Fix warning.
[mono.git] / mcs / gmcs / convert.cs
index 32647f4f602763f4ccf02dde66d1c8bb990628d9..c6c625d01ca228b6f539f0eb424fa568c590f285 100644 (file)
@@ -29,13 +29,6 @@ namespace Mono.CSharp {
                //
                public static EmitContext ConstantEC = null;
                
-               static void Error_CannotConvertType (Location loc, Type source, Type target)
-               {
-                       Report.Error (30, loc, "Cannot convert type '" +
-                                     TypeManager.CSharpName (source) + "' to '" +
-                                     TypeManager.CSharpName (target) + "'");
-               }
-
                static Expression TypeParameter_to_Null (Expression expr, Type target_type,
                                                         Location loc)
                {
@@ -64,15 +57,6 @@ namespace Mono.CSharp {
                        return false;
                }
 
-               static Type TypeParam_EffectiveBaseType (EmitContext ec, Type t)
-               {
-                       GenericConstraints gc = TypeManager.GetTypeParameterConstraints (t);
-                       if (gc == null)
-                               return TypeManager.object_type;
-
-                       return TypeParam_EffectiveBaseType (ec, gc);
-               }
-
                static Type TypeParam_EffectiveBaseType (EmitContext ec, GenericConstraints gc)
                {
                        ArrayList list = new ArrayList ();
@@ -88,14 +72,6 @@ namespace Mono.CSharp {
                        return FindMostEncompassedType (ec, list);
                }
 
-               static Expression TypeParameterConversion (Expression expr, bool is_reference, Type target_type)
-               {
-                       if (is_reference)
-                               return new EmptyCast (expr, target_type);
-                       else
-                               return new BoxedCast (expr, target_type);
-               }
-
                static Expression ImplicitTypeParameterConversion (EmitContext ec, Expression expr,
                                                                   Type target_type)
                {
@@ -105,25 +81,24 @@ namespace Mono.CSharp {
 
                        if (gc == null) {
                                if (target_type == TypeManager.object_type)
-                                       return new BoxedCast (expr);
+                                       return new BoxedCast (expr, target_type);
 
                                return null;
                        }
 
                        // We're converting from a type parameter which is known to be a reference type.
-                       bool is_reference = gc.IsReferenceType;
                        Type base_type = TypeParam_EffectiveBaseType (ec, gc);
 
                        if (TypeManager.IsSubclassOf (base_type, target_type))
-                               return TypeParameterConversion (expr, is_reference, target_type);
+                               return new ClassCast (expr, target_type);
 
                        if (target_type.IsInterface) {
                                if (TypeManager.ImplementsInterface (base_type, target_type))
-                                       return TypeParameterConversion (expr, is_reference, target_type);
+                                       return new ClassCast (expr, target_type);
 
                                foreach (Type t in gc.InterfaceConstraints) {
                                        if (TypeManager.IsSubclassOf (t, target_type))
-                                               return TypeParameterConversion (expr, is_reference, target_type);
+                                               return new ClassCast (expr, target_type);
                                }
                        }
 
@@ -131,7 +106,7 @@ namespace Mono.CSharp {
                                if (!t.IsGenericParameter)
                                        continue;
                                if (TypeManager.IsSubclassOf (t, target_type))
-                                       return TypeParameterConversion (expr, is_reference, target_type);
+                                       return new ClassCast (expr, target_type);
                        }
 
                        return null;
@@ -166,9 +141,9 @@ namespace Mono.CSharp {
                                        return null;
 
                                if (TypeManager.IsValueType (expr_type))
-                                       return new BoxedCast (expr);
+                                       return new BoxedCast (expr, target_type);
                                if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
-                                       if (target_type == TypeManager.anonymous_method_type)
+                                       if (expr_type == TypeManager.anonymous_method_type)
                                                return null;
                                        return new EmptyCast (expr, target_type);
                                }
@@ -176,7 +151,7 @@ namespace Mono.CSharp {
                                return null;
                        } else if (target_type == TypeManager.value_type) {
                                if (TypeManager.IsValueType (expr_type))
-                                       return new BoxedCast (expr);
+                                       return new BoxedCast (expr, target_type);
                                if (expr_type == TypeManager.null_type)
                                        return new NullCast (expr, target_type);
 
@@ -188,7 +163,7 @@ namespace Mono.CSharp {
                                // a boxing conversion
                                //
                                if (expr_type.IsEnum || expr_type.IsGenericParameter)
-                                       return new BoxedCast (expr);
+                                       return new BoxedCast (expr, target_type);
 
                                return new EmptyCast (expr, target_type);
                        }
@@ -201,7 +176,7 @@ namespace Mono.CSharp {
                        // from the null type to any reference-type.
                        if (expr_type == TypeManager.null_type){
                                if (target_type.IsPointer)
-                                       return new EmptyCast (expr, target_type);
+                                       return new EmptyCast (NullPointer.Null, target_type);
                                        
                                if (!target_type.IsValueType)
                                        return new NullCast (expr, target_type);
@@ -234,7 +209,7 @@ namespace Mono.CSharp {
                                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 ()) {
@@ -257,7 +232,11 @@ namespace Mono.CSharp {
                        // from an array-type to System.Array
                        if (expr_type.IsArray && target_type == TypeManager.array_type)
                                return new EmptyCast (expr, target_type);
-                               
+
+                       // from an array-type of type T to IEnumerable<T>
+                       if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
+                               return new EmptyCast (expr, target_type);
+
                        // from any delegate type to System.Delegate
                        if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
                            target_type == TypeManager.delegate_type)
@@ -282,6 +261,9 @@ namespace Mono.CSharp {
                //
                public static bool ImplicitReferenceConversionExists (EmitContext ec, Expression expr, Type target_type)
                {
+                       if (target_type.IsValueType)
+                               return false;
+
                        Type expr_type = expr.Type;
 
