mcs/mcs/assign.cs

   1 //
   2 // assign.cs: Assignments.
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Martin Baulig (martin@ximian.com)
   7 //   Marek Safar (marek.safar@gmail.com)
   8 //
   9 // Dual licensed under the terms of the MIT X11 or GNU GPL
  10 //
  11 // Copyright 2001, 2002, 2003 Ximian, Inc.
  12 // Copyright 2004-2008 Novell, Inc
  13 //
  14 using System;
  15 using System.Reflection;
  16 using System.Reflection.Emit;
  17
  18 namespace Mono.CSharp {
  19
  20         /// <summary>
  21         ///   This interface is implemented by expressions that can be assigned to.
  22         /// </summary>
  23         /// <remarks>
  24         ///   This interface is implemented by Expressions whose values can not
  25         ///   store the result on the top of the stack.
  26         ///
  27         ///   Expressions implementing this (Properties, Indexers and Arrays) would
  28         ///   perform an assignment of the Expression "source" into its final
  29         ///   location.
  30         ///
  31         ///   No values on the top of the stack are expected to be left by
  32         ///   invoking this method.
  33         /// </remarks>
  34         public interface IAssignMethod {
  35                 //
  36                 // This is an extra version of Emit. If leave_copy is `true'
  37                 // A copy of the expression will be left on the stack at the
  38                 // end of the code generated for EmitAssign
  39                 //
  40                 void Emit (EmitContext ec, bool leave_copy);
  41
  42                 //
  43                 // This method does the assignment
  44                 // `source' will be stored into the location specified by `this'
  45                 // if `leave_copy' is true, a copy of `source' will be left on the stack
  46                 // if `prepare_for_load' is true, when `source' is emitted, there will
  47                 // be data on the stack that it can use to compuatate its value. This is
  48                 // for expressions like a [f ()] ++, where you can't call `f ()' twice.
  49                 //
  50                 void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool prepare_for_load);
  51
  52                 /*
  53                 For simple assignments, this interface is very simple, EmitAssign is called with source
  54                 as the source expression and leave_copy and prepare_for_load false.
  55
  56                 For compound assignments it gets complicated.
  57
  58                 EmitAssign will be called as before, however, prepare_for_load will be
  59                 true. The @source expression will contain an expression
  60                 which calls Emit. So, the calls look like:
  61
  62                 this.EmitAssign (ec, source, false, true) ->
  63                         source.Emit (ec); ->
  64                                 [...] ->
  65                                         this.Emit (ec, false); ->
  66                                         end this.Emit (ec, false); ->
  67                                 end [...]
  68                         end source.Emit (ec);
  69                 end this.EmitAssign (ec, source, false, true)
  70
  71
  72                 When prepare_for_load is true, EmitAssign emits a `token' on the stack that
  73                 Emit will use for its state.
  74
  75                 Let's take FieldExpr as an example. assume we are emitting f ().y += 1;
  76
  77                 Here is the call tree again. This time, each call is annotated with the IL
  78                 it produces:
  79
  80                 this.EmitAssign (ec, source, false, true)
  81                         call f
  82                         dup
  83
  84                         Binary.Emit ()
  85                                 this.Emit (ec, false);
  86                                 ldfld y
  87                                 end this.Emit (ec, false);
  88
  89                                 IntConstant.Emit ()
  90                                 ldc.i4.1
  91                                 end IntConstant.Emit
  92
  93                                 add
  94                         end Binary.Emit ()
  95
  96                         stfld
  97                 end this.EmitAssign (ec, source, false, true)
  98
  99                 Observe two things:
 100                         1) EmitAssign left a token on the stack. It was the result of f ().
