mcs/gmcs/iterators.cs

   1 //
   2 // iterators.cs: Support for implementing iterators
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //
   7 // (C) 2003 Ximian, Inc.
   8 //
   9 // TODO:
  10 //    Flow analysis for Yield.
  11 //    Emit calls to base object constructor.
  12 //
  13 // Generics note:
  14 //    Current should be defined to return T, and IEnumerator.Current returns object
  15 //
  16
  17 using System;
  18 using System.Collections;
  19 using System.Reflection;
  20 using System.Reflection.Emit;
  21
  22 namespace Mono.CSharp {
  23
  24         public interface IIteratorContainer {
  25
  26                 //
  27                 // Invoked if a yield statement is found in the body
  28                 //
  29                 void SetYields ();
  30         }
  31
  32         public class Yield : Statement {
  33                 public Expression expr;
  34                 ArrayList finally_blocks;
  35
  36                 public Yield (Expression expr, Location l)
  37                 {
  38                         this.expr = expr;
  39                         loc = l;
  40                 }
  41
  42                 public static bool CheckContext (EmitContext ec, Location loc)
  43                 {
  44                         if (ec.CurrentBranching.InFinally (true)){
  45                                 Report.Error (1625, loc, "Cannot yield in the body of a " +
  46                                               "finally clause");
  47                                 return false;
  48                         }
  49                         if (ec.CurrentBranching.InCatch ()){
  50                                 Report.Error (1631, loc, "Cannot yield in the body of a " +
  51                                               "catch clause");
  52                                 return false;
  53                         }
  54                         if (ec.CurrentAnonymousMethod != null){
  55                                 Report.Error (1621, loc, "yield statement can not appear inside an anonymoud method");
  56                                 return false;
  57                         }
  58
  59                         //
  60                         // FIXME: Missing check for Yield inside try block that contains catch clauses
  61                         //
  62                         return true;
  63                 }
  64
  65                 public override bool Resolve (EmitContext ec)
  66                 {
  67                         expr = expr.Resolve (ec);
  68                         if (expr == null)
  69                                 return false;
  70                         if (!CheckContext (ec, loc))
  71                                 return false;
  72
  73                         Iterator iterator = ec.CurrentIterator;
  74                         if (expr.Type != iterator.IteratorType){
  75                                 expr = Convert.ImplicitConversionRequired (
  76                                         ec, expr, iterator.IteratorType, loc);
  77                                 if (expr == null)
  78                                         return false;
  79                         }
  80
  81                         ec.CurrentBranching.StealFinallyClauses (ref finally_blocks);
  82                         return true;
  83                 }
  84
  85                 protected override void DoEmit (EmitContext ec)
  86                 {
  87                         ec.CurrentIterator.MarkYield (ec, expr, finally_blocks);
  88                 }
  89         }
  90
  91         public class YieldBreak : Statement {
  92
  93                 public YieldBreak (Location l)
  94                 {
  95                         loc = l;
  96                 }
  97
  98                 public override bool Resolve (EmitContext ec)
  99                 {
 100                         if (!Yield.CheckContext (ec, loc))
 101                                 return false;
 102
 103                         ec.CurrentBranching.CurrentUsageVector.Goto ();
 104                         return true;
 105                 }
 106
 107                 protected override void DoEmit (EmitContext ec)
 108                 {
 109                         ec.CurrentIterator.EmitYieldBreak (ec.ig);
 110                 }
 111         }
 112
 113         public class Iterator : Class {
 114                 ToplevelBlock original_block;
 115                 ToplevelBlock block;
 116                 string original_name;
 117
 118                 Type iterator_type;
 119                 TypeExpr iterator_type_expr;
 120                 bool is_enumerable;
 121                 bool is_static;
 122
 123                 Hashtable fields;
 124
 125                 //
 126                 // The state as we generate the iterator
 127                 //
 128                 Label move_next_ok, move_next_error;
 129                 ArrayList resume_points = new ArrayList ();
 130                 int pc;
 131
 132                 //
 133                 // Context from the original method
 134                 //
 135                 TypeContainer container;
 136                 TypeExpr current_type;
 137                 Type this_type;
 138                 Type return_type;
 139                 Type [] param_types;
 140                 InternalParameters parameters;
 141
 142                 MethodInfo dispose_method;
 143
 144                 Expression enumerator_type;
 145                 Expression enumerable_type;
 146                 Expression generic_enumerator_type;
 147                 Expression generic_enumerable_type;
 148                 TypeArguments generic_args;
 149
 150                 protected enum State {
 151                         Uninitialized   = -2,
 152                         After,