                        if (expr_type.IsGenericParameter)
@@ -346,7 +328,11 @@ namespace Mono.CSharp {
                        // from an array-type to System.Array
                        if (expr_type.IsArray && (target_type == TypeManager.array_type))
                                return true;
-                               
+
+                       // from an array-type of type T to IEnumerable<T>
+                       if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
+                               return true;
+
                        // from any delegate type to System.Delegate
                        if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
                            target_type == TypeManager.delegate_type)
@@ -382,7 +368,7 @@ namespace Mono.CSharp {
                ///   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 target_type)
                {
                        Type expr_type = expr.Type;
 
@@ -405,7 +391,7 @@ namespace Mono.CSharp {
                                        //
                                        long v = ((LongConstant) expr).Value;
                                        if (v >= 0)
-                                               return new ULongConstant ((ulong) v);
+                                               return new ULongConstant ((ulong) v, expr.Location);
                                } 
                        }
                        
@@ -413,7 +399,7 @@ namespace Mono.CSharp {
 
                        if (expr_type == TypeManager.sbyte_type){
                                //
-                               // From sbyte to short, int, long, float, double.
+                               // From sbyte to short, int, long, float, double, decimal
                                //
                                if (real_target_type == TypeManager.int32_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
@@ -425,9 +411,11 @@ namespace Mono.CSharp {
                                        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 new CastToDecimal (expr);
                        } else if (expr_type == TypeManager.byte_type){
                                //
-                               // From byte to short, ushort, int, uint, long, ulong, float, double
+                               // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
                                // 
                                if ((real_target_type == TypeManager.short_type) ||
                                    (real_target_type == TypeManager.ushort_type) ||
@@ -443,9 +431,12 @@ namespace Mono.CSharp {
                                        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 new CastToDecimal (expr);
+                               
                        } else if (expr_type == TypeManager.short_type){
                                //
-                               // From short to int, long, float, double
+                               // From short to int, long, float, double, decimal
                                // 
                                if (real_target_type == TypeManager.int32_type)
                                        return new EmptyCast (expr, target_type);
@@ -455,9 +446,12 @@ namespace Mono.CSharp {
                                        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 new CastToDecimal (expr);
+                               
                        } else if (expr_type == TypeManager.ushort_type){
                                //
-                               // From ushort to int, uint, long, ulong, float, double
+                               // From ushort to int, uint, long, ulong, float, double, decimal
                                //
                                if (real_target_type == TypeManager.uint32_type)
                                        return new EmptyCast (expr, target_type);
@@ -472,9 +466,11 @@ namespace Mono.CSharp {
                                        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 new CastToDecimal (expr);
                        } else if (expr_type == TypeManager.int32_type){
                                //
-                               // From int to long, float, double
+                               // From int to long, float, double, decimal
                                //
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
@@ -482,9 +478,11 @@ namespace Mono.CSharp {
                                        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 new CastToDecimal (expr);
                        } else if (expr_type == TypeManager.uint32_type){
                                //
-                               // From uint to long, ulong, float, double
+                               // From uint to long, ulong, float, double, decimal
                                //
                                if (real_target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
@@ -496,6 +494,8 @@ namespace Mono.CSharp {
                                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 new CastToDecimal (expr);
                        } else if (expr_type == TypeManager.int64_type){
                                //
                                // From long/ulong to float, double
@@ -503,7 +503,9 @@ namespace Mono.CSharp {
                                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);     
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
+                               if (real_target_type == TypeManager.decimal_type)
+                                       return new CastToDecimal (expr);
                        } else if (expr_type == TypeManager.uint64_type){
                                //
                                // From ulong to float, double
@@ -513,10 +515,12 @@ namespace Mono.CSharp {
                                                               OpCodes.Conv_R8);
                                if (real_target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
-                                                              OpCodes.Conv_R4);        
+                                                              OpCodes.Conv_R4);
+                               if (real_target_type == TypeManager.decimal_type)
+                                       return new CastToDecimal (expr);
                        } else if (expr_type == TypeManager.char_type){
                                //
-                               // From char to ushort, int, uint, long, ulong, float, double
+                               // From char to ushort, int, uint, long, ulong, float, double, decimal
                                // 
                                if ((real_target_type == TypeManager.ushort_type) ||
                                    (real_target_type == TypeManager.int32_type) ||
@@ -530,6 +534,8 @@ namespace Mono.CSharp {
                                        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 new CastToDecimal (expr);
                        } else if (expr_type == TypeManager.float_type){
                                //
                                // float to double
@@ -541,15 +547,19 @@ namespace Mono.CSharp {
                        return null;
                }
 
-
                /// <summary>
                ///  Same as ImplicitStandardConversionExists 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 ((expr is NullLiteral) && target_type.IsGenericParameter)
-                               return TypeParameter_to_Null (target_type);
+                       if (expr is NullLiteral) {
+                               if (target_type.IsGenericParameter)
+                                       return TypeParameter_to_Null (target_type);
+
+                               if (TypeManager.IsNullableType (target_type))
+                                       return true;
+                       }
 
                        if (ImplicitStandardConversionExists (ec, expr, target_type))
                                return true;
@@ -564,9 +574,7 @@ namespace Mono.CSharp {
 
                public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
                {
-                       Expression dummy = ImplicitUserConversion (
-                               ec, new EmptyExpression (source), target, Location.Null);
-                       return dummy != null;
+                       return ImplicitUserConversion (ec, new EmptyExpression (source), target, Location.Null) != null;
                }
 
                /// <summary>
@@ -587,11 +595,12 @@ namespace Mono.CSharp {
                        if (expr_type.Equals (target_type))
                                return true;
 
+
                        // First numeric conversions 
 
                        if (expr_type == TypeManager.sbyte_type){
                                //
-                               // From sbyte to short, int, long, float, double.
+                               // From sbyte to short, int, long, float, double, decimal
                                //
                                if ((target_type == TypeManager.int32_type) || 
                                    (target_type == TypeManager.int64_type) ||
@@ -603,7 +612,7 @@ namespace Mono.CSharp {
                                
