array-type S to an array-type of type T
                                if (expr_type.IsArray && target_type.IsArray) {
                                        if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
                                                
                                                Type expr_element_type = expr_type.GetElementType ();

                                                if (MyEmptyExpr == null)
                                                        MyEmptyExpr = new EmptyExpression ();
                                                
                                                MyEmptyExpr.SetType (expr_element_type);
                                                Type target_element_type = target_type.GetElementType ();
                                                
                                                if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
                                                        if (StandardConversionExists (MyEmptyExpr,
                                                                                      target_element_type))
                                                                return true;
                                        }
                                }
                                
                                // from an array-type to System.Array
                                if (expr_type.IsArray && (target_type == TypeManager.array_type))
                                        return true;
                                
                                // from any delegate type to System.Delegate
                                if (expr_type.IsSubclassOf (TypeManager.delegate_type) &&
                                    target_type == TypeManager.delegate_type)
                                        if (target_type.IsAssignableFrom (expr_type))
                                                return true;
                                        
                                // from any array-type or delegate type into System.ICloneable.
                                if (expr_type.IsArray || expr_type.IsSubclassOf (TypeManager.delegate_type))
                                        if (target_type == TypeManager.icloneable_type)
                                                return true;
                                
                                // from the null type to any reference-type.
                                if (expr is NullLiteral && !target_type.IsValueType &&
                                    !TypeManager.IsEnumType (target_type))
                                        return true;
                                
                        }

                        return false;
                }

                /// <summary>
                ///  Same as StandardConversionExists except that it also looks at
                ///  implicit user defined conversions - needed for overload resolution
                /// </summary>
                public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
                {
                        if (StandardConversionExists (expr, target_type) == true)
                                return true;

                        Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);

                        if (dummy != null)
                                return true;

                        return false;
                }
                
                /// <summary>
                ///  Determines if a standard implicit conversion exists from
                ///  expr_type to target_type
                /// </summary>
                public static bool StandardConversionExists (Expression expr, Type target_type)
                {
                        Type expr_type = expr.Type;
                        
                        if (expr_type == target_type)
                                return true;

                        // First numeric conversions 

                        if (expr_type == TypeManager.sbyte_type){
                                //
                                // From sbyte to short, int, long, float, double.
                                //
                                if ((target_type == TypeManager.int32_type) || 
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type)  ||
                                    (target_type == TypeManager.short_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                
                        } else if (expr_type == TypeManager.byte_type){
                                //
                                // From byte to short, ushort, int, uint, long, ulong, float, double
                                // 
                                if ((target_type == TypeManager.short_type) ||
                                    (target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.uint32_type) ||
                                    (target_type == TypeManager.uint64_type) ||
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
        
                        } else if (expr_type == TypeManager.short_type){
                                //
                                // From short to int, long, float, double
                                // 
                                if ((target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                        
                        } else if (expr_type == TypeManager.ushort_type){
                                //
                                // From ushort to int, uint, long, ulong, float, double
                                //
                                if ((target_type == TypeManager.uint32_type) ||
                                    (target_type == TypeManager.uint64_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                    
                        } else if (expr_type == TypeManager.int32_type){
                                //
                                // From int to long, float, double
                                //
                                if ((target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                        
                        } else if (expr_type == TypeManager.uint32_type){
                                //
                                // From uint to long, ulong, float, double
                                //
                                if ((target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.uint64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                        
                        } else if ((expr_type == TypeManager.uint64_type) ||
                                   (expr_type == TypeManager.int64_type)) {
                                //
                                // From long/ulong to float, double
                                //
                                if ((target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                    
                        } else if (expr_type == TypeManager.char_type){
                                //
                                // From char to ushort, int, uint, long, ulong, float, double
                                // 
                                if ((target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.uint32_type) ||
                                    (target_type == TypeManager.uint64_type) ||
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;

                        } else if (expr_type == TypeManager.float_type){
                                //
                                // float to double
                                //
                                if (target_type == TypeManager.double_type)
                                        return true;
                        }       
                        
                        if (ImplicitReferenceConversionExists (expr, target_type))
                                return true;
                        
                        if (expr is IntConstant){
                                int value = ((IntConstant) expr).Value;

                                if (target_type == TypeManager.sbyte_type){
                                        if (value >= SByte.MinValue && value <= SByte.MaxValue)
                                                return true;
                                } else if (target_type == TypeManager.byte_type){
                                        if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
                                                return true;
                                } else if (target_type == TypeManager.short_type){
                                        if (value >= Int16.MinValue && value <= Int16.MaxValue)
                                                return true;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
                                                return true;
                                } else if (target_type == TypeManager.uint32_type){
                                        if (value >= 0)
                                                return true;
                                } else if (target_type == TypeManager.uint64_type){
                                         //
                                         // we can optimize this case: a positive int32
                                         // always fits on a uint64.  But we need an opcode
                                         // to do it.
                                         //
                                        if (value >= 0)
                                                return true;
                                }
                                
                                if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
                                        return true;
                        }

                        if (expr is LongConstant && target_type == TypeManager.uint64_type){
                                //
                                // Try the implicit constant expression conversion
                                // from long to ulong, instead of a nice routine,
                                // we just inline it
                                //
                                long v = ((LongConstant) expr).Value;
                                if (v > 0)
                                        return true;
                        }
                        
                        if (target_type.IsSubclassOf (TypeManager.enum_type) && expr is IntLiteral){
                                IntLiteral i = (IntLiteral) expr;

                                if (i.Value == 0)
                                        return true;
                        }
                        return false;
                }

                //
                // Used internally by FindMostEncompassedType, this is used
                // to avoid creating lots of objects in the tight loop inside
                // FindMostEncompassedType
                //
                static EmptyExpression priv_fmet_param;
                
                /// <summary>
                ///  Finds "most encompassed type" according to the spec (13.4.2)
                ///  amongst the methods in the MethodGroupExpr
                /// </summary>
                static Type FindMostEncompassedType (ArrayList types)
                {
                        Type best = null;

                        if (priv_fmet_param == null)
                                priv_fmet_param = new EmptyExpression ();

                        foreach (Type t in types){
                                priv_fmet_param.SetType (t);
                                
                                if (best == null) {
                                        best = t;
                                        continue;
                                }
                                
                                if (StandardConversionExists (priv_fmet_param, best))
                                        best = t;
                        }

                        return best;
                }

                //
                // Used internally by FindMostEncompassingType, this is used
                // to avoid creating lots of objects in the tight loop inside
                // FindMostEncompassingType
                //
                static EmptyExpression priv_fmee_ret;
                
                /// <summary>
                ///  Finds "most encompassing type" according to the spec (13.4.2)
                ///  amongst the types in the given set
                /// </summary>
                static Type FindMostEncompassingType (ArrayList types)
                {
                        Type best = null;

                        if (priv_fmee_ret == null)
                                priv_fmee_ret = new EmptyExpression ();

                        foreach (Type t in types){
                                priv_fmee_ret.SetType (best);

                                if (best == null) {
                                        best = t;
                                        continue;
                                }

                                if (StandardConversionExists (priv_fmee_ret, t))
                                        best = t;
                        }
                        
                        return best;
                }

                //
                // Used to avoid creating too many objects
                //
                static EmptyExpression priv_fms_expr;
                
                /// <summary>
                ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
                ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
                ///   for explicit and implicit conversion operators.
                /// </summary>
                static public Type FindMostSpecificSource (MethodGroupExpr me, Type source_type,
                                                           bool apply_explicit_conv_rules,
                                                           Location loc)
                {
                        ArrayList src_types_set = new ArrayList ();
                        
                        if (priv_fms_expr == null)
                                priv_fms_expr = new EmptyExpression ();
                        
                        //
                        // If any operator converts from S then Sx = S
                        //
                        foreach (MethodBase mb in me.Methods){
                                ParameterData pd = Invocation.GetParameterData (mb);
                                Type param_type = pd.ParameterType (0);

                                if (param_type == source_type)
                                        return param_type;

                                if (apply_explicit_conv_rules) {
                                        //
                                        // From the spec :
                                        // Find the set of applicable user-defined conversion operators, U.  This set
                                        // consists of the
                                        // user-defined implicit or explicit conversion operators declared by
                                        // the classes or structs in D that convert from a type encompassing
                                        // or encompassed by S to a type encompassing or encompassed by T
                                        //
                                        priv_fms_expr.SetType (param_type);
                                        if (StandardConversionExists (priv_fms_expr, source_type))
                                                src_types_set.Add (param_type);
                                        else {
                                                priv_fms_expr.SetType (source_type);
                                                if (StandardConversionExists (priv_fms_expr, param_type))
                                                        src_types_set.Add (param_type);
                                        }
                                } else {
                                        //
                                        // Only if S is encompassed by param_type
                                        //
                                        priv_fms_expr.SetType (source_type);
                                        if (StandardConversionExists (priv_fms_expr, param_type))
                                                src_types_set.Add (param_type);
                                }
                        }
                        
                        //
                        // Explicit Conv rules
                        //
                        if (apply_explicit_conv_rules) {
                                ArrayList candidate_set = new ArrayList ();

                                foreach (Type param_type in src_types_set){
                                        priv_fms_expr.SetType (source_type);
                                        
                                        if (StandardConversionExists (priv_fms_expr, param_type))
                                                candidate_set.Add (param_type);
                                }

                                if (candidate_set.Count != 0)
                                        return FindMostEncompassedType (candidate_set);
                        }

                        //
                        // Final case
                        //
                        if (apply_explicit_conv_rules)
                                return FindMostEncompassingType (src_types_set);
                        else
                                return FindMostEncompassedType (src_types_set);
                }

                //
                // Useful in avoiding proliferation of objects
                //
                static EmptyExpression priv_fmt_expr;
                
                /// <summary>
                ///  Finds the most specific target Tx according to section 13.4.4
                /// </summary>
                static public Type FindMostSpecificTarget (MethodGroupExpr me, Type target,
                                                           bool apply_explicit_conv_rules,
                                                           Location loc)
                {
                        ArrayList tgt_types_set = new ArrayList ();
                        
                        if (priv_fmt_expr == null)
                                priv_fmt_expr = new EmptyExpression ();
                        
                        //
                        // If any operator converts to T then Tx = T
                        //
                        foreach (MethodInfo mi in me.Methods){
                                Type ret_type = mi.ReturnType;

                                if (ret_type == target)
                                        return ret_type;

                                if (apply_explicit_conv_rules) {
                                        //
                                        // From the spec :
                                        // Find the set of applicable user-defined conversion operators, U.
                                        //
                                        // This set consists of the
                                        // user-defined implicit or explicit conversion operators declared by
                                        // the classes or structs in D that convert from a type encompassing
                                        // or encompassed by S to a type encompassing or encompassed by T
                                        //
                                        priv_fms_expr.SetType (ret_type);
                                        if (StandardConversionExists (priv_fms_expr, target))
                                                tgt_types_set.Add (ret_type);
                                        else {
                                                priv_fms_expr.SetType (target);
                                                if (StandardConversionExists (priv_fms_expr, ret_type))
                                                        tgt_types_set.Add (ret_type);
                                        }
                                } else {
                                        //
                                        // Only if T is encompassed by param_type
                                        //
                                        priv_fms_expr.SetType (ret_type);
                                        if (StandardConversionExists (priv_fms_expr, target))
                                                tgt_types_set.Add (ret_type);
                                }
                        }