 153                         Running
 154                 }
 155
 156                 static int proxy_count;
 157
 158                 public void EmitYieldBreak (ILGenerator ig)
 159                 {
 160                         ig.Emit (OpCodes.Ldarg_0);
 161                         IntConstant.EmitInt (ig, (int) State.After);
 162                         ig.Emit (OpCodes.Stfld, pc_field.FieldBuilder);
 163                         ig.Emit (OpCodes.Br, move_next_error);
 164                 }
 165
 166                 public void EmitMoveNext (EmitContext ec)
 167                 {
 168                         ILGenerator ig = ec.ig;
 169
 170                         move_next_ok = ig.DefineLabel ();
 171                         move_next_error = ig.DefineLabel ();
 172
 173                         LocalBuilder retval = ec.GetTemporaryLocal (TypeManager.int32_type);
 174
 175                         ig.BeginExceptionBlock ();
 176
 177                         Label dispatcher = ig.DefineLabel ();
 178                         ig.Emit (OpCodes.Br, dispatcher);
 179
 180                         ResumePoint entry_point = new ResumePoint (null);
 181                         resume_points.Add (entry_point);
 182                         entry_point.Define (ig);
 183
 184                         ec.EmitTopBlock (original_block, parameters, Location);
 185                         EmitYieldBreak (ig);
 186
 187                         ig.MarkLabel (dispatcher);
 188
 189                         Label [] labels = new Label [resume_points.Count];
 190                         for (int i = 0; i < labels.Length; i++)
 191                                 labels [i] = ((ResumePoint) resume_points [i]).Label;
 192
 193                         ig.Emit (OpCodes.Ldarg_0);
 194                         ig.Emit (OpCodes.Ldfld, pc_field.FieldBuilder);
 195                         ig.Emit (OpCodes.Switch, labels);
 196
 197                         Label end = ig.DefineLabel ();
 198
 199                         ig.MarkLabel (move_next_error);
 200                         ig.Emit (OpCodes.Ldc_I4_0);
 201                         ig.Emit (OpCodes.Stloc, retval);
 202                         ig.Emit (OpCodes.Leave, end);
 203
 204                         ig.MarkLabel (move_next_ok);
 205                         ig.Emit (OpCodes.Ldc_I4_1);
 206                         ig.Emit (OpCodes.Stloc, retval);
 207                         ig.Emit (OpCodes.Leave, end);
 208
 209                         ig.BeginFaultBlock ();
 210
 211                         ig.Emit (OpCodes.Ldarg_0);
 212                         ig.Emit (OpCodes.Callvirt, dispose_method);
 213
 214                         ig.EndExceptionBlock ();
 215
 216                         ig.MarkLabel (end);
 217                         ig.Emit (OpCodes.Ldloc, retval);
 218                         ig.Emit (OpCodes.Ret);
 219                 }
 220
 221                 public void EmitDispose (EmitContext ec)
 222                 {
 223                         ILGenerator ig = ec.ig;
 224
 225                         Label end = ig.DefineLabel ();
 226                         Label dispatcher = ig.DefineLabel ();
 227                         ig.Emit (OpCodes.Br, dispatcher);
 228
 229                         ec.RemapToProxy = true;
 230                         Label [] labels = new Label [resume_points.Count];
 231                         for (int i = 0; i < labels.Length; i++) {
 232                                 ResumePoint point = (ResumePoint) resume_points [i];
 233
 234                                 if (point.FinallyBlocks == null) {
 235                                         labels [i] = end;
 236                                         continue;
 237                                 }
 238
 239                                 labels [i] = ig.DefineLabel ();
 240                                 ig.MarkLabel (labels [i]);
 241
 242                                 ig.BeginExceptionBlock ();
 243                                 ig.BeginFinallyBlock ();
 244
 245                                 foreach (ExceptionStatement stmt in point.FinallyBlocks) {
 246                                         if (stmt != null)
 247                                                 stmt.EmitFinally (ec);
 248                                 }
 249
 250                                 ig.EndExceptionBlock ();
 251                                 ig.Emit (OpCodes.Br, end);
 252                         }
 253                         ec.RemapToProxy = false;
 254
 255                         ig.MarkLabel (dispatcher);
 256                         ig.Emit (OpCodes.Ldarg_0);
 257                         ig.Emit (OpCodes.Ldfld, pc_field.FieldBuilder);
 258                         ig.Emit (OpCodes.Switch, labels);
 259
 260                         ig.Emit (OpCodes.Ldarg_0);
 261                         IntConstant.EmitInt (ig, (int) State.After);
 262                         ig.Emit (OpCodes.Stfld, pc_field.FieldBuilder);
 263
 264                         ig.MarkLabel (end);
 265                 }
 266
 267                 protected class ResumePoint
 268                 {
 269                         public Label Label;
 270                         public readonly ExceptionStatement[] FinallyBlocks;
 271
 272                         public ResumePoint (ArrayList list)
 273                         {
 274                                 if (list != null) {
 275                                         FinallyBlocks = new ExceptionStatement [list.Count];
 276                                         list.CopyTo (FinallyBlocks, 0);
 277                                 }
 278                         }
 279
 280                         public void Define (ILGenerator ig)
 281                         {
