mcs/gmcs/generic.cs

   1 //
   2 // generic.cs: Generics support
   3 //
   4 // Authors: Martin Baulig (martin@ximian.com)
   5 //          Miguel de Icaza (miguel@ximian.com)
   6 //
   7 // Licensed under the terms of the GNU GPL
   8 //
   9 // (C) 2001, 2002, 2003 Ximian, Inc (http://www.ximian.com)
  10 // (C) 2004 Novell, Inc
  11 //
  12 using System;
  13 using System.Reflection;
  14 using System.Reflection.Emit;
  15 using System.Globalization;
  16 using System.Collections;
  17 using System.Text;
  18 using System.Text.RegularExpressions;
  19
  20 namespace Mono.CSharp {
  21
  22         /// <summary>
  23         ///   Abstract base class for type parameter constraints.
  24         ///   The type parameter can come from a generic type definition or from reflection.
  25         /// </summary>
  26         public abstract class GenericConstraints {
  27                 public abstract string TypeParameter {
  28                         get;
  29                 }
  30
  31                 public abstract GenericParameterAttributes Attributes {
  32                         get;
  33                 }
  34
  35                 public bool HasConstructorConstraint {
  36                         get { return (Attributes & GenericParameterAttributes.DefaultConstructorConstraint) != 0; }
  37                 }
  38
  39                 public bool HasReferenceTypeConstraint {
  40                         get { return (Attributes & GenericParameterAttributes.ReferenceTypeConstraint) != 0; }
  41                 }
  42
  43                 public bool HasValueTypeConstraint {
  44                         get { return (Attributes & GenericParameterAttributes.NotNullableValueTypeConstraint) != 0; }
  45                 }
  46
  47                 public virtual bool HasClassConstraint {
  48                         get { return ClassConstraint != null; }
  49                 }
  50
  51                 public abstract Type ClassConstraint {
  52                         get;
  53                 }
  54
  55                 public abstract Type[] InterfaceConstraints {
  56                         get;
  57                 }
  58
  59                 public abstract Type EffectiveBaseClass {
  60                         get;
  61                 }
  62
  63                 // <summary>
  64                 //   Returns whether the type parameter is "known to be a reference type".
  65                 // </summary>
  66                 public virtual bool IsReferenceType {
  67                         get {
  68                                 if (HasReferenceTypeConstraint)
  69                                         return true;
  70                                 if (HasValueTypeConstraint)
  71                                         return false;
  72
  73                                 if (ClassConstraint != null) {
  74                                         if (ClassConstraint.IsValueType)
  75                                                 return false;
  76
  77                                         if (ClassConstraint != TypeManager.object_type)
  78                                                 return true;
  79                                 }
  80
  81                                 foreach (Type t in InterfaceConstraints) {
  82                                         if (!t.IsGenericParameter)
  83                                                 continue;
  84
  85                                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (t);
  86                                         if ((gc != null) && gc.IsReferenceType)
  87                                                 return true;
  88                                 }
  89
  90                                 return false;
  91                         }
  92                 }
  93
  94                 // <summary>
  95                 //   Returns whether the type parameter is "known to be a value type".
  96                 // </summary>
  97                 public virtual bool IsValueType {
  98                         get {
  99                                 if (HasValueTypeConstraint)
 100                                         return true;
 101                                 if (HasReferenceTypeConstraint)
 102                                         return false;
 103
 104                                 if (ClassConstraint != null) {
 105                                         if (!ClassConstraint.IsValueType)
 106                                                 return false;
 107
 108                                         if (ClassConstraint != TypeManager.value_type)
 109                                                 return true;
 110                                 }
 111
 112                                 foreach (Type t in InterfaceConstraints) {
 113                                         if (!t.IsGenericParameter)
 114                                                 continue;
 115
 116                                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (t);
 117                                         if ((gc != null) && gc.IsValueType)
 118                                                 return true;
 119                                 }
 120
 121                                 return false;
 122                         }
 123                 }
 124         }
 125
 126         public enum SpecialConstraint
 127         {
 128                 Constructor,
 129                 ReferenceType,
 130                 ValueType
 131         }
 132
 133         /// <summary>
 134         ///   Tracks the constraints for a type parameter from a generic type definition.
 135         /// </summary>
 136         public class Constraints : GenericConstraints {
 137                 string name;
 138                 ArrayList constraints;
 139                 Location loc;
 140
 141                 //
 142                 // name is the identifier, constraints is an arraylist of
 143                 // Expressions (with types) or `true' for the constructor constraint.
 144                 //
 145                 public Constraints (string name, ArrayList constraints,
 146                                     Location loc)
 147                 {
 148                         this.name = name;
 149                         this.constraints = constraints;
 150                         this.loc = loc;
 151                 }
 152
 153                 public override string TypeParameter {
 154                         get {
 155                                 return name;
 156                         }
 157                 }
 158
 159                 public Constraints Clone ()
 160                 {
 161                         return new Constraints (name, constraints, loc);
 162                 }
 163
 164                 GenericParameterAttributes attrs;
 165                 TypeExpr class_constraint;
 166                 ArrayList iface_constraints;
 167                 ArrayList type_param_constraints;
 168                 int num_constraints;
 169                 Type class_constraint_type;
 170                 Type[] iface_constraint_types;
 171                 Type effective_base_type;
 172                 bool resolved;
 173                 bool resolved_types;
 174
 175                 /// <summary>
 176                 ///   Resolve the constraints - but only resolve things into Expression's, not
 177                 ///   into actual types.
 178                 /// </summary>
 179                 public bool Resolve (IResolveContext ec)
 180                 {
 181                         if (resolved)
 182                                 return true;
 183
 184                         iface_constraints = new ArrayList ();
 185                         type_param_constraints = new ArrayList ();
 186
 187                         foreach (object obj in constraints) {
 188                                 if (HasConstructorConstraint) {
 189                                         Report.Error (401, loc,
 190                                                       "The new() constraint must be the last constraint specified");
 191                                         return false;
 192                                 }
 193
 194                                 if (obj is SpecialConstraint) {
 195                                         SpecialConstraint sc = (SpecialConstraint) obj;
 196
 197                                         if (sc == SpecialConstraint.Constructor) {
 198                                                 if (!HasValueTypeConstraint) {
 199                                                         attrs |= GenericParameterAttributes.DefaultConstructorConstraint;
 200                                                         continue;
 201                                                 }
 202
 203                                                 Report.Error (451, loc, "The `new()' constraint " +
 204                                                         "cannot be used with the `struct' constraint");
 205                                                 return false;
 206                                         }
 207
 208                                         if ((num_constraints > 0) || HasReferenceTypeConstraint || HasValueTypeConstraint) {
 209                                                 Report.Error (449, loc, "The `class' or `struct' " +
 210                                                               "constraint must be the first constraint specified");
 211                                                 return false;
 212                                         }
 213
 214                                         if (sc == SpecialConstraint.ReferenceType)
 215                                                 attrs |= GenericParameterAttributes.ReferenceTypeConstraint;
 216                                         else
 217                                                 attrs |= GenericParameterAttributes.NotNullableValueTypeConstraint;
 218                                         continue;
 219                                 }
 220
 221                                 int errors = Report.Errors;
 222                                 FullNamedExpression fn = ((Expression) obj).ResolveAsTypeStep (ec, false);
 223
 224                                 if (fn == null) {
 225                                         if (errors != Report.Errors)
 226                                                 return false;
 227
 228                                         NamespaceEntry.Error_NamespaceNotFound (loc, ((Expression)obj).GetSignatureForError ());
 229                                         return false;
 230                                 }
 231
 232                                 TypeExpr expr;
 233                                 ConstructedType cexpr = fn as ConstructedType;
 234                                 if (cexpr != null) {
 235                                         if (!cexpr.ResolveConstructedType (ec))
 236                                                 return false;
 237
 238                                         expr = cexpr;
 239                                 } else
 240                                         expr = ((Expression) obj).ResolveAsTypeTerminal (ec, false);
 241
 242                                 if ((expr == null) || (expr.Type == null))
 243                                         return false;
 244
 245                                 // TODO: It's aleady done in ResolveAsBaseTerminal
 246                                 if (!ec.GenericDeclContainer.AsAccessible (fn.Type, ec.GenericDeclContainer.ModFlags)) {
 247                                         Report.SymbolRelatedToPreviousError (fn.Type);
 248                                         Report.Error (703, loc,
 249                                                 "Inconsistent accessibility: constraint type `{0}' is less accessible than `{1}'",
 250                                                 fn.GetSignatureForError (), ec.GenericDeclContainer.GetSignatureForError ());
 251                                         return false;
 252                                 }
 253
 254                                 TypeParameterExpr texpr = expr as TypeParameterExpr;
 255                                 if (texpr != null)
 256                                         type_param_constraints.Add (expr);
 257                                 else if (expr.IsInterface)
 258                                         iface_constraints.Add (expr);
 259                                 else if (class_constraint != null) {
 260                                         Report.Error (406, loc,
 261                                                       "`{0}': the class constraint for `{1}' " +
 262                                                       "must come before any other constraints.",
 263                                                       expr.Name, name);
 264                                         return false;
 265                                 } else if (HasReferenceTypeConstraint || HasValueTypeConstraint) {
 266                                         Report.Error (450, loc, "`{0}': cannot specify both " +
 267                                                       "a constraint class and the `class' " +
 268                                                       "or `struct' constraint", expr.GetSignatureForError ());
 269                                         return false;
 270                                 } else
 271                                         class_constraint = expr;
 272
 273                                 num_constraints++;
 274                         }
 275
 276                         ArrayList list = new ArrayList ();
 277                         foreach (TypeExpr iface_constraint in iface_constraints) {
 278                                 foreach (Type type in list) {
 279                                         if (!type.Equals (iface_constraint.Type))
 280                                                 continue;
 281
 282                                         Report.Error (405, loc,
 283                                                       "Duplicate constraint `{0}' for type " +
 284                                                       "parameter `{1}'.", iface_constraint.GetSignatureForError (),
 285                                                       name);
 286                                         return false;
 287                                 }
 288
 289                                 list.Add (iface_constraint.Type);
 290                         }
 291
 292                         foreach (TypeParameterExpr expr in type_param_constraints) {
 293                                 foreach (Type type in list) {
 294                                         if (!type.Equals (expr.Type))
 295                                                 continue;
 296
 297                                         Report.Error (405, loc,
 298                                                       "Duplicate constraint `{0}' for type " +
 299                                                       "parameter `{1}'.", expr.GetSignatureForError (), name);
 300                                         return false;
 301                                 }
 302
 303                                 list.Add (expr.Type);
 304                         }
 305
 306                         iface_constraint_types = new Type [list.Count];
 307                         list.CopyTo (iface_constraint_types, 0);
 308
 309                         if (class_constraint != null) {
 310                                 class_constraint_type = class_constraint.Type;
 311                                 if (class_constraint_type == null)
 312                                         return false;
 313
 314                                 if (class_constraint_type.IsSealed) {
 315                                         if (class_constraint_type.IsAbstract)
 316                                         {
 317                                                 Report.Error (717, loc, "`{0}' is not a valid constraint. Static classes cannot be used as constraints",
 318                                                         TypeManager.CSharpName (class_constraint_type));
 319                                         }
 320                                         else
 321                                         {
 322                                                 Report.Error (701, loc, "`{0}' is not a valid constraint. A constraint must be an interface, " +
 323                                                         "a non-sealed class or a type parameter", TypeManager.CSharpName(class_constraint_type));
 324                                         }
 325                                         return false;
 326                                 }
 327
 328                                 if ((class_constraint_type == TypeManager.array_type) ||
 329                                     (class_constraint_type == TypeManager.delegate_type) ||
 330                                     (class_constraint_type == TypeManager.enum_type) ||
 331                                     (class_constraint_type == TypeManager.value_type) ||
 332                                     (class_constraint_type == TypeManager.object_type)) {
 333                                         Report.Error (702, loc,
 334                                                       "Bound cannot be special class `{0}'",
 335                                                       TypeManager.CSharpName (class_constraint_type));
 336                                         return false;
 337                                 }
 338                         }
 339
 340                         if (class_constraint_type != null)
 341                                 effective_base_type = class_constraint_type;
 342                         else if (HasValueTypeConstraint)
 343                                 effective_base_type = TypeManager.value_type;
 344                         else
 345                                 effective_base_type = TypeManager.object_type;
 346
 347                         resolved = true;
 348                         return true;
 349                 }
 350
 351                 bool CheckTypeParameterConstraints (TypeParameter tparam, Hashtable seen)
 352                 {
 353                         seen.Add (tparam, true);
 354
 355                         Constraints constraints = tparam.Constraints;
 356                         if (constraints == null)
 357                                 return true;
 358
 359                         if (constraints.HasValueTypeConstraint) {
 360                                 Report.Error (456, loc, "Type parameter `{0}' has " +
 361                                               "the `struct' constraint, so it cannot " +
 362                                               "be used as a constraint for `{1}'",
 363                                               tparam.Name, name);
 364                                 return false;
 365                         }
 366
 367                         if (constraints.type_param_constraints == null)
 368                                 return true;
 369
 370                         foreach (TypeParameterExpr expr in constraints.type_param_constraints) {
 371                                 if (seen.Contains (expr.TypeParameter)) {
 372                                         Report.Error (454, loc, "Circular constraint " +
 373                                                       "dependency involving `{0}' and `{1}'",
 374                                                       tparam.Name, expr.Name);
 375                                         return false;
 376                                 }
 377
 378                                 if (!CheckTypeParameterConstraints (expr.TypeParameter, seen))
 379                                         return false;
 380                         }
 381
 382                         return true;
 383                 }
 384
 385                 /// <summary>
 386                 ///   Resolve the constraints into actual types.
 387                 /// </summary>
 388                 public bool ResolveTypes (IResolveContext ec)
 389                 {
 390                         if (resolved_types)
 391                                 return true;
 392
 393                         resolved_types = true;
 394
 395                         foreach (object obj in constraints) {
 396                                 ConstructedType cexpr = obj as ConstructedType;
 397                                 if (cexpr == null)
 398                                         continue;
 399
 400                                 if (!cexpr.CheckConstraints (ec))
 401                                         return false;
 402                         }
 403
 404                         foreach (TypeParameterExpr expr in type_param_constraints) {
 405                                 Hashtable seen = new Hashtable ();
 406                                 if (!CheckTypeParameterConstraints (expr.TypeParameter, seen))
 407                                         return false;
 408                         }
 409
 410                         for (int i = 0; i < iface_constraints.Count; ++i) {
 411                                 TypeExpr iface_constraint = (TypeExpr) iface_constraints [i];
 412                                 iface_constraint = iface_constraint.ResolveAsTypeTerminal (ec, false);
 413                                 if (iface_constraint == null)
 414                                         return false;
 415                                 iface_constraints [i] = iface_constraint;
 416                         }
 417
 418                         if (class_constraint != null) {
 419                                 class_constraint = class_constraint.ResolveAsTypeTerminal (ec, false);
 420                                 if (class_constraint == null)
 421                                         return false;
 422                         }
 423
 424                         return true;
 425                 }
 426
 427                 /// <summary>
 428                 ///   Check whether there are no conflicts in our type parameter constraints.