                        } else if (expr_type == TypeManager.byte_type){
                                //
-                               // From byte to short, ushort, int, uint, long, ulong, float, double
+                               // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
                                // 
                                if ((target_type == TypeManager.short_type) ||
                                    (target_type == TypeManager.ushort_type) ||
@@ -618,7 +627,7 @@ namespace Mono.CSharp {
        
                        } else if (expr_type == TypeManager.short_type){
                                //
-                               // From short to int, long, float, double
+                               // From short to int, long, double, float, decimal
                                // 
                                if ((target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.int64_type) ||
@@ -629,7 +638,7 @@ namespace Mono.CSharp {
                                        
                        } else if (expr_type == TypeManager.ushort_type){
                                //
-                               // From ushort to int, uint, long, ulong, float, double
+                               // From ushort to int, uint, long, ulong, double, float, decimal
                                //
                                if ((target_type == TypeManager.uint32_type) ||
                                    (target_type == TypeManager.uint64_type) ||
@@ -642,7 +651,7 @@ namespace Mono.CSharp {
                                    
                        } else if (expr_type == TypeManager.int32_type){
                                //
-                               // From int to long, float, double
+                               // From int to long, double, float, decimal
                                //
                                if ((target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
@@ -652,7 +661,7 @@ namespace Mono.CSharp {
                                        
                        } else if (expr_type == TypeManager.uint32_type){
                                //
-                               // From uint to long, ulong, float, double
+                               // From uint to long, ulong, double, float, decimal
                                //
                                if ((target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.uint64_type) ||
@@ -664,7 +673,7 @@ namespace Mono.CSharp {
                        } else if ((expr_type == TypeManager.uint64_type) ||
                                   (expr_type == TypeManager.int64_type)) {
                                //
-                               // From long/ulong to float, double
+                               // From long/ulong to double, float, decimal
                                //
                                if ((target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
@@ -673,7 +682,7 @@ namespace Mono.CSharp {
                                    
                        } else if (expr_type == TypeManager.char_type){
                                //
-                               // From char to ushort, int, uint, long, ulong, float, double
+                               // From char to ushort, int, uint, ulong, long, float, double, decimal
                                // 
                                if ((target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
@@ -693,6 +702,21 @@ namespace Mono.CSharp {
                                        return true;
                        }       
                        
+                       if (expr.eclass == ExprClass.MethodGroup){
+                               if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
+                                       MethodGroupExpr mg = expr as MethodGroupExpr;
+                                       if (mg != null){
+                                               //
+                                               // This should not happen frequently, so we can create an object
+                                               // to test compatibility
+                                               //
+                                               Expression c = ImplicitDelegateCreation.Create (
+                                                       ec, mg, target_type, true, Location.Null);
+                                               return c != null;
+                                       }
+                               }
+                       }
+                       
                        if (ImplicitReferenceConversionExists (ec, expr, target_type))
                                return true;
 
@@ -706,7 +730,7 @@ namespace Mono.CSharp {
                                        if (value >= SByte.MinValue && value <= SByte.MaxValue)
                                                return true;
                                } else if (target_type == TypeManager.byte_type){
-                                       if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
+                                       if (value >= 0 && value <= Byte.MaxValue)
                                                return true;
                                } else if (target_type == TypeManager.short_type){
                                        if (value >= Int16.MinValue && value <= Int16.MaxValue)
@@ -738,7 +762,7 @@ namespace Mono.CSharp {
                                // we just inline it
                                //
                                long v = ((LongConstant) expr).Value;
-                               if (v > 0)
+                               if (v >= 0)
                                        return true;
                        }
                        
@@ -751,31 +775,33 @@ namespace Mono.CSharp {
                                        return true;
                        }
 
+                       //
+                       // If `expr_type' implements `target_type' (which is an iface)
+                       // see TryImplicitIntConversion
+                       // 
+                       if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
+                               return true;
+
                        if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
                                return true;
 
+                       if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
+                               return true;
+
                        if (expr_type == TypeManager.anonymous_method_type){
                                if (!TypeManager.IsDelegateType (target_type))
                                        return false;
 
                                AnonymousMethod am = (AnonymousMethod) expr;
-                               int errors = Report.Errors;
 
                                Expression conv = am.Compatible (ec, target_type, true);
                                if (conv != null)
                                        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
@@ -784,31 +810,40 @@ namespace Mono.CSharp {
                {
                        Type best = null;
 
-                       if (priv_fmet_param == null)
-                               priv_fmet_param = new EmptyExpression ();
+                       if (types.Count == 0)
+                               return null;
 
-                       foreach (Type t in types){
-                               priv_fmet_param.SetType (t);
-                               
+                       if (types.Count == 1)
+                               return (Type) types [0];
+
+                       EmptyExpression expr = EmptyExpression.Grab ();
+
+                       foreach (Type t in types) {
                                if (best == null) {
                                        best = t;
                                        continue;
                                }
-                               
-                               if (ImplicitStandardConversionExists (ec, priv_fmet_param, best))
+
+                               expr.SetType (t);
+                               if (ImplicitStandardConversionExists (ec, expr, best))
                                        best = t;
                        }
 
+                       expr.SetType (best);
+                       foreach (Type t in types) {
+                               if (best == t)
+                                       continue;
+                               if (!ImplicitStandardConversionExists (ec, expr, t)) {
+                                       best = null;
+                                       break;
+                               }
+                       }
+
+                       EmptyExpression.Release (expr);
+
                        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
@@ -817,77 +852,62 @@ namespace Mono.CSharp {
                {
                        Type best = null;
 
-                       if (priv_fmee_ret == null)
-                               priv_fmee_ret = new EmptyExpression ();
+                       if (types.Count == 0)
+                               return null;
+
+                       if (types.Count == 1)
+                               return (Type) types [0];
 