 282                                 Label = ig.DefineLabel ();
 283                                 ig.MarkLabel (Label);
 284                         }
 285                 }
 286
 287                 //
 288                 // Invoked when a local variable declaration needs to be mapped to
 289                 // a field in our proxy class
 290                 //
 291                 // Prefixes registered:
 292                 //   v_   for EmitContext.MapVariable
 293                 //   s_   for Storage
 294                 //
 295                 public FieldBuilder MapVariable (string pfx, string name, Type t)
 296                 {
 297                         string full_name = pfx + name;
 298                         FieldBuilder fb = (FieldBuilder) fields [full_name];
 299                         if (fb != null)
 300                                 return fb;
 301
 302                         fb = TypeBuilder.DefineField (full_name, t, FieldAttributes.Private);
 303                         fields.Add (full_name, fb);
 304                         return fb;
 305                 }
 306
 307                 //
 308                 // Called back from Yield
 309                 //
 310                 public void MarkYield (EmitContext ec, Expression expr,
 311                                        ArrayList finally_blocks)
 312                 {
 313                         ILGenerator ig = ec.ig;
 314
 315                         // Store the new current
 316                         ig.Emit (OpCodes.Ldarg_0);
 317                         expr.Emit (ec);
 318                         ig.Emit (OpCodes.Stfld, current_field.FieldBuilder);
 319
 320                         // increment pc
 321                         pc++;
 322                         ig.Emit (OpCodes.Ldarg_0);
 323                         IntConstant.EmitInt (ig, pc);
 324                         ig.Emit (OpCodes.Stfld, pc_field.FieldBuilder);
 325
 326                         // Return ok
 327                         ig.Emit (OpCodes.Br, move_next_ok);
 328
 329                         ResumePoint point = new ResumePoint (finally_blocks);
 330                         resume_points.Add (point);
 331                         point.Define (ig);
 332                 }
 333
 334                 public void MarkFinally (EmitContext ec, ArrayList finally_blocks)
 335                 {
 336                         ILGenerator ig = ec.ig;
 337
 338                         // increment pc
 339                         pc++;
 340                         ig.Emit (OpCodes.Ldarg_0);
 341                         IntConstant.EmitInt (ig, pc);
 342                         ig.Emit (OpCodes.Stfld, pc_field.FieldBuilder);
 343
 344                         ResumePoint point = new ResumePoint (finally_blocks);
 345                         resume_points.Add (point);
 346                         point.Define (ig);
 347                 }
 348
 349                 private static MemberName MakeProxyName (string name)
 350                 {
 351                         int pos = name.LastIndexOf ('.');
 352                         if (pos > 0)
 353                                 name = name.Substring (pos + 1);
 354
 355                         return new MemberName ("<" + name + ">__" + (proxy_count++));
 356                 }
 357
 358                 //
 359                 // Our constructor
 360                 //
 361                 public Iterator (TypeContainer container, string name, Type return_type,
 362                                  Type [] param_types, InternalParameters parameters,
 363                                  int modifiers, ToplevelBlock block, Location loc)
 364                         : base (container.NamespaceEntry, container, MakeProxyName (name),
 365                                 Modifiers.PRIVATE, null, loc)
 366                 {
 367                         this.container = container;
 368                         this.return_type = return_type;
 369                         this.param_types = param_types;
 370                         this.parameters = parameters;
 371                         this.original_name = name;
 372                         this.original_block = block;
 373                         this.block = new ToplevelBlock (loc);
 374
 375                         fields = new Hashtable ();
 376
 377                         is_static = (modifiers & Modifiers.STATIC) != 0;
 378                 }
 379
 380                 public bool DefineIterator ()
 381                 {
 382                         ec = new EmitContext (this, Mono.CSharp.Location.Null, null, null, ModFlags);
 383
 384                         if (!CheckType (return_type)) {
 385                                 Report.Error (
 386                                         1624, Location,
 387                                         "The body of `{0}' cannot be an iterator block " +
 388                                         "because '{1}' is not an iterator interface type",
 389                                         original_name, TypeManager.CSharpName (return_type));
 390                                 return false;
 391                         }
 392
 393                         for (int i = 0; i < parameters.Count; i++){
 394                                 Parameter.Modifier mod = parameters.ParameterModifier (i);
 395                                 if ((mod & (Parameter.Modifier.REF | Parameter.Modifier.OUT)) != 0){
 396                                         Report.Error (
 397                                                 1623, Location,
 398                                                 "Iterators cannot have ref or out parameters");
 399                                         return false;
 400                                 }
 401                         }
 402
