mcs/mcs/lambda.cs

   1 //
   2 // lambda.cs: support for lambda expressions
   3 //
   4 // Authors: Miguel de Icaza (miguel@gnu.org)
   5 //
   6 // Licensed under the terms of the GNU GPL
   7 //
   8 // (C) 2007 Novell, Inc
   9 //
  10
  11 using System;
  12 using System.Collections;
  13 using System.Reflection;
  14 using System.Reflection.Emit;
  15
  16 namespace Mono.CSharp {
  17         public class LambdaExpression : AnonymousMethodExpression {
  18                 bool explicit_parameters;
  19
  20                 //
  21                 // The parameters can either be:
  22                 //    A list of Parameters (explicitly typed parameters)
  23                 //    An ImplicitLambdaParameter
  24                 //
  25                 public LambdaExpression (AnonymousMethodExpression parent,
  26                                          GenericMethod generic, TypeContainer host,
  27                                          Parameters parameters, Block container,
  28                                          Location loc)
  29                         : base (parent, generic, host, parameters, container, loc)
  30                 {
  31                         explicit_parameters = parameters.FixedParameters [0].TypeName != null;
  32                 }
  33
  34                 public bool HasExplicitParameters {
  35                         get {
  36                                 return explicit_parameters;
  37                         }
  38                 }
  39
  40                 public override Expression DoResolve (EmitContext ec)
  41                 {
  42                         //
  43                         // Only explicit parameters can be resolved at this point
  44                         //
  45                         if (explicit_parameters) {
  46                                 if (!Parameters.Resolve (ec))
  47                                         return null;
  48                         }
  49
  50                         eclass = ExprClass.Value;
  51                         type = TypeManager.anonymous_method_type;
  52                         return this;
  53                 }
  54
  55                 public override bool ImplicitStandardConversionExists (Type delegate_type)
  56                 {
  57                         EmitContext ec = EmitContext.TempEc;
  58
  59                         bool result;
  60
  61                         try {
  62                                 Report.DisableErrors ();
  63                                 result = DoCompatibleTest (ec, delegate_type, true) != null;
  64                         } finally {
  65                                 Report.EnableErrors ();
  66                         }
  67
  68                         // Ignore the result
  69                         anonymous = null;
  70
  71                         return result;
  72                 }
  73
  74                 //
  75                 // Returns true if this anonymous method can be implicitly
  76                 // converted to the delegate type `delegate_type'
  77                 //
  78                 public override Expression Compatible (EmitContext ec, Type delegate_type)
  79                 {
  80                         return DoCompatibleTest (ec, delegate_type, false);
  81                 }
  82
  83                 Expression DoCompatibleTest (EmitContext ec, Type delegate_type, bool clone)
  84                 {
  85                         if (anonymous != null)
  86                                 return anonymous.AnonymousDelegate;
  87
  88                         if (CompatibleChecks (ec, delegate_type) == null)
  89                                 return null;
  90
  91                         MethodGroupExpr invoke_mg = Delegate.GetInvokeMethod (
  92                                 ec.ContainerType, delegate_type, loc);
  93                         MethodInfo invoke_mb = (MethodInfo) invoke_mg.Methods [0];
  94                         ParameterData invoke_pd = TypeManager.GetParameterData (invoke_mb);
  95
  96                         //
  97                         // The lambda expression is compatible with the delegate type,
  98                         // provided that:
  99                         //
 100
 101                         //
 102                         // D and L have the same number of arguments.
 103                         if (Parameters.Count != invoke_pd.Count)
 104                                 return null;
 105
 106                         if (explicit_parameters){
 107                                 //
 108                                 // If L has an explicitly typed parameter list, each parameter
 109                                 // in D has the same type and modifiers as the corresponding
 110                                 // parameter in L.
 111                                 //
 112                                 if (!VerifyExplicitParameterCompatibility (delegate_type, invoke_pd, false))
 113                                         return null;
 114                         } else {
 115                                 //
 116                                 // If L has an implicitly typed parameter list, D has no ref or
 117                                 // out parameters
 118                                 //
 119                                 // Note: We currently do nothing, because the preview does not
 120                                 // follow the above rule.
 121
 122                                 //
 123                                 // each parameter of L is given the type of the corresponding parameter in D
 124                                 //
 125
 126                                 for (int i = 0; i < invoke_pd.Count; i++)
 127                                         Parameters [i].TypeName = new TypeExpression (
 128                                                 invoke_pd.ParameterType (i),
 129                                                 Parameters [i].Location);
 130                         }
 131
 132                         return CoreCompatibilityTest (ec, clone, invoke_mb.ReturnType, delegate_type);
 133                 }
 134
 135                 Expression CoreCompatibilityTest (EmitContext ec, bool clone, Type return_type, Type delegate_type)
 136                 {
 137                         //
 138                         // The return type of the delegate must be compatible with
 139                         // the anonymous type.   Instead of doing a pass to examine the block
 140                         // we satisfy the rule by setting the return type on the EmitContext
 141                         // to be the delegate type return type.