-                       foreach (Type t in types){
-                               priv_fmee_ret.SetType (best);
+                       EmptyExpression expr = EmptyExpression.Grab ();
 
+                       foreach (Type t in types) {
                                if (best == null) {
                                        best = t;
                                        continue;
                                }
 
-                               if (ImplicitStandardConversionExists (ec, priv_fmee_ret, t))
+                               expr.SetType (best);
+                               if (ImplicitStandardConversionExists (ec, expr, t))
                                        best = t;
                        }
-                       
+
+                       foreach (Type t in types) {
+                               if (best == t)
+                                       continue;
+                               expr.SetType (t);
+                               if (!ImplicitStandardConversionExists (ec, expr, best)) {
+                                       best = null;
+                                       break;
+                               }
+                       }
+
+                       EmptyExpression.Release (expr);
+
                        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 (EmitContext ec, MethodGroupExpr me,
-                                                          Expression source, bool apply_explicit_conv_rules,
-                                                          Location loc)
+               static public Type FindMostSpecificSource (EmitContext ec, IList list,
+                                                          Expression source, bool apply_explicit_conv_rules)
                {
                        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
                        //
                        Type source_type = source.Type;
-                       foreach (MethodBase mb in me.Methods){
-                               ParameterData pd = Invocation.GetParameterData (mb);
+                       foreach (MethodBase mb in list){
+                               ParameterData pd = TypeManager.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 (ImplicitStandardConversionExists (ec, priv_fms_expr, source_type))
-                                               src_types_set.Add (param_type);
-                                       else {
-                                               if (ImplicitStandardConversionExists (ec, source, param_type))
-                                                       src_types_set.Add (param_type);
-                                       }
-                               } else {
-                                       //
-                                       // Only if S is encompassed by param_type
-                                       //
-                                       if (ImplicitStandardConversionExists (ec, source, param_type))
-                                               src_types_set.Add (param_type);
-                               }
+                               src_types_set.Add (param_type);
                        }
                        
                        //
@@ -914,58 +934,23 @@ namespace Mono.CSharp {
                                return FindMostEncompassedType (ec, 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 (EmitContext ec, MethodGroupExpr me,
-                                                          Type target, bool apply_explicit_conv_rules,
-                                                          Location loc)
+               static public Type FindMostSpecificTarget (EmitContext ec, IList list,
+                                                          Type target, bool apply_explicit_conv_rules)
                {
                        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){
+                       foreach (MethodInfo mi in list){
                                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 (ImplicitStandardConversionExists (ec, priv_fms_expr, target))
-                                               tgt_types_set.Add (ret_type);
-                                       else {
-                                               priv_fms_expr.SetType (target);
-                                               if (ImplicitStandardConversionExists (ec, 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 (ImplicitStandardConversionExists (ec, priv_fms_expr, target))
-                                               tgt_types_set.Add (ret_type);
-                               }
+                               tgt_types_set.Add (ret_type);
                        }
 
                        //
@@ -974,13 +959,17 @@ namespace Mono.CSharp {
                        if (apply_explicit_conv_rules) {
                                ArrayList candidate_set = new ArrayList ();
 
+                               EmptyExpression expr = EmptyExpression.Grab ();
+
                                foreach (Type ret_type in tgt_types_set){
-                                       priv_fmt_expr.SetType (ret_type);
+                                       expr.SetType (ret_type);
                                        
-                                       if (ImplicitStandardConversionExists (ec, priv_fmt_expr, target))
+                                       if (ImplicitStandardConversionExists (ec, expr, target))
                                                candidate_set.Add (ret_type);
                                }
 
+                               EmptyExpression.Release (expr);
+
                                if (candidate_set.Count != 0)
                                        return FindMostEncompassingType (ec, candidate_set);
                        }
@@ -1012,82 +1001,108 @@ namespace Mono.CSharp {
                        return UserDefinedConversion (ec, source, target, loc, true);
                }
 
-               static DoubleHash explicit_conv = new DoubleHash (100);
-               static DoubleHash implicit_conv = new DoubleHash (100);
-               /// <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)
+               static void AddConversionOperators (EmitContext ec, ArrayList list, 
+                                                   Expression source, Type target_type, 
+                                                   bool look_for_explicit,
+                                                   MethodGroupExpr mg)
                {
-                       Expression mg1 = null, mg2 = null;
-                       Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
-                       string op_name;
+                       if (mg == null)
+                               return;
 
-                       op_name = "op_Implicit";
+                       Type source_type = source.Type;
+                       EmptyExpression expr = EmptyExpression.Grab ();
+                       foreach (MethodInfo m in mg.Methods) {
+                               ParameterData pd = TypeManager.GetParameterData (m);
+                               Type return_type = m.ReturnType;
+                               Type arg_type = pd.ParameterType (0);
+
+                               if (source_type != arg_type) {
+                                       if (!ImplicitStandardConversionExists (ec, source, arg_type)) {
+                                               if (!look_for_explicit)
+                                                       continue;
+                                               expr.SetType (arg_type);
+                                               if (!ImplicitStandardConversionExists (ec, expr, source_type))
+                                                       continue;
+                                       }
+                               }
 
-                       MethodGroupExpr union3;
-                       object r;
-                       if ((look_for_explicit ? explicit_conv : implicit_conv).Lookup (source_type, target_type, out r))
-                               return (MethodGroupExpr) r;
+                               if (target_type != return_type) {
+                                       expr.SetType (return_type);
+                                       if (!ImplicitStandardConversionExists (ec, expr, target_type)) {
+                                               if (!look_for_explicit)
+                                                       continue;
+                                               expr.SetType (target_type);
+                                               if (!ImplicitStandardConversionExists (ec, expr, return_type))
+                                                       continue;
+                                       }
+                               }
 