 429                 ///
 430                 ///   This is an example:
 431                 ///
 432                 ///   class Foo<T,U>
 433                 ///      where T : class
 434                 ///      where U : T, struct
 435                 /// </summary>
 436                 public bool CheckDependencies ()
 437                 {
 438                         foreach (TypeParameterExpr expr in type_param_constraints) {
 439                                 if (!CheckDependencies (expr.TypeParameter))
 440                                         return false;
 441                         }
 442
 443                         return true;
 444                 }
 445
 446                 bool CheckDependencies (TypeParameter tparam)
 447                 {
 448                         Constraints constraints = tparam.Constraints;
 449                         if (constraints == null)
 450                                 return true;
 451
 452                         if (HasValueTypeConstraint && constraints.HasClassConstraint) {
 453                                 Report.Error (455, loc, "Type parameter `{0}' inherits " +
 454                                               "conflicting constraints `{1}' and `{2}'",
 455                                               name, TypeManager.CSharpName (constraints.ClassConstraint),
 456                                               "System.ValueType");
 457                                 return false;
 458                         }
 459
 460                         if (HasClassConstraint && constraints.HasClassConstraint) {
 461                                 Type t1 = ClassConstraint;
 462                                 TypeExpr e1 = class_constraint;
 463                                 Type t2 = constraints.ClassConstraint;
 464                                 TypeExpr e2 = constraints.class_constraint;
 465
 466                                 if (!Convert.ImplicitReferenceConversionExists (e1, t2) &&
 467                                     !Convert.ImplicitReferenceConversionExists (e2, t1)) {
 468                                         Report.Error (455, loc,
 469                                                       "Type parameter `{0}' inherits " +
 470                                                       "conflicting constraints `{1}' and `{2}'",
 471                                                       name, TypeManager.CSharpName (t1), TypeManager.CSharpName (t2));
 472                                         return false;
 473                                 }
 474                         }
 475
 476                         if (constraints.type_param_constraints == null)
 477                                 return true;
 478
 479                         foreach (TypeParameterExpr expr in constraints.type_param_constraints) {
 480                                 if (!CheckDependencies (expr.TypeParameter))
 481                                         return false;
 482                         }
 483
 484                         return true;
 485                 }
 486
 487                 public override GenericParameterAttributes Attributes {
 488                         get { return attrs; }
 489                 }
 490
 491                 public override bool HasClassConstraint {
 492                         get { return class_constraint != null; }
 493                 }
 494
 495                 public override Type ClassConstraint {
 496                         get { return class_constraint_type; }
 497                 }
 498
 499                 public override Type[] InterfaceConstraints {
 500                         get { return iface_constraint_types; }
 501                 }
 502
 503                 public override Type EffectiveBaseClass {
 504                         get { return effective_base_type; }
 505                 }
 506
 507                 public bool IsSubclassOf (Type t)
 508                 {
 509                         if ((class_constraint_type != null) &&
 510                             class_constraint_type.IsSubclassOf (t))
 511                                 return true;
 512
 513                         if (iface_constraint_types == null)
 514                                 return false;
 515
 516                         foreach (Type iface in iface_constraint_types) {
 517                                 if (TypeManager.IsSubclassOf (iface, t))
 518                                         return true;
 519                         }
 520
 521                         return false;
 522                 }
 523
 524                 public Location Location {
 525                         get {
 526                                 return loc;
 527                         }
 528                 }
 529
 530                 /// <summary>
 531                 ///   This is used when we're implementing a generic interface method.
 532                 ///   Each method type parameter in implementing method must have the same
 533                 ///   constraints than the corresponding type parameter in the interface
 534                 ///   method.  To do that, we're called on each of the implementing method's
 535                 ///   type parameters.
 536                 /// </summary>
 537                 public bool CheckInterfaceMethod (GenericConstraints gc)
 538                 {
 539                         if (gc.Attributes != attrs)
 540                                 return false;
 541
 542                         if (HasClassConstraint != gc.HasClassConstraint)
 543                                 return false;
 544                         if (HasClassConstraint && !TypeManager.IsEqual (gc.ClassConstraint, ClassConstraint))
 545                                 return false;
 546
 547                         int gc_icount = gc.InterfaceConstraints != null ?
 548                                 gc.InterfaceConstraints.Length : 0;
 549                         int icount = InterfaceConstraints != null ?
 550                                 InterfaceConstraints.Length : 0;
 551
 552                         if (gc_icount != icount)
 553                                 return false;
 554
 555                         foreach (Type iface in gc.InterfaceConstraints) {
 556                                 bool ok = false;
 557                                 foreach (Type check in InterfaceConstraints) {
 558                                         if (TypeManager.IsEqual (iface, check)) {
 559                                                 ok = true;
 560                                                 break;
 561                                         }
 562                                 }
 563
 564                                 if (!ok)
 565                                         return false;
 566                         }
 567
 568                         return true;
 569                 }
 570
 571                 public void VerifyClsCompliance ()
 572                 {
 573                         if (class_constraint_type != null && !AttributeTester.IsClsCompliant (class_constraint_type))
 574                                 Warning_ConstrainIsNotClsCompliant (class_constraint_type, class_constraint.Location);
 575
 576                         if (iface_constraint_types != null) {
 577                                 for (int i = 0; i < iface_constraint_types.Length; ++i) {
 578                                         if (!AttributeTester.IsClsCompliant (iface_constraint_types [i]))
 579                                                 Warning_ConstrainIsNotClsCompliant (iface_constraint_types [i],
 580                                                         ((TypeExpr)iface_constraints [i]).Location);
 581                                 }
 582                         }
 583                 }
 584
 585                 void Warning_ConstrainIsNotClsCompliant (Type t, Location loc)
 586                 {
 587                         Report.SymbolRelatedToPreviousError (t);
 588                         Report.Warning (3024, 1, loc, "Constraint type `{0}' is not CLS-compliant",
 589                                 TypeManager.CSharpName (t));
 590                 }
 591         }
 592
 593         /// <summary>
 594         ///   A type parameter from a generic type definition.
 595         /// </summary>
 596         public class TypeParameter : MemberCore, IMemberContainer {
 597                 string name;
 598                 DeclSpace decl;
 599                 GenericConstraints gc;
 600                 Constraints constraints;
 601                 Location loc;
 602                 GenericTypeParameterBuilder type;
 603
 604                 public TypeParameter (DeclSpace parent, DeclSpace decl, string name,
 605                                       Constraints constraints, Attributes attrs, Location loc)
 606                         : base (parent, new MemberName (name, loc), attrs)
 607                 {
 608                         this.name = name;
 609                         this.decl = decl;
 610                         this.constraints = constraints;
 611                         this.loc = loc;
 612                 }
 613
 614                 public GenericConstraints GenericConstraints {
 615                         get { return gc != null ? gc : constraints; }
 616                 }
 617
 618                 public Constraints Constraints {
 619                         get { return constraints; }
 620                 }
 621
 622                 public bool HasConstructorConstraint {
 623                         get { return constraints != null && constraints.HasConstructorConstraint; }
 624                 }
 625
 626                 public DeclSpace DeclSpace {
 627                         get { return decl; }
 628                 }
 629
 630                 public Type Type {
 631                         get { return type; }
 632                 }
 633
 634                 /// <summary>
 635                 ///   This is the first method which is called during the resolving
 636                 ///   process; we're called immediately after creating the type parameters
 637                 ///   with SRE (by calling `DefineGenericParameters()' on the TypeBuilder /
 638                 ///   MethodBuilder).
 639                 ///
 640                 ///   We're either called from TypeContainer.DefineType() or from
 641                 ///   GenericMethod.Define() (called from Method.Define()).
 642                 /// </summary>
 643                 public void Define (GenericTypeParameterBuilder type)
 644                 {
 645                         if (this.type != null)
 646                                 throw new InvalidOperationException ();
 647
 648                         this.type = type;
 649                         TypeManager.AddTypeParameter (type, this);
 650                 }
 651
 652                 /// <summary>
 653                 ///   This is the second method which is called during the resolving
 654                 ///   process - in case of class type parameters, we're called from
 655                 ///   TypeContainer.ResolveType() - after it resolved the class'es
 656                 ///   base class and interfaces. For method type parameters, we're
 657                 ///   called immediately after Define().
 658                 ///
 659                 ///   We're just resolving the constraints into expressions here, we
 660                 ///   don't resolve them into actual types.
 661                 ///
 662                 ///   Note that in the special case of partial generic classes, we may be
 663                 ///   called _before_ Define() and we may also be called multiple types.
 664                 /// </summary>
 665                 public bool Resolve (DeclSpace ds)
 666                 {
 667                         if (constraints != null) {
 668                                 if (!constraints.Resolve (ds)) {
 669                                         constraints = null;
 670                                         return false;
 671                                 }
 672                         }
 673
 674                         return true;
 675                 }
 676
 677                 /// <summary>
 678                 ///   This is the third method which is called during the resolving
 679                 ///   process.  We're called immediately after calling DefineConstraints()
 680                 ///   on all of the current class'es type parameters.
 681                 ///
 682                 ///   Our job is to resolve the constraints to actual types.
 683                 ///
 684                 ///   Note that we may have circular dependencies on type parameters - this
 685                 ///   is why Resolve() and ResolveType() are separate.
 686                 /// </summary>
 687                 public bool ResolveType (IResolveContext ec)
 688                 {
 689                         if (constraints != null) {
 690                                 if (!constraints.ResolveTypes (ec)) {
 691                                         constraints = null;
 692                                         return false;
 693                                 }
 694                         }
 695
 696                         return true;
 697                 }
 698
 699                 /// <summary>
 700                 ///   This is the fourth and last method which is called during the resolving
 701                 ///   process.  We're called after everything is fully resolved and actually
 702                 ///   register the constraints with SRE and the TypeManager.
 703                 /// </summary>
 704                 public bool DefineType (IResolveContext ec)
 705                 {
 706                         return DefineType (ec, null, null, false);
 707                 }
 708
 709                 /// <summary>
 710                 ///   This is the fith and last method which is called during the resolving
 711                 ///   process.  We're called after everything is fully resolved and actually
 712                 ///   register the constraints with SRE and the TypeManager.
 713                 ///
 714                 ///   The `builder', `implementing' and `is_override' arguments are only
 715                 ///   applicable to method type parameters.
 716                 /// </summary>
 717                 public bool DefineType (IResolveContext ec, MethodBuilder builder,
 718                                         MethodInfo implementing, bool is_override)
 719                 {
 720                         if (!ResolveType (ec))
 721                                 return false;
 722
 723                         if (implementing != null) {
 724                                 if (is_override && (constraints != null)) {
 725                                         Report.Error (460, loc,
 726                                                 "`{0}': Cannot specify constraints for overrides or explicit interface implementation methods",
 727                                                 TypeManager.CSharpSignature (builder));
 728                                         return false;
 729                                 }
 730
 731                                 MethodBase mb = TypeManager.DropGenericMethodArguments (implementing);
 732
 733                                 int pos = type.GenericParameterPosition;
 734                                 Type mparam = mb.GetGenericArguments () [pos];
 735                                 GenericConstraints temp_gc = ReflectionConstraints.GetConstraints (mparam);
 736
 737                                 if (temp_gc != null)
 738                                         gc = new InflatedConstraints (temp_gc, implementing.DeclaringType);
 739                                 else if (constraints != null)
 740                                         gc = new InflatedConstraints (constraints, implementing.DeclaringType);
 741
 742                                 bool ok = true;
 743                                 if (constraints != null) {
 744                                         if (temp_gc == null)
 745                                                 ok = false;
 746                                         else if (!constraints.CheckInterfaceMethod (gc))
 747                                                 ok = false;
 748                                 } else {
 749                                         if (!is_override && (temp_gc != null))
 750                                                 ok = false;
 751                                 }
 752
 753                                 if (!ok) {
 754                                         Report.SymbolRelatedToPreviousError (implementing);
 755
 756                                         Report.Error (
 757                                                 425, loc, "The constraints for type " +
 758                                                 "parameter `{0}' of method `{1}' must match " +
 759                                                 "the constraints for type parameter `{2}' " +
 760                                                 "of interface method `{3}'. Consider using " +
 761                                                 "an explicit interface implementation instead",
 762                                                 Name, TypeManager.CSharpSignature (builder),
 763                                                 TypeManager.CSharpName (mparam), TypeManager.CSharpSignature (mb));
 764                                         return false;
 765                                 }
 766                         } else if (DeclSpace is CompilerGeneratedClass) {
 767                                 TypeParameter[] tparams = DeclSpace.TypeParameters;
 768                                 Type[] types = new Type [tparams.Length];
 769                                 for (int i = 0; i < tparams.Length; i++)
 770                                         types [i] = tparams [i].Type;
 771
 772                                 if (constraints != null)
 773                                         gc = new InflatedConstraints (constraints, types);
 774                         } else {
 775                                 gc = (GenericConstraints) constraints;
 776                         }
 777
 778                         if (gc == null)
 779                                 return true;
 780
 781                         if (gc.HasClassConstraint)
 782                                 type.SetBaseTypeConstraint (gc.ClassConstraint);
 783
 784                         type.SetInterfaceConstraints (gc.InterfaceConstraints);
 785                         type.SetGenericParameterAttributes (gc.Attributes);
 786                         TypeManager.RegisterBuilder (type, gc.InterfaceConstraints);
 787
 788                         return true;
 789                 }
 790
 791                 /// <summary>
 792                 ///   Check whether there are no conflicts in our type parameter constraints.
 793                 ///
 794                 ///   This is an example:
 795                 ///
 796                 ///   class Foo<T,U>
 797                 ///      where T : class
 798                 ///      where U : T, struct
 799                 /// </summary>
 800                 public bool CheckDependencies ()
 801                 {
 802                         if (constraints != null)
 803                                 return constraints.CheckDependencies ();
 804
 805                         return true;
 806                 }
 807
 808                 /// <summary>
 809                 ///   This is called for each part of a partial generic type definition.
 810                 ///
 811                 ///   If `new_constraints' is not null and we don't already have constraints,
 812                 ///   they become our constraints.  If we already have constraints, we must
 813                 ///   check that they're the same.
