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 parameter list can either be:
  22                 //    null: no parameters
  23                 //    arraylist of Parameter (explicitly typed parameters)
  24                 //    arraylist of strings (implicitly typed parameters)
  25                 //
  26                 public LambdaExpression (AnonymousMethodExpression parent,
  27                                          GenericMethod generic, TypeContainer host,
  28                                          Parameters parameters, Block container,
  29                                          Location loc)
  30                         : base (parent, generic, host, parameters, container, loc)
  31                 {
  32                         explicit_parameters = (parameters != null && parameters.Count > 0 && parameters [0].TypeName != null);
  33                         if (parameters == null)
  34                                 Parameters = Parameters.EmptyReadOnlyParameters;
  35                 }
  36
  37                 public bool HasImplicitParameters {
  38                         get {
  39                                 return !explicit_parameters;
  40                         }
  41                 }
  42
  43                 public bool HasExplicitParameters {
  44                         get {
  45                                 return explicit_parameters;
  46                         }
  47                 }
  48
  49                 public override Expression DoResolve (EmitContext ec)
  50                 {
  51                         eclass = ExprClass.Value;
  52                         type = TypeManager.anonymous_method_type;
  53
  54                         if (explicit_parameters){
  55                                 if (!Parameters.Resolve (ec))
  56                                         return null;
  57                         }
  58
  59                         // We will resolve parameters later, we do not
  60                         // have information at this point.
  61
  62                         return this;
  63                 }
  64
  65                 public override void Emit (EmitContext ec)
  66                 {
  67                         base.Emit (ec);
  68                 }
  69
  70                 public override bool ImplicitStandardConversionExists (Type delegate_type)
  71                 {
  72                         EmitContext ec = EmitContext.TempEc;
  73
  74                         bool result;
  75
  76                         try {
  77                                 Report.DisableErrors ();
  78                                 result = DoCompatibleTest (ec, delegate_type, true) != null;
  79                         } finally {
  80                                 Report.EnableErrors ();
  81                         }
  82
  83                         // Ignore the result
  84                         anonymous = null;
  85
  86                         return result;
  87                 }
  88
  89                 //
  90                 // Returns true if this anonymous method can be implicitly
  91                 // converted to the delegate type `delegate_type'
  92                 //
  93                 public override Expression Compatible (EmitContext ec, Type delegate_type)
  94                 {
  95                         return DoCompatibleTest (ec, delegate_type, false);
  96                 }
  97
  98                 Expression DoCompatibleTest (EmitContext ec, Type delegate_type, bool clone)
  99                 {
 100                         if (anonymous != null)
 101                                 return anonymous.AnonymousDelegate;
 102
 103                         if (CompatibleChecks (ec, delegate_type) == null)
 104                                 return null;
 105
 106                         MethodGroupExpr invoke_mg = Delegate.GetInvokeMethod (
 107                                 ec.ContainerType, delegate_type, loc);
 108                         MethodInfo invoke_mb = (MethodInfo) invoke_mg.Methods [0];
 109                         ParameterData invoke_pd = TypeManager.GetParameterData (invoke_mb);
 110
 111                         //
 112                         // The lambda expression is compatible with the delegate type,
 113                         // provided that:
 114                         //
 115
 116                         //
 117                         // D and L have the same number of arguments.
 118                         if (Parameters.Count != invoke_pd.Count)
 119                                 return null;
 120
 121                         if (explicit_parameters){
 122                                 //
 123                                 // If L has an explicitly typed parameter list, each parameter
 124                                 // in D has the same type and modifiers as the corresponding
 125                                 // parameter in L.
 126                                 //
 127                                 if (!VerifyExplicitParameterCompatibility (delegate_type, invoke_pd))
 128                                         return null;
 129                         } else {
 130                                 //
 131                                 // If L has an implicitly typed parameter list, D has no ref or
 132                                 // out parameters
 133                                 //
 134                                 // Note: We currently do nothing, because the preview does not
 135                                 // follow the above rule.
 136
 137                                 //
 138                                 // each parameter of L is given the type of the corresponding parameter in D
 139                                 //
 140
 141                                 for (int i = 0; i < invoke_pd.Count; i++)
 142                                         Parameters [i].TypeName = new TypeExpression (
 143                                                 invoke_pd.ParameterType (i),
 144                                                 Parameters [i].Location);
 145                         }
 146
 147                         return CoreCompatibilityTest (ec, clone, invoke_mb.ReturnType, delegate_type);
 148                 }
 149
 150                 Expression CoreCompatibilityTest (EmitContext ec, bool clone, Type return_type, Type delegate_type)
 151                 {
 152                         //
 153                         // The return type of the delegate must be compatible with
 154                         // the anonymous type.   Instead of doing a pass to examine the block
 155                         // we satisfy the rule by setting the return type on the EmitContext
 156                         // to be the delegate type return type.
