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                         if (source == null) {
 329                                 // Ensure that we don't propagate the error as spurious "uninitialized variable" errors.
 330                                 target = target.ResolveLValue (ec, EmptyExpression.Null, Location);
 331                                 return null;
 332                         }
 333
 334                         //
 335                         // This is used in an embedded assignment.
 336                         // As an example, consider the statement "A = X = Y = Z".
 337                         //
 338                         if (is_embedded && !(source is Constant)) {
 339                                 // If this is the innermost assignment (the "Y = Z" in our example),
 340                                 // create a new temporary local, otherwise inherit that variable
 341                                 // from our child (the "X = (Y = Z)" inherits the local from the
 342                                 // "Y = Z" assignment).
 343
 344                                 if (embedded == null) {
 345                                         if (this is CompoundAssign)
 346                                                 real_temp = temp = new LocalTemporary (target.Type);
 347                                         else
 348                                                 real_temp = temp = new LocalTemporary (source.Type);
 349                                 } else
 350                                         temp = embedded.temp;
 351
 352                                 // Set the source to the new temporary variable.
 353                                 // This means that the following target.ResolveLValue () will tell
 354                                 // the target to read it's source value from that variable.
 355                                 source = temp;
 356                         }
 357
 358                         // If we have an embedded assignment, use the embedded assignment's temporary
 359                         // local variable as source.
 360                         if (embedded != null)
 361                                 source = (embedded.temp != null) ? embedded.temp : embedded.source;
 362
 363                         target = target.ResolveLValue (ec, source, Location);
 364
 365                         if (target == null)
 366                                 return null;
 367
 368                         bool same_assignment = (embedded != null) ? embedded.Target.Equals(target) : source.Equals (target);
 369                         if (same_assignment) {
 370                                 Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");
 371                         }
 372
 373                         Type target_type = target.Type;
 374                         Type source_type = real_source.Type;
 375
 376                         // If we're an embedded assignment, our parent will reuse our source as its
 377                         // source, it won't read from our target.
 378                         if (is_embedded)
 379                                 type = source_type;
 380                         else
 381                                 type = target_type;
 382                         eclass = ExprClass.Value;
 383
 384                         if (target is EventExpr) {
 385                                 EventInfo ei = ((EventExpr) target).EventInfo;
 386
 387                                 Expression ml = MemberLookup (
 388                                         ec.ContainerType, ec.ContainerType, ei.Name,
 389                                         MemberTypes.Event, AllBindingFlags | BindingFlags.DeclaredOnly, loc);
 390
 391                                 if (ml == null) {
 392                                         //
 393                                         // If this is the case, then the Event does not belong
 394                                         // to this Type and so, according to the spec
 395                                         // is allowed to only appear on the left hand of
 396                                         // the += and -= operators
 397                                         //
 398                                         // Note that target will not appear as an EventExpr
 399                                         // in the case it is being referenced within the same type container;
 400                                         // it will appear as a FieldExpr in that case.
 401                                         //
 402
 403                                         if (!(source is BinaryDelegate)) {
 404                                                 error70 (ei, loc);
 405                                                 return null;
 406                                         }
 407                                 }
 408                         }
 409
 410                         if (!(target is IAssignMethod) && (target.eclass != ExprClass.EventAccess)) {
 411                                 Report.Error (131, loc,
 412                                               "Left hand of an assignment must be a variable, " +
 413                                               "a property or an indexer");
 414                                 return null;
 415                         }
 416
 417                         if ((source.eclass == ExprClass.Type) && (source is TypeExpr)) {
 418                                 source.Error_UnexpectedKind (ec.DeclContainer, "variable or value", loc);
 419                                 return null;
 420                         } else if ((RootContext.Version == LanguageVersion.ISO_1) &&
 421                                    (source is MethodGroupExpr)){
 422                                 ((MethodGroupExpr) source).ReportUsageError ();
 423                                 return null;
 424
 425                         }
 426
 427                         if (target_type == source_type){
 428                                 if (source is New && target_type.IsValueType &&
 429                                     (target.eclass != ExprClass.IndexerAccess) && (target.eclass != ExprClass.PropertyAccess)){
 430                                         New n = (New) source;
 431
 432                                         if (n.SetValueTypeVariable (target))
 433                                                 return n;
 434                                         else
 435                                                 return null;
 436                                 }
 437
 438                                 return this;
 439                         }
 440
 441                         //
 442                         // If this assignment/operator was part of a compound binary
 443                         // operator, then we allow an explicit conversion, as detailed
 444                         // in the spec.
 445                         //
 446
 447                         if (this is CompoundAssign){
 448                                 CompoundAssign a = (CompoundAssign) this;
 449
 450                                 Binary b = source as Binary;
 451                                 if (b != null){
 452                                         //
 453                                         // 1. if the source is explicitly convertible to the
 454                                         //    target_type
 455                                         //
 456
 457                                         source = Convert.ExplicitConversion (ec, source, target_type, loc);
 458                                         if (source == null){
 459                                                 a.original_source.Error_ValueCannotBeConverted (loc, target_type, true);
 460                                                 return null;
 461                                         }
 462
 463                                         //
 464                                         // 2. and the original right side is implicitly convertible to
 465                                         // the type of target
 466                                         //
 467                                         if (Convert.ImplicitStandardConversionExists (a.original_source, target_type))
 468                                                 return this;
 469
 470                                         //
 471                                         // In the spec 2.4 they added: or if type of the target is int
 472                                         // and the operator is a shift operator...