 814                 ///   con
 815                 /// </summary>
 816                 public bool UpdateConstraints (IResolveContext ec, Constraints new_constraints)
 817                 {
 818                         if (type == null)
 819                                 throw new InvalidOperationException ();
 820
 821                         if (new_constraints == null)
 822                                 return true;
 823
 824                         if (!new_constraints.Resolve (ec))
 825                                 return false;
 826                         if (!new_constraints.ResolveTypes (ec))
 827                                 return false;
 828
 829                         if (constraints != null)
 830                                 return constraints.CheckInterfaceMethod (new_constraints);
 831
 832                         constraints = new_constraints;
 833                         return true;
 834                 }
 835
 836                 public void EmitAttributes ()
 837                 {
 838                         if (OptAttributes != null)
 839                                 OptAttributes.Emit ();
 840                 }
 841
 842                 public override string DocCommentHeader {
 843                         get {
 844                                 throw new InvalidOperationException (
 845                                         "Unexpected attempt to get doc comment from " + this.GetType () + ".");
 846                         }
 847                 }
 848
 849                 //
 850                 // MemberContainer
 851                 //
 852
 853                 public override bool Define ()
 854                 {
 855                         return true;
 856                 }
 857
 858                 public override void ApplyAttributeBuilder (Attribute a,
 859                                                             CustomAttributeBuilder cb)
 860                 {
 861                         type.SetCustomAttribute (cb);
 862                 }
 863
 864                 public override AttributeTargets AttributeTargets {
 865                         get {
 866                                 return (AttributeTargets) AttributeTargets.GenericParameter;
 867                         }
 868                 }
 869
 870                 public override string[] ValidAttributeTargets {
 871                         get {
 872                                 return new string [] { "type parameter" };
 873                         }
 874                 }
 875
 876                 //
 877                 // IMemberContainer
 878                 //
 879
 880                 string IMemberContainer.Name {
 881                         get { return Name; }
 882                 }
 883
 884                 MemberCache IMemberContainer.BaseCache {
 885                         get { return null; }
 886                 }
 887
 888                 bool IMemberContainer.IsInterface {
 889                         get { return true; }
 890                 }
 891
 892                 MemberList IMemberContainer.GetMembers (MemberTypes mt, BindingFlags bf)
 893                 {
 894                         return FindMembers (mt, bf, null, null);
 895                 }
 896
 897                 MemberCache IMemberContainer.MemberCache {
 898                         get { return null; }
 899                 }
 900
 901                 public MemberList FindMembers (MemberTypes mt, BindingFlags bf,
 902                                                MemberFilter filter, object criteria)
 903                 {
 904                         if (gc == null)
 905                                 return MemberList.Empty;
 906
 907                         ArrayList members = new ArrayList ();
 908
 909                         if (gc.HasClassConstraint) {
 910                                 MemberList list = TypeManager.FindMembers (
 911                                         gc.ClassConstraint, mt, bf, filter, criteria);
 912
 913                                 members.AddRange (list);
 914                         }
 915
 916                         Type[] ifaces = TypeManager.ExpandInterfaces (gc.InterfaceConstraints);
 917                         foreach (Type t in ifaces) {
 918                                 MemberList list = TypeManager.FindMembers (
 919                                         t, mt, bf, filter, criteria);
 920
 921                                 members.AddRange (list);
 922                         }
 923
 924                         return new MemberList (members);
 925                 }
 926
 927                 public bool IsSubclassOf (Type t)
 928                 {
 929                         if (type.Equals (t))
 930                                 return true;
 931
 932                         if (constraints != null)
 933                                 return constraints.IsSubclassOf (t);
 934
 935                         return false;
 936                 }
 937
 938                 public override string ToString ()
 939                 {
 940                         return "TypeParameter[" + name + "]";
 941                 }
 942
 943                 public static string GetSignatureForError (TypeParameter[] tp)
 944                 {
 945                         if (tp == null || tp.Length == 0)
 946                                 return "";
 947
 948                         StringBuilder sb = new StringBuilder ("<");
 949                         for (int i = 0; i < tp.Length; ++i) {
 950                                 if (i > 0)
 951                                         sb.Append (",");
 952                                 sb.Append (tp[i].GetSignatureForError ());
 953                         }
 954                         sb.Append ('>');
 955                         return sb.ToString ();
 956                 }
 957
 958                 public void InflateConstraints (Type declaring)
 959                 {
 960                         if (constraints != null)
 961                                 gc = new InflatedConstraints (constraints, declaring);
 962                 }
 963
 964                 protected class InflatedConstraints : GenericConstraints
 965                 {
 966                         GenericConstraints gc;
 967                         Type base_type;
 968                         Type class_constraint;
 969                         Type[] iface_constraints;
 970                         Type[] dargs;
 971
 972                         public InflatedConstraints (GenericConstraints gc, Type declaring)
 973                                 : this (gc, TypeManager.GetTypeArguments (declaring))
 974                         { }
 975
 976                         public InflatedConstraints (GenericConstraints gc, Type[] dargs)
 977                         {
 978                                 this.gc = gc;
 979                                 this.dargs = dargs;
 980
 981                                 ArrayList list = new ArrayList ();
 982                                 if (gc.HasClassConstraint)
 983                                         list.Add (inflate (gc.ClassConstraint));
 984                                 foreach (Type iface in gc.InterfaceConstraints)
 985                                         list.Add (inflate (iface));
 986
 987                                 bool has_class_constr = false;
 988                                 if (list.Count > 0) {
 989                                         Type first = (Type) list [0];
 990                                         has_class_constr = !first.IsInterface && !first.IsGenericParameter;
 991                                 }
 992
 993                                 if ((list.Count > 0) && has_class_constr) {
 994                                         class_constraint = (Type) list [0];
 995                                         iface_constraints = new Type [list.Count - 1];
 996                                         list.CopyTo (1, iface_constraints, 0, list.Count - 1);
 997                                 } else {
 998                                         iface_constraints = new Type [list.Count];
 999                                         list.CopyTo (iface_constraints, 0);
1000                                 }
1001
1002                                 if (HasValueTypeConstraint)
1003                                         base_type = TypeManager.value_type;
1004                                 else if (class_constraint != null)
1005                                         base_type = class_constraint;
1006                                 else
1007                                         base_type = TypeManager.object_type;
1008                         }
1009
1010                         Type inflate (Type t)
1011                         {
1012                                 if (t == null)
1013                                         return null;
1014                                 if (t.IsGenericParameter)
1015                                         return dargs [t.GenericParameterPosition];
1016                                 if (t.IsGenericType) {
1017                                         Type[] args = t.GetGenericArguments ();
1018                                         Type[] inflated = new Type [args.Length];
1019
1020                                         for (int i = 0; i < args.Length; i++)
1021                                                 inflated [i] = inflate (args [i]);
1022
1023                                         t = t.GetGenericTypeDefinition ();
1024                                         t = t.MakeGenericType (inflated);
1025                                 }
1026
1027                                 return t;
1028                         }
1029
1030                         public override string TypeParameter {
1031                                 get { return gc.TypeParameter; }
1032                         }
1033
1034                         public override GenericParameterAttributes Attributes {
1035                                 get { return gc.Attributes; }
1036                         }
1037
1038                         public override Type ClassConstraint {
1039                                 get { return class_constraint; }
1040                         }
1041
1042                         public override Type EffectiveBaseClass {
1043                                 get { return base_type; }
1044                         }
1045
1046                         public override Type[] InterfaceConstraints {
1047                                 get { return iface_constraints; }
1048                         }
1049                 }
1050         }
1051
1052         /// <summary>
1053         ///   A TypeExpr which already resolved to a type parameter.
1054         /// </summary>
1055         public class TypeParameterExpr : TypeExpr {
1056                 TypeParameter type_parameter;
1057
1058                 public override string Name {
1059                         get {
1060                                 return type_parameter.Name;
1061                         }
1062                 }
1063
1064                 public override string FullName {
1065                         get {
1066                                 return type_parameter.Name;
1067                         }
1068                 }
1069
1070                 public TypeParameter TypeParameter {
1071                         get {
1072                                 return type_parameter;
1073                         }
1074                 }
1075
1076                 public TypeParameterExpr (TypeParameter type_parameter, Location loc)
1077                 {
1078                         this.type_parameter = type_parameter;
1079                         this.loc = loc;
1080                 }
1081
1082                 protected override TypeExpr DoResolveAsTypeStep (IResolveContext ec)
1083                 {
1084                         type = type_parameter.Type;
1085
1086                         return this;
1087                 }
1088
1089                 public override bool IsInterface {
1090                         get { return false; }
1091                 }
1092
1093                 public override bool CheckAccessLevel (DeclSpace ds)
1094                 {
1095                         return true;
1096                 }
1097
1098                 public void Error_CannotUseAsUnmanagedType (Location loc)
1099                 {
1100                         Report.Error (-203, loc, "Can not use type parameter as unmanaged type");
1101                 }
1102         }
1103
1104         /// <summary>
1105         ///   Tracks the type arguments when instantiating a generic type.  We're used in
1106         ///   ConstructedType.
1107         /// </summary>
1108         public class TypeArguments {
1109                 public readonly Location Location;
1110                 ArrayList args;
1111                 Type[] atypes;
1112                 int dimension;
1113                 bool has_type_args;
1114                 bool created;
1115
1116                 public TypeArguments (Location loc)
1117                 {
1118                         args = new ArrayList ();
1119                         this.Location = loc;
1120                 }
1121
1122                 public TypeArguments (int dimension, Location loc)
1123                 {
1124                         this.dimension = dimension;
1125                         this.Location = loc;
1126                 }
1127
1128                 public void Add (Expression type)
1129                 {
1130                         if (created)
1131                                 throw new InvalidOperationException ();
1132
1133                         args.Add (type);
1134                 }
1135
1136                 public void Add (TypeArguments new_args)
1137                 {
1138                         if (created)
1139                                 throw new InvalidOperationException ();
1140
1141                         args.AddRange (new_args.args);
1142                 }
1143
1144                 /// <summary>
1145                 ///   We're used during the parsing process: the parser can't distinguish
1146                 ///   between type parameters and type arguments.  Because of that, the
1147                 ///   parser creates a `MemberName' with `TypeArguments' for both cases and
1148                 ///   in case of a generic type definition, we call GetDeclarations().
1149                 /// </summary>
1150                 public TypeParameterName[] GetDeclarations ()
1151                 {
1152                         TypeParameterName[] ret = new TypeParameterName [args.Count];
1153                         for (int i = 0; i < args.Count; i++) {
1154                                 TypeParameterName name = args [i] as TypeParameterName;
1155                                 if (name != null) {
1156                                         ret [i] = name;
1157                                         continue;
1158                                 }
1159                                 SimpleName sn = args [i] as SimpleName;
1160                                 if (sn != null) {
1161                                         ret [i] = new TypeParameterName (sn.Name, null, sn.Location);
1162                                         continue;
1163                                 }
1164
1165                                 Report.Error (81, Location, "Type parameter declaration " +
1166                                               "must be an identifier not a type");
1167                                 return null;
1168                         }
1169                         return ret;
1170                 }
1171
1172                 /// <summary>
1173                 ///   We may only be used after Resolve() is called and return the fully
1174                 ///   resolved types.
1175                 /// </summary>
1176                 public Type[] Arguments {
1177                         get {
1178                                 return atypes;
1179                         }
1180                 }
1181
1182                 public bool HasTypeArguments {
1183                         get {
1184                                 return has_type_args;
1185                         }
1186                 }
1187
1188                 public int Count {
1189                         get {
1190                                 if (dimension > 0)
1191                                         return dimension;
1192                                 else
1193                                         return args.Count;
1194                         }
1195                 }
1196
1197                 public bool IsUnbound {
1198                         get {
1199                                 return dimension > 0;
1200                         }
1201                 }
1202
1203                 public override string ToString ()
1204                 {
1205                         StringBuilder s = new StringBuilder ();
1206
1207                         int count = Count;
1208                         for (int i = 0; i < count; i++){
1209                                 //
1210                                 // FIXME: Use TypeManager.CSharpname once we have the type
1211                                 //
1212                                 if (args != null)
1213                                         s.Append (args [i].ToString ());
1214                                 if (i+1 < count)
1215                                         s.Append (",");
1216                         }
1217                         return s.ToString ();
1218                 }
1219
1220                 public string GetSignatureForError()
1221                 {
1222                         StringBuilder sb = new StringBuilder();
1223                         for (int i = 0; i < Count; ++i)
1224                         {
1225                                 Expression expr = (Expression)args [i];
1226                                 sb.Append(expr.GetSignatureForError());
1227                                 if (i + 1 < Count)
1228                                         sb.Append(',');
1229                         }
1230                         return sb.ToString();
1231                 }
1232
1233                 /// <summary>
1234                 ///   Resolve the type arguments.
1235                 /// </summary>
1236                 public bool Resolve (IResolveContext ec)
1237                 {
1238                         int count = args.Count;
1239                         bool ok = true;
1240
1241                         atypes = new Type [count];
1242
1243                         for (int i = 0; i < count; i++){
1244                                 TypeExpr te = ((Expression) args [i]).ResolveAsTypeTerminal (ec, false);
1245                                 if (te == null) {
1246                                         ok = false;
1247                                         continue;
1248                                 }
1249                                 if (te is TypeParameterExpr)
1250                                         has_type_args = true;
1251
1252 #if !MS_COMPATIBLE
1253                                 if (te.Type.IsSealed && te.Type.IsAbstract) {
1254                                         Report.Error (718, Location, "`{0}': static classes cannot be used as generic arguments",
1255                                                 te.GetSignatureForError ());
1256                                         return false;
1257                                 }
1258 #endif
1259                                 if (te.Type.IsPointer) {
1260                                         Report.Error (306, Location, "The type `{0}' may not be used " +
1261                                                           "as a type argument", TypeManager.CSharpName (te.Type));
1262                                         return false;
1263                                 }
1264
1265                                 if (te.Type == TypeManager.void_type) {
1266                                         Expression.Error_VoidInvalidInTheContext (Location);
1267                                         return false;
1268                                 }
1269
1270                                 atypes [i] = te.Type;
1271                         }
1272                         return ok;
1273                 }
1274
1275                 public TypeArguments Clone ()
1276                 {
1277                         TypeArguments copy = new TypeArguments (Location);
1278                         foreach (Expression ta in args)
1279                                 copy.args.Add (ta);
1280
1281                         return copy;
1282                 }
1283         }
1284
1285         public class TypeParameterName : SimpleName
1286         {
1287                 Attributes attributes;
1288
1289                 public TypeParameterName (string name, Attributes attrs, Location loc)
1290                         : base (name, loc)
1291                 {
1292                         attributes = attrs;
1293                 }
1294
1295                 public Attributes OptAttributes {
1296                         get {
1297                                 return attributes;
1298                         }
1299                 }
1300         }
1301
1302         /// <summary>
1303         ///   An instantiation of a generic type.