-                       mg1 = Expression.MethodLookup (ec, source_type, op_name, loc);
-                       if (source_type.BaseType != null)
-                               mg2 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
+                               list.Add (m);
+                       }
 
-                       if (mg1 == null)
-                               union3 = (MethodGroupExpr) mg2;
-                       else if (mg2 == null)
-                               union3 = (MethodGroupExpr) mg1;
-                       else
-                               union3 = Invocation.MakeUnionSet (mg1, mg2, loc);
+                       EmptyExpression.Release (expr);
+               }
 
-                       mg1 = Expression.MethodLookup (ec, target_type, op_name, loc);
-                       if (mg1 != null){
-                               if (union3 != null)
-                                       union3 = Invocation.MakeUnionSet (union3, mg1, loc);
-                               else
-                                       union3 = (MethodGroupExpr) mg1;
+               /// <summary>
+               ///   Compute the user-defined conversion operator from source_type to target_type. 
+               ///   `look_for_explicit' controls whether we should also include the list of explicit operators
+               /// </summary>
+               static MethodInfo GetConversionOperator (EmitContext ec, Expression source, Type target_type, bool look_for_explicit)
+               {
+                       ArrayList ops = new ArrayList (4);
+
+                       Type source_type = source.Type;
+
+                       if (source_type != TypeManager.decimal_type) {
+                               AddConversionOperators (ec, ops, source, target_type, look_for_explicit,
+                                       Expression.MethodLookup (ec, source_type, "op_Implicit", Location.Null) as MethodGroupExpr);
+                               if (look_for_explicit) {
+                                       AddConversionOperators (ec, ops, source, target_type, look_for_explicit,
+                                               Expression.MethodLookup (
+                                                       ec, source_type, "op_Explicit", Location.Null) as MethodGroupExpr);
+                               }
                        }
 
-                       if (target_type.BaseType != null)
-                               mg1 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
-                       
-                       if (mg1 != null){
-                               if (union3 != null)
-                                       union3 = Invocation.MakeUnionSet (union3, mg1, loc);
-                               else
-                                       union3 = (MethodGroupExpr) mg1;
+                       if (target_type != TypeManager.decimal_type) {
+                               AddConversionOperators (ec, ops, source, target_type, look_for_explicit,
+                                       Expression.MethodLookup (ec, target_type, "op_Implicit", Location.Null) as MethodGroupExpr);
+                               if (look_for_explicit) {
+                                       AddConversionOperators (ec, ops, source, target_type, look_for_explicit,
+                                               Expression.MethodLookup (
+                                                       ec, target_type, "op_Explicit", Location.Null) as MethodGroupExpr);
+                               }
                        }
 
-                       MethodGroupExpr union4 = null;
+                       if (ops.Count == 0)
+                               return null;
+
+                       Type most_specific_source = FindMostSpecificSource (ec, ops, source, look_for_explicit);
+                       if (most_specific_source == null)
+                               return null;
 
-                       if (look_for_explicit) {
-                               op_name = "op_Explicit";
+                       Type most_specific_target = FindMostSpecificTarget (ec, ops, target_type, look_for_explicit);
+                       if (most_specific_target == null)
+                               return null;
 
-                               mg5 = Expression.MemberLookup (ec, source_type, op_name, loc);
-                               if (source_type.BaseType != null)
-                                       mg6 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
-                               
-                               mg7 = Expression.MemberLookup (ec, target_type, op_name, loc);
-                               if (target_type.BaseType != null)
-                                       mg8 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
-                               
-                               MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
-                               MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);
+                       MethodInfo method = null;
 
-                               union4 = Invocation.MakeUnionSet (union5, union6, loc);
+                       foreach (MethodInfo m in ops) {
+                               if (m.ReturnType != most_specific_target)
+                                       continue;
+                               if (TypeManager.GetParameterData (m).ParameterType (0) != most_specific_source)
+                                       continue;
+                               // Ambiguous: more than one conversion operator satisfies the signature.
+                               if (method != null)
+                                       return null;
+                               method = m;
                        }
-                       
-                       MethodGroupExpr ret = Invocation.MakeUnionSet (union3, union4, loc);
-                       (look_for_explicit ? explicit_conv : implicit_conv).Insert (source_type, target_type, ret);
-                       return ret;
+
+                       return method;
                }
-               
+
+               static DoubleHash explicit_conv = new DoubleHash (100);
+               static DoubleHash implicit_conv = new DoubleHash (100);
+
                /// <summary>
                ///   User-defined conversions
                /// </summary>
@@ -1095,42 +1110,29 @@ namespace Mono.CSharp {
                                                                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;
+                       MethodInfo method = null;
 
-                       most_specific_source = FindMostSpecificSource (ec, union, source, look_for_explicit, loc);
-                       if (most_specific_source == null)
-                               return null;
-
-                       most_specific_target = FindMostSpecificTarget (ec, union, target, look_for_explicit, loc);
-                       if (most_specific_target == null) 
-                               return null;
+                       if (TypeManager.IsNullableType (source_type) && TypeManager.IsNullableType (target))
+                               return new Nullable.LiftedConversion (
+                                       source, target, true, look_for_explicit, loc).Resolve (ec);
 
-                       int count = 0;
+                       object o;
+                       DoubleHash hash = look_for_explicit ? explicit_conv : implicit_conv;
 
-                       
-                       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 (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
+                               method = (MethodInfo) o;
+                       } else {
+                               method = GetConversionOperator (ec, source, target, look_for_explicit);
+                               if (!(source is Constant))
+                                       hash.Insert (source_type, target, method);
                        }
-                       
-                       if (method == null || count > 1)
+
+                       if (method == null)
                                return null;
                        
-                       
+                       Type most_specific_source = TypeManager.GetParameterData (method).ParameterType (0);
+
                        //
                        // This will do the conversion to the best match that we
                        // found.  Now we need to perform an implict standard conversion
@@ -1146,7 +1148,7 @@ namespace Mono.CSharp {
                                return null;
 