                        //
                        // Explicit conv rules
                        //
                        if (apply_explicit_conv_rules) {
                                ArrayList candidate_set = new ArrayList ();

                                foreach (Type ret_type in tgt_types_set){
                                        priv_fmt_expr.SetType (ret_type);
                                        
                                        if (StandardConversionExists (priv_fmt_expr, target))
                                                candidate_set.Add (ret_type);
                                }

                                if (candidate_set.Count != 0)
                                        return FindMostEncompassingType (candidate_set);
                        }
                        
                        //
                        // Okay, final case !
                        //
                        if (apply_explicit_conv_rules)
                                return FindMostEncompassedType (tgt_types_set);
                        else
                                return FindMostEncompassingType (tgt_types_set);
                }
                
                /// <summary>
                ///  User-defined Implicit conversions
                /// </summary>
                static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
                                                                 Type target, Location loc)
                {
                        return UserDefinedConversion (ec, source, target, loc, false);
                }

                /// <summary>
                ///  User-defined Explicit conversions
                /// </summary>
                static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
                                                                 Type target, Location loc)
                {
                        return UserDefinedConversion (ec, source, target, loc, true);
                }

                /// <summary>
                ///   Computes the MethodGroup for the user-defined conversion
                ///   operators from source_type to target_type.  `look_for_explicit'
                ///   controls whether we should also include the list of explicit
                ///   operators
                /// </summary>
                static MethodGroupExpr GetConversionOperators (EmitContext ec,
                                                               Type source_type, Type target_type,
                                                               Location loc, bool look_for_explicit)
                {
                        Expression mg1 = null, mg2 = null;
                        Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
                        string op_name;

                        //
                        // FIXME : How does the False operator come into the picture ?
                        // This doesn't look complete and very correct !
                        //
                        if (target_type == TypeManager.bool_type && !look_for_explicit)
                                op_name = "op_True";
                        else
                                op_name = "op_Implicit";

                        MethodGroupExpr union3;
                        
                        mg1 = MethodLookup (ec, source_type, op_name, loc);
                        if (source_type.BaseType != null)
                                mg2 = MethodLookup (ec, source_type.BaseType, op_name, loc);

                        if (mg1 == null)
                                union3 = (MethodGroupExpr) mg2;
                        else if (mg2 == null)
                                union3 = (MethodGroupExpr) mg1;
                        else
                                union3 = Invocation.MakeUnionSet (mg1, mg2, loc);

                        mg1 = MethodLookup (ec, target_type, op_name, loc);
                        if (mg1 != null){
                                if (union3 != null)
                                        union3 = Invocation.MakeUnionSet (union3, mg1, loc);
                                else
                                        union3 = (MethodGroupExpr) mg1;
                        }

                        if (target_type.BaseType != null)
                                mg1 = MethodLookup (ec, target_type.BaseType, op_name, loc);
                        
                        if (mg1 != null){
                                if (union3 != null)
                                        union3 = Invocation.MakeUnionSet (union3, mg1, loc);
                                else
                                        union3 = (MethodGroupExpr) mg1;
                        }

                        MethodGroupExpr union4 = null;

                        if (look_for_explicit) {
                                op_name = "op_Explicit";

                                mg5 = MemberLookup (ec, source_type, op_name, loc);
                                if (source_type.BaseType != null)
                                        mg6 = MethodLookup (ec, source_type.BaseType, op_name, loc);
                                
                                mg7 = MemberLookup (ec, target_type, op_name, loc);
                                if (target_type.BaseType != null)
                                        mg8 = MethodLookup (ec, target_type.BaseType, op_name, loc);
                                
                                MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
                                MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);

                                union4 = Invocation.MakeUnionSet (union5, union6, loc);
                        }
                        
                        return Invocation.MakeUnionSet (union3, union4, loc);
                }
                
                /// <summary>
                ///   User-defined conversions
                /// </summary>
                static public Expression UserDefinedConversion (EmitContext ec, Expression source,
                                                                Type target, Location loc,
                                                                bool look_for_explicit)
                {
                        MethodGroupExpr union;
                        Type source_type = source.Type;
                        MethodBase method = null;
                        
                        union = GetConversionOperators (ec, source_type, target, loc, look_for_explicit);
                        if (union == null)
                                return null;
                        
                        Type most_specific_source, most_specific_target;

#if BLAH
                        foreach (MethodBase m in union.Methods){
                                Console.WriteLine ("Name: " + m.Name);
                                Console.WriteLine ("    : " + ((MethodInfo)m).ReturnType);
                        }
#endif
                        
                        most_specific_source = FindMostSpecificSource (union, source_type, look_for_explicit, loc);
                        if (most_specific_source == null)
                                return null;

                        most_specific_target = FindMostSpecificTarget (union, target, look_for_explicit, loc);
                        if (most_specific_target == null) 
                                return null;
                        
                        int count = 0;

                        foreach (MethodBase mb in union.Methods){
                                ParameterData pd = Invocation.GetParameterData (mb);
                                MethodInfo mi = (MethodInfo) mb;
                                
                                if (pd.ParameterType (0) == most_specific_source &&
                                    mi.ReturnType == most_specific_target) {
                                        method = mb;
                                        count++;
                                }
                        }
                        
                        if (method == null || count > 1) {
                                Report.Error (-11, loc, "Ambiguous user defined conversion");
                                return null;
                        }
                        
                        //
                        // This will do the conversion to the best match that we
                        // found.  Now we need to perform an implict standard conversion
                        // if the best match was not the type that we were requested
                        // by target.
                        //
                        if (look_for_explicit)
                                source = ConvertExplicitStandard (ec, source, most_specific_source, loc);
                        else
                                source = ConvertImplicitStandard (ec, source, most_specific_source, loc);

                        if (source == null)
                                return null;

                        Expression e;
                        e =  new UserCast ((MethodInfo) method, source, loc);
                        if (e.Type != target){
                                if (!look_for_explicit)
                                        e = ConvertImplicitStandard (ec, e, target, loc);
                                else
                                        e = ConvertExplicitStandard (ec, e, target, loc);
                        } 
                        return e;
                }
                
                /// <summary>
                ///   Converts implicitly the resolved expression `expr' into the
                ///   `target_type'.  It returns a new expression that can be used
                ///   in a context that expects a `target_type'. 
                /// </summary>
                static public Expression ConvertImplicit (EmitContext ec, Expression expr,
                                                          Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
                        Expression e;

                        if (expr_type == target_type)
                                return expr;

                        if (target_type == null)
                                throw new Exception ("Target type is null");

                        e = ConvertImplicitStandard (ec, expr, target_type, loc);
                        if (e != null)
                                return e;

                        e = ImplicitUserConversion (ec, expr, target_type, loc);
                        if (e != null)
                                return e;

                        return null;
                }

                
                /// <summary>
                ///   Attempts to apply the `Standard Implicit
                ///   Conversion' rules to the expression `expr' into
                ///   the `target_type'.  It returns a new expression
                ///   that can be used in a context that expects a
                ///   `target_type'.
                ///
                ///   This is different from `ConvertImplicit' in that the
                ///   user defined implicit conversions are excluded. 
                /// </summary>
                static public Expression ConvertImplicitStandard (EmitContext ec, Expression expr,
                                                                  Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
                        Expression e;

                        if (expr_type == target_type)
                                return expr;

                        e = ImplicitNumericConversion (ec, expr, target_type, loc);
                        if (e != null)
                                return e;

                        e = ImplicitReferenceConversion (expr, target_type);
                        if (e != null)
                                return e;

                        if (target_type.IsSubclassOf (TypeManager.enum_type) && expr is IntLiteral){
                                IntLiteral i = (IntLiteral) expr;

                                if (i.Value == 0)
                                        return new EmptyCast (expr, target_type);
                        }

                        if (ec.InUnsafe) {
                                if (expr_type.IsPointer){
                                        if (target_type == TypeManager.void_ptr_type)
                                                return new EmptyCast (expr, target_type);

                                        //
                                        // yep, comparing pointer types cant be done with
                                        // t1 == t2, we have to compare their element types.
                                        //
                                        if (target_type.IsPointer){
                                                if (target_type.GetElementType()==expr_type.GetElementType())
                                                        return expr;
                                        }
                                }
                                
                                if (target_type.IsPointer){
                                        if (expr is NullLiteral)
                                                return new EmptyCast (expr, target_type);
                                }
                        }

                        return null;
                }

                /// <summary>
                ///   Attemps to perform an implict constant conversion of the IntConstant
                ///   into a different data type using casts (See Implicit Constant
                ///   Expression Conversions)
                /// </summary>
                static protected Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
                {
                        int value = ic.Value;

                        //
                        // FIXME: This could return constants instead of EmptyCasts
                        //
                        if (target_type == TypeManager.sbyte_type){
                                if (value >= SByte.MinValue && value <= SByte.MaxValue)
                                        return new SByteConstant ((sbyte) value);
                        } else if (target_type == TypeManager.byte_type){
                                if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
                                        return new ByteConstant ((byte) value);
                        } else if (target_type == TypeManager.short_type){
                                if (value >= Int16.MinValue && value <= Int16.MaxValue)
                                        return new ShortConstant ((short) value);
                        } else if (target_type == TypeManager.ushort_type){
                                if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
                                        return new UShortConstant ((ushort) value);
                        } else if (target_type == TypeManager.uint32_type){
                                if (value >= 0)
                                        return new UIntConstant ((uint) value);
                        } else if (target_type == TypeManager.uint64_type){
                                //
                                // we can optimize this case: a positive int32
                                // always fits on a uint64.  But we need an opcode
                                // to do it.
                                //
                                if (value >= 0)
                                        return new ULongConstant ((ulong) value);
                        }
                        
                        if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type))
                                return new EnumConstant (ic, target_type);

                        return null;
                }

                static public void Error_CannotConvertImplicit (Location loc, Type source, Type target)
                {
                        string msg = "Cannot convert implicitly from `"+
                                TypeManager.CSharpName (source) + "' to `" +
                                TypeManager.CSharpName (target) + "'";

                        Report.Error (29, loc, msg);
                }

                /// <summary>
                ///   Attemptes to implicityly convert `target' into `type', using
                ///   ConvertImplicit.  If there is no implicit conversion, then
                ///   an error is signaled
                /// </summary>
                static public Expression ConvertImplicitRequired (EmitContext ec, Expression source,
                                                                  Type target_type, Location loc)
                {
                        Expression e;
                        
                        e = ConvertImplicit (ec, source, target_type, loc);
                        if (e != null)
                                return e;