 101                         2) This token was used by Emit
 102
 103                 leave_copy (in both EmitAssign and Emit) tells the compiler to leave a copy
 104                 of the expression at that point in evaluation. This is used for pre/post inc/dec
 105                 and for a = x += y. Let's do the above example with leave_copy true in EmitAssign
 106
 107                 this.EmitAssign (ec, source, true, true)
 108                         call f
 109                         dup
 110
 111                         Binary.Emit ()
 112                                 this.Emit (ec, false);
 113                                 ldfld y
 114                                 end this.Emit (ec, false);
 115
 116                                 IntConstant.Emit ()
 117                                 ldc.i4.1
 118                                 end IntConstant.Emit
 119
 120                                 add
 121                         end Binary.Emit ()
 122
 123                         dup
 124                         stloc temp
 125                         stfld
 126                         ldloc temp
 127                 end this.EmitAssign (ec, source, true, true)
 128
 129                 And with it true in Emit
 130
 131                 this.EmitAssign (ec, source, false, true)
 132                         call f
 133                         dup
 134
 135                         Binary.Emit ()
 136                                 this.Emit (ec, true);
 137                                 ldfld y
 138                                 dup
 139                                 stloc temp
 140                                 end this.Emit (ec, true);
 141
 142                                 IntConstant.Emit ()
 143                                 ldc.i4.1
 144                                 end IntConstant.Emit
 145
 146                                 add
 147                         end Binary.Emit ()
 148
 149                         stfld
 150                         ldloc temp
 151                 end this.EmitAssign (ec, source, false, true)
 152
 153                 Note that these two examples are what happens for ++x and x++, respectively.
 154                 */
 155         }
 156
 157         /// <summary>
 158         ///   An Expression to hold a temporary value.
 159         /// </summary>
 160         /// <remarks>
 161         ///   The LocalTemporary class is used to hold temporary values of a given
 162         ///   type to "simulate" the expression semantics. The local variable is
 163         ///   never captured.
 164         ///
 165         ///   The local temporary is used to alter the normal flow of code generation
 166         ///   basically it creates a local variable, and its emit instruction generates
 167         ///   code to access this value, return its address or save its value.
 168         ///
 169         ///   If `is_address' is true, then the value that we store is the address to the
 170         ///   real value, and not the value itself.
 171         ///
 172         ///   This is needed for a value type, because otherwise you just end up making a
 173         ///   copy of the value on the stack and modifying it. You really need a pointer
 174         ///   to the origional value so that you can modify it in that location. This
 175         ///   Does not happen with a class because a class is a pointer -- so you always
 176         ///   get the indirection.
 177         ///
 178         /// </remarks>
 179         public class LocalTemporary : Expression, IMemoryLocation, IAssignMethod {
 180                 LocalBuilder builder;
 181
 182                 public LocalTemporary (TypeSpec t)
 183                 {
 184                         type = t;
 185                         eclass = ExprClass.Value;
 186                 }
 187
 188                 public LocalTemporary (LocalBuilder b, TypeSpec t)
 189                         : this (t)
 190                 {
 191                         builder = b;
 192                 }
 193
 194                 public void Release (EmitContext ec)
 195                 {
 196                         ec.FreeTemporaryLocal (builder, type);
 197                         builder = null;
 198                 }
 199
 200                 public override Expression CreateExpressionTree (ResolveContext ec)
 201                 {
 202                         Arguments args = new Arguments (1);
 203                         args.Add (new Argument (this));
 204                         return CreateExpressionFactoryCall (ec, "Constant", args);
 205                 }
 206
 207                 protected override Expression DoResolve (ResolveContext ec)
 208                 {
 209                         return this;
 210                 }
 211
 212                 public override Expression DoResolveLValue (ResolveContext ec, Expression right_side)
 213                 {
 214                         return this;
 215                 }
 216
 217                 public override void Emit (EmitContext ec)
 218                 {
 219                         if (builder == null)
 220                                 throw new InternalErrorException ("Emit without Store, or after Release");