                        Expression e;
-                       e =  new UserCast ((MethodInfo) method, source, loc);
+                       e =  new UserCast (method, source, loc);
                        if (e.Type != target){
                                if (!look_for_explicit)
                                        e = ImplicitConversionStandard (ec, e, target, loc);
@@ -1198,8 +1200,17 @@ namespace Mono.CSharp {
                        Type expr_type = expr.Type;
                        Expression e;
 
-                       if ((expr is NullLiteral) && target_type.IsGenericParameter)
-                               return TypeParameter_to_Null (expr, target_type, loc);
+                       if (expr is NullLiteral) {
+                               if (target_type.IsGenericParameter)
+                                       return TypeParameter_to_Null (expr, target_type, loc);
+
+                               if (TypeManager.IsNullableType (target_type))
+                                       return new Nullable.NullableLiteral (target_type, loc);
+                       }
+
+                       if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
+                               return new Nullable.LiftedConversion (
+                                       expr, target_type, false, false, loc).Resolve (ec);
 
                        if (expr.eclass == ExprClass.MethodGroup){
                                if (!TypeManager.IsDelegateType (target_type)){
@@ -1212,14 +1223,15 @@ namespace Mono.CSharp {
                                if (RootContext.Version != LanguageVersion.ISO_1){
                                        MethodGroupExpr mg = expr as MethodGroupExpr;
                                        if (mg != null)
-                                               return ImplicitDelegateCreation.Create (ec, mg, target_type, loc);
+                                               return ImplicitDelegateCreation.Create (
+                                                       ec, mg, target_type, false, loc);
                                }
                        }
 
                        if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
                                return expr;
 
-                       e = ImplicitNumericConversion (ec, expr, target_type, loc);
+                       e = ImplicitNumericConversion (ec, expr, target_type);
                        if (e != null)
                                return e;
 
@@ -1248,23 +1260,20 @@ namespace Mono.CSharp {
                                        if (target_type.IsPointer){
                                                if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
                                                        return expr;
+
+                                               //return null;
                                        }
                                }
                                
-                               if (target_type.IsPointer) {
-                                       if (expr_type == TypeManager.null_type)
-                                               return new EmptyCast (expr, target_type);
-
-                                       if (expr_type == TypeManager.void_ptr_type)
-                                               return new EmptyCast (expr, target_type);
-                               }
+                               if (expr_type == TypeManager.null_type && target_type.IsPointer)
+                                       return new EmptyCast (NullPointer.Null, target_type);
                        }
 
                        if (expr_type == TypeManager.anonymous_method_type){
                                if (!TypeManager.IsDelegateType (target_type)){
                                        Report.Error (1660, loc,
-                                                             "Cannot convert anonymous method to `{0}', since it is not a delegate",
-                                                             TypeManager.CSharpName (target_type));
+                                               "Cannot convert anonymous method block to type `{0}' because it is not a delegate type",
+                                               TypeManager.CSharpName (target_type));
                                        return null;
                                }
 
@@ -1288,7 +1297,7 @@ namespace Mono.CSharp {
                }
 
                /// <summary>
-               ///   Attemps to perform an implict constant conversion of the IntConstant
+               ///   Attempts to perform an implicit constant conversion of the IntConstant
                ///   into a different data type using casts (See Implicit Constant
                ///   Expression Conversions)
                /// </summary>
@@ -1298,19 +1307,19 @@ namespace Mono.CSharp {
 
                        if (target_type == TypeManager.sbyte_type){
                                if (value >= SByte.MinValue && value <= SByte.MaxValue)
-                                       return new SByteConstant ((sbyte) value);
+                                       return new SByteConstant ((sbyte) value, ic.Location);
                        } else if (target_type == TypeManager.byte_type){
                                if (value >= Byte.MinValue && value <= Byte.MaxValue)
-                                       return new ByteConstant ((byte) value);
+                                       return new ByteConstant ((byte) value, ic.Location);
                        } else if (target_type == TypeManager.short_type){
                                if (value >= Int16.MinValue && value <= Int16.MaxValue)
-                                       return new ShortConstant ((short) value);
+                                       return new ShortConstant ((short) value, ic.Location);
                        } else if (target_type == TypeManager.ushort_type){
                                if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
-                                       return new UShortConstant ((ushort) value);
+                                       return new UShortConstant ((ushort) value, ic.Location);
                        } else if (target_type == TypeManager.uint32_type){
                                if (value >= 0)
-                                       return new UIntConstant ((uint) value);
+                                       return new UIntConstant ((uint) value, ic.Location);
                        } else if (target_type == TypeManager.uint64_type){
                                //
                                // we can optimize this case: a positive int32
@@ -1318,11 +1327,11 @@ namespace Mono.CSharp {
                                // to do it.
                                //
                                if (value >= 0)
-                                       return new ULongConstant ((ulong) value);
+                                       return new ULongConstant ((ulong) value, ic.Location);
                        } else if (target_type == TypeManager.double_type)
-                               return new DoubleConstant ((double) value);
+                               return new DoubleConstant ((double) value, ic.Location);
                        else if (target_type == TypeManager.float_type)
-                               return new FloatConstant ((float) value);
+                               return new FloatConstant ((float) value, ic.Location);
                        
                        if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
                                Type underlying = TypeManager.EnumToUnderlying (target_type);
@@ -1331,27 +1340,27 @@ namespace Mono.CSharp {
                                //
                                // Possibly, we need to create a different 0 literal before passing
                                // to EnumConstant
-                               //n
+                               //
                                if (underlying == TypeManager.int64_type)
-                                       e = new LongLiteral (0);
+                                       e = new LongLiteral (0, ic.Location);
                                else if (underlying == TypeManager.uint64_type)
-                                       e = new ULongLiteral (0);
+                                       e = new ULongLiteral (0, ic.Location);
 