                        if (source is DoubleLiteral && target_type == TypeManager.float_type){
                                Report.Error (664, loc,
                                              "Double literal cannot be implicitly converted to " +
                                              "float type, use F suffix to create a float literal");
                        }
                        
                        Error_CannotConvertImplicit (loc, source.Type, target_type);

                        return null;
                }

                /// <summary>
                ///   Performs the explicit numeric conversions
                /// </summary>
                static Expression ConvertNumericExplicit (EmitContext ec, Expression expr, Type target_type)
                {
                        Type expr_type = expr.Type;

                        //
                        // If we have an enumeration, extract the underlying type,
                        // use this during the comparission, but wrap around the original
                        // target_type
                        //
                        Type real_target_type = target_type;

                        if (TypeManager.IsEnumType (real_target_type))
                                real_target_type = TypeManager.EnumToUnderlying (real_target_type);

                        if (expr_type == TypeManager.sbyte_type){
                                //
                                // From sbyte to byte, ushort, uint, ulong, char
                                //
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U1);
                                if (real_target_type == TypeManager.ushort_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U2);
                                if (real_target_type == TypeManager.uint32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U4);
                                if (real_target_type == TypeManager.uint64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U8);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_CH);
                        } else if (expr_type == TypeManager.byte_type){
                                //
                                // From byte to sbyte and char
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_I1);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_CH);
                        } else if (expr_type == TypeManager.short_type){
                                //
                                // From short to sbyte, byte, ushort, uint, ulong, char
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
                                if (real_target_type == TypeManager.ushort_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U2);
                                if (real_target_type == TypeManager.uint32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U4);
                                if (real_target_type == TypeManager.uint64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U8);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_CH);
                        } else if (expr_type == TypeManager.ushort_type){
                                //
                                // From ushort to sbyte, byte, short, char
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_U1);
                                if (real_target_type == TypeManager.short_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I2);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_CH);
                        } else if (expr_type == TypeManager.int32_type){
                                //
                                // From int to sbyte, byte, short, ushort, uint, ulong, char
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
                                if (real_target_type == TypeManager.short_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
                                if (real_target_type == TypeManager.ushort_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U2);
                                if (real_target_type == TypeManager.uint32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U4);
                                if (real_target_type == TypeManager.uint64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U8);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_CH);
                        } else if (expr_type == TypeManager.uint32_type){
                                //
                                // From uint to sbyte, byte, short, ushort, int, char
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U1);
                                if (real_target_type == TypeManager.short_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I2);
                                if (real_target_type == TypeManager.ushort_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U2);
                                if (real_target_type == TypeManager.int32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I4);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_CH);
                        } else if (expr_type == TypeManager.int64_type){
                                //
                                // From long to sbyte, byte, short, ushort, int, uint, ulong, char
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
                                if (real_target_type == TypeManager.short_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
                                if (real_target_type == TypeManager.ushort_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U2);
                                if (real_target_type == TypeManager.int32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
                                if (real_target_type == TypeManager.uint32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U4);
                                if (real_target_type == TypeManager.uint64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U8);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_CH);
                        } else if (expr_type == TypeManager.uint64_type){
                                //
                                // From ulong to sbyte, byte, short, ushort, int, uint, long, char
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U1);
                                if (real_target_type == TypeManager.short_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I2);
                                if (real_target_type == TypeManager.ushort_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U2);
                                if (real_target_type == TypeManager.int32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I4);
                                if (real_target_type == TypeManager.uint32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U4);
                                if (real_target_type == TypeManager.int64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I8);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_CH);
                        } else if (expr_type == TypeManager.char_type){
                                //
                                // From char to sbyte, byte, short
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_U1);
                                if (real_target_type == TypeManager.short_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I2);
                        } else if (expr_type == TypeManager.float_type){
                                //
                                // From float to sbyte, byte, short,
                                // ushort, int, uint, long, ulong, char
                                // or decimal
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U1);
                                if (real_target_type == TypeManager.short_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I2);
                                if (real_target_type == TypeManager.ushort_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U2);
                                if (real_target_type == TypeManager.int32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I4);
                                if (real_target_type == TypeManager.uint32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U4);
                                if (real_target_type == TypeManager.int64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I8);
                                if (real_target_type == TypeManager.uint64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U8);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_CH);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.double_type){
                                //
                                // From double to byte, byte, short,
                                // ushort, int, uint, long, ulong,
                                // char, float or decimal
                                //
                                if (real_target_type == TypeManager.sbyte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I1);
                                if (real_target_type == TypeManager.byte_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
                                if (real_target_type == TypeManager.short_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
                                if (real_target_type == TypeManager.ushort_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U2);
                                if (real_target_type == TypeManager.int32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
                                if (real_target_type == TypeManager.uint32_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U4);
                                if (real_target_type == TypeManager.int64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
                                if (real_target_type == TypeManager.uint64_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U8);
                                if (real_target_type == TypeManager.char_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_CH);
                                if (real_target_type == TypeManager.float_type)
                                        return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
                                if (real_target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } 

                        // decimal is taken care of by the op_Explicit methods.

                        return null;
                }

                /// <summary>
                ///  Returns whether an explicit reference conversion can be performed
                ///  from source_type to target_type
                /// </summary>
                public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
                {
                        bool target_is_value_type = target_type.IsValueType;
                        
                        if (source_type == target_type)
                                return true;
                        
                        //
                        // From object to any reference type
                        //
                        if (source_type == TypeManager.object_type && !target_is_value_type)
                                return true;
                                        
                        //
                        // From any class S to any class-type T, provided S is a base class of T
                        //
                        if (target_type.IsSubclassOf (source_type))
                                return true;

                        //
                        // From any interface type S to any interface T provided S is not derived from T
                        //
                        if (source_type.IsInterface && target_type.IsInterface){
                                if (!target_type.IsSubclassOf (source_type))
                                        return true;
                        }
                            
                        //
                        // From any class type S to any interface T, provided S is not sealed
                        // and provided S does not implement T.
                        //
                        if (target_type.IsInterface && !source_type.IsSealed &&
                            !TypeManager.ImplementsInterface (source_type, target_type))
                                return true;

                        //
                        // From any interface-type S to to any class type T, provided T is not
                        // sealed, or provided T implements S.
                        //
                        if (source_type.IsInterface &&
                            (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
                                return true;
                        
                        
                        // From an array type S with an element type Se to an array type T with an 
                        // element type Te provided all the following are true:
                        //     * S and T differe only in element type, in other words, S and T
                        //       have the same number of dimensions.
                        //     * Both Se and Te are reference types
                        //     * An explicit referenc conversions exist from Se to Te
                        //
                        if (source_type.IsArray && target_type.IsArray) {
                                if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
                                        
                                        Type source_element_type = source_type.GetElementType ();
                                        Type target_element_type = target_type.GetElementType ();
                                        
                                        if (!source_element_type.IsValueType && !target_element_type.IsValueType)
                                                if (ExplicitReferenceConversionExists (source_element_type,
                                                                                       target_element_type))
                                                        return true;
                                }
                        }
                        

                        // From System.Array to any array-type
                        if (source_type == TypeManager.array_type &&
                            target_type.IsArray){
                                return true;
                        }

                        //
                        // From System delegate to any delegate-type
                        //
                        if (source_type == TypeManager.delegate_type &&
                            target_type.IsSubclassOf (TypeManager.delegate_type))
                                return true;

                        //
                        // From ICloneable to Array or Delegate types
                        //
                        if (source_type == TypeManager.icloneable_type &&
                            (target_type == TypeManager.array_type ||
                             target_type == TypeManager.delegate_type))
                                return true;
                        
                        return false;
                }

                /// <summary>
                ///   Implements Explicit Reference conversions
                /// </summary>
                static Expression ConvertReferenceExplicit (Expression source, Type target_type)
                {
                        Type source_type = source.Type;
                        bool target_is_value_type = target_type.IsValueType;

                        //
                        // From object to any reference type
                        //
                        if (source_type == TypeManager.object_type && !target_is_value_type)
                                return new ClassCast (source, target_type);


                        //
                        // From any class S to any class-type T, provided S is a base class of T
                        //
                        if (target_type.IsSubclassOf (source_type))
                                return new ClassCast (source, target_type);

                        //
                        // From any interface type S to any interface T provided S is not derived from T
                        //
                        if (source_type.IsInterface && target_type.IsInterface){
                                if (TypeManager.ImplementsInterface (source_type, target_type))
                                        return null;
                                else
                                        return new ClassCast (source, target_type);
                        }
                            
                        //
                        // From any class type S to any interface T, provides S is not sealed
                        // and provided S does not implement T.
                        //
                        if (target_type.IsInterface && !source_type.IsSealed) {
                                if (TypeManager.ImplementsInterface (source_type, target_type))
                                        return null;
                                else
                                        return new ClassCast (source, target_type);
                                
                        }

                        //
                        // From any interface-type S to to any class type T, provided T is not
                        // sealed, or provided T implements S.
                        //
                        if (source_type.IsInterface) {
                                if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type))
                                        return new ClassCast (source, target_type);
                                else
                                        return null;
                        }
                        
                        // From an array type S with an element type Se to an array type T with an 
                        // element type Te provided all the following are true:
                        //     * S and T differe only in element type, in other words, S and T
                        //       have the same number of dimensions.
                        //     * Both Se and Te are reference types
                        //     * An explicit referenc conversions exist from Se to Te
                        //
                        if (source_type.IsArray && target_type.IsArray) {
                                if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
                                        
                                        Type source_element_type = source_type.GetElementType ();
                                        Type target_element_type = target_type.GetElementType ();
                                        
                                        if (!source_element_type.IsValueType && !target_element_type.IsValueType)
                                                if (ExplicitReferenceConversionExists (source_element_type,
                                                                                       target_element_type))
                                                        return new ClassCast (source, target_type);
                                }
                        }
                        

                        // From System.Array to any array-type
                        if (source_type == TypeManager.array_type &&
                            target_type.IsArray) {
                                return new ClassCast (source, target_type);
                        }

                        //
                        // From System delegate to any delegate-type
                        //
                        if (source_type == TypeManager.delegate_type &&
                            target_type.IsSubclassOf (TypeManager.delegate_type))
                                return new ClassCast (source, target_type);

                        //
                        // From ICloneable to Array or Delegate types
                        //
                        if (source_type == TypeManager.icloneable_type &&
                            (target_type == TypeManager.array_type ||
                             target_type == TypeManager.delegate_type))
                                return new ClassCast (source, target_type);
                        
                        return null;
                }
                
                /// <summary>
                ///   Performs an explicit conversion of the expression `expr' whose
                ///   type is expr.Type to `target_type'.
                /// </summary>
                static public Expression ConvertExplicit (EmitContext ec, Expression expr,
                                                          Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
                        Expression ne = ConvertImplicitStandard (ec, expr, target_type, loc);

                        if (ne != null)
                                return ne;

                        ne = ConvertNumericExplicit (ec, expr, target_type);
                        if (ne != null)
                                return ne;