 221
 222                         ec.Emit (OpCodes.Ldloc, builder);
 223                 }
 224
 225                 #region IAssignMethod Members
 226
 227                 public void Emit (EmitContext ec, bool leave_copy)
 228                 {
 229                         Emit (ec);
 230
 231                         if (leave_copy)
 232                                 Emit (ec);
 233                 }
 234
 235                 public void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool prepare_for_load)
 236                 {
 237                         if (prepare_for_load)
 238                                 throw new NotImplementedException ();
 239
 240                         source.Emit (ec);
 241
 242                         Store (ec);
 243
 244                         if (leave_copy)
 245                                 Emit (ec);
 246                 }
 247
 248                 #endregion
 249
 250                 public LocalBuilder Builder {
 251                         get { return builder; }
 252                 }
 253
 254                 public void Store (EmitContext ec)
 255                 {
 256                         if (builder == null)
 257                                 builder = ec.GetTemporaryLocal (type);
 258
 259                         ec.Emit (OpCodes.Stloc, builder);
 260                 }
 261
 262                 public void AddressOf (EmitContext ec, AddressOp mode)
 263                 {
 264                         if (builder == null)
 265                                 builder = ec.GetTemporaryLocal (type);
 266
 267                         if (builder.LocalType.IsByRef) {
 268                                 //
 269                                 // if is_address, than this is just the address anyways,
 270                                 // so we just return this.
 271                                 //
 272                                 ec.Emit (OpCodes.Ldloc, builder);
 273                         } else {
 274                                 ec.Emit (OpCodes.Ldloca, builder);
 275                         }
 276                 }
 277         }
 278
 279         /// <summary>
 280         ///   The Assign node takes care of assigning the value of source into
 281         ///   the expression represented by target.
 282         /// </summary>
 283         public abstract class Assign : ExpressionStatement {
 284                 protected Expression target, source;
 285
 286                 protected Assign (Expression target, Expression source, Location loc)
 287                 {
 288                         this.target = target;
 289                         this.source = source;
 290                         this.loc = loc;
 291                 }
 292
 293                 public override Expression CreateExpressionTree (ResolveContext ec)
 294                 {
 295                         ec.Report.Error (832, loc, "An expression tree cannot contain an assignment operator");
 296                         return null;
 297                 }
 298
 299                 public Expression Target {
 300                         get { return target; }
 301                 }
 302
 303                 public Expression Source {
 304                         get { return source; }
 305                 }
 306
 307                 protected override Expression DoResolve (ResolveContext ec)
 308                 {
 309                         bool ok = true;
 310                         source = source.Resolve (ec);
 311
 312                         if (source == null) {
 313                                 ok = false;
 314                                 source = EmptyExpression.Null;
 315                         }
 316
 317                         target = target.ResolveLValue (ec, source);
 318
 319                         if (target == null || !ok)
 320                                 return null;
 321
 322                         TypeSpec target_type = target.Type;
 323                         TypeSpec source_type = source.Type;
 324
 325                         eclass = ExprClass.Value;
 326                         type = target_type;
 327
 328                         if (!(target is IAssignMethod)) {
 329                                 Error_ValueAssignment (ec, loc);
 330                                 return null;
 331                         }
 332
 333                         if (!TypeManager.IsEqual (target_type, source_type)) {
 334                                 Expression resolved = ResolveConversions (ec);
 335
 336                                 if (resolved != this)
 337                                         return resolved;
 338                         }
 339
 340                         return this;
 341                 }
 342
 343 #if NET_4_0
 344                 public override System.Linq.Expressions.Expression MakeExpression (BuilderContext ctx)
 345                 {
 346                         var tassign = target as IDynamicAssign;
 347                         if (tassign == null)
 348                                 throw new InternalErrorException (target.GetType () + " does not support dynamic assignment");
 349
 350                         var target_object = tassign.MakeAssignExpression (ctx, source);
