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 //
   8 // (C) 2001, 2002, 2003 Ximian, Inc.
   9 // (C) 2004 Novell, Inc
  10 //
  11 using System;
  12 using System.Reflection;
  13 using System.Reflection.Emit;
  14
  15 namespace Mono.CSharp {
  16
  17         /// <summary>
  18         ///   This interface is implemented by expressions that can be assigned to.
  19         /// </summary>
  20         /// <remarks>
  21         ///   This interface is implemented by Expressions whose values can not
  22         ///   store the result on the top of the stack.
  23         ///
  24         ///   Expressions implementing this (Properties, Indexers and Arrays) would
  25         ///   perform an assignment of the Expression "source" into its final
  26         ///   location.
  27         ///
  28         ///   No values on the top of the stack are expected to be left by
  29         ///   invoking this method.
  30         /// </remarks>
  31         public interface IAssignMethod {
  32                 //
  33                 // This is an extra version of Emit. If leave_copy is `true'
  34                 // A copy of the expression will be left on the stack at the
  35                 // end of the code generated for EmitAssign
  36                 //
  37                 void Emit (EmitContext ec, bool leave_copy);
  38
  39                 //
  40                 // This method does the assignment
  41                 // `source' will be stored into the location specified by `this'
  42                 // if `leave_copy' is true, a copy of `source' will be left on the stack
  43                 // if `prepare_for_load' is true, when `source' is emitted, there will
  44                 // be data on the stack that it can use to compuatate its value. This is
  45                 // for expressions like a [f ()] ++, where you can't call `f ()' twice.
  46                 //
  47                 void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool prepare_for_load);
  48
  49                 /*
  50                 For simple assignments, this interface is very simple, EmitAssign is called with source
  51                 as the source expression and leave_copy and prepare_for_load false.
  52
  53                 For compound assignments it gets complicated.
  54
  55                 EmitAssign will be called as before, however, prepare_for_load will be
  56                 true. The @source expression will contain an expression
  57                 which calls Emit. So, the calls look like:
  58
  59                 this.EmitAssign (ec, source, false, true) ->
  60                         source.Emit (ec); ->
  61                                 [...] ->
  62                                         this.Emit (ec, false); ->
  63                                         end this.Emit (ec, false); ->
  64                                 end [...]
  65                         end source.Emit (ec);
  66                 end this.EmitAssign (ec, source, false, true)
  67
  68
  69                 When prepare_for_load is true, EmitAssign emits a `token' on the stack that
  70                 Emit will use for its state.
  71
  72                 Let's take FieldExpr as an example. assume we are emitting f ().y += 1;
  73
  74                 Here is the call tree again. This time, each call is annotated with the IL
  75                 it produces:
  76
  77                 this.EmitAssign (ec, source, false, true)
  78                         call f
  79                         dup
  80
  81                         Binary.Emit ()
  82                                 this.Emit (ec, false);
  83                                 ldfld y
  84                                 end this.Emit (ec, false);
  85
  86                                 IntConstant.Emit ()
  87                                 ldc.i4.1
  88                                 end IntConstant.Emit
  89
  90                                 add
  91                         end Binary.Emit ()
  92
  93                         stfld
  94                 end this.EmitAssign (ec, source, false, true)
  95
  96                 Observe two things:
  97                         1) EmitAssign left a token on the stack. It was the result of f ().