1304         /// </summary>
1305         public class ConstructedType : TypeExpr {
1306                 string full_name;
1307                 FullNamedExpression name;
1308                 TypeArguments args;
1309                 Type[] gen_params, atypes;
1310                 Type gt;
1311
1312                 /// <summary>
1313                 ///   Instantiate the generic type `fname' with the type arguments `args'.
1314                 /// </summary>
1315                 public ConstructedType (FullNamedExpression fname, TypeArguments args, Location l)
1316                 {
1317                         loc = l;
1318                         this.name = fname;
1319                         this.args = args;
1320
1321                         eclass = ExprClass.Type;
1322                         full_name = name + "<" + args.ToString () + ">";
1323                 }
1324
1325                 protected ConstructedType (TypeArguments args, Location l)
1326                 {
1327                         loc = l;
1328                         this.args = args;
1329
1330                         eclass = ExprClass.Type;
1331                 }
1332
1333                 protected ConstructedType (TypeParameter[] type_params, Location l)
1334                 {
1335                         loc = l;
1336
1337                         args = new TypeArguments (l);
1338                         foreach (TypeParameter type_param in type_params)
1339                                 args.Add (new TypeParameterExpr (type_param, l));
1340
1341                         eclass = ExprClass.Type;
1342                 }
1343
1344                 /// <summary>
1345                 ///   This is used to construct the `this' type inside a generic type definition.
1346                 /// </summary>
1347                 public ConstructedType (Type t, TypeParameter[] type_params, Location l)
1348                         : this (type_params, l)
1349                 {
1350                         gt = t.GetGenericTypeDefinition ();
1351
1352                         this.name = new TypeExpression (gt, l);
1353                         full_name = gt.FullName + "<" + args.ToString () + ">";
1354                 }
1355
1356                 /// <summary>
1357                 ///   Instantiate the generic type `t' with the type arguments `args'.
1358                 ///   Use this constructor if you already know the fully resolved
1359                 ///   generic type.
1360                 /// </summary>
1361                 public ConstructedType (Type t, TypeArguments args, Location l)
1362                         : this (args, l)
1363                 {
1364                         gt = t.GetGenericTypeDefinition ();
1365
1366                         this.name = new TypeExpression (gt, l);
1367                         full_name = gt.FullName + "<" + args.ToString () + ">";
1368                 }
1369
1370                 public TypeArguments TypeArguments {
1371                         get { return args; }
1372                 }
1373
1374                 public override string GetSignatureForError ()
1375                 {
1376                         return TypeManager.RemoveGenericArity (gt.FullName) + "<" + args.GetSignatureForError () + ">";
1377                 }
1378
1379                 protected override TypeExpr DoResolveAsTypeStep (IResolveContext ec)
1380                 {
1381                         if (!ResolveConstructedType (ec))
1382                                 return null;
1383
1384                         return this;
1385                 }
1386
1387                 /// <summary>
1388                 ///   Check the constraints; we're called from ResolveAsTypeTerminal()
1389                 ///   after fully resolving the constructed type.
1390                 /// </summary>
1391                 public bool CheckConstraints (IResolveContext ec)
1392                 {
1393                         return ConstraintChecker.CheckConstraints (ec, gt, gen_params, atypes, loc);
1394                 }
1395
1396                 /// <summary>
1397                 ///   Resolve the constructed type, but don't check the constraints.
1398                 /// </summary>
1399                 public bool ResolveConstructedType (IResolveContext ec)
1400                 {
1401                         if (type != null)
1402                                 return true;
1403                         // If we already know the fully resolved generic type.
1404                         if (gt != null)
1405                                 return DoResolveType (ec);
1406
1407                         int num_args;
1408                         Type t = name.Type;
1409
1410                         if (t == null) {
1411                                 Report.Error (246, loc, "Cannot find type `{0}'<...>", Name);
1412                                 return false;
1413                         }
1414
1415                         num_args = TypeManager.GetNumberOfTypeArguments (t);
1416                         if (num_args == 0) {
1417                                 Report.Error (308, loc,
1418                                               "The non-generic type `{0}' cannot " +
1419                                               "be used with type arguments.",
1420                                               TypeManager.CSharpName (t));
1421                                 return false;
1422                         }
1423
1424                         gt = t.GetGenericTypeDefinition ();
1425                         return DoResolveType (ec);
1426                 }
1427
1428                 bool DoResolveType (IResolveContext ec)
1429                 {
1430                         //
1431                         // Resolve the arguments.
1432                         //
1433                         if (args.Resolve (ec) == false)
1434                                 return false;
1435
1436                         gen_params = gt.GetGenericArguments ();
1437                         atypes = args.Arguments;
1438
1439                         if (atypes.Length != gen_params.Length) {
1440                                 Report.Error (305, loc,
1441                                               "Using the generic type `{0}' " +
1442                                               "requires {1} type arguments",
1443                                               TypeManager.CSharpName (gt),
1444                                               gen_params.Length.ToString ());
1445                                 return false;
1446                         }
1447
1448                         //
1449                         // Now bind the parameters.
1450                         //
1451                         type = gt.MakeGenericType (atypes);
1452                         return true;
1453                 }
1454
1455                 public Expression GetSimpleName (EmitContext ec)
1456                 {
1457                         return this;
1458                 }
1459
1460                 public override bool CheckAccessLevel (DeclSpace ds)
1461                 {
1462                         return ds.CheckAccessLevel (gt);
1463                 }
1464
1465                 public override bool AsAccessible (DeclSpace ds, int flags)
1466                 {
1467                         foreach (Type t in atypes) {
1468                                 if (!ds.AsAccessible (t, flags))
1469                                         return false;
1470                         }
1471
1472                         return ds.AsAccessible (gt, flags);
1473                 }
1474
1475                 public override bool IsClass {
1476                         get { return gt.IsClass; }
1477                 }
1478
1479                 public override bool IsValueType {
1480                         get { return gt.IsValueType; }
1481                 }
1482
1483                 public override bool IsInterface {
1484                         get { return gt.IsInterface; }
1485                 }
1486
1487                 public override bool IsSealed {
1488                         get { return gt.IsSealed; }
1489                 }
1490
1491                 public override bool Equals (object obj)
1492                 {
1493                         ConstructedType cobj = obj as ConstructedType;
1494                         if (cobj == null)
1495                                 return false;
1496
1497                         if ((type == null) || (cobj.type == null))
1498                                 return false;
1499
1500                         return type == cobj.type;
1501                 }
1502
1503                 public override int GetHashCode ()
1504                 {
1505                         return base.GetHashCode ();
1506                 }
1507
1508                 public override string Name {
1509                         get {
1510                                 return full_name;
1511                         }
1512                 }
1513
1514                 public override string FullName {
1515                         get {
1516                                 return full_name;
1517                         }
1518                 }
1519         }
1520
1521         public abstract class ConstraintChecker
1522         {
1523                 protected readonly Type[] gen_params;
1524                 protected readonly Type[] atypes;
1525                 protected readonly Location loc;
1526
1527                 protected ConstraintChecker (Type[] gen_params, Type[] atypes, Location loc)
1528                 {
1529                         this.gen_params = gen_params;
1530                         this.atypes = atypes;
1531                         this.loc = loc;
1532                 }
1533
1534                 /// <summary>
1535                 ///   Check the constraints; we're called from ResolveAsTypeTerminal()
1536                 ///   after fully resolving the constructed type.
1537                 /// </summary>
1538                 public bool CheckConstraints (IResolveContext ec)
1539                 {
1540                         for (int i = 0; i < gen_params.Length; i++) {
1541                                 if (!CheckConstraints (ec, i))
1542                                         return false;
1543                         }
1544
1545                         return true;
1546                 }
1547
1548                 protected bool CheckConstraints (IResolveContext ec, int index)
1549                 {
1550                         Type atype = atypes [index];
1551                         Type ptype = gen_params [index];
1552
1553                         if (atype == ptype)
1554                                 return true;
1555
1556                         Expression aexpr = new EmptyExpression (atype);
1557
1558                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (ptype);
1559                         if (gc == null)
1560                                 return true;
1561
1562                         bool is_class, is_struct;
1563                         if (atype.IsGenericParameter) {
1564                                 GenericConstraints agc = TypeManager.GetTypeParameterConstraints (atype);
1565                                 if (agc != null) {
1566                                         if (agc is Constraints)
1567                                                 ((Constraints) agc).Resolve (ec);
1568                                         is_class = agc.IsReferenceType;
1569                                         is_struct = agc.IsValueType;
1570                                 } else {
1571                                         is_class = is_struct = false;
1572                                 }
1573                         } else {
1574 #if MS_COMPATIBLE
1575                                 is_class = false;
1576                                 if (!atype.IsGenericType)
1577 #endif
1578                                 is_class = atype.IsClass || atype.IsInterface;
1579                                 is_struct = atype.IsValueType && !TypeManager.IsNullableType (atype);
1580                         }
1581
1582                         //
1583                         // First, check the `class' and `struct' constraints.
1584                         //
1585                         if (gc.HasReferenceTypeConstraint && !is_class) {
1586                                 Report.Error (452, loc, "The type `{0}' must be " +
1587                                               "a reference type in order to use it " +
1588                                               "as type parameter `{1}' in the " +
1589                                               "generic type or method `{2}'.",
1590                                               TypeManager.CSharpName (atype),
1591                                               TypeManager.CSharpName (ptype),
1592                                               GetSignatureForError ());
1593                                 return false;
1594                         } else if (gc.HasValueTypeConstraint && !is_struct) {
1595                                 Report.Error (453, loc, "The type `{0}' must be a " +
1596                                               "non-nullable value type in order to use it " +
1597                                               "as type parameter `{1}' in the " +
1598                                               "generic type or method `{2}'.",
1599                                               TypeManager.CSharpName (atype),
1600                                               TypeManager.CSharpName (ptype),
1601                                               GetSignatureForError ());
1602                                 return false;
1603                         }
1604
1605                         //
1606                         // The class constraint comes next.
1607                         //
1608                         if (gc.HasClassConstraint) {
1609                                 if (!CheckConstraint (ec, ptype, aexpr, gc.ClassConstraint))
1610                                         return false;
1611                         }
1612
1613                         //
1614                         // Now, check the interface constraints.
1615                         //
1616                         if (gc.InterfaceConstraints != null) {
1617                                 foreach (Type it in gc.InterfaceConstraints) {
1618                                         if (!CheckConstraint (ec, ptype, aexpr, it))
1619                                                 return false;
1620                                 }
1621                         }
1622
1623                         //
1624                         // Finally, check the constructor constraint.
1625                         //
1626
1627                         if (!gc.HasConstructorConstraint)
1628                                 return true;
1629
1630                         if (TypeManager.IsBuiltinType (atype) || atype.IsValueType)
1631                                 return true;
1632
1633                         if (HasDefaultConstructor (ec.DeclContainer.TypeBuilder, atype))
1634                                 return true;
1635
1636                         Report_SymbolRelatedToPreviousError ();
1637                         Report.SymbolRelatedToPreviousError (atype);
1638                         Report.Error (310, loc, "The type `{0}' must have a public " +
1639                                       "parameterless constructor in order to use it " +
1640                                       "as parameter `{1}' in the generic type or " +
1641                                       "method `{2}'",
1642                                       TypeManager.CSharpName (atype),
1643                                       TypeManager.CSharpName (ptype),
1644                                       GetSignatureForError ());
1645                         return false;
1646                 }
1647
1648                 protected bool CheckConstraint (IResolveContext ec, Type ptype, Expression expr,
1649                                                 Type ctype)
1650                 {
1651                         if (TypeManager.HasGenericArguments (ctype)) {
1652                                 Type[] types = TypeManager.GetTypeArguments (ctype);
1653
1654                                 TypeArguments new_args = new TypeArguments (loc);
1655
1656                                 for (int i = 0; i < types.Length; i++) {
1657                                         Type t = types [i];
1658
1659                                         if (t.IsGenericParameter) {
1660                                                 int pos = t.GenericParameterPosition;
1661                                                 t = atypes [pos];
1662                                         }
1663                                         new_args.Add (new TypeExpression (t, loc));
1664                                 }
1665
1666                                 TypeExpr ct = new ConstructedType (ctype, new_args, loc);
1667                                 if (ct.ResolveAsTypeStep (ec, false) == null)
1668                                         return false;
1669                                 ctype = ct.Type;
1670                         } else if (ctype.IsGenericParameter) {
1671                                 int pos = ctype.GenericParameterPosition;
1672                                 ctype = atypes [pos];
1673                         }
1674
1675                         if (Convert.ImplicitStandardConversionExists (expr, ctype))
1676                                 return true;
1677
1678                         Error_TypeMustBeConvertible (expr.Type, ctype, ptype);
1679                         return false;
1680                 }
1681
1682                 bool HasDefaultConstructor (Type containerType, Type atype)
1683                 {
1684                         if (atype.IsAbstract)
1685                                 return false;
1686
1687                 again:
1688                         atype = TypeManager.DropGenericTypeArguments (atype);
1689                         if (atype is TypeBuilder) {
1690                                 TypeContainer tc = TypeManager.LookupTypeContainer (atype);
1691                                 if (tc.InstanceConstructors == null) {
1692                                         atype = atype.BaseType;
1693                                         goto again;
1694                                 }
1695
1696                                 foreach (Constructor c in tc.InstanceConstructors) {
1697                                         if ((c.ModFlags & Modifiers.PUBLIC) == 0)
1698                                                 continue;
1699                                         if ((c.Parameters.FixedParameters != null) &&
1700                                             (c.Parameters.FixedParameters.Length != 0))
1701                                                 continue;
1702                                         if (c.Parameters.HasArglist || c.Parameters.HasParams)
1703                                                 continue;
1704
1705                                         return true;
1706                                 }
1707                         }
1708
1709                         TypeParameter tparam = TypeManager.LookupTypeParameter (atype);
1710                         if (tparam != null)
1711                                 return tparam.HasConstructorConstraint;
1712
1713                         MemberList list = TypeManager.FindMembers (
1714                                 atype, MemberTypes.Constructor,
1715                                 BindingFlags.Public | BindingFlags.Instance |
1716                                 BindingFlags.DeclaredOnly, null, null);
1717
1718                         if (atype.IsAbstract || (list == null))
1719                                 return false;
1720
1721                         foreach (MethodBase mb in list) {
1722                                 ParameterData pd = TypeManager.GetParameterData (mb);
1723                                 if ((pd.Count == 0) && mb.IsPublic && !mb.IsStatic)
1724                                         return true;
1725                         }
1726
1727                         return false;
1728                 }
1729
1730                 protected abstract string GetSignatureForError ();
1731                 protected abstract void Report_SymbolRelatedToPreviousError ();
1732
1733                 void Error_TypeMustBeConvertible (Type atype, Type gc, Type ptype)
1734                 {
1735                         Report_SymbolRelatedToPreviousError ();
1736                         Report.SymbolRelatedToPreviousError (atype);
1737                         Report.Error (309, loc,
1738                                       "The type `{0}' must be convertible to `{1}' in order to " +
1739                                       "use it as parameter `{2}' in the generic type or method `{3}'",
1740                                       TypeManager.CSharpName (atype), TypeManager.CSharpName (gc),
1741                                       TypeManager.CSharpName (ptype), GetSignatureForError ());
1742                 }
1743
1744                 public static bool CheckConstraints (EmitContext ec, MethodBase definition,
1745                                                      MethodBase instantiated, Location loc)
1746                 {
1747                         MethodConstraintChecker checker = new MethodConstraintChecker (
1748                                 definition, definition.GetGenericArguments (),
1749                                 instantiated.GetGenericArguments (), loc);
1750
1751                         return checker.CheckConstraints (ec);
1752                 }
1753
1754                 public static bool CheckConstraints (IResolveContext ec, Type gt, Type[] gen_params,
1755                                                      Type[] atypes, Location loc)
1756                 {
1757                         TypeConstraintChecker checker = new TypeConstraintChecker (
1758                                 gt, gen_params, atypes, loc);
1759
1760                         return checker.CheckConstraints (ec);
1761                 }
1762
1763                 protected class MethodConstraintChecker : ConstraintChecker
1764                 {
1765                         MethodBase definition;
1766
1767                         public MethodConstraintChecker (MethodBase definition, Type[] gen_params,
1768                                                         Type[] atypes, Location loc)
1769                                 : base (gen_params, atypes, loc)
1770                         {
1771                                 this.definition = definition;
1772                         }
1773
1774                         protected override string GetSignatureForError ()
1775                         {
1776                                 return TypeManager.CSharpSignature (definition);
1777                         }
1778
1779                         protected override void Report_SymbolRelatedToPreviousError ()
1780                         {
1781                                 Report.SymbolRelatedToPreviousError (definition);
1782                         }
1783                 }
1784
1785                 protected class TypeConstraintChecker : ConstraintChecker
1786                 {
1787                         Type gt;
1788
1789                         public TypeConstraintChecker (Type gt, Type[] gen_params, Type[] atypes,
1790                                                       Location loc)
1791                                 : base (gen_params, atypes, loc)
1792                         {
1793                                 this.gt = gt;
1794                         }
1795
1796                         protected override string GetSignatureForError ()
1797                         {
1798                                 return TypeManager.CSharpName (gt);
1799                         }
1800
1801                         protected override void Report_SymbolRelatedToPreviousError ()
1802                         {
1803                                 Report.SymbolRelatedToPreviousError (gt);
1804                         }
1805                 }
1806         }
1807
1808         /// <summary>
1809         ///   A generic method definition.