 403                         if (container.CurrentType != null)
 404                                 this_type = container.CurrentType;
 405                         else
 406                                 this_type = container.TypeBuilder;
 407
 408                         generic_args = new TypeArguments (Location);
 409                         generic_args.Add (new TypeExpression (iterator_type, Location));
 410
 411                         ArrayList list = new ArrayList ();
 412                         if (is_enumerable) {
 413                                 enumerable_type = new TypeExpression (
 414                                         TypeManager.ienumerable_type, Location);
 415                                 list.Add (enumerable_type);
 416
 417                                 generic_enumerable_type = new ConstructedType (
 418                                         TypeManager.generic_ienumerable_type,
 419                                         generic_args, Location);
 420                                 list.Add (generic_enumerable_type);
 421                         }
 422
 423                         enumerator_type = new TypeExpression (
 424                                 TypeManager.ienumerator_type, Location);
 425                         list.Add (enumerator_type);
 426
 427                         list.Add (new TypeExpression (TypeManager.idisposable_type, Location));
 428
 429                         generic_enumerator_type = new ConstructedType (
 430                                 TypeManager.generic_ienumerator_type,
 431                                 generic_args, Location);
 432                         list.Add (generic_enumerator_type);
 433
 434                         iterator_type_expr = new TypeExpression (iterator_type, Location);
 435
 436                         container.AddIterator (this);
 437
 438                         Bases = list;
 439                         return true;
 440                 }
 441
 442                 MethodInfo FetchMethodDispose ()
 443                 {
 444                         MemberList dispose_list;
 445
 446                         dispose_list = FindMembers (
 447                                 current_type.Type,
 448                                 MemberTypes.Method, BindingFlags.Public | BindingFlags.Instance,
 449                                 Type.FilterName, "Dispose");
 450
 451                         if (dispose_list.Count != 1)
 452                                 throw new InternalErrorException ("Cannot find Dipose() method.");
 453
 454                         return (MethodInfo) dispose_list [0];
 455                 }
 456
 457                 protected override bool DoDefineMembers ()
 458                 {
 459                         if (!base.DoDefineMembers ())
 460                                 return false;
 461
 462                         dispose_method = FetchMethodDispose ();
 463                         if (dispose_method == null)
 464                                 return false;
 465
 466                         return true;
 467                 }
 468
 469                 //
 470                 // Returns the new block for the method, or null on failure
 471                 //
 472                 protected override bool DefineNestedTypes ()
 473                 {
 474                         if (CurrentType != null)
 475                                 current_type = new TypeExpression (CurrentType, Location);
 476                         else
 477                                 current_type = new TypeExpression (TypeBuilder, Location);
 478
 479                         Define_Fields ();
 480                         Define_Constructor ();
 481                         Define_Current (false);
 482                         Define_Current (true);
 483                         Define_MoveNext ();
 484                         Define_Reset ();
 485                         Define_Dispose ();
 486
 487                         if (is_enumerable) {
 488                                 Define_GetEnumerator (false);
 489                                 Define_GetEnumerator (true);
 490                         }
 491
 492                         Create_Block ();
 493
 494                         return base.DefineNestedTypes ();
 495                 }
 496
 497
 498                 Field pc_field;
 499                 Field current_field;
 500                 Method dispose;
 501
 502                 public Field this_field;
 503                 public Field[] parameter_fields;
 504
 505                 void Create_Block ()
 506                 {
 507                         int first = is_static ? 0 : 1;
 508
 509                         ArrayList args = new ArrayList ();
 510                         if (!is_static) {
 511                                 Type t = this_type;
 512                                 args.Add (new Argument (
 513                                         new ThisParameterReference (t, 0, Location)));
 514                         }
 515
 516                         args.Add (new Argument (new BoolLiteral (false)));
 517
 518                         for (int i = 0; i < parameters.Count; i++) {
 519                                 Type t = parameters.ParameterType (i);
 520                                 args.Add (new Argument (
 521                                         new SimpleParameterReference (t, first + i, Location)));
 522                         }
 523
 524                         Expression new_expr = new New (current_type, args, Location);
 525
 526                         block.AddStatement (new NoCheckReturn (new_expr, Location));
 527                 }
 528
 529                 void Define_Fields ()
 530                 {
 531                         Location loc = Location.Null;
 532