  98                         2) This token was used by Emit
  99
 100                 leave_copy (in both EmitAssign and Emit) tells the compiler to leave a copy
 101                 of the expression at that point in evaluation. This is used for pre/post inc/dec
 102                 and for a = x += y. Let's do the above example with leave_copy true in EmitAssign
 103
 104                 this.EmitAssign (ec, source, true, true)
 105                         call f
 106                         dup
 107
 108                         Binary.Emit ()
 109                                 this.Emit (ec, false);
 110                                 ldfld y
 111                                 end this.Emit (ec, false);
 112
 113                                 IntConstant.Emit ()
 114                                 ldc.i4.1
 115                                 end IntConstant.Emit
 116
 117                                 add
 118                         end Binary.Emit ()
 119
 120                         dup
 121                         stloc temp
 122                         stfld
 123                         ldloc temp
 124                 end this.EmitAssign (ec, source, true, true)
 125
 126                 And with it true in Emit
 127
 128                 this.EmitAssign (ec, source, false, true)
 129                         call f
 130                         dup
 131
 132                         Binary.Emit ()
 133                                 this.Emit (ec, true);
 134                                 ldfld y
 135                                 dup
 136                                 stloc temp
 137                                 end this.Emit (ec, true);
 138
 139                                 IntConstant.Emit ()
 140                                 ldc.i4.1
 141                                 end IntConstant.Emit
 142
 143                                 add
 144                         end Binary.Emit ()
 145
 146                         stfld
 147                         ldloc temp
 148                 end this.EmitAssign (ec, source, false, true)
 149
 150                 Note that these two examples are what happens for ++x and x++, respectively.
 151                 */
 152         }
 153
 154         /// <summary>
 155         ///   An Expression to hold a temporary value.
 156         /// </summary>
 157         /// <remarks>
 158         ///   The LocalTemporary class is used to hold temporary values of a given
 159         ///   type to "simulate" the expression semantics on property and indexer
 160         ///   access whose return values are void.
 161         ///
 162         ///   The local temporary is used to alter the normal flow of code generation
 163         ///   basically it creates a local variable, and its emit instruction generates
 164         ///   code to access this value, return its address or save its value.
 165         ///
 166         ///   If `is_address' is true, then the value that we store is the address to the
 167         ///   real value, and not the value itself.
 168         ///
 169         ///   This is needed for a value type, because otherwise you just end up making a
 170         ///   copy of the value on the stack and modifying it. You really need a pointer
 171         ///   to the origional value so that you can modify it in that location. This
 172         ///   Does not happen with a class because a class is a pointer -- so you always
 173         ///   get the indirection.
 174         ///
 175         ///   The `is_address' stuff is really just a hack. We need to come up with a better
 176         ///   way to handle it.
 177         /// </remarks>
 178         public class LocalTemporary : Expression, IMemoryLocation {
 179                 LocalBuilder builder;
 180                 bool is_address;
 181
 182                 public LocalTemporary (Type t) : this (t, false) {}
 183
 184                 public LocalTemporary (Type t, bool is_address)
 185                 {
 186                         type = t;
 187                         eclass = ExprClass.Value;
 188                         this.is_address = is_address;
 189                 }
 190
 191                 public LocalTemporary (LocalBuilder b, Type t)
 192                 {
 193                         type = t;
 194                         eclass = ExprClass.Value;
 195                         loc = Location.Null;
 196                         builder = b;
 197                 }
 198
 199                 public void Release (EmitContext ec)
 200                 {
 201                         ec.FreeTemporaryLocal (builder, type);
 202                         builder = null;
 203                 }
 204
 205                 public override Expression DoResolve (EmitContext ec)
 206                 {
 207                         return this;
 208                 }
 209
 210                 public override void Emit (EmitContext ec)
 211                 {
 212                         ILGenerator ig = ec.ig;
 213
 214                         if (builder == null)
 215                                 throw new InternalErrorException ("Emit without Store, or after Release");
 216
 217                         ig.Emit (OpCodes.Ldloc, builder);
 218                         // we need to copy from the pointer
 219                         if (is_address)
 220                                 LoadFromPtr (ig, type);
 221                 }
 222
 223                 // NB: if you have `is_address' on the stack there must
 224                 // be a managed pointer. Otherwise, it is the type from
 225                 // the ctor.
 226                 public void Store (EmitContext ec)
 227                 {
 228                         ILGenerator ig = ec.ig;
 229                         if (builder == null)
 230                                 builder = ec.GetTemporaryLocal (is_address ? TypeManager.GetReferenceType (type): type);
 231
 232                         ig.Emit (OpCodes.Stloc, builder);
 233                 }
 234
 235                 public void AddressOf (EmitContext ec, AddressOp mode)
 236                 {
 237                         if (builder == null)
 238                                 builder = ec.GetTemporaryLocal (is_address ? TypeManager.GetReferenceType (type): type);
 239
 240                         // if is_address, than this is just the address anyways,
 241                         // so we just return this.