1810         /// </summary>
1811         public class GenericMethod : DeclSpace
1812         {
1813                 Expression return_type;
1814                 Parameters parameters;
1815
1816                 public GenericMethod (NamespaceEntry ns, DeclSpace parent, MemberName name,
1817                                       Expression return_type, Parameters parameters)
1818                         : base (ns, parent, name, null)
1819                 {
1820                         this.return_type = return_type;
1821                         this.parameters = parameters;
1822                 }
1823
1824                 public override TypeBuilder DefineType ()
1825                 {
1826                         throw new Exception ();
1827                 }
1828
1829                 public override bool Define ()
1830                 {
1831                         for (int i = 0; i < TypeParameters.Length; i++)
1832                                 if (!TypeParameters [i].Resolve (this))
1833                                         return false;
1834
1835                         return true;
1836                 }
1837
1838                 /// <summary>
1839                 ///   Define and resolve the type parameters.
1840                 ///   We're called from Method.Define().
1841                 /// </summary>
1842                 public bool Define (MethodBuilder mb, ToplevelBlock block)
1843                 {
1844                         TypeParameterName[] names = MemberName.TypeArguments.GetDeclarations ();
1845                         string[] snames = new string [names.Length];
1846                         for (int i = 0; i < names.Length; i++) {
1847                                 string type_argument_name = names[i].Name;
1848                                 Parameter p = parameters.GetParameterByName (type_argument_name);
1849                                 if (p != null) {
1850                                         Error_ParameterNameCollision (p.Location, type_argument_name, "method parameter");
1851                                         return false;
1852                                 }
1853                                 if (block != null) {
1854                                         LocalInfo li = (LocalInfo)block.Variables[type_argument_name];
1855                                         if (li != null) {
1856                                                 Error_ParameterNameCollision (li.Location, type_argument_name, "local variable");
1857                                                 return false;
1858                                         }
1859                                 }
1860                                 snames[i] = type_argument_name;
1861                         }
1862
1863                         GenericTypeParameterBuilder[] gen_params = mb.DefineGenericParameters (snames);
1864                         for (int i = 0; i < TypeParameters.Length; i++)
1865                                 TypeParameters [i].Define (gen_params [i]);
1866
1867                         if (!Define ())
1868                                 return false;
1869
1870                         for (int i = 0; i < TypeParameters.Length; i++) {
1871                                 if (!TypeParameters [i].ResolveType (this))
1872                                         return false;
1873                         }
1874
1875                         return true;
1876                 }
1877
1878                 static void Error_ParameterNameCollision (Location loc, string name, string collisionWith)
1879                 {
1880                         Report.Error (412, loc, "The type parameter name `{0}' is the same as `{1}'",
1881                                 name, collisionWith);
1882                 }
1883
1884                 /// <summary>
1885                 ///   We're called from MethodData.Define() after creating the MethodBuilder.
1886                 /// </summary>
1887                 public bool DefineType (EmitContext ec, MethodBuilder mb,
1888                                         MethodInfo implementing, bool is_override)
1889                 {
1890                         for (int i = 0; i < TypeParameters.Length; i++)
1891                                 if (!TypeParameters [i].DefineType (
1892                                             ec, mb, implementing, is_override))
1893                                         return false;
1894
1895                         bool ok = true;
1896                         foreach (Parameter p in parameters.FixedParameters){
1897                                 if (!p.Resolve (ec))
1898                                         ok = false;
1899                         }
1900                         if ((return_type != null) && (return_type.ResolveAsTypeTerminal (ec, false) == null))
1901                                 ok = false;
1902
1903                         return ok;
1904                 }
1905
1906                 public void EmitAttributes ()
1907                 {
1908                         for (int i = 0; i < TypeParameters.Length; i++)
1909                                 TypeParameters [i].EmitAttributes ();
1910
1911                         if (OptAttributes != null)
1912                                 OptAttributes.Emit ();
1913                 }
1914
1915                 public override bool DefineMembers ()
1916                 {
1917                         return true;
1918                 }
1919
1920                 public override MemberList FindMembers (MemberTypes mt, BindingFlags bf,
1921                                                         MemberFilter filter, object criteria)
1922                 {
1923                         throw new Exception ();
1924                 }
1925
1926                 public override MemberCache MemberCache {
1927                         get {
1928                                 return null;
1929                         }
1930                 }
1931
1932                 public override AttributeTargets AttributeTargets {
1933                         get {
1934                                 return AttributeTargets.Method | AttributeTargets.ReturnValue;
1935                         }
1936                 }
1937
1938                 public override string DocCommentHeader {
1939                         get { return "M:"; }
1940                 }
1941
1942                 public new void VerifyClsCompliance ()
1943                 {
1944                         foreach (TypeParameter tp in TypeParameters) {
1945                                 if (tp.Constraints == null)
1946                                         continue;
1947
1948                                 tp.Constraints.VerifyClsCompliance ();
1949                         }
1950                 }
1951         }
1952
1953         public class DefaultValueExpression : Expression
1954         {
1955                 Expression expr;
1956
1957                 public DefaultValueExpression (Expression expr, Location loc)
1958                 {
1959                         this.expr = expr;
1960                         this.loc = loc;
1961                 }
1962
1963                 public override Expression DoResolve (EmitContext ec)
1964                 {
1965                         TypeExpr texpr = expr.ResolveAsTypeTerminal (ec, false);
1966                         if (texpr == null)
1967                                 return null;
1968
1969                         type = texpr.Type;
1970
1971                         if (type == TypeManager.void_type) {
1972                                 Error_VoidInvalidInTheContext (loc);
1973                                 return null;
1974                         }
1975
1976                         if (type.IsGenericParameter)
1977                         {
1978                                 GenericConstraints constraints = TypeManager.GetTypeParameterConstraints(type);
1979                                 if (constraints != null && constraints.IsReferenceType)
1980                                         return new NullDefault (new NullLiteral (Location), type);
1981                         }
1982                         else
1983                         {
1984                                 Constant c = New.Constantify(type);
1985                                 if (c != null)
1986                                         return new NullDefault (c, type);
1987
1988                                 if (!TypeManager.IsValueType (type))
1989                                         return new NullDefault (new NullLiteral (Location), type);
1990                         }
1991                         eclass = ExprClass.Variable;
1992                         return this;
1993                 }
1994
1995                 public override void Emit (EmitContext ec)
1996                 {
1997                         LocalTemporary temp_storage = new LocalTemporary(type);
1998
1999                         temp_storage.AddressOf(ec, AddressOp.LoadStore);
2000                         ec.ig.Emit(OpCodes.Initobj, type);
2001                         temp_storage.Emit(ec);
2002                 }
2003         }
2004
2005         public class NullableType : TypeExpr
2006         {
2007                 Expression underlying;
2008
2009                 public NullableType (Expression underlying, Location l)
2010                 {
2011                         this.underlying = underlying;
2012                         loc = l;
2013
2014                         eclass = ExprClass.Type;
2015                 }
2016
2017                 public NullableType (Type type, Location loc)
2018                         : this (new TypeExpression (type, loc), loc)
2019                 { }
2020
2021                 public override string Name {
2022                         get { return underlying.ToString () + "?"; }
2023                 }
2024
2025                 public override string FullName {
2026                         get { return underlying.ToString () + "?"; }
2027                 }
2028
2029                 protected override TypeExpr DoResolveAsTypeStep (IResolveContext ec)
2030                 {
2031                         TypeArguments args = new TypeArguments (loc);
2032                         args.Add (underlying);
2033
2034                         ConstructedType ctype = new ConstructedType (TypeManager.generic_nullable_type, args, loc);
2035                         return ctype.ResolveAsTypeTerminal (ec, false);
2036                 }
2037         }
2038
2039         public partial class TypeManager
2040         {
2041                 //
2042                 // A list of core types that the compiler requires or uses
2043                 //
2044                 static public Type activator_type;
2045                 static public Type generic_ilist_type;
2046                 static public Type generic_icollection_type;
2047                 static public Type generic_ienumerator_type;
2048                 static public Type generic_ienumerable_type;
2049                 static public Type generic_nullable_type;
2050
2051                 //
2052                 // These methods are called by code generated by the compiler
2053                 //
2054                 static public MethodInfo activator_create_instance;
2055
2056                 static void InitGenericCoreTypes ()
2057                 {
2058                         activator_type = CoreLookupType ("System", "Activator");
2059
2060                         generic_ilist_type = CoreLookupType (
2061                                 "System.Collections.Generic", "IList", 1);
2062                         generic_icollection_type = CoreLookupType (
2063                                 "System.Collections.Generic", "ICollection", 1);
2064                         generic_ienumerator_type = CoreLookupType (
2065                                 "System.Collections.Generic", "IEnumerator", 1);
2066                         generic_ienumerable_type = CoreLookupType (
2067                                 "System.Collections.Generic", "IEnumerable", 1);
2068                         generic_nullable_type = CoreLookupType (
2069                                 "System", "Nullable", 1);
2070                 }
2071
2072                 static void InitGenericCodeHelpers ()
2073                 {
2074                         // Activator
2075                         Type [] type_arg = { type_type };
2076                         activator_create_instance = GetMethod (
2077                                 activator_type, "CreateInstance", type_arg);
2078                 }
2079
2080                 static Type CoreLookupType (string ns, string name, int arity)
2081                 {
2082                         return CoreLookupType (ns, MemberName.MakeName (name, arity));
2083                 }
2084
2085                 public static TypeContainer LookupGenericTypeContainer (Type t)
2086                 {
2087                         t = DropGenericTypeArguments (t);
2088                         return LookupTypeContainer (t);
2089                 }
2090
2091                 public static GenericConstraints GetTypeParameterConstraints (Type t)
2092                 {
2093                         if (!t.IsGenericParameter)
2094                                 throw new InvalidOperationException ();
2095
2096                         TypeParameter tparam = LookupTypeParameter (t);
2097                         if (tparam != null)
2098                                 return tparam.GenericConstraints;
2099
2100                         return ReflectionConstraints.GetConstraints (t);
2101                 }
2102
2103                 /// <summary>
2104                 ///   Check whether `a' and `b' may become equal generic types.
2105                 ///   The algorithm to do that is a little bit complicated.
2106                 /// </summary>
2107                 public static bool MayBecomeEqualGenericTypes (Type a, Type b, Type[] class_inferred,
2108                                                                Type[] method_inferred)
2109                 {
2110                         if (a.IsGenericParameter) {
2111                                 //
2112                                 // If a is an array of a's type, they may never
2113                                 // become equal.
2114                                 //
2115                                 while (b.IsArray) {
2116                                         b = b.GetElementType ();
2117                                         if (a.Equals (b))
2118                                                 return false;
2119                                 }
2120
2121                                 //
2122                                 // If b is a generic parameter or an actual type,
2123                                 // they may become equal:
2124                                 //
2125                                 //    class X<T,U> : I<T>, I<U>
2126                                 //    class X<T> : I<T>, I<float>
2127                                 //
2128                                 if (b.IsGenericParameter || !b.IsGenericType) {
2129                                         int pos = a.GenericParameterPosition;
2130                                         Type[] args = a.DeclaringMethod != null ? method_inferred : class_inferred;
2131                                         if (args [pos] == null) {
2132                                                 args [pos] = b;
2133                                                 return true;
2134                                         }
2135
2136                                         return args [pos] == a;
2137                                 }
2138
2139                                 //
2140                                 // We're now comparing a type parameter with a
2141                                 // generic instance.  They may become equal unless
2142                                 // the type parameter appears anywhere in the
2143                                 // generic instance:
2144                                 //
2145                                 //    class X<T,U> : I<T>, I<X<U>>
2146                                 //        -> error because you could instanciate it as
2147                                 //           X<X<int>,int>
2148                                 //
2149                                 //    class X<T> : I<T>, I<X<T>> -> ok
2150                                 //
2151
2152                                 Type[] bargs = GetTypeArguments (b);
2153                                 for (int i = 0; i < bargs.Length; i++) {
2154                                         if (a.Equals (bargs [i]))
2155                                                 return false;
2156                                 }
2157
2158                                 return true;
2159                         }
2160
2161                         if (b.IsGenericParameter)
2162                                 return MayBecomeEqualGenericTypes (b, a, class_inferred, method_inferred);
2163
2164                         //
2165                         // At this point, neither a nor b are a type parameter.