 533                         pc_field = new Field (
 534                                 this, TypeManager.system_int32_expr, Modifiers.PRIVATE, "PC",
 535                                 null, null, loc);
 536                         AddField (pc_field);
 537
 538                         current_field = new Field (
 539                                 this, iterator_type_expr, Modifiers.PRIVATE, "current",
 540                                 null, null, loc);
 541                         AddField (current_field);
 542
 543                         if (!is_static) {
 544                                 this_field = new Field (
 545                                         this, new TypeExpression (this_type, loc),
 546                                         Modifiers.PRIVATE, "this", null, null, loc);
 547                                 AddField (this_field);
 548                         }
 549
 550                         parameter_fields = new Field [parameters.Count];
 551                         for (int i = 0; i < parameters.Count; i++) {
 552                                 string fname = String.Format (
 553                                         "field{0}_{1}", i, parameters.ParameterName (i));
 554
 555                                 parameter_fields [i] = new Field (
 556                                         this,
 557                                         new TypeExpression (parameters.ParameterType (i), loc),
 558                                         Modifiers.PRIVATE, fname, null, null, loc);
 559                                 AddField (parameter_fields [i]);
 560                         }
 561                 }
 562
 563                 void Define_Constructor ()
 564                 {
 565                         Parameters ctor_params;
 566
 567                         ArrayList list = new ArrayList ();
 568
 569                         if (!is_static)
 570                                 list.Add (new Parameter (
 571                                         new TypeExpression (this_type, Location),
 572                                         "this", Parameter.Modifier.NONE, null));
 573                         list.Add (new Parameter (
 574                                 TypeManager.system_boolean_expr, "initialized",
 575                                 Parameter.Modifier.NONE, null));
 576
 577                         Parameter[] old_fixed = parameters.Parameters.FixedParameters;
 578                         if (old_fixed != null)
 579                                 list.AddRange (old_fixed);
 580
 581                         Parameter[] fixed_params = new Parameter [list.Count];
 582                         list.CopyTo (fixed_params);
 583
 584                         ctor_params = new Parameters (
 585                                 fixed_params, parameters.Parameters.ArrayParameter,
 586                                 Location);
 587
 588                         Constructor ctor = new Constructor (
 589                                 this, Name, Modifiers.PUBLIC, ctor_params,
 590                                 new ConstructorBaseInitializer (
 591                                         null, Parameters.EmptyReadOnlyParameters, Location),
 592                                 Location);
 593                         AddConstructor (ctor);
 594
 595                         ToplevelBlock block = ctor.Block = new ToplevelBlock (Location);
 596
 597                         if (!is_static) {
 598                                 Type t = this_type;
 599
 600                                 Assign assign = new Assign (
 601                                         new FieldExpression (this_field),
 602                                         new SimpleParameterReference (t, 1, Location),
 603                                         Location);
 604
 605                                 block.AddStatement (new StatementExpression (assign, Location));
 606                         }
 607
 608                         int first = is_static ? 2 : 3;
 609
 610                         for (int i = 0; i < parameters.Count; i++) {
 611                                 Type t = parameters.ParameterType (i);
 612
 613                                 Assign assign = new Assign (
 614                                         new FieldExpression (parameter_fields [i]),
 615                                         new SimpleParameterReference (t, first + i, Location),
 616                                         Location);
 617
 618                                 block.AddStatement (new StatementExpression (assign, Location));
 619                         }
 620
 621                         State initial = is_enumerable ? State.Uninitialized : State.Running;
 622                         block.AddStatement (new SetState (this, initial, Location));
 623
 624                         block.AddStatement (new If (
 625                                 new SimpleParameterReference (
 626                                         TypeManager.bool_type, first - 1, Location),
 627                                 new SetState (this, State.Running, Location),
 628                                 Location));
 629                 }
 630
 631                 Statement Create_ThrowInvalidOperation ()
 632                 {
 633                         TypeExpr ex_type = new TypeExpression (
 634                                 TypeManager.invalid_operation_exception_type, Location);
 635
 636                         return new Throw (new New (ex_type, null, Location), Location);
 637                 }
 638
 639                 Statement Create_ThrowNotSupported ()
 640                 {
 641                         TypeExpr ex_type = new TypeExpression (
 642                                 TypeManager.not_supported_exception_type, Location);
 643