 242                         ILGenerator ig = ec.ig;
 243
 244                         if (is_address)
 245                                 ig.Emit (OpCodes.Ldloc, builder);
 246                         else
 247                                 ig.Emit (OpCodes.Ldloca, builder);
 248                 }
 249
 250                 public bool PointsToAddress {
 251                         get {
 252                                 return is_address;
 253                         }
 254                 }
 255         }
 256
 257         /// <summary>
 258         ///   The Assign node takes care of assigning the value of source into
 259         ///   the expression represented by target.
 260         /// </summary>
 261         public class Assign : ExpressionStatement {
 262                 protected Expression target, source, real_source;
 263                 protected LocalTemporary temp = null, real_temp = null;
 264                 protected Assign embedded = null;
 265                 protected bool is_embedded = false;
 266                 protected bool must_free_temp = false;
 267
 268                 public Assign (Expression target, Expression source)
 269                         : this (target, source, target.Location)
 270                 {
 271                 }
 272
 273                 public Assign (Expression target, Expression source, Location l)
 274                 {
 275                         this.target = target;
 276                         this.source = this.real_source = source;
 277                         this.loc = l;
 278                 }
 279
 280                 protected Assign (Assign embedded, Location l)
 281                         : this (embedded.target, embedded.source, l)
 282                 {
 283                         this.is_embedded = true;
 284                 }
 285
 286                 protected virtual Assign GetEmbeddedAssign (Location loc)
 287                 {
 288                         return new Assign (this, loc);
 289                 }
 290
 291                 public Expression Target {
 292                         get {
 293                                 return target;
 294                         }
 295
 296                         set {
 297                                 target = value;
 298                         }
 299                 }
 300
 301                 public Expression Source {
 302                         get {
 303                                 return source;
 304                         }
 305
 306                         set {
 307                                 source = value;
 308                         }
 309                 }
 310
 311                 public static void error70 (EventInfo ei, Location l)
 312                 {
 313                         Report.Error (70, l, "The event `" + TypeManager.CSharpSignature (ei) +
 314                                       "' can only appear on the left hand side of += or -= (except when" +
 315                                       " used from within the type `" + ei.DeclaringType + "')");
 316                 }
 317
 318                 //
 319                 // Will return either `this' or an instance of `New'.
 320                 //
 321                 public override Expression DoResolve (EmitContext ec)
 322                 {
 323                         // Create an embedded assignment if our source is an assignment.
 324                         if (source is Assign)
 325                                 source = embedded = ((Assign) source).GetEmbeddedAssign (loc);
 326
 327                         real_source = source = source.Resolve (ec);
 328
 329                         // Check for and handle varible type inference
 330                         LocalVariableReference l = target as LocalVariableReference;
 331                         if (l != null) {
 332                                 VarExpr v = l.Block.GetVariableType(l.Name) as VarExpr;
 333                                 if (v != null && !v.Handled) {
 334                                         ((LocalInfo)l.Block.Variables[l.Name]).VariableType = real_source.Type;
 335                                         v.Handled = true;
 336                                 }
 337                         }
 338
 339                         if (source == null) {
 340                                 // Ensure that we don't propagate the error as spurious "uninitialized variable" errors.
 341                                 target = target.ResolveLValue (ec, EmptyExpression.Null, Location);
 342                                 return null;
 343                         }
 344
 345                         //
 346                         // This is used in an embedded assignment.
 347                         // As an example, consider the statement "A = X = Y = Z".
 348                         //
 349                         if (is_embedded && !(source is Constant)) {
 350                                 // If this is the innermost assignment (the "Y = Z" in our example),
 351                                 // create a new temporary local, otherwise inherit that variable
 352                                 // from our child (the "X = (Y = Z)" inherits the local from the
 353                                 // "Y = Z" assignment).