2166                         //
2167                         // If one of them is a generic instance, let
2168                         // MayBecomeEqualGenericInstances() compare them (if the
2169                         // other one is not a generic instance, they can never
2170                         // become equal).
2171                         //
2172
2173                         if (a.IsGenericType || b.IsGenericType)
2174                                 return MayBecomeEqualGenericInstances (a, b, class_inferred, method_inferred);
2175
2176                         //
2177                         // If both of them are arrays.
2178                         //
2179
2180                         if (a.IsArray && b.IsArray) {
2181                                 if (a.GetArrayRank () != b.GetArrayRank ())
2182                                         return false;
2183
2184                                 a = a.GetElementType ();
2185                                 b = b.GetElementType ();
2186
2187                                 return MayBecomeEqualGenericTypes (a, b, class_inferred, method_inferred);
2188                         }
2189
2190                         //
2191                         // Ok, two ordinary types.
2192                         //
2193
2194                         return a.Equals (b);
2195                 }
2196
2197                 //
2198                 // Checks whether two generic instances may become equal for some
2199                 // particular instantiation (26.3.1).
2200                 //
2201                 public static bool MayBecomeEqualGenericInstances (Type a, Type b,
2202                                                                    Type[] class_inferred,
2203                                                                    Type[] method_inferred)
2204                 {
2205                         if (!a.IsGenericType || !b.IsGenericType)
2206                                 return false;
2207                         if (a.GetGenericTypeDefinition () != b.GetGenericTypeDefinition ())
2208                                 return false;
2209
2210                         return MayBecomeEqualGenericInstances (
2211                                 GetTypeArguments (a), GetTypeArguments (b), class_inferred, method_inferred);
2212                 }
2213
2214                 public static bool MayBecomeEqualGenericInstances (Type[] aargs, Type[] bargs,
2215                                                                    Type[] class_inferred,
2216                                                                    Type[] method_inferred)
2217                 {
2218                         if (aargs.Length != bargs.Length)
2219                                 return false;
2220
2221                         for (int i = 0; i < aargs.Length; i++) {
2222                                 if (!MayBecomeEqualGenericTypes (aargs [i], bargs [i], class_inferred, method_inferred))
2223                                         return false;
2224                         }
2225
2226                         return true;
2227                 }
2228
2229                 static bool UnifyType (Type pt, Type at, Type[] inferred)
2230                 {
2231                         if (pt.IsGenericParameter) {
2232                                 if (pt.DeclaringMethod == null)
2233                                         return pt == at;
2234
2235                                 int pos = pt.GenericParameterPosition;
2236
2237                                 if (inferred [pos] == null)
2238                                         inferred [pos] = at;
2239
2240                                 return inferred [pos] == at;
2241                         }
2242
2243                         if (!pt.ContainsGenericParameters) {
2244                                 if (at.ContainsGenericParameters)
2245                                         return UnifyType (at, pt, inferred);
2246                                 else
2247                                         return true;
2248                         }
2249
2250                         if (at.IsArray) {
2251                                 if (pt.IsArray) {
2252                                         if (at.GetArrayRank () != pt.GetArrayRank ())
2253                                                 return false;
2254
2255                                         return UnifyType (pt.GetElementType (), at.GetElementType (), inferred);
2256                                 }
2257
2258                                 if (!pt.IsGenericType)
2259                                         return false;
2260
2261                                 Type gt = pt.GetGenericTypeDefinition ();
2262                                 if ((gt != generic_ilist_type) && (gt != generic_icollection_type) &&
2263                                     (gt != generic_ienumerable_type))
2264                                         return false;
2265
2266                                 Type[] args = GetTypeArguments (pt);
2267                                 return UnifyType (args [0], at.GetElementType (), inferred);
2268                         }
2269
2270                         if (pt.IsArray) {
2271                                 if (!at.IsArray ||
2272                                     (pt.GetArrayRank () != at.GetArrayRank ()))
2273                                         return false;
2274
2275                                 return UnifyType (pt.GetElementType (), at.GetElementType (), inferred);
2276                         }
2277
2278                         if (pt.IsByRef && at.IsByRef)
2279                                 return UnifyType (pt.GetElementType (), at.GetElementType (), inferred);
2280                         ArrayList list = new ArrayList ();
2281                         if (at.IsGenericType)
2282                                 list.Add (at);
2283                         for (Type bt = at.BaseType; bt != null; bt = bt.BaseType)
2284                                 list.Add (bt);
2285
2286                         list.AddRange (TypeManager.GetInterfaces (at));
2287
2288                         foreach (Type type in list) {
2289                                 if (!type.IsGenericType)
2290                                         continue;
2291
2292                                 if (DropGenericTypeArguments (pt) != DropGenericTypeArguments (type))
2293                                         continue;
2294
2295                                 if (!UnifyTypes (pt.GetGenericArguments (), type.GetGenericArguments (), inferred))
2296                                         return false;
2297                         }
2298
2299                         return true;
2300                 }
2301
2302                 static bool UnifyTypes (Type[] pts, Type [] ats, Type [] inferred)
2303                 {
2304                         for (int i = 0; i < ats.Length; i++) {
2305                                 if (!UnifyType (pts [i], ats [i], inferred))
2306                                         return false;
2307                         }
2308                         return true;
2309                 }
2310
2311                 /// <summary>
2312                 ///   Type inference.  Try to infer the type arguments from the params method
2313                 ///   `method', which is invoked with the arguments `arguments'.  This is used
2314                 ///   when resolving an Invocation or a DelegateInvocation and the user
2315                 ///   did not explicitly specify type arguments.
2316                 /// </summary>
2317                 public static bool InferParamsTypeArguments (EmitContext ec, ArrayList arguments,
2318                                                              ref MethodBase method)
2319                 {
2320                         if (!TypeManager.IsGenericMethod (method))
2321                                 return true;
2322
2323                         // if there are no arguments, there's no way to infer the type-arguments
2324                         if (arguments == null || arguments.Count == 0)
2325                                 return false;
2326
2327                         ParameterData pd = TypeManager.GetParameterData (method);
2328                         int pd_count = pd.Count;
2329                         int arg_count = arguments.Count;
2330
2331                         if (pd_count == 0)
2332                                 return false;
2333
2334                         if (pd.ParameterModifier (pd_count - 1) != Parameter.Modifier.PARAMS)
2335                                 return false;
2336
2337                         if (pd_count - 1 > arg_count)
2338                                 return false;
2339
2340                         Type[] method_args = method.GetGenericArguments ();
2341                         Type[] inferred_types = new Type [method_args.Length];
2342
2343                         //
2344                         // If we have come this far, the case which
2345                         // remains is when the number of parameters is
2346                         // less than or equal to the argument count.
2347                         //
2348                         for (int i = 0; i < pd_count - 1; ++i) {
2349                                 Argument a = (Argument) arguments [i];
2350
2351                                 if ((a.Expr is NullLiteral) || (a.Expr is MethodGroupExpr))
2352                                         continue;
2353
2354                                 Type pt = pd.ParameterType (i);
2355                                 Type at = a.Type;
2356
2357                                 if (!UnifyType (pt, at, inferred_types))
2358                                         return false;
2359                         }
2360
2361                         Type element_type = TypeManager.GetElementType (pd.ParameterType (pd_count - 1));
2362
2363                         for (int i = pd_count - 1; i < arg_count; i++) {
2364                                 Argument a = (Argument) arguments [i];
2365
2366                                 if ((a.Expr is NullLiteral) || (a.Expr is MethodGroupExpr))
2367                                         continue;
2368
2369                                 if (!UnifyType (element_type, a.Type, inferred_types))
2370                                         return false;
2371                         }
2372
2373                         for (int i = 0; i < inferred_types.Length; i++)
2374                                 if (inferred_types [i] == null)
2375                                         return false;
2376
2377                         method = ((MethodInfo)method).MakeGenericMethod (inferred_types);
2378                         return true;
2379                 }
2380
2381                 static bool InferTypeArguments (Type[] param_types, Type[] arg_types,
2382                                                 Type[] inferred_types)
2383                 {
2384                         for (int i = 0; i < arg_types.Length; i++) {
2385                                 if (arg_types [i] == null)
2386                                         continue;
2387
2388                                 if (!UnifyType (param_types [i], arg_types [i], inferred_types))
2389                                         return false;
2390                         }
2391
2392                         for (int i = 0; i < inferred_types.Length; i++)
2393                                 if (inferred_types [i] == null)
2394                                         return false;
2395
2396                         return true;
2397                 }
2398
2399                 /// <summary>
2400                 ///   Type inference.  Try to infer the type arguments from `method',
2401                 ///   which is invoked with the arguments `arguments'.  This is used
2402                 ///   when resolving an Invocation or a DelegateInvocation and the user
2403                 ///   did not explicitly specify type arguments.
2404                 /// </summary>
2405                 public static bool InferTypeArguments (ArrayList arguments,
2406                                                        ref MethodBase method)
2407                 {
2408                         if (!TypeManager.IsGenericMethod (method))
2409                                 return true;
2410
2411                         int arg_count;
2412                         if (arguments != null)
2413                                 arg_count = arguments.Count;
2414                         else
2415                                 arg_count = 0;
2416
2417                         ParameterData pd = TypeManager.GetParameterData (method);
2418                         if (arg_count != pd.Count)
2419                                 return false;
2420
2421                         Type[] method_args = method.GetGenericArguments ();
2422
2423                         bool is_open = false;
2424                         for (int i = 0; i < method_args.Length; i++) {
2425                                 if (method_args [i].IsGenericParameter) {
2426                                         is_open = true;
2427                                         break;
2428                                 }
2429                         }
2430
2431                         // If none of the method parameters mention a generic parameter, we can't infer the generic parameters
2432                         if (!is_open)
2433                                 return !TypeManager.IsGenericMethodDefinition (method);
2434
2435                         Type[] inferred_types = new Type [method_args.Length];
2436
2437                         Type[] param_types = new Type [pd.Count];
2438                         Type[] arg_types = new Type [pd.Count];
2439
2440                         for (int i = 0; i < arg_count; i++) {
2441                                 param_types [i] = pd.ParameterType (i);
2442
2443                                 Argument a = (Argument) arguments [i];
2444                                 if ((a.Expr is NullLiteral) || (a.Expr is MethodGroupExpr) ||
2445                                     (a.Expr is AnonymousMethodExpression))
2446                                         continue;
2447
2448                                 arg_types [i] = a.Type;
2449                         }
2450
2451                         if (!InferTypeArguments (param_types, arg_types, inferred_types))
2452                                 return false;
2453
2454                         method = ((MethodInfo)method).MakeGenericMethod (inferred_types);
2455                         return true;
2456                 }
2457
2458                 /// <summary>
2459                 ///   Type inference.