                                return new EnumConstant (e, target_type);
                        }
-                       return null;
-               }
 
-               static public void Error_CannotImplicitConversion (Location loc, Type source, Type target)
-               {
-                       Report.Error (29, loc, "Cannot convert implicitly from {0} to `{1}'",
-                                     source == TypeManager.anonymous_method_type ?
-                                     "anonymous method" : "`" + TypeManager.CSharpName (source) + "'",
-                                     TypeManager.CSharpName (target));
+                       //
+                       // If `target_type' is an interface and the type of `ic' implements the interface
+                       // e.g. target_type is IComparable, IConvertible, IFormattable
+                       //
+                       if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
+                               return new BoxedCast (ic, target_type);
+
+                       return null;
                }
 
                /// <summary>
-               ///   Attemptes to implicityly convert `target' into `type', using
+               ///   Attempts to implicitly convert `source' into `target_type', using
                ///   ImplicitConversion.  If there is no implicit conversion, then
                ///   an error is signaled
                /// </summary>
@@ -1378,183 +1387,158 @@ namespace Mono.CSharp {
                                }
                        }
 
-                       if (source is Constant){
-                               Constant c = (Constant) source;
-
-                               Expression.Error_ConstantValueCannotBeConverted (loc, c.AsString (), target_type);
-                               return null;
-                       }
-                       
-                       Error_CannotImplicitConversion (loc, source.Type, target_type);
-
+                       source.Error_ValueCannotBeConverted (loc, target_type, false);
                        return null;
                }
 
                static void Error_664 (Location loc, string type, string suffix) {
                        Report.Error (664, loc,
-                               "Literal of type double cannot be implicitly converted to type '{0}'. Add suffix '{1}' to create a literal of this type",
+                               "Literal of type double cannot be implicitly converted to type `{0}'. Add suffix `{1}' to create a literal of this type",
                                type, suffix);
                }
 
                /// <summary>
                ///   Performs the explicit numeric conversions
                /// </summary>
-               static Expression ExplicitNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
+               public static Expression ExplicitNumericConversion (Expression expr, Type target_type)
                {
                        Type expr_type = expr.Type;
-
-                       //
-                       // If we have an enumeration, extract the underlying type,
-                       // use this during the comparison, 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 (ImplicitStandardConversionExists (ec, expr, real_target_type)){
-                               Expression ce = ImplicitConversionStandard (ec, expr, real_target_type, loc);
-
-                               if (real_target_type != target_type)
-                                       return new EmptyCast (ce, target_type);
-                               return ce;
-                       }
-                       
                        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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
                        } else if (expr_type == TypeManager.float_type){
                                //
                                // From float to sbyte, byte, short,
@@ -1562,53 +1546,56 @@ namespace Mono.CSharp {
                                // or decimal
                                //
                                if (real_target_type == TypeManager.sbyte_type)
-                                       return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
+                               if (real_target_type == TypeManager.decimal_type)
+                                       return new CastToDecimal (expr, true);
                        } else if (expr_type == TypeManager.double_type){
                                //
-                               // From double to byte, byte, short,
+                               // From double to sbyte, 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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
+                                       return new ConvCast (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);
-                       } 
-
-                       // decimal is taken care of by the op_Explicit methods.
-
+                                       return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
+                               if (real_target_type == TypeManager.decimal_type)
+                                       return new CastToDecimal (expr, true);
+                       } else if (expr_type == TypeManager.decimal_type) {
+                               return new CastFromDecimal (expr, target_type).Resolve ();
+                       }
                        return null;
                }
 
@@ -1623,6 +1610,12 @@ namespace Mono.CSharp {
                        
                        if (source_type == target_type)
                                return true;
+                       
+                       //
+                       // From generic parameter to any type
+                       //
+                       if (source_type.IsGenericParameter)
+                               return true;
 
                        //
                        // From object to a generic parameter
@@ -1679,8 +1672,9 @@ namespace Mono.CSharp {
                                        
                                        Type source_element_type = TypeManager.GetElementType (source_type);
                                        Type target_element_type = TypeManager.GetElementType (target_type);
-                                       
-                                       if (!source_element_type.IsValueType && !target_element_type.IsValueType)
+
+                                       if (source_element_type.IsGenericParameter ||
+                                           (!source_element_type.IsValueType && !target_element_type.IsValueType))
                                                if (ExplicitReferenceConversionExists (source_element_type,
                                                                                       target_element_type))
                                                        return true;
@@ -1833,52 +1827,40 @@ namespace Mono.CSharp {
                ///   Performs an explicit conversion of the expression `expr' whose
                ///   type is expr.Type to `target_type'.
                /// </summary>
-               static public Expression ExplicitConversion (EmitContext ec, Expression expr,
+               static public Expression ExplicitConversionCore (EmitContext ec, Expression expr,
                                                             Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
-                       Type original_expr_type = expr_type;
-
-                       if (expr_type.IsSubclassOf (TypeManager.enum_type)){
-                               if (target_type == TypeManager.enum_type ||
-                                   target_type == TypeManager.object_type) {
-                                       if (expr is EnumConstant)
-                                               expr = ((EnumConstant) expr).Child;
-                                       // We really need all these casts here .... :-(
-                                       expr = new BoxedCast (new EmptyCast (expr, expr_type));
-                                       return new EmptyCast (expr, target_type);
-                               } else if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
-                                          target_type.IsSubclassOf (TypeManager.enum_type))
-                                       return new UnboxCast (expr, target_type);
 
-                               //
-                               // Notice that we have kept the expr_type unmodified, which is only
-                               // used later on to 
-                               if (expr is EnumConstant)
-                                       expr = ((EnumConstant) expr).Child;
-                               else
-                                       expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
-                               expr_type = expr.Type;
-                       }
-
-                       int errors = Report.Errors;
+                       // Explicit conversion includes implicit conversion and it used for enum underlying types too
                        Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
-                       if (Report.Errors > errors)
-                               return null;
-
-                       if (ne != null)
-                               return ne;
-
-                       ne = ExplicitNumericConversion (ec, expr, target_type, loc);
                        if (ne != null)
                                return ne;
 