 354
 355                                 if (embedded == null) {
 356                                         if (this is CompoundAssign)
 357                                                 real_temp = temp = new LocalTemporary (target.Type);
 358                                         else
 359                                                 real_temp = temp = new LocalTemporary (source.Type);
 360                                 } else
 361                                         temp = embedded.temp;
 362
 363                                 // Set the source to the new temporary variable.
 364                                 // This means that the following target.ResolveLValue () will tell
 365                                 // the target to read it's source value from that variable.
 366                                 source = temp;
 367                         }
 368
 369                         // If we have an embedded assignment, use the embedded assignment's temporary
 370                         // local variable as source.
 371                         if (embedded != null)
 372                                 source = (embedded.temp != null) ? embedded.temp : embedded.source;
 373
 374                         target = target.ResolveLValue (ec, source, Location);
 375
 376                         if (target == null)
 377                                 return null;
 378
 379                         // Handle initializations e.g. Person p = new Person () { Name = "Scott" };
 380                         IInitializable initializer = source as IInitializable;
 381                         if (initializer != null && !initializer.Initialize (ec, target))
 382                                 return null;
 383
 384                         bool same_assignment = (embedded != null) ? embedded.Target.Equals(target) : source.Equals (target);
 385                         if (same_assignment) {
 386                                 Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");
 387                         }
 388
 389                         Type target_type = target.Type;
 390                         Type source_type = real_source.Type;
 391
 392                         // If we're an embedded assignment, our parent will reuse our source as its
 393                         // source, it won't read from our target.
 394                         if (is_embedded)
 395                                 type = source_type;
 396                         else
 397                                 type = target_type;
 398                         eclass = ExprClass.Value;
 399
 400                         if (target is EventExpr) {
 401                                 EventInfo ei = ((EventExpr) target).EventInfo;
 402
 403                                 Expression ml = MemberLookup (
 404                                         ec.ContainerType, ec.ContainerType, ei.Name,
 405                                         MemberTypes.Event, AllBindingFlags | BindingFlags.DeclaredOnly, loc);
 406
 407                                 if (ml == null) {
 408                                         //
 409                                         // If this is the case, then the Event does not belong
 410                                         // to this Type and so, according to the spec
 411                                         // is allowed to only appear on the left hand of
 412                                         // the += and -= operators
 413                                         //
 414                                         // Note that target will not appear as an EventExpr
 415                                         // in the case it is being referenced within the same type container;
 416                                         // it will appear as a FieldExpr in that case.
 417                                         //
 418
 419                                         if (!(source is BinaryDelegate)) {
 420                                                 error70 (ei, loc);
 421                                                 return null;
 422                                         }
 423                                 }
 424                         }
 425
 426                         if (!(target is IAssignMethod) && (target.eclass != ExprClass.EventAccess)) {
 427                                 Error_ValueAssignment (loc);
 428                                 return null;
 429                         }
 430
 431                         if ((source.eclass == ExprClass.Type) && (source is TypeExpr)) {
 432                                 source.Error_UnexpectedKind (ec.DeclContainer, "variable or value", loc);
 433                                 return null;
 434                         } else if ((RootContext.Version == LanguageVersion.ISO_1) &&
 435                                    (source is MethodGroupExpr)){
 436                                 ((MethodGroupExpr) source).ReportUsageError ();
 437                                 return null;
 438
 439                         }
 440
 441                         if (target_type == source_type){
 442                                 if (source is New && target_type.IsValueType &&
 443                                     (target.eclass != ExprClass.IndexerAccess) && (target.eclass != ExprClass.PropertyAccess)){
 444                                         New n = (New) source;
 445
 446                                         if (n.SetValueTypeVariable (target))
 447                                                 return n;
 448                                         else
 449                                                 return null;
 450                                 }
 451
 452                                 return this;
 453                         }
 454
 455                         //
 456                         // If this assignment/operator was part of a compound binary
 457                         // operator, then we allow an explicit conversion, as detailed
 458                         // in the spec.