2460                 /// </summary>
2461                 public static bool InferTypeArguments (ParameterData apd,
2462                                                        ref MethodBase method)
2463                 {
2464                         if (!TypeManager.IsGenericMethod (method))
2465                                 return true;
2466
2467                         ParameterData pd = TypeManager.GetParameterData (method);
2468                         if (apd.Count != pd.Count)
2469                                 return false;
2470
2471                         Type[] method_args = method.GetGenericArguments ();
2472                         Type[] inferred_types = new Type [method_args.Length];
2473
2474                         Type[] param_types = new Type [pd.Count];
2475                         Type[] arg_types = new Type [pd.Count];
2476
2477                         for (int i = 0; i < apd.Count; i++) {
2478                                 param_types [i] = pd.ParameterType (i);
2479                                 arg_types [i] = apd.ParameterType (i);
2480                         }
2481
2482                         if (!InferTypeArguments (param_types, arg_types, inferred_types))
2483                                 return false;
2484
2485                         method = ((MethodInfo)method).MakeGenericMethod (inferred_types);
2486                         return true;
2487                 }
2488         }
2489
2490         public abstract class Nullable
2491         {
2492                 public sealed class NullableInfo
2493                 {
2494                         public readonly Type Type;
2495                         public readonly Type UnderlyingType;
2496                         public readonly MethodInfo HasValue;
2497                         public readonly MethodInfo Value;
2498                         public readonly ConstructorInfo Constructor;
2499
2500                         public NullableInfo (Type type)
2501                         {
2502                                 Type = type;
2503                                 UnderlyingType = TypeManager.GetTypeArguments (type) [0];
2504
2505                                 PropertyInfo has_value_pi = TypeManager.GetProperty (type, "HasValue");
2506                                 PropertyInfo value_pi = TypeManager.GetProperty (type, "Value");
2507
2508                                 HasValue = has_value_pi.GetGetMethod (false);
2509                                 Value = value_pi.GetGetMethod (false);
2510                                 Constructor = type.GetConstructor (new Type[] { UnderlyingType });
2511                         }
2512                 }
2513
2514                 public class Unwrap : Expression, IMemoryLocation, IAssignMethod
2515                 {
2516                         Expression expr;
2517                         NullableInfo info;
2518
2519                         LocalTemporary temp;
2520                         bool has_temp;
2521
2522                         protected Unwrap (Expression expr)
2523                         {
2524                                 this.expr = expr;
2525                                 this.loc = expr.Location;
2526                         }
2527
2528                         public static Unwrap Create (Expression expr, EmitContext ec)
2529                         {
2530                                 return new Unwrap (expr).Resolve (ec) as Unwrap;
2531                         }
2532
2533                         public override Expression DoResolve (EmitContext ec)
2534                         {
2535                                 expr = expr.Resolve (ec);
2536                                 if (expr == null)
2537                                         return null;
2538
2539                                 temp = new LocalTemporary (expr.Type);
2540
2541                                 info = new NullableInfo (expr.Type);
2542                                 type = info.UnderlyingType;
2543                                 eclass = expr.eclass;
2544                                 return this;
2545                         }
2546
2547                         public override void Emit (EmitContext ec)
2548                         {
2549                                 AddressOf (ec, AddressOp.LoadStore);
2550                                 ec.ig.EmitCall (OpCodes.Call, info.Value, null);
2551                         }
2552
2553                         public void EmitCheck (EmitContext ec)
2554                         {
2555                                 AddressOf (ec, AddressOp.LoadStore);
2556                                 ec.ig.EmitCall (OpCodes.Call, info.HasValue, null);
2557                         }
2558
2559                         public void Store (EmitContext ec)
2560                         {
2561                                 create_temp (ec);
2562                         }
2563
2564                         void create_temp (EmitContext ec)
2565                         {
2566                                 if ((temp != null) && !has_temp) {
2567                                         expr.Emit (ec);
2568                                         temp.Store (ec);
2569                                         has_temp = true;
2570                                 }
2571                         }
2572
2573                         public void AddressOf (EmitContext ec, AddressOp mode)
2574                         {
2575                                 create_temp (ec);
2576                                 if (temp != null)
2577                                         temp.AddressOf (ec, AddressOp.LoadStore);
2578                                 else
2579                                         ((IMemoryLocation) expr).AddressOf (ec, AddressOp.LoadStore);
2580                         }
2581
2582                         public void Emit (EmitContext ec, bool leave_copy)
2583                         {
2584                                 create_temp (ec);
2585                                 if (leave_copy) {
2586                                         if (temp != null)
2587                                                 temp.Emit (ec);
2588                                         else
2589                                                 expr.Emit (ec);
2590                                 }
2591
2592                                 Emit (ec);
2593                         }
2594
2595                         public void EmitAssign (EmitContext ec, Expression source,
2596                                                 bool leave_copy, bool prepare_for_load)
2597                         {
2598                                 InternalWrap wrap = new InternalWrap (source, info, loc);
2599                                 ((IAssignMethod) expr).EmitAssign (ec, wrap, leave_copy, false);
2600                         }
2601
2602                         protected class InternalWrap : Expression
2603                         {
2604                                 public Expression expr;
2605                                 public NullableInfo info;
2606
2607                                 public InternalWrap (Expression expr, NullableInfo info, Location loc)
2608                                 {
2609                                         this.expr = expr;
2610                                         this.info = info;
2611                                         this.loc = loc;
2612
2613                                         type = info.Type;
2614                                         eclass = ExprClass.Value;
2615                                 }
2616
2617                                 public override Expression DoResolve (EmitContext ec)
2618                                 {
2619                                         return this;
2620                                 }
2621
2622                                 public override void Emit (EmitContext ec)
2623                                 {
2624                                         expr.Emit (ec);
2625                                         ec.ig.Emit (OpCodes.Newobj, info.Constructor);
2626                                 }
2627                         }
2628                 }
2629
2630                 public class Wrap : Expression
2631                 {
2632                         Expression expr;
2633                         NullableInfo info;
2634
2635                         protected Wrap (Expression expr)
2636                         {
2637                                 this.expr = expr;
2638                                 this.loc = expr.Location;
2639                         }
2640
2641                         public static Wrap Create (Expression expr, EmitContext ec)
2642                         {
2643                                 return new Wrap (expr).Resolve (ec) as Wrap;
2644                         }
2645
2646                         public override Expression DoResolve (EmitContext ec)
2647                         {
2648                                 expr = expr.Resolve (ec);
2649                                 if (expr == null)
2650                                         return null;
2651
2652                                 TypeExpr target_type = new NullableType (expr.Type, loc);
2653                                 target_type = target_type.ResolveAsTypeTerminal (ec, false);
2654                                 if (target_type == null)
2655                                         return null;
2656
2657                                 type = target_type.Type;
2658                                 info = new NullableInfo (type);
2659                                 eclass = ExprClass.Value;
2660                                 return this;
2661                         }
2662
2663                         public override void Emit (EmitContext ec)
2664                         {
2665                                 expr.Emit (ec);
2666                                 ec.ig.Emit (OpCodes.Newobj, info.Constructor);
2667                         }
2668                 }
2669
2670                 public class NullableLiteral : NullLiteral, IMemoryLocation {
2671                         public NullableLiteral (Type target_type, Location loc)
2672                                 : base (loc)
2673                         {
2674                                 this.type = target_type;
2675
2676                                 eclass = ExprClass.Value;
2677                         }
2678
2679                         public override Expression DoResolve (EmitContext ec)
2680                         {
2681                                 return this;
2682                         }
2683
2684                         public override void Emit (EmitContext ec)
2685                         {
2686                                 LocalTemporary value_target = new LocalTemporary (type);
2687
2688                                 value_target.AddressOf (ec, AddressOp.Store);
2689                                 ec.ig.Emit (OpCodes.Initobj, type);
2690                                 value_target.Emit (ec);
2691                         }
2692
2693                         public void AddressOf (EmitContext ec, AddressOp Mode)
2694                         {
2695                                 LocalTemporary value_target = new LocalTemporary (type);
2696
2697                                 value_target.AddressOf (ec, AddressOp.Store);
2698                                 ec.ig.Emit (OpCodes.Initobj, type);
2699                                 ((IMemoryLocation) value_target).AddressOf (ec, Mode);
2700                         }
2701                 }
2702
2703                 public abstract class Lifted : Expression, IMemoryLocation
2704                 {
2705                         Expression expr, underlying, wrap, null_value;
2706                         Unwrap unwrap;
2707
2708                         protected Lifted (Expression expr, Location loc)
2709                         {
2710                                 this.expr = expr;
2711                                 this.loc = loc;
2712                         }
2713
2714                         public override Expression DoResolve (EmitContext ec)
2715                         {
2716                                 expr = expr.Resolve (ec);
2717                                 if (expr == null)
2718                                         return null;
2719
2720                                 unwrap = Unwrap.Create (expr, ec);
2721                                 if (unwrap == null)
2722                                         return null;
2723
2724                                 underlying = ResolveUnderlying (unwrap, ec);
2725                                 if (underlying == null)
2726                                         return null;
2727
2728                                 wrap = Wrap.Create (underlying, ec);
2729                                 if (wrap == null)
2730                                         return null;
2731
2732                                 null_value = new NullableLiteral (wrap.Type, loc).Resolve (ec);
2733                                 if (null_value == null)
2734                                         return null;
2735
2736                                 type = wrap.Type;
2737                                 eclass = ExprClass.Value;
2738                                 return this;
2739                         }
2740
2741                         protected abstract Expression ResolveUnderlying (Expression unwrap, EmitContext ec);
2742
2743                         public override void Emit (EmitContext ec)
2744                         {
2745                                 ILGenerator ig = ec.ig;
2746                                 Label is_null_label = ig.DefineLabel ();
2747                                 Label end_label = ig.DefineLabel ();
2748
2749                                 unwrap.EmitCheck (ec);
2750                                 ig.Emit (OpCodes.Brfalse, is_null_label);
2751
2752                                 wrap.Emit (ec);
2753                                 ig.Emit (OpCodes.Br, end_label);
2754
2755                                 ig.MarkLabel (is_null_label);
2756                                 null_value.Emit (ec);
2757
2758                                 ig.MarkLabel (end_label);
2759                         }
2760
2761                         public void AddressOf (EmitContext ec, AddressOp mode)
2762                         {
2763                                 unwrap.AddressOf (ec, mode);
2764                         }
2765                 }
2766
2767                 public class LiftedConversion : Lifted
2768                 {
2769                         public readonly bool IsUser;
2770                         public readonly bool IsExplicit;
2771                         public readonly Type TargetType;
2772
2773                         public LiftedConversion (Expression expr, Type target_type, bool is_user,
2774                                                  bool is_explicit, Location loc)
2775                                 : base (expr, loc)
2776                         {
2777                                 this.IsUser = is_user;
2778                                 this.IsExplicit = is_explicit;
2779                                 this.TargetType = target_type;
2780                         }
2781
2782                         protected override Expression ResolveUnderlying (Expression unwrap, EmitContext ec)
2783                         {
2784                                 Type type = TypeManager.GetTypeArguments (TargetType) [0];
2785
2786                                 if (IsUser) {
2787                                         return Convert.UserDefinedConversion (ec, unwrap, type, loc, IsExplicit);
2788                                 } else {
2789                                         if (IsExplicit)
2790                                                 return Convert.ExplicitConversion (ec, unwrap, type, loc);
2791                                         else
2792                                                 return Convert.ImplicitConversion (ec, unwrap, type, loc);
2793                                 }
2794                         }
2795                 }
2796
2797                 public class LiftedUnaryOperator : Lifted
2798                 {
2799                         public readonly Unary.Operator Oper;
2800
2801                         public LiftedUnaryOperator (Unary.Operator op, Expression expr, Location loc)
2802                                 : base (expr, loc)
2803                         {
2804                                 this.Oper = op;
2805                         }
2806
2807                         protected override Expression ResolveUnderlying (Expression unwrap, EmitContext ec)
2808                         {
2809                                 return new Unary (Oper, unwrap, loc);
2810                         }
2811                 }
2812
2813                 public class LiftedConditional : Lifted
2814                 {
2815                         Expression true_expr, false_expr;
2816
2817                         public LiftedConditional (Expression expr, Expression true_expr, Expression false_expr,
2818                                                   Location loc)
2819                                 : base (expr, loc)
2820                         {
2821                                 this.true_expr = true_expr;
2822                                 this.false_expr = false_expr;
2823                         }
2824
2825                         protected override Expression ResolveUnderlying (Expression unwrap, EmitContext ec)
2826                         {
2827                                 return new Conditional (unwrap, true_expr, false_expr);
2828                         }
2829                 }
2830
2831                 public class LiftedBinaryOperator : Expression
2832                 {
2833                         public readonly Binary.Operator Oper;
2834
2835                         Expression left, right, original_left, original_right;
2836                         Expression underlying, null_value, bool_wrap;
2837                         Unwrap left_unwrap, right_unwrap;
2838                         bool is_equality, is_comparision, is_boolean;
2839
2840                         public LiftedBinaryOperator (Binary.Operator op, Expression left, Expression right,
2841                                                      Location loc)
2842                         {
2843                                 this.Oper = op;
2844                                 this.left = original_left = left;
2845                                 this.right = original_right = right;
2846                                 this.loc = loc;
2847                         }
2848
2849                         public override Expression DoResolve (EmitContext ec)
2850                         {
2851                                 if (TypeManager.IsNullableType (left.Type)) {
2852                                         left = left_unwrap = Unwrap.Create (left, ec);
2853                                         if (left == null)
2854                                                 return null;
2855                                 }
2856
2857                                 if (TypeManager.IsNullableType (right.Type)) {
2858                                         right = right_unwrap = Unwrap.Create (right, ec);
2859                                         if (right == null)
2860                                                 return null;
2861                                 }
2862
2863                                 if ((Oper == Binary.Operator.LogicalAnd) ||
2864                                     (Oper == Binary.Operator.LogicalOr)) {
2865                                         Binary.Error_OperatorCannotBeApplied (
2866                                                 loc, Binary.OperName (Oper),
2867                                                 original_left.GetSignatureForError (),
2868                                                 original_right.GetSignatureForError ());
2869                                         return null;
2870                                 }
2871
2872                                 if (((Oper == Binary.Operator.BitwiseAnd) || (Oper == Binary.Operator.BitwiseOr)) &&
2873                                     ((left.Type == TypeManager.bool_type) && (right.Type == TypeManager.bool_type))) {
2874                                         Expression empty = new EmptyExpression (TypeManager.bool_type);
2875                                         bool_wrap = Wrap.Create (empty, ec);
2876                                         null_value = new NullableLiteral (bool_wrap.Type, loc).Resolve (ec);
2877
2878                                         type = bool_wrap.Type;
2879                                         is_boolean = true;
2880                                 } else if ((Oper == Binary.Operator.Equality) || (Oper == Binary.Operator.Inequality)) {
2881                                         if (!(left is NullLiteral) && !(right is NullLiteral)) {
2882                                                 underlying = new Binary (Oper, left, right).Resolve (ec);
2883                                                 if (underlying == null)
2884                                                         return null;
2885                                         }
2886
2887                                         type = TypeManager.bool_type;
2888                                         is_equality = true;
2889                                 } else if ((Oper == Binary.Operator.LessThan) ||
2890                                            (Oper == Binary.Operator.GreaterThan) ||
2891                                            (Oper == Binary.Operator.LessThanOrEqual) ||
2892                                            (Oper == Binary.Operator.GreaterThanOrEqual)) {
2893                                         underlying = new Binary (Oper, left, right).Resolve (ec);
2894                                         if (underlying == null)
2895                                                 return null;
2896
2897                                         type = TypeManager.bool_type;
2898                                         is_comparision = true;
2899                                 } else {
2900                                         underlying = new Binary (Oper, left, right).Resolve (ec);
2901                                         if (underlying == null)