 157                         //
 158
 159                         ToplevelBlock b = clone ? (ToplevelBlock) Block.PerformClone () : Block;
 160
 161                         anonymous = new AnonymousMethod (
 162                                 Parent != null ? Parent.AnonymousMethod : null, RootScope, Host,
 163                                 GenericMethod, Parameters, Container, b, return_type,
 164                                 delegate_type, loc);
 165
 166                         bool r;
 167                         if (clone)
 168                                 r = anonymous.ResolveNoDefine (ec);
 169                         else
 170                                 r = anonymous.Resolve (ec);
 171
 172                         // Resolution failed.
 173                         if (!r)
 174                                 return null;
 175
 176                         return anonymous.AnonymousDelegate;
 177                 }
 178
 179                 //
 180                 // TryBuild: tries to compile this LambdaExpression with the given
 181                 // types as the lambda expression parameter types.
 182                 //
 183                 // If the lambda expression successfully builds with those types, the
 184                 // return value will be the inferred type for the lambda expression,
 185                 // otherwise the result will be null.
 186                 //
 187                 public Type TryBuild (EmitContext ec, Type [] types)
 188                 {
 189                         for (int i = 0; i < types.Length; i++)
 190                                 Parameters [i].TypeName = new TypeExpression (types [i], Parameters [i].Location);
 191
 192                         Expression e;
 193                         try {
 194                                 Report.DisableErrors ();
 195                                 e = CoreCompatibilityTest (ec, true, null, null);
 196                         } finally {
 197                                 Report.EnableErrors ();
 198                         }
 199
 200                         if (e == null)
 201                                 return null;
 202
 203                         return e.Type;
 204                 }
 205         }
 206
 207         //
 208         // This is a return statement that is prepended lambda expression bodies that happen
 209         // to be expressions.  Depending on the return type of the delegate this will behave
 210         // as either { expr (); return (); } or { return expr (); }
 211         //
 212         public class ContextualReturn : Statement {
 213                 public Expression Expr;
 214
 215                 public ContextualReturn (Expression e)
 216                 {
 217                         Expr = e;
 218                         loc = Expr.Location;
 219                 }
 220
 221                 bool unwind_protect;
 222
 223                 public override bool Resolve (EmitContext ec)
 224                 {
 225                         AnonymousContainer am = ec.CurrentAnonymousMethod;
 226                         if ((am != null) && am.IsIterator && ec.InIterator) {
 227                                 Report.Error (1622, loc, "Cannot return a value from iterators. Use the yield return " +
 228                                               "statement to return a value, or yield break to end the iteration");
 229                                 return false;
 230                         }
 231
 232                         Expr = Expr.Resolve (ec);
 233                         if (Expr == null)
 234                                 return false;
 235
 236                         if (ec.ReturnType == null){
 237                                 ec.ReturnType = Expr.Type;
 238                         } else {
 239                                 if (Expr.Type != ec.ReturnType) {
 240                                         Expression nExpr = Convert.ImplicitConversionRequired (
 241                                                 ec, Expr, ec.ReturnType, loc);
 242                                         if (nExpr == null){
 243                                                 Report.Error (1662, loc, "Could not implicitly convert from {0} to {1}",
 244                                                               TypeManager.CSharpName (Expr.Type),
 245                                                               TypeManager.CSharpName (ec.ReturnType));
 246                                                 return false;
 247                                         }
 248                                         Expr = nExpr;
 249                                 }
 250                         }
 251
 252                         int errors = Report.Errors;
 253                         unwind_protect = ec.CurrentBranching.AddReturnOrigin (ec.CurrentBranching.CurrentUsageVector, loc);
 254                         if (unwind_protect)
 255                                 ec.NeedReturnLabel ();
 256                         ec.CurrentBranching.CurrentUsageVector.Goto ();
 257                         return errors == Report.Errors;
 258                 }
 259
 260                 protected override void DoEmit (EmitContext ec)
 261                 {
 262                         Expr.Emit (ec);
 263
 264                         if (unwind_protect){
 265                                 ec.ig.Emit (OpCodes.Stloc, ec.TemporaryReturn ());
 266                                 ec.ig.Emit (OpCodes.Leave, ec.ReturnLabel);
 267                         }
 268                         ec.ig.Emit (OpCodes.Ret);
 269                 }
 270
 271                 protected override void CloneTo (CloneContext clonectx, Statement t)
 272                 {
 273                         ContextualReturn cr = (ContextualReturn) t;
 274
 275                         cr.Expr = Expr.Clone (clonectx);
 276                 }
 277         }
 278 }