                        //
                        // Unboxing conversion.
                        //
                        if (expr_type == TypeManager.object_type && target_type.IsValueType)
                                return new UnboxCast (expr, target_type);

                        //
                        // Enum types
                        //
                        if (expr_type.IsSubclassOf (TypeManager.enum_type)) {
                                Expression e;

                                //
                                // FIXME: Is there any reason we should have EnumConstant
                                // dealt with here instead of just using always the
                                // UnderlyingSystemType to wrap the type?
                                //
                                if (expr is EnumConstant)
                                        e = ((EnumConstant) expr).Child;
                                else {
                                        e = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
                                }
                                
                                Expression t = ConvertImplicit (ec, e, target_type, loc);
                                if (t != null)
                                        return t;
                                
                                return ConvertNumericExplicit (ec, e, target_type);
                        }
                        
                        ne = ConvertReferenceExplicit (expr, target_type);
                        if (ne != null)
                                return ne;

                        if (ec.InUnsafe){
                                if (target_type.IsPointer){
                                        if (expr_type.IsPointer)
                                                return new EmptyCast (expr, target_type);
                                        
                                        if (expr_type == TypeManager.sbyte_type ||
                                            expr_type == TypeManager.byte_type ||
                                            expr_type == TypeManager.short_type ||
                                            expr_type == TypeManager.ushort_type ||
                                            expr_type == TypeManager.int32_type ||
                                            expr_type == TypeManager.uint32_type ||
                                            expr_type == TypeManager.uint64_type ||
                                            expr_type == TypeManager.int64_type)
                                                return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
                                }
                                if (expr_type.IsPointer){
                                        if (target_type == TypeManager.sbyte_type ||
                                            target_type == TypeManager.byte_type ||
                                            target_type == TypeManager.short_type ||
                                            target_type == TypeManager.ushort_type ||
                                            target_type == TypeManager.int32_type ||
                                            target_type == TypeManager.uint32_type ||
                                            target_type == TypeManager.uint64_type ||
                                            target_type == TypeManager.int64_type){
                                                Expression e = new EmptyCast (expr, TypeManager.uint32_type);
                                                Expression ci, ce;

                                                ci = ConvertImplicitStandard (ec, e, target_type, loc);

                                                if (ci != null)
                                                        return ci;

                                                ce = ConvertNumericExplicit (ec, e, target_type);
                                                if (ce != null)
                                                        return ce;
                                                //
                                                // We should always be able to go from an uint32
                                                // implicitly or explicitly to the other integral
                                                // types
                                                //
                                                throw new Exception ("Internal compiler error");
                                        }
                                }
                        }
                        
                        ne = ExplicitUserConversion (ec, expr, target_type, loc);
                        if (ne != null)
                                return ne;

                        Error_CannotConvertType (loc, expr_type, target_type);
                        return null;
                }

                /// <summary>
                ///   Same as ConvertExplicit, only it doesn't include user defined conversions
                /// </summary>
                static public Expression ConvertExplicitStandard (EmitContext ec, Expression expr,
                                                                  Type target_type, Location l)
                {
                        Expression ne = ConvertImplicitStandard (ec, expr, target_type, l);

                        if (ne != null)
                                return ne;

                        ne = ConvertNumericExplicit (ec, expr, target_type);
                        if (ne != null)
                                return ne;

                        ne = ConvertReferenceExplicit (expr, target_type);
                        if (ne != null)
                                return ne;

                        Error_CannotConvertType (l, expr.Type, target_type);
                        return null;
                }

                static string ExprClassName (ExprClass c)
                {
                        switch (c){
                        case ExprClass.Invalid:
                                return "Invalid";
                        case ExprClass.Value:
                                return "value";
                        case ExprClass.Variable:
                                return "variable";
                        case ExprClass.Namespace:
                                return "namespace";
                        case ExprClass.Type:
                                return "type";
                        case ExprClass.MethodGroup:
                                return "method group";
                        case ExprClass.PropertyAccess:
                                return "property access";
                        case ExprClass.EventAccess:
                                return "event access";
                        case ExprClass.IndexerAccess:
                                return "indexer access";
                        case ExprClass.Nothing:
                                return "null";
                        }
                        throw new Exception ("Should not happen");
                }
                
                /// <summary>
                ///   Reports that we were expecting `expr' to be of class `expected'
                /// </summary>
                public void Error118 (string expected)
                {
                        string kind = "Unknown";
                        
                        kind = ExprClassName (eclass);

                        Error (118, "Expression denotes a `" + kind +
                               "' where a `" + expected + "' was expected");
                }

                public void Error118 (ResolveFlags flags)
                {
                        ArrayList valid = new ArrayList (10);

                        if ((flags & ResolveFlags.VariableOrValue) != 0) {
                                valid.Add ("variable");
                                valid.Add ("value");
                        }

                        if ((flags & ResolveFlags.Type) != 0)
                                valid.Add ("type");

                        if ((flags & ResolveFlags.MethodGroup) != 0)
                                valid.Add ("method group");

                        if ((flags & ResolveFlags.SimpleName) != 0)
                                valid.Add ("simple name");

                        if (valid.Count == 0)
                                valid.Add ("unknown");

                        StringBuilder sb = new StringBuilder ();
                        for (int i = 0; i < valid.Count; i++) {
                                if (i > 0)
                                        sb.Append (", ");
                                else if (i == valid.Count)
                                        sb.Append (" or ");
                                sb.Append (valid [i]);
                        }

                        string kind = ExprClassName (eclass);

                        Error (119, "Expression denotes a `" + kind + "' where " +
                               "a `" + sb.ToString () + "' was expected");
                }
                
                static void Error_ConstantValueCannotBeConverted (Location l, string val, Type t)
                {
                        Report.Error (31, l, "Constant value `" + val + "' cannot be converted to " +
                                      TypeManager.CSharpName (t));
                }

                public static void UnsafeError (Location loc)
                {
                        Report.Error (214, loc, "Pointers may only be used in an unsafe context");
                }
                
                /// <summary>
                ///   Converts the IntConstant, UIntConstant, LongConstant or
                ///   ULongConstant into the integral target_type.   Notice
                ///   that we do not return an `Expression' we do return
                ///   a boxed integral type.
                ///
                ///   FIXME: Since I added the new constants, we need to
                ///   also support conversions from CharConstant, ByteConstant,
                ///   SByteConstant, UShortConstant, ShortConstant
                ///
                ///   This is used by the switch statement, so the domain
                ///   of work is restricted to the literals above, and the
                ///   targets are int32, uint32, char, byte, sbyte, ushort,
                ///   short, uint64 and int64
                /// </summary>
                public static object ConvertIntLiteral (Constant c, Type target_type, Location loc)
                {
                        string s = "";

                        if (c.Type == target_type)
                                return ((Constant) c).GetValue ();

                        //
                        // Make into one of the literals we handle, we dont really care
                        // about this value as we will just return a few limited types
                        // 
                        if (c is EnumConstant)
                                c = ((EnumConstant)c).WidenToCompilerConstant ();

                        if (c is IntConstant){
                                int v = ((IntConstant) c).Value;
                                
                                if (target_type == TypeManager.uint32_type){
                                        if (v >= 0)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v >= SByte.MinValue && v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v >= Int16.MinValue && v <= UInt16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v >= UInt16.MinValue && v <= UInt16.MaxValue)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type){
                                        if (v > 0)
                                                return (ulong) v;
                                }

                                s = v.ToString ();
                        } else if (c is UIntConstant){
                                uint v = ((UIntConstant) c).Value;

                                if (target_type == TypeManager.int32_type){
                                        if (v <= Int32.MaxValue)
                                                return (int) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v <= UInt16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v <= UInt16.MaxValue)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;
                                s = v.ToString ();
                        } else if (c is LongConstant){ 
                                long v = ((LongConstant) c).Value;

                                if (target_type == TypeManager.int32_type){
                                        if (v >= UInt32.MinValue && v <= UInt32.MaxValue)
                                                return (int) v;
                                } else if (target_type == TypeManager.uint32_type){
                                        if (v >= 0 && v <= UInt32.MaxValue)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v >= SByte.MinValue && v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v >= Int16.MinValue && v <= UInt16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v >= UInt16.MinValue && v <= UInt16.MaxValue)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.uint64_type){
                                        if (v > 0)
                                                return (ulong) v;
                                }
                                s = v.ToString ();
                        } else if (c is ULongConstant){
                                ulong v = ((ULongConstant) c).Value;

                                if (target_type == TypeManager.int32_type){
                                        if (v <= Int32.MaxValue)
                                                return (int) v;
                                } else if (target_type == TypeManager.uint32_type){
                                        if (v <= UInt32.MaxValue)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v <= (int) SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v <= UInt16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v <= UInt16.MaxValue)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type){
                                        if (v <= Int64.MaxValue)
                                                return (long) v;
                                }
                                s = v.ToString ();
                        } else if (c is ByteConstant){
                                byte v = ((ByteConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type)
                                        return (int) v;
                                else if (target_type == TypeManager.uint32_type)
                                        return (uint) v;
                                else if (target_type == TypeManager.char_type)
                                        return (char) v;
                                else if (target_type == TypeManager.sbyte_type){
                                        if (v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type)
                                        return (short) v;
                                else if (target_type == TypeManager.ushort_type)
                                        return (ushort) v;
                                else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;
                                s = v.ToString ();
                        } else if (c is SByteConstant){
                                sbyte v = ((SByteConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type)
                                        return (int) v;
                                else if (target_type == TypeManager.uint32_type){
                                        if (v >= 0)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= 0)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= 0)
                                                return (byte) v;
                                } else if (target_type == TypeManager.short_type)
                                        return (short) v;
                                else if (target_type == TypeManager.ushort_type){
                                        if (v >= 0)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type){
                                        if (v >= 0)
                                                return (ulong) v;
                                }
                                s = v.ToString ();
                        } else if (c is ShortConstant){
                                short v = ((ShortConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type){
                                        return (int) v;
                                } else if (target_type == TypeManager.uint32_type){
                                        if (v >= 0)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= 0)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v >= SByte.MinValue && v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v >= 0)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;

                                s = v.ToString ();
                        } else if (c is UShortConstant){
                                ushort v = ((UShortConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type)
                                        return (int) v;
                                else if (target_type == TypeManager.uint32_type)
                                        return (uint) v;
                                else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v <= SByte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v <= Int16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;

                                s = v.ToString ();
                        } else if (c is CharConstant){
                                char v = ((CharConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type)
                                        return (int) v;
                                else if (target_type == TypeManager.uint32_type)
                                        return (uint) v;
                                else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v <= Int16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type)
                                        return (short) v;
                                else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;

                                s = v.ToString ();
                        }
                        Error_ConstantValueCannotBeConverted (loc, s, target_type);
                        return null;
                }