 351
 352                         //
 353                         // Some hacking is needed as DLR does not support void type and requires
 354                         // always have object convertible return type to support caching and chaining
 355                         //
 356                         // We do this by introducing an explicit block which returns RHS value when
 357                         // available or null
 358                         //
 359                         if (target_object.NodeType == System.Linq.Expressions.ExpressionType.Block)
 360                                 return target_object;
 361
 362                         var source_object = System.Linq.Expressions.Expression.Convert (source.MakeExpression (ctx), target_object.Type);
 363                         return System.Linq.Expressions.Expression.Assign (target_object, source_object);
 364                 }
 365 #endif
 366                 protected virtual Expression ResolveConversions (ResolveContext ec)
 367                 {
 368                         source = Convert.ImplicitConversionRequired (ec, source, target.Type, loc);
 369                         if (source == null)
 370                                 return null;
 371
 372                         return this;
 373                 }
 374
 375                 void Emit (EmitContext ec, bool is_statement)
 376                 {
 377                         IAssignMethod t = (IAssignMethod) target;
 378                         t.EmitAssign (ec, source, !is_statement, this is CompoundAssign);
 379                 }
 380
 381                 public override void Emit (EmitContext ec)
 382                 {
 383                         Emit (ec, false);
 384                 }
 385
 386                 public override void EmitStatement (EmitContext ec)
 387                 {
 388                         Emit (ec, true);
 389                 }
 390
 391                 protected override void CloneTo (CloneContext clonectx, Expression t)
 392                 {
 393                         Assign _target = (Assign) t;
 394
 395                         _target.target = target.Clone (clonectx);
 396                         _target.source = source.Clone (clonectx);
 397                 }
 398         }
 399
 400         public class SimpleAssign : Assign {
 401                 public SimpleAssign (Expression target, Expression source)
 402                         : this (target, source, target.Location)
 403                 {
 404                 }
 405
 406                 public SimpleAssign (Expression target, Expression source, Location loc)
 407                         : base (target, source, loc)
 408                 {
 409                 }
 410
 411                 bool CheckEqualAssign (Expression t)
 412                 {
 413                         if (source is Assign) {
 414                                 Assign a = (Assign) source;
 415                                 if (t.Equals (a.Target))
 416                                         return true;
 417                                 return a is SimpleAssign && ((SimpleAssign) a).CheckEqualAssign (t);
 418                         }
 419                         return t.Equals (source);
 420                 }
 421
 422                 protected override Expression DoResolve (ResolveContext ec)
 423                 {
 424                         Expression e = base.DoResolve (ec);
 425                         if (e == null || e != this)
 426                                 return e;
 427
 428                         if (CheckEqualAssign (target))
 429                                 ec.Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");
 430
 431                         return this;
 432                 }
 433         }
 434
 435         // This class implements fields and events class initializers
 436         public class FieldInitializer : Assign
 437         {
 438                 //
 439                 // Keep resolved value because field initializers have their own rules
 440                 //
 441                 ExpressionStatement resolved;
 442                 IMemberContext rc;
 443
 444                 public FieldInitializer (FieldSpec spec, Expression expression, IMemberContext rc)
 445                         : base (new FieldExpr (spec, expression.Location), expression, expression.Location)
 446                 {
 447                         this.rc = rc;
 448                         if (!spec.IsStatic)
 449                                 ((FieldExpr)target).InstanceExpression = CompilerGeneratedThis.Instance;
 450                 }
 451
 452                 protected override Expression DoResolve (ResolveContext ec)
 453                 {
 454                         // Field initializer can be resolved (fail) many times
 455                         if (source == null)
 456                                 return null;
 457
 458                         if (resolved == null) {
 459                                 //
 460                                 // Field initializers are tricky for partial classes. They have to
 461                                 // share same constructor (block) but they have they own resolve scope.