                        //
-                       // Unboxing conversion.
+                       // Unboxing conversions; only object types can be convertible to enum
                        //
-                       if (expr_type == TypeManager.object_type && target_type.IsValueType)
+                       if (expr_type == TypeManager.object_type && target_type.IsValueType || expr_type == TypeManager.enum_type)
                                return new UnboxCast (expr, target_type);
 
+                       if (TypeManager.IsEnumType (expr_type)) {
+                               if (expr is EnumConstant)
+                                       return ExplicitConversionCore (ec, ((EnumConstant) expr).Child, target_type, loc);
+
+                               return ExplicitConversionCore (ec, new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type)), target_type, loc);
+                       }
+
+                       if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
+                               return new Nullable.LiftedConversion (
+                                       expr, target_type, false, true, loc).Resolve (ec);
+
+                       if (TypeManager.IsEnumType (target_type))
+                               return new EmptyCast (ExplicitConversionCore (ec, expr, TypeManager.EnumToUnderlying (target_type), loc), target_type);
+
+                       ne = ExplicitNumericConversion (expr, target_type);
+                       if (ne != null)
+                               return ne;
+
                        //
                        // Skip the ExplicitReferenceConversion because we can not convert
                        // from Null to a ValueType, and ExplicitReference wont check against
@@ -1890,75 +1872,59 @@ namespace Mono.CSharp {
                                        return ne;
                        }
 
-               skip_explicit:
                        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){
-                                       Expression e = null;
-                                       
-                                       if (target_type == TypeManager.sbyte_type)
-                                               e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
-                                       else if (target_type == TypeManager.byte_type)
-                                               e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
-                                       else if (target_type == TypeManager.short_type)
-                                               e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
-                                       else if (target_type == TypeManager.ushort_type)
-                                               e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
-                                       else if (target_type == TypeManager.int32_type)
-                                               e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
-                                       else if (target_type == TypeManager.uint32_type)
-                                               e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
-                                       else if (target_type == TypeManager.uint64_type)
-                                               e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
-                                       else if (target_type == TypeManager.int64_type){
-                                               e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
-                                       }
+                               ne = ExplicitUnsafe (expr, target_type);
+                               if (ne != null)
+                                       return ne;
+                       }
 
-                                       if (e != null){
-                                               Expression ci, ce;
+                       ne = ExplicitUserConversion (ec, expr, target_type, loc);
+                       if (ne != null)
+                               return ne;
 
-                                               ci = ImplicitConversionStandard (ec, e, target_type, loc);
+                       return null;
+               }
 
-                                               if (ci != null)
-                                                       return ci;
+               public static Expression ExplicitUnsafe (Expression expr, Type target_type)
+               {
+                       Type expr_type = expr.Type;
 
-                                               ce = ExplicitNumericConversion (ec, e, target_type, loc);
-                                               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");
-                                       }
-                               }
+                       if (target_type.IsPointer){
+                               if (expr_type.IsPointer)
+                                       return new EmptyCast (expr, target_type);
+                                       
+                               if (expr_type == TypeManager.sbyte_type ||
+                                       expr_type == TypeManager.short_type ||
+                                       expr_type == TypeManager.int32_type ||
+                                       expr_type == TypeManager.int64_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
+
+                               if (expr_type == TypeManager.ushort_type ||
+                                       expr_type == TypeManager.uint32_type ||
+                                       expr_type == TypeManager.uint64_type ||
+                                       expr_type == TypeManager.byte_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
                        }
                        
-                       ne = ExplicitUserConversion (ec, expr, target_type, loc);
-                       if (ne != null)
-                               return ne;
-
-                       if (expr is NullLiteral){
-                               Report.Error (37, loc, "Cannot convert null to value type `" +
-                                             TypeManager.CSharpName (target_type) + "'");
-                               return null;
+                       if (expr_type.IsPointer){
+                               if (target_type == TypeManager.sbyte_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
+                               else if (target_type == TypeManager.byte_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
+                               else if (target_type == TypeManager.short_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
+                               else if (target_type == TypeManager.ushort_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
+                               else if (target_type == TypeManager.int32_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
+                               else if (target_type == TypeManager.uint32_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
+                               else if (target_type == TypeManager.uint64_type)
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
+                               else if (target_type == TypeManager.int64_type){
+                                       return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
+                               }
                        }
-                               
-                       Error_CannotConvertType (loc, original_expr_type, target_type);
                        return null;
                }
 
@@ -1976,7 +1942,11 @@ namespace Mono.CSharp {
                        if (ne != null)
                                return ne;
 
-                       ne = ExplicitNumericConversion (ec, expr, target_type, l);
+                       if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
+                               return new Nullable.LiftedConversion (
+                                       expr, target_type, false, true, l).Resolve (ec);
+
+                       ne = ExplicitNumericConversion (expr, target_type);
                        if (ne != null)
                                return ne;
 
@@ -1984,7 +1954,25 @@ namespace Mono.CSharp {
                        if (ne != null)
                                return ne;
 
-                       Error_CannotConvertType (l, expr.Type, target_type);
+                       if (ec.InUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
+                               return new EmptyCast (expr, target_type);
+
+                       expr.Error_ValueCannotBeConverted (l, target_type, true);
+                       return null;
+               }
+
+               /// <summary>
+               ///   Performs an explicit conversion of the expression `expr' whose
+               ///   type is expr.Type to `target_type'.
+               /// </summary>
+               static public Expression ExplicitConversion (EmitContext ec, Expression expr,
+                       Type target_type, Location loc)
+               {
+                       Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
+                       if (e != null)
+                               return e;
+
+                       expr.Error_ValueCannotBeConverted (loc, target_type, true);
                        return null;
                }
        }