                //
                // Load the object from the pointer.  
                //
                public static void LoadFromPtr (ILGenerator ig, Type t)
                {
                        if (t == TypeManager.int32_type)
                                ig.Emit (OpCodes.Ldind_I4);
                        else if (t == TypeManager.uint32_type)
                                ig.Emit (OpCodes.Ldind_U4);
                        else if (t == TypeManager.short_type)
                                ig.Emit (OpCodes.Ldind_I2);
                        else if (t == TypeManager.ushort_type)
                                ig.Emit (OpCodes.Ldind_U2);
                        else if (t == TypeManager.char_type)
                                ig.Emit (OpCodes.Ldind_U2);
                        else if (t == TypeManager.byte_type)
                                ig.Emit (OpCodes.Ldind_U1);
                        else if (t == TypeManager.sbyte_type)
                                ig.Emit (OpCodes.Ldind_I1);
                        else if (t == TypeManager.uint64_type)
                                ig.Emit (OpCodes.Ldind_I8);
                        else if (t == TypeManager.int64_type)
                                ig.Emit (OpCodes.Ldind_I8);
                        else if (t == TypeManager.float_type)
                                ig.Emit (OpCodes.Ldind_R4);
                        else if (t == TypeManager.double_type)
                                ig.Emit (OpCodes.Ldind_R8);
                        else if (t == TypeManager.bool_type)
                                ig.Emit (OpCodes.Ldind_I1);
                        else if (t == TypeManager.intptr_type)
                                ig.Emit (OpCodes.Ldind_I);
                        else if (TypeManager.IsEnumType (t)) {
                                if (t == TypeManager.enum_type)
                                        ig.Emit (OpCodes.Ldind_Ref);
                                else
                                        LoadFromPtr (ig, TypeManager.EnumToUnderlying (t));
                        } else if (t.IsValueType)
                                ig.Emit (OpCodes.Ldobj, t);
                        else
                                ig.Emit (OpCodes.Ldind_Ref);
                }

                //
                // The stack contains the pointer and the value of type `type'
                //
                public static void StoreFromPtr (ILGenerator ig, Type type)
                {
                        if (type.IsEnum)
                                type = TypeManager.EnumToUnderlying (type);
                        if (type == TypeManager.int32_type || type == TypeManager.uint32_type)
                                ig.Emit (OpCodes.Stind_I4);
                        else if (type == TypeManager.int64_type || type == TypeManager.uint64_type)
                                ig.Emit (OpCodes.Stind_I8);
                        else if (type == TypeManager.char_type || type == TypeManager.short_type ||
                                 type == TypeManager.ushort_type)
                                ig.Emit (OpCodes.Stind_I2);
                        else if (type == TypeManager.float_type)
                                ig.Emit (OpCodes.Stind_R4);
                        else if (type == TypeManager.double_type)
                                ig.Emit (OpCodes.Stind_R8);
                        else if (type == TypeManager.byte_type || type == TypeManager.sbyte_type ||
                                 type == TypeManager.bool_type)
                                ig.Emit (OpCodes.Stind_I1);
                        else if (type == TypeManager.intptr_type)
                                ig.Emit (OpCodes.Stind_I);
                        else if (type.IsValueType)
                                ig.Emit (OpCodes.Stobj, type);
                        else
                                ig.Emit (OpCodes.Stind_Ref);
                }
                
                //
                // Returns the size of type `t' if known, otherwise, 0
                //
                public static int GetTypeSize (Type t)
                {
                        t = TypeManager.TypeToCoreType (t);
                        if (t == TypeManager.int32_type ||
                            t == TypeManager.uint32_type ||
                            t == TypeManager.float_type)
                                return 4;
                        else if (t == TypeManager.int64_type ||
                                 t == TypeManager.uint64_type ||
                                 t == TypeManager.double_type)
                                return 8;
                        else if (t == TypeManager.byte_type ||
                                 t == TypeManager.sbyte_type ||
                                 t == TypeManager.bool_type)    
                                return 1;
                        else if (t == TypeManager.short_type ||
                                 t == TypeManager.char_type ||
                                 t == TypeManager.ushort_type)
                                return 2;
                        else
                                return 0;
                }

                //
                // Default implementation of IAssignMethod.CacheTemporaries
                //
                public void CacheTemporaries (EmitContext ec)
                {
                }

                static void Error_NegativeArrayIndex (Location loc)
                {
                        Report.Error (284, loc, "Can not create array with a negative size");
                }
                
                //
                // Converts `source' to an int, uint, long or ulong.
                //
                public Expression ExpressionToArrayArgument (EmitContext ec, Expression source, Location loc)
                {
                        Expression target;
                        
                        bool old_checked = ec.CheckState;
                        ec.CheckState = true;
                        
                        target = ConvertImplicit (ec, source, TypeManager.int32_type, loc);
                        if (target == null){
                                target = ConvertImplicit (ec, source, TypeManager.uint32_type, loc);
                                if (target == null){
                                        target = ConvertImplicit (ec, source, TypeManager.int64_type, loc);
                                        if (target == null){
                                                target = ConvertImplicit (ec, source, TypeManager.uint64_type, loc);
                                                if (target == null)
                                                        Expression.Error_CannotConvertImplicit (loc, source.Type, TypeManager.int32_type);
                                        }
                                }
                        } 
                        ec.CheckState = old_checked;

                        //
                        // Only positive constants are allowed at compile time
                        //
                        if (target is Constant){
                                if (target is IntConstant){
                                        if (((IntConstant) target).Value < 0){
                                                Error_NegativeArrayIndex (loc);
                                                return null;
                                        }
                                }

                                if (target is LongConstant){
                                        if (((LongConstant) target).Value < 0){
                                                Error_NegativeArrayIndex (loc);
                                                return null;
                                        }
                                }
                                
                        }

                        return target;
                }
                
        }

        /// <summary>
        ///   This is just a base class for expressions that can
        ///   appear on statements (invocations, object creation,
        ///   assignments, post/pre increment and decrement).  The idea
        ///   being that they would support an extra Emition interface that
        ///   does not leave a result on the stack.
        /// </summary>
        public abstract class ExpressionStatement : Expression {

                /// <summary>
                ///   Requests the expression to be emitted in a `statement'
                ///   context.  This means that no new value is left on the
                ///   stack after invoking this method (constrasted with
                ///   Emit that will always leave a value on the stack).
                /// </summary>
                public abstract void EmitStatement (EmitContext ec);
        }

        /// <summary>
        ///   This kind of cast is used to encapsulate the child
        ///   whose type is child.Type into an expression that is
        ///   reported to return "return_type".  This is used to encapsulate
        ///   expressions which have compatible types, but need to be dealt
        ///   at higher levels with.
        ///
        ///   For example, a "byte" expression could be encapsulated in one
        ///   of these as an "unsigned int".  The type for the expression
        ///   would be "unsigned int".
        ///
        /// </summary>
        public class EmptyCast : Expression {
                protected Expression child;

                public EmptyCast (Expression child, Type return_type)
                {
                        eclass = child.eclass;
                        type = return_type;
                        this.child = child;
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        child.Emit (ec);
                }
        }

        /// <summary>
        ///  This class is used to wrap literals which belong inside Enums
        /// </summary>
        public class EnumConstant : Constant {
                public Constant Child;

                public EnumConstant (Constant child, Type enum_type)
                {
                        eclass = child.eclass;
                        this.Child = child;
                        type = enum_type;
                }
                
                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        Child.Emit (ec);
                }

                public override object GetValue ()
                {
                        return Child.GetValue ();
                }

                //
                // Converts from one of the valid underlying types for an enumeration
                // (int32, uint32, int64, uint64, short, ushort, byte, sbyte) to
                // one of the internal compiler literals: Int/UInt/Long/ULong Literals.
                //
                public Constant WidenToCompilerConstant ()
                {
                        Type t = TypeManager.EnumToUnderlying (Child.Type);
                        object v = ((Constant) Child).GetValue ();;
                        
                        if (t == TypeManager.int32_type)
                                return new IntConstant ((int) v);
                        if (t == TypeManager.uint32_type)
                                return new UIntConstant ((uint) v);
                        if (t == TypeManager.int64_type)
                                return new LongConstant ((long) v);
                        if (t == TypeManager.uint64_type)
                                return new ULongConstant ((ulong) v);
                        if (t == TypeManager.short_type)
                                return new ShortConstant ((short) v);
                        if (t == TypeManager.ushort_type)
                                return new UShortConstant ((ushort) v);
                        if (t == TypeManager.byte_type)
                                return new ByteConstant ((byte) v);
                        if (t == TypeManager.sbyte_type)
                                return new SByteConstant ((sbyte) v);

                        throw new Exception ("Invalid enumeration underlying type: " + t);
                }

                //
                // Extracts the value in the enumeration on its native representation
                //
                public object GetPlainValue ()
                {
                        Type t = TypeManager.EnumToUnderlying (Child.Type);
                        object v = ((Constant) Child).GetValue ();;
                        
                        if (t == TypeManager.int32_type)
                                return (int) v;
                        if (t == TypeManager.uint32_type)
                                return (uint) v;
                        if (t == TypeManager.int64_type)
                                return (long) v;
                        if (t == TypeManager.uint64_type)
                                return (ulong) v;
                        if (t == TypeManager.short_type)
                                return (short) v;
                        if (t == TypeManager.ushort_type)
                                return (ushort) v;
                        if (t == TypeManager.byte_type)
                                return (byte) v;
                        if (t == TypeManager.sbyte_type)
                                return (sbyte) v;

                        return null;
                }
                
                public override string AsString ()
                {
                        return Child.AsString ();
                }

                public override DoubleConstant ConvertToDouble ()
                {
                        return Child.ConvertToDouble ();
                }

                public override FloatConstant ConvertToFloat ()
                {
                        return Child.ConvertToFloat ();
                }

                public override ULongConstant ConvertToULong ()
                {
                        return Child.ConvertToULong ();
                }

                public override LongConstant ConvertToLong ()
                {
                        return Child.ConvertToLong ();
                }

                public override UIntConstant ConvertToUInt ()
                {
                        return Child.ConvertToUInt ();
                }

                public override IntConstant ConvertToInt ()
                {
                        return Child.ConvertToInt ();
                }
        }

        /// <summary>
        ///   This kind of cast is used to encapsulate Value Types in objects.
        ///
        ///   The effect of it is to box the value type emitted by the previous
        ///   operation.
        /// </summary>
        public class BoxedCast : EmptyCast {

                public BoxedCast (Expression expr)
                        : base (expr, TypeManager.object_type)
                {
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        base.Emit (ec);
                        
                        ec.ig.Emit (OpCodes.Box, child.Type);
                }
        }

        public class UnboxCast : EmptyCast {
                public UnboxCast (Expression expr, Type return_type)
                        : base (expr, return_type)
                {
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        Type t = type;
                        ILGenerator ig = ec.ig;
                        
                        base.Emit (ec);
                        ig.Emit (OpCodes.Unbox, t);