 462                                 //
 463
 464                                 IMemberContext old = ec.MemberContext;
 465                                 ec.MemberContext = rc;
 466
 467                                 using (ec.Set (ResolveContext.Options.FieldInitializerScope)) {
 468                                         resolved = base.DoResolve (ec) as ExpressionStatement;
 469                                 }
 470
 471                                 ec.MemberContext = old;
 472                         }
 473
 474                         return resolved;
 475                 }
 476
 477                 public override void EmitStatement (EmitContext ec)
 478                 {
 479                         if (resolved == null)
 480                                 return;
 481
 482                         if (resolved != this)
 483                                 resolved.EmitStatement (ec);
 484                         else
 485                                 base.EmitStatement (ec);
 486                 }
 487
 488                 public bool IsComplexInitializer {
 489                         get { return !(source is Constant); }
 490                 }
 491
 492                 public bool IsDefaultInitializer {
 493                         get {
 494                                 Constant c = source as Constant;
 495                                 if (c == null)
 496                                         return false;
 497
 498                                 FieldExpr fe = (FieldExpr)target;
 499                                 return c.IsDefaultInitializer (fe.Type);
 500                         }
 501                 }
 502         }
 503
 504         //
 505         // This class is used for compound assignments.
 506         //
 507         public class CompoundAssign : Assign
 508         {
 509                 // This is just a hack implemented for arrays only
 510                 public sealed class TargetExpression : Expression
 511                 {
 512                         Expression child;
 513                         public TargetExpression (Expression child)
 514                         {
 515                                 this.child = child;
 516                                 this.loc = child.Location;
 517                         }
 518
 519                         public override Expression CreateExpressionTree (ResolveContext ec)
 520                         {
 521                                 throw new NotSupportedException ("ET");
 522                         }
 523
 524                         protected override Expression DoResolve (ResolveContext ec)
 525                         {
 526                                 type = child.Type;
 527                                 eclass = ExprClass.Value;
 528                                 return this;
 529                         }
 530
 531                         public override void Emit (EmitContext ec)
 532                         {
 533                                 child.Emit (ec);
 534                         }
 535                 }
 536
 537                 // Used for underlying binary operator
 538                 readonly Binary.Operator op;
 539                 Expression right;
 540                 Expression left;
 541
 542                 public CompoundAssign (Binary.Operator op, Expression target, Expression source, Location loc)
 543                         : base (target, source, loc)
 544                 {
 545                         right = source;
 546                         this.op = op;
 547                 }
 548
 549                 public CompoundAssign (Binary.Operator op, Expression target, Expression source, Expression left, Location loc)
 550                         : this (op, target, source, loc)
 551                 {
 552                         this.left = left;
 553                 }
 554
 555                 protected override Expression DoResolve (ResolveContext ec)
 556                 {
 557                         right = right.Resolve (ec);
 558                         if (right == null)
 559                                 return null;
 560
 561                         MemberAccess ma = target as MemberAccess;
 562                         using (ec.Set (ResolveContext.Options.CompoundAssignmentScope)) {
 563                                 target = target.Resolve (ec);
 564                         }
 565
 566                         if (target == null)
 567                                 return null;
 568
 569                         if (target is MethodGroupExpr){
 570                                 ec.Report.Error (1656, loc,
 571                                         "Cannot assign to `{0}' because it is a `{1}'",
 572                                         ((MethodGroupExpr)target).Name, target.ExprClassName);
 573                                 return null;
 574                         }
 575
 576                         var event_expr = target as EventExpr;
 577                         if (event_expr != null) {
 578                                 source = Convert.ImplicitConversionRequired (ec, right, target.Type, loc);
 579                                 if (source == null)
 580                                         return null;
 581
 582                                 Expression rside;
 583                                 if (op == Binary.Operator.Addition)
 584                                         rside = EmptyExpression.EventAddition;
 585                                 else if (op == Binary.Operator.Subtraction)
 586                                         rside = EmptyExpression.EventSubtraction;
 587                                 else
 588                                         rside = null;
 589
 590                                 target = target.ResolveLValue (ec, rside);
 591                                 if (target == null)
 592                                         return null;
 593
 594                                 eclass = ExprClass.Value;
 595                                 type = event_expr.Operator.ReturnType;
 596                                 return this;
 597                         }
 598
 599                         //
 600                         // Only now we can decouple the original source/target
 601                         // into a tree, to guarantee that we do not have side
 602                         // effects.