2902                                                 return null;
2903
2904                                         underlying = Wrap.Create (underlying, ec);
2905                                         if (underlying == null)
2906                                                 return null;
2907
2908                                         type = underlying.Type;
2909                                         null_value = new NullableLiteral (type, loc).Resolve (ec);
2910                                 }
2911
2912                                 eclass = ExprClass.Value;
2913                                 return this;
2914                         }
2915
2916                         void EmitBoolean (EmitContext ec)
2917                         {
2918                                 ILGenerator ig = ec.ig;
2919
2920                                 Label left_is_null_label = ig.DefineLabel ();
2921                                 Label right_is_null_label = ig.DefineLabel ();
2922                                 Label is_null_label = ig.DefineLabel ();
2923                                 Label wrap_label = ig.DefineLabel ();
2924                                 Label end_label = ig.DefineLabel ();
2925
2926                                 if (left_unwrap != null) {
2927                                         left_unwrap.EmitCheck (ec);
2928                                         ig.Emit (OpCodes.Brfalse, left_is_null_label);
2929                                 }
2930
2931                                 left.Emit (ec);
2932                                 ig.Emit (OpCodes.Dup);
2933                                 if ((Oper == Binary.Operator.BitwiseOr) || (Oper == Binary.Operator.LogicalOr))
2934                                         ig.Emit (OpCodes.Brtrue, wrap_label);
2935                                 else
2936                                         ig.Emit (OpCodes.Brfalse, wrap_label);
2937
2938                                 if (right_unwrap != null) {
2939                                         right_unwrap.EmitCheck (ec);
2940                                         ig.Emit (OpCodes.Brfalse, right_is_null_label);
2941                                 }
2942
2943                                 if ((Oper == Binary.Operator.LogicalAnd) || (Oper == Binary.Operator.LogicalOr))
2944                                         ig.Emit (OpCodes.Pop);
2945
2946                                 right.Emit (ec);
2947                                 if (Oper == Binary.Operator.BitwiseOr)
2948                                         ig.Emit (OpCodes.Or);
2949                                 else if (Oper == Binary.Operator.BitwiseAnd)
2950                                         ig.Emit (OpCodes.And);
2951                                 ig.Emit (OpCodes.Br, wrap_label);
2952
2953                                 ig.MarkLabel (left_is_null_label);
2954                                 if (right_unwrap != null) {
2955                                         right_unwrap.EmitCheck (ec);
2956                                         ig.Emit (OpCodes.Brfalse, is_null_label);
2957                                 }
2958
2959                                 right.Emit (ec);
2960                                 ig.Emit (OpCodes.Dup);
2961                                 if ((Oper == Binary.Operator.BitwiseOr) || (Oper == Binary.Operator.LogicalOr))
2962                                         ig.Emit (OpCodes.Brtrue, wrap_label);
2963                                 else
2964                                         ig.Emit (OpCodes.Brfalse, wrap_label);
2965
2966                                 ig.MarkLabel (right_is_null_label);
2967                                 ig.Emit (OpCodes.Pop);
2968                                 ig.MarkLabel (is_null_label);
2969                                 null_value.Emit (ec);
2970                                 ig.Emit (OpCodes.Br, end_label);
2971
2972                                 ig.MarkLabel (wrap_label);
2973                                 ig.Emit (OpCodes.Nop);
2974                                 bool_wrap.Emit (ec);
2975                                 ig.Emit (OpCodes.Nop);
2976
2977                                 ig.MarkLabel (end_label);
2978                         }
2979
2980                         void EmitEquality (EmitContext ec)
2981                         {
2982                                 ILGenerator ig = ec.ig;
2983
2984                                 // Given 'X? x;' for any value type X: 'x != null' is the same as 'x.HasValue'
2985                                 if (left is NullLiteral) {
2986                                         if (right_unwrap == null)
2987                                                 throw new InternalErrorException ();
2988                                         right_unwrap.EmitCheck (ec);
2989                                         if (Oper == Binary.Operator.Equality) {
2990                                                 ig.Emit (OpCodes.Ldc_I4_0);
2991                                                 ig.Emit (OpCodes.Ceq);
2992                                         }
2993                                         return;
2994                                 }
2995
2996                                 if (right is NullLiteral) {
2997                                         if (left_unwrap == null)
2998                                                 throw new InternalErrorException ();
2999                                         left_unwrap.EmitCheck (ec);
3000                                         if (Oper == Binary.Operator.Equality) {
3001                                                 ig.Emit (OpCodes.Ldc_I4_0);
3002                                                 ig.Emit (OpCodes.Ceq);
3003                                         }
3004                                         return;
3005                                 }
3006
3007                                 Label both_have_value_label = ig.DefineLabel ();
3008                                 Label end_label = ig.DefineLabel ();
3009
3010                                 if (left_unwrap != null && right_unwrap != null) {
3011                                         Label dissimilar_label = ig.DefineLabel ();
3012
3013                                         left_unwrap.EmitCheck (ec);
3014                                         ig.Emit (OpCodes.Dup);
3015                                         right_unwrap.EmitCheck (ec);
3016                                         ig.Emit (OpCodes.Bne_Un, dissimilar_label);
3017
3018                                         ig.Emit (OpCodes.Brtrue, both_have_value_label);
3019
3020                                         // both are null
3021                                         if (Oper == Binary.Operator.Equality)
3022                                                 ig.Emit (OpCodes.Ldc_I4_1);
3023                                         else
3024                                                 ig.Emit (OpCodes.Ldc_I4_0);
3025                                         ig.Emit (OpCodes.Br, end_label);
3026
3027                                         ig.MarkLabel (dissimilar_label);
3028                                         ig.Emit (OpCodes.Pop);
3029                                 } else if (left_unwrap != null) {
3030                                         left_unwrap.EmitCheck (ec);
3031                                         ig.Emit (OpCodes.Brtrue, both_have_value_label);
3032                                 } else if (right_unwrap != null) {
3033                                         right_unwrap.EmitCheck (ec);
3034                                         ig.Emit (OpCodes.Brtrue, both_have_value_label);
3035                                 } else {
3036                                         throw new InternalErrorException ("shouldn't get here");
3037                                 }
3038
3039                                 // one is null while the other isn't
3040                                 if (Oper == Binary.Operator.Equality)
3041                                         ig.Emit (OpCodes.Ldc_I4_0);
3042                                 else
3043                                         ig.Emit (OpCodes.Ldc_I4_1);
3044                                 ig.Emit (OpCodes.Br, end_label);
3045
3046                                 ig.MarkLabel (both_have_value_label);
3047                                 underlying.Emit (ec);
3048
3049                                 ig.MarkLabel (end_label);
3050                         }
3051
3052                         void EmitComparision (EmitContext ec)
3053                         {
3054                                 ILGenerator ig = ec.ig;
3055
3056                                 Label is_null_label = ig.DefineLabel ();
3057                                 Label end_label = ig.DefineLabel ();
3058
3059                                 if (left_unwrap != null) {
3060                                         left_unwrap.EmitCheck (ec);
3061                                         ig.Emit (OpCodes.Brfalse, is_null_label);
3062                                 }
3063
3064                                 if (right_unwrap != null) {
3065                                         right_unwrap.EmitCheck (ec);
3066                                         ig.Emit (OpCodes.Brfalse, is_null_label);
3067                                 }
3068
3069                                 underlying.Emit (ec);
3070                                 ig.Emit (OpCodes.Br, end_label);
3071
3072                                 ig.MarkLabel (is_null_label);
3073                                 ig.Emit (OpCodes.Ldc_I4_0);
3074
3075                                 ig.MarkLabel (end_label);
3076                         }
3077
3078                         public override void Emit (EmitContext ec)
3079                         {
3080                                 if (left_unwrap != null)
3081                                         left_unwrap.Store (ec);
3082                                 if (right_unwrap != null)
3083                                         right_unwrap.Store (ec);
3084
3085                                 if (is_boolean) {
3086                                         EmitBoolean (ec);
3087                                         return;
3088                                 } else if (is_equality) {
3089                                         EmitEquality (ec);
3090                                         return;
3091                                 } else if (is_comparision) {
3092                                         EmitComparision (ec);
3093                                         return;
3094                                 }
3095
3096                                 ILGenerator ig = ec.ig;
3097
3098                                 Label is_null_label = ig.DefineLabel ();
3099                                 Label end_label = ig.DefineLabel ();
3100
3101                                 if (left_unwrap != null) {
3102                                         left_unwrap.EmitCheck (ec);
3103                                         ig.Emit (OpCodes.Brfalse, is_null_label);
3104                                 }
3105
3106                                 if (right_unwrap != null) {
3107                                         right_unwrap.EmitCheck (ec);
3108                                         ig.Emit (OpCodes.Brfalse, is_null_label);
3109                                 }
3110
3111                                 underlying.Emit (ec);
3112                                 ig.Emit (OpCodes.Br, end_label);
3113
3114                                 ig.MarkLabel (is_null_label);
3115                                 null_value.Emit (ec);
3116
3117                                 ig.MarkLabel (end_label);
3118                         }
3119                 }
3120
3121                 public class OperatorTrueOrFalse : Expression
3122                 {
3123                         public readonly bool IsTrue;
3124
3125                         Expression expr;
3126                         Unwrap unwrap;
3127
3128                         public OperatorTrueOrFalse (Expression expr, bool is_true, Location loc)
3129                         {
3130                                 this.IsTrue = is_true;
3131                                 this.expr = expr;
3132                                 this.loc = loc;
3133                         }
3134
3135                         public override Expression DoResolve (EmitContext ec)
3136                         {
3137                                 unwrap = Unwrap.Create (expr, ec);
3138                                 if (unwrap == null)
3139                                         return null;
3140
3141                                 if (unwrap.Type != TypeManager.bool_type)
3142                                         return null;
3143
3144                                 type = TypeManager.bool_type;
3145                                 eclass = ExprClass.Value;
3146                                 return this;
3147                         }
3148
3149                         public override void Emit (EmitContext ec)
3150                         {
3151                                 ILGenerator ig = ec.ig;
3152
3153                                 Label is_null_label = ig.DefineLabel ();
3154                                 Label end_label = ig.DefineLabel ();
3155
3156                                 unwrap.EmitCheck (ec);
3157                                 ig.Emit (OpCodes.Brfalse, is_null_label);
3158
3159                                 unwrap.Emit (ec);
3160                                 if (!IsTrue) {
3161                                         ig.Emit (OpCodes.Ldc_I4_0);
3162                                         ig.Emit (OpCodes.Ceq);
3163                                 }
3164                                 ig.Emit (OpCodes.Br, end_label);
3165
3166                                 ig.MarkLabel (is_null_label);
3167                                 ig.Emit (OpCodes.Ldc_I4_0);
3168
3169                                 ig.MarkLabel (end_label);
3170                         }
3171                 }
3172
3173                 public class NullCoalescingOperator : Expression
3174                 {
3175                         Expression left, right;
3176                         Expression expr;
3177                         Unwrap unwrap;
3178
3179                         public NullCoalescingOperator (Expression left, Expression right, Location loc)
3180                         {
3181                                 this.left = left;
3182                                 this.right = right;
3183                                 this.loc = loc;
3184
3185                                 eclass = ExprClass.Value;
3186                         }
3187
3188                         public override Expression DoResolve (EmitContext ec)
3189                         {
3190                                 if (type != null)
3191                                         return this;
3192
3193                                 left = left.Resolve (ec);
3194                                 if (left == null)
3195                                         return null;
3196
3197                                 right = right.Resolve (ec);
3198                                 if (right == null)
3199                                         return null;
3200
3201                                 Type ltype = left.Type, rtype = right.Type;
3202
3203                                 if (!TypeManager.IsNullableType (ltype) && ltype.IsValueType) {
3204                                         Binary.Error_OperatorCannotBeApplied (loc, "??", ltype, rtype);
3205                                         return null;
3206                                 }
3207
3208                                 if (TypeManager.IsNullableType (ltype)) {
3209                                         NullableInfo info = new NullableInfo (ltype);
3210
3211                                         unwrap = Unwrap.Create (left, ec);
3212                                         if (unwrap == null)
3213                                                 return null;
3214
3215                                         expr = Convert.ImplicitConversion (ec, right, info.UnderlyingType, loc);
3216                                         if (expr != null) {
3217                                                 left = unwrap;
3218                                                 type = expr.Type;
3219                                                 return this;
3220                                         }
3221                                 }
3222
3223                                 expr = Convert.ImplicitConversion (ec, right, ltype, loc);
3224                                 if (expr != null) {
3225                                         type = expr.Type;
3226                                         return this;
3227                                 }
3228
3229                                 Expression left_null = unwrap != null ? unwrap : left;
3230                                 expr = Convert.ImplicitConversion (ec, left_null, rtype, loc);
3231                                 if (expr != null) {
3232                                         left = expr;
3233                                         expr = right;
3234                                         type = rtype;
3235                                         return this;
3236                                 }
3237
3238                                 Binary.Error_OperatorCannotBeApplied (loc, "??", ltype, rtype);
3239                                 return null;
3240                         }
3241
3242                         public override void Emit (EmitContext ec)
3243                         {
3244                                 ILGenerator ig = ec.ig;
3245
3246                                 Label is_null_label = ig.DefineLabel ();
3247                                 Label end_label = ig.DefineLabel ();
3248
3249                                 if (unwrap != null) {
3250                                         unwrap.EmitCheck (ec);
3251                                         ig.Emit (OpCodes.Brfalse, is_null_label);
3252
3253                                         left.Emit (ec);
3254                                         ig.Emit (OpCodes.Br, end_label);
3255
3256                                         ig.MarkLabel (is_null_label);
3257                                         expr.Emit (ec);
3258
3259                                         ig.MarkLabel (end_label);
3260                                 } else {
3261                                         left.Emit (ec);
3262                                         ig.Emit (OpCodes.Dup);
3263                                         ig.Emit (OpCodes.Brtrue, end_label);
3264
3265                                         ig.MarkLabel (is_null_label);
3266
3267                                         ig.Emit (OpCodes.Pop);
3268                                         expr.Emit (ec);
3269
3270                                         ig.MarkLabel (end_label);
3271                                 }
3272                         }
3273                 }
3274
3275                 public class LiftedUnaryMutator : ExpressionStatement
3276                 {
3277                         public readonly UnaryMutator.Mode Mode;
3278                         Expression expr, null_value;
3279                         UnaryMutator underlying;
3280                         Unwrap unwrap;
3281
3282                         public LiftedUnaryMutator (UnaryMutator.Mode mode, Expression expr, Location loc)
3283                         {
3284                                 this.expr = expr;
3285                                 this.Mode = mode;
3286                                 this.loc = loc;
3287
3288                                 eclass = ExprClass.Value;
3289                         }
3290
3291                         public override Expression DoResolve (EmitContext ec)
3292                         {
3293                                 expr = expr.Resolve (ec);
3294                                 if (expr == null)
3295                                         return null;
3296
3297                                 unwrap = Unwrap.Create (expr, ec);
3298                                 if (unwrap == null)
3299                                         return null;
3300
3301                                 underlying = (UnaryMutator) new UnaryMutator (Mode, unwrap, loc).Resolve (ec);
3302                                 if (underlying == null)
3303                                         return null;
3304
3305                                 null_value = new NullableLiteral (expr.Type, loc).Resolve (ec);
3306                                 if (null_value == null)
3307                                         return null;
3308
3309                                 type = expr.Type;
3310                                 return this;
3311                         }
3312
3313                         void DoEmit (EmitContext ec, bool is_expr)
3314                         {
3315                                 ILGenerator ig = ec.ig;
3316                                 Label is_null_label = ig.DefineLabel ();
3317                                 Label end_label = ig.DefineLabel ();
3318
3319                                 unwrap.EmitCheck (ec);
3320                                 ig.Emit (OpCodes.Brfalse, is_null_label);
3321
3322                                 if (is_expr)
3323                                         underlying.Emit (ec);
3324                                 else
3325                                         underlying.EmitStatement (ec);
3326                                 ig.Emit (OpCodes.Br, end_label);
3327
3328                                 ig.MarkLabel (is_null_label);
3329                                 if (is_expr)
3330                                         null_value.Emit (ec);
3331
3332                                 ig.MarkLabel (end_label);
3333                         }
3334
3335                         public override void Emit (EmitContext ec)
3336                         {
3337                                 DoEmit (ec, true);
3338                         }
3339
3340                         public override void EmitStatement (EmitContext ec)
3341                         {
3342                                 DoEmit (ec, false);
3343                         }
3344                 }
3345         }
3346 }