                        LoadFromPtr (ig, t);
                }
        }
        
        /// <summary>
        ///   This is used to perform explicit numeric conversions.
        ///
        ///   Explicit numeric conversions might trigger exceptions in a checked
        ///   context, so they should generate the conv.ovf opcodes instead of
        ///   conv opcodes.
        /// </summary>
        public class ConvCast : EmptyCast {
                public enum Mode : byte {
                        I1_U1, I1_U2, I1_U4, I1_U8, I1_CH,
                        U1_I1, U1_CH,
                        I2_I1, I2_U1, I2_U2, I2_U4, I2_U8, I2_CH,
                        U2_I1, U2_U1, U2_I2, U2_CH,
                        I4_I1, I4_U1, I4_I2, I4_U2, I4_U4, I4_U8, I4_CH,
                        U4_I1, U4_U1, U4_I2, U4_U2, U4_I4, U4_CH,
                        I8_I1, I8_U1, I8_I2, I8_U2, I8_I4, I8_U4, I8_U8, I8_CH,
                        U8_I1, U8_U1, U8_I2, U8_U2, U8_I4, U8_U4, U8_I8, U8_CH,
                        CH_I1, CH_U1, CH_I2,
                        R4_I1, R4_U1, R4_I2, R4_U2, R4_I4, R4_U4, R4_I8, R4_U8, R4_CH,
                        R8_I1, R8_U1, R8_I2, R8_U2, R8_I4, R8_U4, R8_I8, R8_U8, R8_CH, R8_R4
                }

                Mode mode;
                bool checked_state;
                
                public ConvCast (EmitContext ec, Expression child, Type return_type, Mode m)
                        : base (child, return_type)
                {
                        checked_state = ec.CheckState;
                        mode = m;
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
                        
                        base.Emit (ec);

                        if (checked_state){
                                switch (mode){
                                case Mode.I1_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.I1_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.I1_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.I1_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.I1_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.U1_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.U1_CH: /* nothing */ break;

                                case Mode.I2_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.I2_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.I2_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.I2_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.I2_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.I2_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.U2_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.U2_U1: ig.Emit (OpCodes.Conv_Ovf_U1_Un); break;
                                case Mode.U2_I2: ig.Emit (OpCodes.Conv_Ovf_I2_Un); break;
                                case Mode.U2_CH: /* nothing */ break;

                                case Mode.I4_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.I4_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.I4_I2: ig.Emit (OpCodes.Conv_Ovf_I2); break;
                                case Mode.I4_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.I4_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.I4_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.I4_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.U4_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.U4_U1: ig.Emit (OpCodes.Conv_Ovf_U1_Un); break;
                                case Mode.U4_I2: ig.Emit (OpCodes.Conv_Ovf_I2_Un); break;
                                case Mode.U4_U2: ig.Emit (OpCodes.Conv_Ovf_U2_Un); break;
                                case Mode.U4_I4: ig.Emit (OpCodes.Conv_Ovf_I4_Un); break;
                                case Mode.U4_CH: ig.Emit (OpCodes.Conv_Ovf_U2_Un); break;

                                case Mode.I8_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.I8_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.I8_I2: ig.Emit (OpCodes.Conv_Ovf_I2); break;
                                case Mode.I8_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.I8_I4: ig.Emit (OpCodes.Conv_Ovf_I4); break;
                                case Mode.I8_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.I8_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.I8_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.U8_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.U8_U1: ig.Emit (OpCodes.Conv_Ovf_U1_Un); break;
                                case Mode.U8_I2: ig.Emit (OpCodes.Conv_Ovf_I2_Un); break;
                                case Mode.U8_U2: ig.Emit (OpCodes.Conv_Ovf_U2_Un); break;
                                case Mode.U8_I4: ig.Emit (OpCodes.Conv_Ovf_I4_Un); break;
                                case Mode.U8_U4: ig.Emit (OpCodes.Conv_Ovf_U4_Un); break;
                                case Mode.U8_I8: ig.Emit (OpCodes.Conv_Ovf_I8_Un); break;
                                case Mode.U8_CH: ig.Emit (OpCodes.Conv_Ovf_U2_Un); break;

                                case Mode.CH_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.CH_U1: ig.Emit (OpCodes.Conv_Ovf_U1_Un); break;
                                case Mode.CH_I2: ig.Emit (OpCodes.Conv_Ovf_I2_Un); break;

                                case Mode.R4_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.R4_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.R4_I2: ig.Emit (OpCodes.Conv_Ovf_I2); break;
                                case Mode.R4_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.R4_I4: ig.Emit (OpCodes.Conv_Ovf_I4); break;
                                case Mode.R4_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.R4_I8: ig.Emit (OpCodes.Conv_Ovf_I8); break;
                                case Mode.R4_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.R4_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.R8_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.R8_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.R8_I2: ig.Emit (OpCodes.Conv_Ovf_I2); break;
                                case Mode.R8_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.R8_I4: ig.Emit (OpCodes.Conv_Ovf_I4); break;
                                case Mode.R8_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.R8_I8: ig.Emit (OpCodes.Conv_Ovf_I8); break;
                                case Mode.R8_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.R8_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.R8_R4: ig.Emit (OpCodes.Conv_R4); break;
                                }
                        } else {
                                switch (mode){
                                case Mode.I1_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.I1_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.I1_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.I1_U8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.I1_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.U1_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.U1_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.I2_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.I2_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.I2_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.I2_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.I2_U8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.I2_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.U2_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.U2_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.U2_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.U2_CH: /* nothing */ break;

                                case Mode.I4_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.I4_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.I4_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.I4_U4: /* nothing */ break;
                                case Mode.I4_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.I4_U8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.I4_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.U4_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.U4_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.U4_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.U4_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.U4_I4: /* nothing */ break;
                                case Mode.U4_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.I8_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.I8_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.I8_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.I8_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.I8_I4: ig.Emit (OpCodes.Conv_I4); break;
                                case Mode.I8_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.I8_U8: /* nothing */ break;
                                case Mode.I8_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.U8_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.U8_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.U8_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.U8_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.U8_I4: ig.Emit (OpCodes.Conv_I4); break;
                                case Mode.U8_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.U8_I8: /* nothing */ break;
                                case Mode.U8_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.CH_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.CH_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.CH_I2: ig.Emit (OpCodes.Conv_I2); break;

                                case Mode.R4_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.R4_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.R4_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.R4_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.R4_I4: ig.Emit (OpCodes.Conv_I4); break;
                                case Mode.R4_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.R4_I8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.R4_U8: ig.Emit (OpCodes.Conv_U8); break;
                                case Mode.R4_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.R8_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.R8_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.R8_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.R8_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.R8_I4: ig.Emit (OpCodes.Conv_I4); break;
                                case Mode.R8_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.R8_I8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.R8_U8: ig.Emit (OpCodes.Conv_U8); break;
                                case Mode.R8_CH: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.R8_R4: ig.Emit (OpCodes.Conv_R4); break;
                                }
                        }
                }
        }
        
        public class OpcodeCast : EmptyCast {
                OpCode op, op2;
                bool second_valid;
                
                public OpcodeCast (Expression child, Type return_type, OpCode op)
                        : base (child, return_type)
                        
                {
                        this.op = op;
                        second_valid = false;
                }

                public OpcodeCast (Expression child, Type return_type, OpCode op, OpCode op2)
                        : base (child, return_type)
                        
                {
                        this.op = op;
                        this.op2 = op2;
                        second_valid = true;
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        base.Emit (ec);
                        ec.ig.Emit (op);

                        if (second_valid)
                                ec.ig.Emit (op2);
                }                       
        }

        /// <summary>
        ///   This kind of cast is used to encapsulate a child and cast it
        ///   to the class requested
        /// </summary>
        public class ClassCast : EmptyCast {
                public ClassCast (Expression child, Type return_type)
                        : base (child, return_type)
                        
                {
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        base.Emit (ec);

                        ec.ig.Emit (OpCodes.Castclass, type);
                }                       
                
        }
        
        /// <summary>
        ///   SimpleName expressions are initially formed of a single
        ///   word and it only happens at the beginning of the expression.
        /// </summary>
        ///
        /// <remarks>
        ///   The expression will try to be bound to a Field, a Method
        ///   group or a Property.  If those fail we pass the name to our
        ///   caller and the SimpleName is compounded to perform a type
        ///   lookup.  The idea behind this process is that we want to avoid
        ///   creating a namespace map from the assemblies, as that requires
        ///   the GetExportedTypes function to be called and a hashtable to
        ///   be constructed which reduces startup time.  If later we find
        ///   that this is slower, we should create a `NamespaceExpr' expression
        ///   that fully participates in the resolution process. 
        ///   
        ///   For example `System.Console.WriteLine' is decomposed into
        ///   MemberAccess (MemberAccess (SimpleName ("System"), "Console"), "WriteLine")
        ///   
        ///   The first SimpleName wont produce a match on its own, so it will
        ///   be turned into:
        ///   MemberAccess (SimpleName ("System.Console"), "WriteLine").
        ///   
        ///   System.Console will produce a TypeExpr match.
        ///   
        ///   The downside of this is that we might be hitting `LookupType' too many
        ///   times with this scheme.
        /// </remarks>
        public class SimpleName : Expression, ITypeExpression {
                public readonly string Name;
                
                public SimpleName (string name, Location l)
                {
                        Name = name;
                        loc = l;
                }

                public static void Error_ObjectRefRequired (EmitContext ec, Location l, string name)
                {
                        if (ec.IsFieldInitializer)
                                Report.Error (
                                        236, l,
                                        "A field initializer cannot reference the non-static field, " +
                                        "method or property `"+name+"'");
                        else
                                Report.Error (
                                        120, l,
                                        "An object reference is required " +
                                        "for the non-static field `"+name+"'");
                }
                
                //
                // Checks whether we are trying to access an instance
                // property, method or field from a static body.
                //
                Expression MemberStaticCheck (EmitContext ec, Expression e)
                {
                        if (e is IMemberExpr){
                                IMemberExpr member = (IMemberExpr) e;
                                
                                if (!member.IsStatic){
                                        Error_ObjectRefRequired (ec, loc, Name);
                                        return null;
                                }
                        }

                        return e;
                }
                
                public override Expression DoResolve (EmitContext ec)
                {
                        return SimpleNameResolve (ec, null, false);
                }

                public override Expression DoResolveLValue (EmitContext ec, Expression right_side)
                {
                        return SimpleNameResolve (ec, right_side, false);
                }
                

                public Expression DoResolveAllowStatic (EmitContext ec)
                {
                        return SimpleNameResolve (ec, null, true);
                }

                public Expression DoResolveType (EmitContext ec)
                {
                        //
                        // Stage 3: Lookup symbol in the various namespaces. 
                        //
                        DeclSpace ds = ec.DeclSpace;
                        Type t;
                        string alias_value;

                        if ((t = RootContext.LookupType (ds, Name, true, loc)) != null)
                                return new TypeExpr (t, loc);
                                
                        //
                        // Stage 2 part b: Lookup up if we are an alias to a type
                        // or a namespace.
                        //
                        // Since we are cheating: we only do the Alias lookup for
                        // namespaces if the name does not include any dots in it
                        //
                                