 603                         //
 604                         if (left == null)
 605                                 left = new TargetExpression (target);
 606
 607                         source = new Binary (op, left, right, true, loc);
 608
 609                         if (target is DynamicMemberBinder) {
 610                                 Arguments targs = ((DynamicMemberBinder) target).Arguments;
 611                                 source = source.Resolve (ec);
 612
 613                                 Arguments args = new Arguments (2);
 614                                 args.AddRange (targs);
 615                                 args.Add (new Argument (source));
 616                                 source = new DynamicMemberBinder (ma.Name, args, loc).ResolveLValue (ec, right);
 617
 618                                 // Handles possible event addition/subtraction
 619                                 if (op == Binary.Operator.Addition || op == Binary.Operator.Subtraction) {
 620                                         args = new Arguments (2);
 621                                         args.AddRange (targs);
 622                                         args.Add (new Argument (right));
 623                                         string method_prefix = op == Binary.Operator.Addition ?
 624                                                 Event.AEventAccessor.AddPrefix : Event.AEventAccessor.RemovePrefix;
 625
 626                                         var invoke = DynamicInvocation.CreateSpecialNameInvoke (
 627                                                 new MemberAccess (right, method_prefix + ma.Name, loc), args, loc).Resolve (ec);
 628
 629                                         args = new Arguments (1);
 630                                         args.AddRange (targs);
 631                                         source = new DynamicEventCompoundAssign (ma.Name, args,
 632                                                 (ExpressionStatement) source, (ExpressionStatement) invoke, loc).Resolve (ec);
 633                                 }
 634
 635                                 return source;
 636                         }
 637
 638                         return base.DoResolve (ec);
 639                 }
 640
 641                 protected override Expression ResolveConversions (ResolveContext ec)
 642                 {
 643                         TypeSpec target_type = target.Type;
 644
 645                         //
 646                         // 1. the return type is implicitly convertible to the type of target
 647                         //
 648                         if (Convert.ImplicitConversionExists (ec, source, target_type)) {
 649                                 source = Convert.ImplicitConversion (ec, source, target_type, loc);
 650                                 return this;
 651                         }
 652
 653                         //
 654                         // Otherwise, if the selected operator is a predefined operator
 655                         //
 656                         Binary b = source as Binary;
 657                         if (b != null) {
 658                                 //
 659                                 // 2a. the operator is a shift operator
 660                                 //
 661                                 // 2b. the return type is explicitly convertible to the type of x, and
 662                                 // y is implicitly convertible to the type of x
 663                                 //
 664                                 if ((b.Oper & Binary.Operator.ShiftMask) != 0 ||
 665                                         Convert.ImplicitConversionExists (ec, right, target_type)) {
 666                                         source = Convert.ExplicitConversion (ec, source, target_type, loc);
 667                                         return this;
 668                                 }
 669                         }
 670
 671                         if (source.Type == InternalType.Dynamic) {
 672                                 Arguments arg = new Arguments (1);
 673                                 arg.Add (new Argument (source));
 674                                 return new SimpleAssign (target, new DynamicConversion (target_type, CSharpBinderFlags.ConvertExplicit, arg, loc), loc).Resolve (ec);
 675                         }
 676
 677                         right.Error_ValueCannotBeConverted (ec, loc, target_type, false);
 678                         return null;
 679                 }
 680
 681                 protected override void CloneTo (CloneContext clonectx, Expression t)
 682                 {
 683                         CompoundAssign ctarget = (CompoundAssign) t;
 684
 685                         ctarget.right = ctarget.source = source.Clone (clonectx);
 686                         ctarget.target = target.Clone (clonectx);
 687                 }
 688         }
 689 }