 459                         //
 460
 461                         if (this is CompoundAssign){
 462                                 CompoundAssign a = (CompoundAssign) this;
 463
 464                                 Binary b = source as Binary;
 465                                 if (b != null){
 466                                         //
 467                                         // 1. if the source is explicitly convertible to the
 468                                         //    target_type
 469                                         //
 470
 471                                         source = Convert.ExplicitConversion (ec, source, target_type, loc);
 472                                         if (source == null){
 473                                                 a.original_source.Error_ValueCannotBeConverted (ec, loc, target_type, true);
 474                                                 return null;
 475                                         }
 476
 477                                         //
 478                                         // 2. and the original right side is implicitly convertible to
 479                                         // the type of target
 480                                         //
 481                                         if (Convert.ImplicitConversionExists (ec, a.original_source, target_type))
 482                                                 return this;
 483
 484                                         //
 485                                         // In the spec 2.4 they added: or if type of the target is int
 486                                         // and the operator is a shift operator...
 487                                         //
 488                                         if (source_type == TypeManager.int32_type &&
 489                                             (b.Oper == Binary.Operator.LeftShift || b.Oper == Binary.Operator.RightShift))
 490                                                 return this;
 491
 492                                         a.original_source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
 493                                         return null;
 494                                 }
 495                         }
 496
 497                         if (source.eclass == ExprClass.MethodGroup && !TypeManager.IsDelegateType (target_type)) {
 498                                 Report.Error (428, source.Location, "Cannot convert method group `{0}' to non-delegate type `{1}'. Did you intend to invoke the method?",
 499                                         ((MethodGroupExpr)source).Name, target.GetSignatureForError ());
 500                                 return null;
 501                         }
 502
 503                         source = Convert.ImplicitConversionRequired (ec, source, target_type, loc);
 504                         if (source == null)
 505                                 return null;
 506
 507                         // If we're an embedded assignment, we need to create a new temporary variable
 508                         // for the converted value.  Our parent will use this new variable as its source.
 509                         // The same applies when we have an embedded assignment - in this case, we need
 510                         // to convert our embedded assignment's temporary local variable to the correct
 511                         // type and store it in a new temporary local.
 512                         if (is_embedded || embedded != null) {
 513                                 type = target_type;
 514                                 temp = new LocalTemporary (type);
 515                                 must_free_temp = true;
 516                         }
 517
 518                         return this;
 519                 }
 520
 521                 Expression EmitEmbedded (EmitContext ec)
 522                 {
 523                         // Emit an embedded assignment.
 524
 525                         if (real_temp != null) {
 526                                 // If we're the innermost assignment, `real_source' is the right-hand
 527                                 // expression which gets assigned to all the variables left of it.
 528                                 // Emit this expression and store its result in real_temp.
 529                                 real_source.Emit (ec);
 530                                 real_temp.Store (ec);
 531                         }
 532
 533                         if (embedded != null)
 534                                 embedded.EmitEmbedded (ec);
 535
 536                         // This happens when we've done a type conversion, in this case source will be
 537                         // the expression which does the type conversion from real_temp.
 538                         // So emit it and store the result in temp; this is the var which will be read
 539                         // by our parent.