 142                         //
 143
 144                         ToplevelBlock b = clone ? (ToplevelBlock) Block.PerformClone () : Block;
 145
 146                         anonymous = new AnonymousMethod (
 147                                 Parent != null ? Parent.AnonymousMethod : null, RootScope, Host,
 148                                 GenericMethod, Parameters, Container, b, return_type,
 149                                 delegate_type, loc);
 150
 151                         bool r;
 152                         if (clone)
 153                                 r = anonymous.ResolveNoDefine (ec);
 154                         else
 155                                 r = anonymous.Resolve (ec);
 156
 157                         // Resolution failed.
 158                         if (!r)
 159                                 return null;
 160
 161                         return anonymous.AnonymousDelegate;
 162                 }
 163
 164                 public override string GetSignatureForError ()
 165                 {
 166                         return "lambda expression";
 167                 }
 168
 169                 //
 170                 // TryBuild: tries to compile this LambdaExpression with the given
 171                 // types as the lambda expression parameter types.
 172                 //
 173                 // If the lambda expression successfully builds with those types, the
 174                 // return value will be the inferred type for the lambda expression,
 175                 // otherwise the result will be null.
 176                 //
 177                 public Type TryBuild (EmitContext ec, Type [] types)
 178                 {
 179                         for (int i = 0; i < types.Length; i++)
 180                                 Parameters [i].TypeName = new TypeExpression (types [i], Parameters [i].Location);
 181
 182                         Expression e;
 183                         try {
 184                                 Report.DisableErrors ();
 185                                 e = CoreCompatibilityTest (ec, true, null, null);
 186                         } finally {
 187                                 Report.EnableErrors ();
 188                         }
 189
 190                         if (e == null)
 191                                 return null;
 192
 193                         return e.Type;
 194                 }
 195         }
 196
 197         //
 198         // This is a return statement that is prepended lambda expression bodies that happen
 199         // to be expressions.  Depending on the return type of the delegate this will behave
 200         // as either { expr (); return (); } or { return expr (); }
 201         //
 202         public class ContextualReturn : Statement {
 203                 public Expression Expr;
 204
 205                 public ContextualReturn (Expression e)
 206                 {
 207                         Expr = e;
 208                         loc = Expr.Location;
 209                 }
 210
 211                 bool unwind_protect;
 212
 213                 public override bool Resolve (EmitContext ec)
 214                 {
 215                         AnonymousContainer am = ec.CurrentAnonymousMethod;
 216                         if ((am != null) && am.IsIterator && ec.InIterator) {
 217                                 Report.Error (1622, loc, "Cannot return a value from iterators. Use the yield return " +
 218                                               "statement to return a value, or yield break to end the iteration");
 219                                 return false;
 220                         }
 221
 222                         Expr = Expr.Resolve (ec);
 223                         if (Expr == null)
 224                                 return false;
 225
 226                         if (ec.ReturnType == null){
 227                                 ec.ReturnType = Expr.Type;
 228                         } else {
 229                                 if (Expr.Type != ec.ReturnType) {
 230                                         Expression nExpr = Convert.ImplicitConversionRequired (
 231                                                 ec, Expr, ec.ReturnType, loc);
 232                                         if (nExpr == null){
 233                                                 Report.Error (1662, loc, "Could not implicitly convert from {0} to {1}",
 234                                                               TypeManager.CSharpName (Expr.Type),
 235                                                               TypeManager.CSharpName (ec.ReturnType));
 236                                                 return false;
 237                                         }
 238                                         Expr = nExpr;
 239                                 }
 240                         }
 241
 242                         int errors = Report.Errors;
 243                         unwind_protect = ec.CurrentBranching.AddReturnOrigin (ec.CurrentBranching.CurrentUsageVector, loc);
 244                         if (unwind_protect)
 245                                 ec.NeedReturnLabel ();
 246                         ec.CurrentBranching.CurrentUsageVector.Goto ();
 247                         return errors == Report.Errors;
 248                 }
 249
 250                 protected override void DoEmit (EmitContext ec)
 251                 {
 252                         Expr.Emit (ec);
 253
 254                         if (unwind_protect){
 255                                 ec.ig.Emit (OpCodes.Stloc, ec.TemporaryReturn ());
 256                                 ec.ig.Emit (OpCodes.Leave, ec.ReturnLabel);
 257                         }
 258                         ec.ig.Emit (OpCodes.Ret);
 259                 }
 260
 261                 protected override void CloneTo (CloneContext clonectx, Statement t)
 262                 {
 263                         ContextualReturn cr = (ContextualReturn) t;
 264
 265                         cr.Expr = Expr.Clone (clonectx);
 266                 }
 267         }
 268 }