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