 644                         return new Throw (new New (ex_type, null, Location), Location);
 645                 }
 646
 647                 void Define_Current (bool is_generic)
 648                 {
 649                         MemberName left;
 650                         Expression type;
 651                         if (is_generic) {
 652                                 left = new MemberName (
 653                                         "System.Collections.Generic.IEnumerator",
 654                                         generic_args);
 655                                 type = iterator_type_expr;
 656                         } else {
 657                                 left = new MemberName ("System.Collections.IEnumerator");
 658                                 type = TypeManager.system_object_expr;
 659                         }
 660
 661                         MemberName name = new MemberName (left, "Current", null);
 662
 663                         ToplevelBlock get_block = new ToplevelBlock (Location);
 664
 665                         get_block.AddStatement (new If (
 666                                 new Binary (
 667                                         Binary.Operator.LessThanOrEqual,
 668                                         new FieldExpression (pc_field),
 669                                         new IntLiteral ((int) State.Running), Location),
 670                                 Create_ThrowInvalidOperation (),
 671                                 new Return (
 672                                         new FieldExpression (current_field), Location),
 673                                 Location));
 674
 675                         Accessor getter = new Accessor (get_block, 0, null, Location);
 676
 677                         Property current = new Property (
 678                                 this, type, 0, false, name, null, getter, null, Location);
 679                         AddProperty (current);
 680                 }
 681
 682                 void Define_MoveNext ()
 683                 {
 684                         Method move_next = new Method (
 685                                 this, null, TypeManager.system_boolean_expr,
 686                                 Modifiers.PUBLIC, false, new MemberName ("MoveNext"),
 687                                 Parameters.EmptyReadOnlyParameters, null,
 688                                 Location.Null);
 689                         AddMethod (move_next);
 690
 691                         ToplevelBlock block = move_next.Block = new ToplevelBlock (Location);
 692
 693                         MoveNextMethod inline = new MoveNextMethod (this, Location);
 694                         block.AddStatement (inline);
 695                 }
 696
 697                 void Define_GetEnumerator (bool is_generic)
 698                 {
 699                         MemberName left;
 700                         Expression type;
 701                         if (is_generic) {
 702                                 left = new MemberName (
 703                                         "System.Collections.Generic.IEnumerable",
 704                                         generic_args);
 705                                 type = generic_enumerator_type;
 706                         } else {
 707                                 left = new MemberName ("System.Collections.IEnumerable");
 708                                 type = enumerator_type;
 709                         }
 710
 711                         MemberName name = new MemberName (left, "GetEnumerator", null);
 712
 713                         Method get_enumerator = new Method (
 714                                 this, null, type, 0, false, name,
 715                                 Parameters.EmptyReadOnlyParameters, null,
 716                                 Location.Null);
 717                         AddMethod (get_enumerator);
 718
 719                         get_enumerator.Block = new ToplevelBlock (Location);
 720
 721                         Expression ce = new MemberAccess (
 722                                 new SimpleName ("System.Threading.Interlocked", Location),
 723                                 "CompareExchange", Location);
 724
 725                         Expression pc = new FieldExpression (pc_field);
 726                         Expression before = new IntLiteral ((int) State.Running);
 727                         Expression uninitialized = new IntLiteral ((int) State.Uninitialized);
 728
 729                         ArrayList args = new ArrayList ();
 730                         args.Add (new Argument (pc, Argument.AType.Ref));
 731                         args.Add (new Argument (before, Argument.AType.Expression));
 732                         args.Add (new Argument (uninitialized, Argument.AType.Expression));
 733
 734                         get_enumerator.Block.AddStatement (new If (
 735                                 new Binary (
 736                                         Binary.Operator.Equality,
 737                                         new Invocation (ce, args, Location),
 738                                         uninitialized, Location),
 739                                 new Return (new This (block, Location), Location),
 740                                 Location));
 741
 742                         args = new ArrayList ();
 743                         if (!is_static)
 744                                 args.Add (new Argument (new FieldExpression (this_field)));
 745
 746                         args.Add (new Argument (new BoolLiteral (true)));
 747
 748                         for (int i = 0; i < parameters.Count; i++)
 749                                 args.Add (new Argument (
 750                                                   new FieldExpression (parameter_fields [i])));