 473                                         //
 474                                         if (source_type == TypeManager.int32_type &&
 475                                             (b.Oper == Binary.Operator.LeftShift || b.Oper == Binary.Operator.RightShift))
 476                                                 return this;
 477
 478                                         a.original_source.Error_ValueCannotBeConverted (loc, target_type, false);
 479                                         return null;
 480                                 }
 481                         }
 482
 483                         if (source.eclass == ExprClass.MethodGroup && !TypeManager.IsDelegateType (target_type)) {
 484                                 Report.Error (428, source.Location, "Cannot convert method group `{0}' to non-delegate type `{1}'. Did you intend to invoke the method?",
 485                                         ((MethodGroupExpr)source).Name, target.GetSignatureForError ());
 486                                 return null;
 487                         }
 488
 489                         source = Convert.ImplicitConversionRequired (ec, source, target_type, loc);
 490                         if (source == null)
 491                                 return null;
 492
 493                         // If we're an embedded assignment, we need to create a new temporary variable
 494                         // for the converted value.  Our parent will use this new variable as its source.
 495                         // The same applies when we have an embedded assignment - in this case, we need
 496                         // to convert our embedded assignment's temporary local variable to the correct
 497                         // type and store it in a new temporary local.
 498                         if (is_embedded || embedded != null) {
 499                                 type = target_type;
 500                                 temp = new LocalTemporary (type);
 501                                 must_free_temp = true;
 502                         }
 503
 504                         return this;
 505                 }
 506
 507                 Expression EmitEmbedded (EmitContext ec)
 508                 {
 509                         // Emit an embedded assignment.
 510
 511                         if (real_temp != null) {
 512                                 // If we're the innermost assignment, `real_source' is the right-hand
 513                                 // expression which gets assigned to all the variables left of it.
 514                                 // Emit this expression and store its result in real_temp.
 515                                 real_source.Emit (ec);
 516                                 real_temp.Store (ec);
 517                         }
 518
 519                         if (embedded != null)
 520                                 embedded.EmitEmbedded (ec);
 521
 522                         // This happens when we've done a type conversion, in this case source will be
 523                         // the expression which does the type conversion from real_temp.
 524                         // So emit it and store the result in temp; this is the var which will be read
 525                         // by our parent.
 526                         if (temp != real_temp) {
 527                                 source.Emit (ec);
 528                                 temp.Store (ec);
 529                         }
 530
 531                         Expression temp_source = (temp != null) ? temp : source;
 532                         ((IAssignMethod) target).EmitAssign (ec, temp_source, false, false);
 533                         return temp_source;
 534                 }
 535
 536                 void ReleaseEmbedded (EmitContext ec)
 537                 {
 538                         if (embedded != null)
 539                                 embedded.ReleaseEmbedded (ec);
 540
 541                         if (real_temp != null)
 542                                 real_temp.Release (ec);
 543
 544                         if (must_free_temp)
 545                                 temp.Release (ec);
 546                 }
 547
 548                 void Emit (EmitContext ec, bool is_statement)
 549                 {
 550                         if (target is EventExpr) {
 551                                 ((EventExpr) target).EmitAddOrRemove (ec, source);
 552                                 return;
 553                         }
 554
 555                         IAssignMethod am = (IAssignMethod) target;
 556
 557                         Expression temp_source;
 558                         if (embedded != null) {
 559                                 temp_source = embedded.EmitEmbedded (ec);
 560
 561                                 if (temp != null) {
 562                                         source.Emit (ec);
 563                                         temp.Store (ec);
 564                                         temp_source = temp;
 565                                 }
 566                         } else
 567                                 temp_source = source;
 568
 569                         am.EmitAssign (ec, temp_source, !is_statement, this is CompoundAssign);
 570
 571                         if (embedded != null) {
 572                                 if (temp != null)
 573                                         temp.Release (ec);
 574                                 embedded.ReleaseEmbedded (ec);
 575                         }
 576                 }
 577
 578                 public override void Emit (EmitContext ec)
 579                 {
 580                         Emit (ec, false);
 581                 }
 582
 583                 public override void EmitStatement (EmitContext ec)
 584                 {
 585                         Emit (ec, true);
 586                 }
 587         }
 588
 589
 590         //
 591         // This class is used for compound assignments.
 592         //
 593         class CompoundAssign : Assign {
 594                 Binary.Operator op;
 595                 public Expression original_source;
 596
 597                 public CompoundAssign (Binary.Operator op, Expression target, Expression source)
 598                         : base (target, source, target.Location)
 599                 {
 600                         original_source = source;
 601                         this.op = op;
 602                 }
 603
 604                 protected CompoundAssign (CompoundAssign embedded, Location l)
 605                         : this (embedded.op, embedded.target, embedded.source)
 606                 {
 607                         this.is_embedded = true;
 608                 }
 609
 610                 protected override Assign GetEmbeddedAssign (Location loc)
 611                 {
 612                         return new CompoundAssign (this, loc);
 613                 }
 614
 615                 public override Expression DoResolve (EmitContext ec)
 616                 {
 617                         original_source = original_source.Resolve (ec);
 618                         if (original_source == null)
 619                                 return null;
 620
 621                         target = target.Resolve (ec);
 622                         if (target == null)
 623                                 return null;
 624
 625                         if (target is MethodGroupExpr){
 626                                 Error_CannotAssign (((MethodGroupExpr)target).Name, target.ExprClassName);
 627                                 return null;
 628                         }
 629                         //
 630                         // Only now we can decouple the original source/target
 631                         // into a tree, to guarantee that we do not have side
 632                         // effects.
 633                         //
 634                         source = new Binary (op, target, original_source);
 635                         return base.DoResolve (ec);
 636                 }
 637         }
 638 }