 540                         if (temp != real_temp) {
 541                                 source.Emit (ec);
 542                                 temp.Store (ec);
 543                         }
 544
 545                         Expression temp_source = (temp != null) ? temp : source;
 546                         ((IAssignMethod) target).EmitAssign (ec, temp_source, false, false);
 547                         return temp_source;
 548                 }
 549
 550                 void ReleaseEmbedded (EmitContext ec)
 551                 {
 552                         if (embedded != null)
 553                                 embedded.ReleaseEmbedded (ec);
 554
 555                         if (real_temp != null)
 556                                 real_temp.Release (ec);
 557
 558                         if (must_free_temp)
 559                                 temp.Release (ec);
 560                 }
 561
 562                 void Emit (EmitContext ec, bool is_statement)
 563                 {
 564                         if (target is EventExpr) {
 565                                 ((EventExpr) target).EmitAddOrRemove (ec, source);
 566                                 return;
 567                         }
 568
 569                         IAssignMethod am = (IAssignMethod) target;
 570
 571                         Expression temp_source;
 572                         if (embedded != null) {
 573                                 temp_source = embedded.EmitEmbedded (ec);
 574
 575                                 if (temp != null) {
 576                                         source.Emit (ec);
 577                                         temp.Store (ec);
 578                                         temp_source = temp;
 579                                 }
 580                         } else
 581                                 temp_source = source;
 582
 583                         am.EmitAssign (ec, temp_source, !is_statement, this is CompoundAssign);
 584
 585                         if (embedded != null) {
 586                                 if (temp != null)
 587                                         temp.Release (ec);
 588                                 embedded.ReleaseEmbedded (ec);
 589                         }
 590                 }
 591
 592                 public override void Emit (EmitContext ec)
 593                 {
 594                         Emit (ec, false);
 595                 }
 596
 597                 public override void EmitStatement (EmitContext ec)
 598                 {
 599                         Emit (ec, true);
 600                 }
 601
 602                 protected override void CloneTo (CloneContext clonectx, Expression t)
 603                 {
 604                         Assign _target = (Assign) t;
 605
 606                         _target.target = target.Clone (clonectx);
 607                         _target.source = source.Clone (clonectx);
 608                 }
 609         }
 610
 611
 612         // This class implements fields and events class initializers
 613         public class FieldInitializer : Assign
 614         {
 615                 public readonly DeclSpace TypeContainer;
 616
 617                 public FieldInitializer (FieldBuilder field, Expression expression, DeclSpace container)
 618                         : base (new FieldExpr (field, expression.Location, true), expression)
 619                 {
 620                         this.TypeContainer = container;
 621                         if (!field.IsStatic)
 622                                 ((FieldExpr)target).InstanceExpression = CompilerGeneratedThis.Instance;
 623                 }
 624
 625                 public bool IsComplexInitializer {
 626                         get {
 627                                 if (embedded != null)
 628                                         return true;
 629
 630                                 return !(source is Constant);
 631                         }
 632                 }
 633
 634                 public bool IsDefaultInitializer {
 635                         get {
 636                                 Constant c = source as Constant;
 637                                 if (c == null)
 638                                         return false;
 639
 640                                 FieldExpr fe = (FieldExpr)target;
 641                                 return c.IsDefaultInitializer (fe.Type);
 642                         }
 643                 }
 644         }
 645
 646
 647         //
 648         // This class is used for compound assignments.
 649         //
 650         class CompoundAssign : Assign {
 651                 Binary.Operator op;
 652                 public Expression original_source;
 653
 654                 public CompoundAssign (Binary.Operator op, Expression target, Expression source)
 655                         : base (target, source, target.Location)
 656                 {
 657                         original_source = source;
 658                         this.op = op;
 659                 }
 660
 661                 protected CompoundAssign (CompoundAssign embedded, Location l)
 662                         : this (embedded.op, embedded.target, embedded.source)
 663                 {
 664                         this.is_embedded = true;
 665                 }
 666
 667                 protected override Assign GetEmbeddedAssign (Location loc)
 668                 {
 669                         return new CompoundAssign (this, loc);
 670                 }
 671
 672                 public override Expression DoResolve (EmitContext ec)
 673                 {
 674                         original_source = original_source.Resolve (ec);
 675                         if (original_source == null)
 676                                 return null;
 677
 678                         target = target.Resolve (ec);
 679                         if (target == null)
 680                                 return null;
 681
 682                         if (target is MethodGroupExpr){
 683                                 Error_CannotAssign (((MethodGroupExpr)target).Name, target.ExprClassName);
 684                                 return null;
 685                         }
 686                         //
 687                         // Only now we can decouple the original source/target
 688                         // into a tree, to guarantee that we do not have side
 689                         // effects.
 690                         //
 691                         source = new Binary (op, target, original_source);
 692                         return base.DoResolve (ec);
 693                 }
 694
 695                 protected override void CloneTo (CloneContext clonectx, Expression t)
 696                 {
 697                         CompoundAssign target = (CompoundAssign) t;
 698
 699                         target.original_source = original_source.Clone (clonectx);
 700                 }
 701         }
 702 }