 751
 752                         Expression new_expr = new New (current_type, args, Location);
 753                         get_enumerator.Block.AddStatement (new Return (new_expr, Location));
 754                 }
 755
 756                 protected class SimpleParameterReference : Expression
 757                 {
 758                         int idx;
 759
 760                         public SimpleParameterReference (Type type, int idx, Location loc)
 761                         {
 762                                 this.idx = idx;
 763                                 this.loc = loc;
 764                                 this.type = type;
 765                                 eclass = ExprClass.Variable;
 766                         }
 767
 768                         public override Expression DoResolve (EmitContext ec)
 769                         {
 770                                 return this;
 771                         }
 772
 773                         public override void Emit (EmitContext ec)
 774                         {
 775                                 DoEmit (ec);
 776                         }
 777
 778                         protected virtual void DoEmit (EmitContext ec)
 779                         {
 780                                 ParameterReference.EmitLdArg (ec.ig, idx);
 781                         }
 782                 }
 783
 784                 protected class ThisParameterReference : SimpleParameterReference
 785                 {
 786                         public ThisParameterReference (Type type, int idx, Location loc)
 787                                 : base (type, idx, loc)
 788                         { }
 789
 790                         protected override void DoEmit (EmitContext ec)
 791                         {
 792                                 base.DoEmit (ec);
 793                                 if (ec.TypeContainer is Struct)
 794                                         ec.ig.Emit (OpCodes.Ldobj, type);
 795                         }
 796                 }
 797
 798                 protected class FieldExpression : Expression
 799                 {
 800                         Field field;
 801
 802                         public FieldExpression (Field field)
 803                         {
 804                                 this.field = field;
 805                         }
 806
 807                         public override Expression DoResolve (EmitContext ec)
 808                         {
 809                                 FieldExpr fexpr = new FieldExpr (field.FieldBuilder, loc);
 810                                 fexpr.InstanceExpression = ec.GetThis (loc);
 811                                 return fexpr.Resolve (ec);
 812                         }
 813
 814                         public override void Emit (EmitContext ec)
 815                         {
 816                                 throw new InvalidOperationException ();
 817                         }
 818                 }
 819
 820                 protected class MoveNextMethod : Statement {
 821                         Iterator iterator;
 822
 823                         public MoveNextMethod (Iterator iterator, Location loc)
 824                         {
 825                                 this.loc = loc;
 826                                 this.iterator = iterator;
 827                         }
 828
 829                         public override bool Resolve (EmitContext ec)
 830                         {
 831                                 ec.CurrentBranching.CurrentUsageVector.Return ();
 832                                 return true;
 833                         }
 834
 835                         protected override void DoEmit (EmitContext ec)
 836                         {
 837                                 int code_flags = Modifiers.METHOD_YIELDS;
 838                                 if (iterator.is_static)
 839                                         code_flags |= Modifiers.STATIC;
 840
 841                                 EmitContext new_ec = new EmitContext (
 842                                         iterator.container, loc, ec.ig,
 843                                         TypeManager.int32_type, code_flags);
 844
 845                                 new_ec.CurrentIterator = iterator;
 846
 847                                 iterator.EmitMoveNext (new_ec);
 848                         }
 849                 }
 850
 851                 protected class DisposeMethod : Statement {
 852                         Iterator iterator;
 853
 854                         public DisposeMethod (Iterator iterator, Location loc)
 855                         {
 856                                 this.loc = loc;
 857                                 this.iterator = iterator;
 858                         }
 859
 860                         public override bool Resolve (EmitContext ec)
 861                         {
 862                                 return true;
 863                         }
 864
 865                         protected override void DoEmit (EmitContext ec)
 866                         {
 867                                 iterator.EmitDispose (ec);
 868                         }
 869                 }
 870
 871                 protected class StatementList : Statement {
 872                         ArrayList statements;
 873
 874                         public StatementList (Location loc)
 875                         {
 876                                 this.loc = loc;
 877                                 statements = new ArrayList ();
 878                         }
 879
 880                         public void Add (Statement statement)
 881                         {
 882                                 statements.Add (statement);
 883                         }