                        alias_value = ec.DeclSpace.LookupAlias (Name);
                                
                        if (Name.IndexOf ('.') == -1 && alias_value != null) {
                                if ((t = RootContext.LookupType (ds, alias_value, true, loc)) != null)
                                        return new TypeExpr (t, loc);
                                        
                                // we have alias value, but it isn't Type, so try if it's namespace
                                return new SimpleName (alias_value, loc);
                        }
                                
                        if (ec.ResolvingTypeTree){
                                Type dt = ec.DeclSpace.FindType (Name);
                                if (dt != null)
                                        return new TypeExpr (dt, loc);
                        }

                        // No match, maybe our parent can compose us
                        // into something meaningful.
                        return this;
                }

                /// <remarks>
                ///   7.5.2: Simple Names. 
                ///
                ///   Local Variables and Parameters are handled at
                ///   parse time, so they never occur as SimpleNames.
                ///
                ///   The `allow_static' flag is used by MemberAccess only
                ///   and it is used to inform us that it is ok for us to 
                ///   avoid the static check, because MemberAccess might end
                ///   up resolving the Name as a Type name and the access as
                ///   a static type access.
                ///
                ///   ie: Type Type; .... { Type.GetType (""); }
                ///
                ///   Type is both an instance variable and a Type;  Type.GetType
                ///   is the static method not an instance method of type.
                /// </remarks>
                Expression SimpleNameResolve (EmitContext ec, Expression right_side, bool allow_static)
                {
                        Expression e = null;

                        //
                        // Stage 1: Performed by the parser (binding to locals or parameters).
                        //
                        Block current_block = ec.CurrentBlock;
                        if (current_block != null && current_block.IsVariableDefined (Name)){
                                LocalVariableReference var;

                                var = new LocalVariableReference (ec.CurrentBlock, Name, loc);

                                if (right_side != null)
                                        return var.ResolveLValue (ec, right_side);
                                else
                                        return var.Resolve (ec);
                        }

                        if (current_block != null){
                                int idx = -1;
                                Parameter par = null;
                                Parameters pars = current_block.Parameters;
                                if (pars != null)
                                        par = pars.GetParameterByName (Name, out idx);

                                if (par != null) {
                                        ParameterReference param;
                                        
                                        param = new ParameterReference (pars, idx, Name, loc);

                                        if (right_side != null)
                                                return param.ResolveLValue (ec, right_side);
                                        else
                                                return param.Resolve (ec);
                                }
                        }

                        //
                        // Stage 2: Lookup members 
                        //

                        //
                        // For enums, the TypeBuilder is not ec.DeclSpace.TypeBuilder
                        // Hence we have two different cases
                        //

                        DeclSpace lookup_ds = ec.DeclSpace;
                        do {
                                if (lookup_ds.TypeBuilder == null)
                                        break;

                                e = MemberLookup (ec, lookup_ds.TypeBuilder, Name, loc);
                                if (e != null)
                                        break;

                                //
                                // Classes/structs keep looking, enums break
                                //
                                if (lookup_ds is TypeContainer)
                                        lookup_ds = ((TypeContainer) lookup_ds).Parent;
                                else
                                        break;
                        } while (lookup_ds != null);
                                
                        if (e == null && ec.ContainerType != null)
                                e = MemberLookup (ec, ec.ContainerType, Name, loc);

                        if (e == null)
                                return DoResolveType (ec);

                        if (e is TypeExpr)
                                return e;

                        if (e is IMemberExpr) {
                                e = MemberAccess.ResolveMemberAccess (ec, e, null, loc, this);
                                if (e == null)
                                        return null;

                                IMemberExpr me = e as IMemberExpr;
                                if (me == null)
                                        return e;

                                // This fails if ResolveMemberAccess() was unable to decide whether
                                // it's a field or a type of the same name.
                                if (!me.IsStatic && (me.InstanceExpression == null))
                                        return e;

                                if (right_side != null)
                                        e = e.DoResolveLValue (ec, right_side);
                                else
                                        e = e.DoResolve (ec);

                                return e;                               
                        }

                        if (ec.IsStatic || ec.IsFieldInitializer){
                                if (allow_static)
                                        return e;

                                return MemberStaticCheck (ec, e);
                        } else
                                return e;
                }
                
                public override void Emit (EmitContext ec)
                {
                        //
                        // If this is ever reached, then we failed to
                        // find the name as a namespace
                        //

                        Error (103, "The name `" + Name +
                               "' does not exist in the class `" +
                               ec.DeclSpace.Name + "'");
                }

                public override string ToString ()
                {
                        return Name;
                }
        }
        
        /// <summary>
        ///   Fully resolved expression that evaluates to a type
        /// </summary>
        public class TypeExpr : Expression, ITypeExpression {
                public TypeExpr (Type t, Location l)
                {
                        Type = t;
                        eclass = ExprClass.Type;
                        loc = l;
                }

                public virtual Expression DoResolveType (EmitContext ec)
                {
                        return this;
                }

                override public Expression DoResolve (EmitContext ec)
                {
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        throw new Exception ("Should never be called");
                }
        }

        /// <summary>
        ///   Used to create types from a fully qualified name.  These are just used
        ///   by the parser to setup the core types.  A TypeLookupExpression is always
        ///   classified as a type.
        /// </summary>
        public class TypeLookupExpression : TypeExpr {
                string name;
                
                public TypeLookupExpression (string name) : base (null, Location.Null)
                {
                        this.name = name;
                }

                public override Expression DoResolveType (EmitContext ec)
                {
                        if (type == null)
                                type = RootContext.LookupType (ec.DeclSpace, name, false, Location.Null);
                        return this;
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        return DoResolveType (ec);
                }

                public override void Emit (EmitContext ec)
                {
                        throw new Exception ("Should never be called");
                }

                public override string ToString ()
                {
                        return name;
                }
        }

        /// <summary>
        ///   MethodGroup Expression.
        ///  
        ///   This is a fully resolved expression that evaluates to a type
        /// </summary>
        public class MethodGroupExpr : Expression, IMemberExpr {
                public MethodBase [] Methods;
                Expression instance_expression = null;
                
                public MethodGroupExpr (MemberInfo [] mi, Location l)
                {
                        Methods = new MethodBase [mi.Length];
                        mi.CopyTo (Methods, 0);
                        eclass = ExprClass.MethodGroup;
                        type = TypeManager.object_type;
                        loc = l;
                }

                public MethodGroupExpr (ArrayList list, Location l)
                {
                        Methods = new MethodBase [list.Count];

                        try {
                                list.CopyTo (Methods, 0);
                        } catch {
                                foreach (MemberInfo m in list){
                                        if (!(m is MethodBase)){
                                                Console.WriteLine ("Name " + m.Name);
                                                Console.WriteLine ("Found a: " + m.GetType ().FullName);
                                        }
                                }
                                throw;
                        }
                        loc = l;
                        eclass = ExprClass.MethodGroup;
                        type = TypeManager.object_type;
                }
                
                //
                // `A method group may have associated an instance expression' 
                // 
                public Expression InstanceExpression {
                        get {
                                return instance_expression;
                        }

                        set {
                                instance_expression = value;
                        }
                }

                public string Name {
                        get {
                                return Methods [0].Name;
                        }
                }

                public bool IsInstance {
                        get {
                                foreach (MethodBase mb in Methods)
                                        if (!mb.IsStatic)
                                                return true;

                                return false;
                        }
                }

                public bool IsStatic {
                        get {
                                foreach (MethodBase mb in Methods)
                                        if (mb.IsStatic)
                                                return true;

                                return false;
                        }
                }
                
                override public Expression DoResolve (EmitContext ec)
                {
                        return this;
                }

                public void ReportUsageError ()
                {
                        Report.Error (654, loc, "Method `" + Methods [0].DeclaringType + "." +
                                      Methods [0].Name + "()' is referenced without parentheses");
                }

                override public void Emit (EmitContext ec)
                {
                        ReportUsageError ();
                }

                bool RemoveMethods (bool keep_static)
                {
                        ArrayList smethods = new ArrayList ();

                        foreach (MethodBase mb in Methods){
                                if (mb.IsStatic == keep_static)
                                        smethods.Add (mb);
                        }

                        if (smethods.Count == 0)
                                return false;

                        Methods = new MethodBase [smethods.Count];
                        smethods.CopyTo (Methods, 0);

                        return true;
                }
                
                /// <summary>
                ///   Removes any instance methods from the MethodGroup, returns
                ///   false if the resulting set is empty.
                /// </summary>
                public bool RemoveInstanceMethods ()
                {
                        return RemoveMethods (true);
                }

                /// <summary>
                ///   Removes any static methods from the MethodGroup, returns
                ///   false if the resulting set is empty.
                /// </summary>
                public bool RemoveStaticMethods ()
                {
                        return RemoveMethods (false);
                }
        }

        /// <summary>
        ///   Fully resolved expression that evaluates to a Field
        /// </summary>
        public class FieldExpr : Expression, IAssignMethod, IMemoryLocation, IMemberExpr {
                public readonly FieldInfo FieldInfo;
                Expression instance_expr;
                
                public FieldExpr (FieldInfo fi, Location l)
                {
                        FieldInfo = fi;
                        eclass = ExprClass.Variable;
                        type = fi.FieldType;
                        loc = l;
                }

                public string Name {
                        get {
                                return FieldInfo.Name;
                        }
                }

                public bool IsInstance {
                        get {
                                return !FieldInfo.IsStatic;
                        }
                }

                public bool IsStatic {
                        get {
                                return FieldInfo.IsStatic;
                        }
                }

                public Expression InstanceExpression {
                        get {
                                return instance_expr;
                        }

                        set {
                                instance_expr = value;
                        }
                }

                override public Expression DoResolve (EmitContext ec)
                {
                        if (!FieldInfo.IsStatic){
                                if (instance_expr == null){
                                        throw new Exception ("non-static FieldExpr without instance var\n" +
                                                             "You have to assign the Instance variable\n" +
                                                             "Of the FieldExpr to set this\n");
                                }

                                // Resolve the field's instance expression while flow analysis is turned
                                // off: when accessing a field "a.b", we must check whether the field
                                // "a.b" is initialized, not whether the whole struct "a" is initialized.
                                instance_expr = instance_expr.Resolve (ec, ResolveFlags.VariableOrValue |
                                                                       ResolveFlags.DisableFlowAnalysis);
                                if (instance_expr == null)
                                        return null;
                        }

                        // If the instance expression is a local variable or parameter.
                        IVariable var = instance_expr as IVariable;
                        if ((var != null) && !var.IsFieldAssigned (ec, FieldInfo.Name, loc))
                                return null;

                        return this;
                }

                void Report_AssignToReadonly (bool is_instance)
                {
                        string msg;
                        
                        if (is_instance)
                                msg = "Readonly field can not be assigned outside " +
                                "of constructor or variable initializer";
                        else
                                msg = "A static readonly field can only be assigned in " +
                                "a static constructor";

