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                 // If set, this was a lambda expression with an expression
  22                 // argument.  And if so, we have a pointer to it, so we can
  23                 // change it if needed.
  24                 //
  25                 Expression lambda_expr;
  26
  27                 //
  28                 // The parameter list can either be:
  29                 //    null: no parameters
  30                 //    arraylist of Parameter (explicitly typed parameters)
  31                 //    arraylist of strings (implicitly typed parameters)
  32                 //
  33                 public LambdaExpression (AnonymousMethodExpression parent,
  34                                          GenericMethod generic, TypeContainer host,
  35                                          Parameters parameters, Block container,
  36                                          Location loc)
  37                         : base (parent, generic, host, parameters, container, loc)
  38                 {
  39                         explicit_parameters = (parameters != null && parameters.Count > 0 && parameters [0].TypeName != null);
  40                         if (parameters == null)
  41                                 Parameters = new Parameters (new Parameter [0]);
  42                 }
  43
  44                 public void SetExpression (Expression expr)
  45                 {
  46                         lambda_expr = expr;
  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                 //
  71                 // Returns true if this anonymous method can be implicitly
  72                 // converted to the delegate type `delegate_type'
  73                 //
  74                 public override Expression Compatible (EmitContext ec, Type delegate_type)
  75                 {
  76                         if (anonymous != null)
  77                                 return anonymous.AnonymousDelegate;
  78
  79                         if (CompatibleChecks (ec, delegate_type) == null)
  80                                 return null;
  81
  82                         MethodGroupExpr invoke_mg = Delegate.GetInvokeMethod (
  83                                 ec.ContainerType, delegate_type, loc);
  84                         MethodInfo invoke_mb = (MethodInfo) invoke_mg.Methods [0];
  85                         ParameterData invoke_pd = TypeManager.GetParameterData (invoke_mb);
  86
  87                         //
  88                         // The lambda expression is compatible with the delegate type,
  89                         // provided that:
  90                         //
  91
  92                         //
  93                         // D and L have the same number of arguments.
  94                         if (Parameters.Count != invoke_pd.Count)
  95                                 return null;
  96
  97                         Parameters parameters_copy = Parameters.Clone ();
  98                         if (explicit_parameters){
  99                                 //
 100                                 // If L has an explicitly typed parameter list, each parameter
 101                                 // in D has the same type and modifiers as the corresponding
 102                                 // parameter in L.
 103                                 //
 104                                 if (!VerifyExplicitParameterCompatibility (delegate_type, invoke_pd))
 105                                         return null;
 106
 107                                 parameters_copy = Parameters.Clone ();
 108                         } else {
 109                                 //
 110                                 // If L has an implicitly typed parameter list, D has no ref or
 111                                 // out parameters
 112                                 //
 113                                 // Note: We currently do nothing, because the preview does not
 114                                 // follow the above rule.
 115
 116                                 //
 117                                 // each parameter of L is given the type of the corresponding parameter in D
 118                                 //
 119
 120                                 for (int i = 0; i < invoke_pd.Count; i++)
 121                                         parameters_copy [i].TypeName = new TypeExpression (
 122                                                 invoke_pd.ParameterType (i),
 123                                                 parameters_copy [i].Location);
 124                         }
 125
 126                         //
 127                         // The return type of the delegate must be compatible with
 128                         // the anonymous type.   Instead of doing a pass to examine the block
 129                         // we satisfy the rule by setting the return type on the EmitContext
 130                         // to be the delegate type return type.
 131                         //
 132
 133                         anonymous = new AnonymousMethod (
 134                                 Parent != null ? Parent.AnonymousMethod : null, RootScope, Host,
 135                                 GenericMethod, parameters_copy, Container, Block, invoke_mb.ReturnType,
 136                                 delegate_type, loc);
 137
 138                         if (!anonymous.Resolve (ec))
 139                                 return null;
 140
 141                         return anonymous.AnonymousDelegate;
 142                 }
 143         }
 144
 145         //
 146         // This is a return statement that is prepended lambda expression bodies that happen
 147         // to be expressions.  Depending on the return type of the delegate this will behave
 148         // as either { expr (); return (); } or { return expr (); }
 149         //
 150         public class ContextualReturn : Statement {
 151                 public Expression Expr;
 152
 153                 public ContextualReturn (Expression e)
 154                 {
 155                         Expr = e;
 156                         loc = Expr.Location;
 157                 }
 158
 159                 bool unwind_protect;
 160
 161                 public override bool Resolve (EmitContext ec)
 162                 {
 163                         AnonymousContainer am = ec.CurrentAnonymousMethod;
 164                         if ((am != null) && am.IsIterator && ec.InIterator) {
 165                                 Report.Error (1622, loc, "Cannot return a value from iterators. Use the yield return " +
 166                                               "statement to return a value, or yield break to end the iteration");
 167                                 return false;
 168                         }
 169
 170                         Expr = Expr.Resolve (ec);
 171                         if (Expr == null)
 172                                 return false;
 173
 174                         if (ec.ReturnType == null){
 175                                 if (!(Expr is ExpressionStatement)){
 176                                         Expression.Error_InvalidExpressionStatement (Expr.Location);
 177                                         return false;
 178                                 }
 179                         } else {
 180                                 if (Expr.Type != ec.ReturnType) {
 181                                         Expr = Convert.ImplicitConversionRequired (
 182                                                 ec, Expr, ec.ReturnType, loc);
 183                                         if (Expr == null)
 184                                                 return false;
 185                                 }
 186                         }
 187
 188                         int errors = Report.Errors;
 189                         unwind_protect = ec.CurrentBranching.AddReturnOrigin (ec.CurrentBranching.CurrentUsageVector, loc);
 190                         if (unwind_protect)
 191                                 ec.NeedReturnLabel ();
 192                         ec.CurrentBranching.CurrentUsageVector.Return ();
 193                         return errors == Report.Errors;
 194                 }
 195
 196                 protected override void DoEmit (EmitContext ec)
 197                 {
 198                         Expr.Emit (ec);
 199
 200                         if (unwind_protect){
 201                                 ec.ig.Emit (OpCodes.Stloc, ec.TemporaryReturn ());
 202                                 ec.ig.Emit (OpCodes.Leave, ec.ReturnLabel);
 203                         }
 204                         ec.ig.Emit (OpCodes.Ret);
 205                 }
 206
 207         }
 208 }