 884
 885                         public override bool Resolve (EmitContext ec)
 886                         {
 887                                 foreach (Statement stmt in statements) {
 888                                         if (!stmt.Resolve (ec))
 889                                                 return false;
 890                                 }
 891
 892                                 return true;
 893                         }
 894
 895                         protected override void DoEmit (EmitContext ec)
 896                         {
 897                                 foreach (Statement stmt in statements)
 898                                         stmt.Emit (ec);
 899                         }
 900                 }
 901
 902                 protected class SetState : Statement
 903                 {
 904                         Iterator iterator;
 905                         State state;
 906
 907                         public SetState (Iterator iterator, State state, Location loc)
 908                         {
 909                                 this.iterator = iterator;
 910                                 this.state = state;
 911                                 this.loc = loc;
 912                         }
 913
 914                         public override bool Resolve (EmitContext ec)
 915                         {
 916                                 return true;
 917                         }
 918
 919                         protected override void DoEmit (EmitContext ec)
 920                         {
 921                                 ec.ig.Emit (OpCodes.Ldarg_0);
 922                                 IntConstant.EmitInt (ec.ig, (int) state);
 923                                 ec.ig.Emit (OpCodes.Stfld, iterator.pc_field.FieldBuilder);
 924                         }
 925                 }
 926
 927                 void Define_Reset ()
 928                 {
 929                         Method reset = new Method (
 930                                 this, null, TypeManager.system_void_expr, Modifiers.PUBLIC,
 931                                 false, new MemberName ("Reset"),
 932                                 Parameters.EmptyReadOnlyParameters, null, Location);
 933                         AddMethod (reset);
 934
 935                         reset.Block = new ToplevelBlock (Location);
 936                         reset.Block.AddStatement (Create_ThrowNotSupported ());
 937                 }
 938
 939                 void Define_Dispose ()
 940                 {
 941                         dispose = new Method (
 942                                 this, null, TypeManager.system_void_expr, Modifiers.PUBLIC,
 943                                 false, new MemberName ("Dispose"),
 944                                 Parameters.EmptyReadOnlyParameters, null, Location);
 945                         AddMethod (dispose);
 946
 947                         dispose.Block = new ToplevelBlock (Location);
 948                         dispose.Block.AddStatement (new DisposeMethod (this, Location));
 949                 }
 950
 951                 public ToplevelBlock Block {
 952                         get { return block; }
 953                 }
 954
 955                 public Type IteratorType {
 956                         get { return iterator_type; }
 957                 }
 958
 959                 //
 960                 // This return statement tricks return into not flagging an error for being
 961                 // used in a Yields method
 962                 //
 963                 class NoCheckReturn : Return {
 964                         public NoCheckReturn (Expression expr, Location loc) : base (expr, loc)
 965                         {
 966                         }
 967
 968                         public override bool Resolve (EmitContext ec)
 969                         {
 970                                 ec.InIterator = false;
 971                                 bool ret_val = base.Resolve (ec);
 972                                 ec.InIterator = true;
 973
 974                                 return ret_val;
 975                         }
 976                 }
 977
 978                 bool CheckType (Type t)
 979                 {
 980                         if (t == TypeManager.ienumerable_type) {
 981                                 iterator_type = TypeManager.object_type;
 982                                 is_enumerable = true;
 983                                 return true;
 984                         } else if (t == TypeManager.ienumerator_type) {
 985                                 iterator_type = TypeManager.object_type;
 986                                 is_enumerable = false;
 987                                 return true;
 988                         }
 989
 990                         if (!t.IsGenericInstance)
 991                                 return false;
 992
 993                         Type[] args = TypeManager.GetTypeArguments (t);
 994                         if (args.Length != 1)
 995                                 return false;
 996
 997                         Type gt = t.GetGenericTypeDefinition ();
 998                         if (gt == TypeManager.generic_ienumerable_type) {
 999                                 iterator_type = args [0];
1000                                 is_enumerable = true;
1001                                 return true;
1002                         } else if (gt == TypeManager.generic_ienumerator_type) {
1003                                 iterator_type = args [0];
1004                                 is_enumerable = false;
1005                                 return true;
1006                         }
1007
1008                         return false;
1009                 }
1010         }
1011 }
1012