                        Report.Error (is_instance ? 191 : 198, loc, msg);
                }
                
                override public Expression DoResolveLValue (EmitContext ec, Expression right_side)
                {
                        IVariable var = instance_expr as IVariable;
                        if (var != null)
                                var.SetFieldAssigned (ec, FieldInfo.Name);

                        Expression e = DoResolve (ec);

                        if (e == null)
                                return null;
                        
                        if (!FieldInfo.IsInitOnly)
                                return this;

                        //
                        // InitOnly fields can only be assigned in constructors
                        //

                        if (ec.IsConstructor)
                                return this;

                        Report_AssignToReadonly (true);
                        
                        return null;
                }

                override public void Emit (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
                        bool is_volatile = false;

                        if (FieldInfo is FieldBuilder){
                                FieldBase f = TypeManager.GetField (FieldInfo);

                                if ((f.ModFlags & Modifiers.VOLATILE) != 0)
                                        is_volatile = true;
                                
                                f.status |= Field.Status.USED;
                        }
                        
                        if (FieldInfo.IsStatic){
                                if (is_volatile)
                                        ig.Emit (OpCodes.Volatile);
                                
                                ig.Emit (OpCodes.Ldsfld, FieldInfo);
                        } else {
                                if (instance_expr.Type.IsValueType){
                                        IMemoryLocation ml;
                                        LocalTemporary tempo = null;
                                        
                                        if (!(instance_expr is IMemoryLocation)){
                                                tempo = new LocalTemporary (
                                                        ec, instance_expr.Type);

                                                InstanceExpression.Emit (ec);
                                                tempo.Store (ec);
                                                ml = tempo;
                                        } else
                                                ml = (IMemoryLocation) instance_expr;

                                        ml.AddressOf (ec, AddressOp.Load);
                                } else 
                                        instance_expr.Emit (ec);

                                if (is_volatile)
                                        ig.Emit (OpCodes.Volatile);
                                
                                ig.Emit (OpCodes.Ldfld, FieldInfo);
                        }
                }

                public void EmitAssign (EmitContext ec, Expression source)
                {
                        FieldAttributes fa = FieldInfo.Attributes;
                        bool is_static = (fa & FieldAttributes.Static) != 0;
                        bool is_readonly = (fa & FieldAttributes.InitOnly) != 0;
                        ILGenerator ig = ec.ig;

                        if (is_readonly && !ec.IsConstructor){
                                Report_AssignToReadonly (!is_static);
                                return;
                        }
                        
                        if (!is_static){
                                Expression instance = instance_expr;

                                if (instance.Type.IsValueType){
                                        if (instance is IMemoryLocation){
                                                IMemoryLocation ml = (IMemoryLocation) instance;

                                                ml.AddressOf (ec, AddressOp.Store);
                                        } else
                                                throw new Exception ("The " + instance + " of type " +
                                                                     instance.Type +
                                                                     " represents a ValueType and does " +
                                                                     "not implement IMemoryLocation");
                                } else
                                        instance.Emit (ec);
                        }
                        source.Emit (ec);

                        if (FieldInfo is FieldBuilder){
                                FieldBase f = TypeManager.GetField (FieldInfo);
                                
                                if ((f.ModFlags & Modifiers.VOLATILE) != 0)
                                        ig.Emit (OpCodes.Volatile);
                        }
                        
                        if (is_static)
                                ig.Emit (OpCodes.Stsfld, FieldInfo);
                        else 
                                ig.Emit (OpCodes.Stfld, FieldInfo);

                        if (FieldInfo is FieldBuilder){
                                FieldBase f = TypeManager.GetField (FieldInfo);

                                f.status |= Field.Status.ASSIGNED;
                        }
                }
                
                public void AddressOf (EmitContext ec, AddressOp mode)
                {
                        ILGenerator ig = ec.ig;
                        
                        if (FieldInfo is FieldBuilder){
                                FieldBase f = TypeManager.GetField (FieldInfo);
                                if ((f.ModFlags & Modifiers.VOLATILE) != 0)
                                        ig.Emit (OpCodes.Volatile);
                        }

                        if (FieldInfo is FieldBuilder){
                                FieldBase f = TypeManager.GetField (FieldInfo);

                                if ((mode & AddressOp.Store) != 0)
                                        f.status |= Field.Status.ASSIGNED;
                                if ((mode & AddressOp.Load) != 0)
                                        f.status |= Field.Status.USED;
                        }

                        //
                        // Handle initonly fields specially: make a copy and then
                        // get the address of the copy.
                        //
                        if (FieldInfo.IsInitOnly){
                                if (ec.IsConstructor) {
                                        ig.Emit (OpCodes.Ldsflda, FieldInfo);
                                } else {
                                        LocalBuilder local;
                                
                                        Emit (ec);
                                        local = ig.DeclareLocal (type);
                                        ig.Emit (OpCodes.Stloc, local);
                                        ig.Emit (OpCodes.Ldloca, local);
                                }
                                return;
                        }

                        if (FieldInfo.IsStatic)
                                ig.Emit (OpCodes.Ldsflda, FieldInfo);
                        else {
                                if (instance_expr is IMemoryLocation)
                                        ((IMemoryLocation)instance_expr).AddressOf (ec, AddressOp.LoadStore);
                                else
                                        instance_expr.Emit (ec);
                                ig.Emit (OpCodes.Ldflda, FieldInfo);
                        }
                }
        }
        
        /// <summary>
        ///   Expression that evaluates to a Property.  The Assign class
        ///   might set the `Value' expression if we are in an assignment.
        ///
        ///   This is not an LValue because we need to re-write the expression, we
        ///   can not take data from the stack and store it.  
        /// </summary>
        public class PropertyExpr : ExpressionStatement, IAssignMethod, IMemberExpr {
                public readonly PropertyInfo PropertyInfo;
                public bool IsBase;
                MethodInfo [] Accessors;
                bool is_static;
                
                Expression instance_expr;

                public PropertyExpr (PropertyInfo pi, Location l)
                {
                        PropertyInfo = pi;
                        eclass = ExprClass.PropertyAccess;
                        is_static = false;
                        loc = l;
                        Accessors = TypeManager.GetAccessors (pi);

                        if (Accessors != null)
                                foreach (MethodInfo mi in Accessors){
                                        if (mi != null)
                                                if (mi.IsStatic)
                                                        is_static = true;
                                }
                        else
                                Accessors = new MethodInfo [2];
                        
                        type = TypeManager.TypeToCoreType (pi.PropertyType);
                }

                public string Name {
                        get {
                                return PropertyInfo.Name;
                        }
                }

                public bool IsInstance {
                        get {
                                return !is_static;
                        }
                }

                public bool IsStatic {
                        get {
                                return is_static;
                        }
                }
                
                //
                // The instance expression associated with this expression
                //
                public Expression InstanceExpression {
                        set {
                                instance_expr = value;
                        }

                        get {
                                return instance_expr;
                        }
                }

                public bool VerifyAssignable ()
                {
                        if (!PropertyInfo.CanWrite){
                                Report.Error (200, loc, 
                                              "The property `" + PropertyInfo.Name +
                                              "' can not be assigned to, as it has not set accessor");
                                return false;
                        }

                        return true;
                }

                override public Expression DoResolve (EmitContext ec)
                {
                        if (!PropertyInfo.CanRead){
                                Report.Error (154, loc, 
                                              "The property `" + PropertyInfo.Name +
                                              "' can not be used in " +
                                              "this context because it lacks a get accessor");
                                return null;
                        }

                        return this;
                }

                override public Expression DoResolveLValue (EmitContext ec, Expression right_side)
                {
                        if (!PropertyInfo.CanWrite){
                                Report.Error (154, loc, 
                                              "The property `" + PropertyInfo.Name +
                                              "' can not be used in " +
                                              "this context because it lacks a set accessor");
                                return null;
                        }

                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        MethodInfo method = Accessors [0];

                        //
                        // Special case: length of single dimension array is turned into ldlen
                        //
                        if (method == TypeManager.int_array_get_length){
                                Type iet = instance_expr.Type;

                                //
                                // System.Array.Length can be called, but the Type does not
                                // support invoking GetArrayRank, so test for that case first
                                //
                                if (iet != TypeManager.array_type && (iet.GetArrayRank () == 1)){
                                        instance_expr.Emit (ec);
                                        ec.ig.Emit (OpCodes.Ldlen);
                                        return;
                                }
                        }

                        Invocation.EmitCall (ec, IsBase, IsStatic, instance_expr, method, null, loc);
                        
                }

                //
                // Implements the IAssignMethod interface for assignments
                //
                public void EmitAssign (EmitContext ec, Expression source)
                {
                        Argument arg = new Argument (source, Argument.AType.Expression);
                        ArrayList args = new ArrayList ();

                        args.Add (arg);
                        Invocation.EmitCall (ec, false, IsStatic, instance_expr, Accessors [1], args, loc);
                }

                override public void EmitStatement (EmitContext ec)
                {
                        Emit (ec);
                        ec.ig.Emit (OpCodes.Pop);
                }
        }

        /// <summary>
        ///   Fully resolved expression that evaluates to an Event
        /// </summary>
        public class EventExpr : Expression, IMemberExpr {
                public readonly EventInfo EventInfo;
                public Expression instance_expr;

                bool is_static;
                MethodInfo add_accessor, remove_accessor;
                
                public EventExpr (EventInfo ei, Location loc)
                {
                        EventInfo = ei;
                        this.loc = loc;
                        eclass = ExprClass.EventAccess;

                        add_accessor = TypeManager.GetAddMethod (ei);
                        remove_accessor = TypeManager.GetRemoveMethod (ei);
                        
                        if (add_accessor.IsStatic || remove_accessor.IsStatic)
                                is_static = true;

                        if (EventInfo is MyEventBuilder)
                                type = ((MyEventBuilder) EventInfo).EventType;
                        else
                                type = EventInfo.EventHandlerType;
                }

                public string Name {
                        get {
                                return EventInfo.Name;
                        }
                }

                public bool IsInstance {
                        get {
                                return !is_static;
                        }
                }

                public bool IsStatic {
                        get {
                                return is_static;
                        }
                }

                public Expression InstanceExpression {
                        get {
                                return instance_expr;
                        }

                        set {
                                instance_expr = value;
                        }
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // We are born fully resolved
                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        throw new Exception ("Should not happen I think");
                }

                public void EmitAddOrRemove (EmitContext ec, Expression source)
                {
                        Expression handler = ((Binary) source).Right;
                        
                        Argument arg = new Argument (handler, Argument.AType.Expression);
                        ArrayList args = new ArrayList ();
                                
                        args.Add (arg);
                        
                        if (((Binary) source).Oper == Binary.Operator.Addition)
                                Invocation.EmitCall (
                                        ec, false, IsStatic, instance_expr, add_accessor, args, loc);
                        else
                                Invocation.EmitCall (
                                        ec, false, IsStatic, instance_expr, remove_accessor, args, loc);
                }
        }
}