mcs/mcs/convert.cs

   1 //
   2 // conversion.cs: various routines for implementing conversions.
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Ravi Pratap (ravi@ximian.com)
   7 //   Marek Safar (marek.safar@gmail.com)
   8 //
   9 // Copyright 2001, 2002, 2003 Ximian, Inc.
  10 // Copyright 2003-2008 Novell, Inc.
  11 // Copyright 2011 Xamarin Inc (http://www.xamarin.com)
  12 //
  13
  14 using System;
  15 using System.Collections.Generic;
  16
  17 #if STATIC
  18 using IKVM.Reflection.Emit;
  19 #else
  20 using System.Reflection.Emit;
  21 #endif
  22
  23 namespace Mono.CSharp {
  24
  25         //
  26         // A container class for all the conversion operations
  27         //
  28         static class Convert
  29         {
  30                 [Flags]
  31                 public enum UserConversionRestriction
  32                 {
  33                         None = 0,
  34                         ImplicitOnly = 1,
  35                         ProbingOnly = 1 << 1,
  36                         NullableSourceOnly = 1 << 2
  37
  38                 }
  39                 //
  40                 // From a one-dimensional array-type S[] to System.Collections.IList<T> and base
  41                 // interfaces of this interface, provided there is an implicit reference conversion
  42                 // from S to T.
  43                 //
  44                 static bool ArrayToIList (ArrayContainer array, TypeSpec list, bool isExplicit)
  45                 {
  46                         if (array.Rank != 1 || !list.IsArrayGenericInterface)
  47                                 return false;
  48
  49                         var arg_type = list.TypeArguments[0];
  50                         if (array.Element == arg_type)
  51                                 return true;
  52
  53                         //
  54                         // Reject conversion from T[] to IList<U> even if T has U dependency
  55                         //
  56                         if (arg_type.IsGenericParameter)
  57                                 return false;
  58
  59                         if (isExplicit)
  60                                 return ExplicitReferenceConversionExists (array.Element, arg_type);
  61
  62                         return ImplicitReferenceConversionExists (array.Element, arg_type);
  63                 }
  64
  65                 static bool IList_To_Array(TypeSpec list, ArrayContainer array)
  66                 {
  67                         if (array.Rank != 1 || !list.IsArrayGenericInterface)
  68                                 return false;
  69
  70                         var arg_type = list.TypeArguments[0];
  71                         if (array.Element == arg_type)
  72                                 return true;
  73
  74                         return ImplicitReferenceConversionExists (array.Element, arg_type) || ExplicitReferenceConversionExists (array.Element, arg_type);
  75                 }
  76
  77                 public static Expression ImplicitTypeParameterConversion (Expression expr, TypeParameterSpec expr_type, TypeSpec target_type)
  78                 {
  79                         //
  80                         // From T to a type parameter U, provided T depends on U
  81                         //
  82                         if (target_type.IsGenericParameter) {
  83                                 if (expr_type.TypeArguments != null && expr_type.HasDependencyOn (target_type)) {
  84                                         if (expr == null)
  85                                                 return EmptyExpression.Null;
  86
  87                                         if (expr_type.IsReferenceType && !((TypeParameterSpec) target_type).IsReferenceType)
  88                                                 return new BoxedCast (expr, target_type);
  89
  90                                         return new ClassCast (expr, target_type);
  91                                 }
  92
  93                                 return null;
  94                         }
  95
  96                         //
  97                         // LAMESPEC: From T to dynamic type because it's like T to object
  98                         //
  99                         if (target_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 100                                 if (expr == null)
 101                                         return EmptyExpression.Null;
 102
 103                                 if (expr_type.IsReferenceType)
 104                                         return new ClassCast (expr, target_type);
 105
 106                                 return new BoxedCast (expr, target_type);
 107                         }
 108
 109                         //
 110                         // From T to its effective base class C
 111                         // From T to any base class of C (it cannot contain dynamic or be of dynamic type)
 112                         // From T to any interface implemented by C
 113                         //
 114                         var base_type = expr_type.GetEffectiveBase ();
 115                         if (base_type == target_type || TypeSpec.IsBaseClass (base_type, target_type, false) || base_type.ImplementsInterface (target_type, true)) {
 116                                 if (expr == null)
 117                                         return EmptyExpression.Null;
 118
 119                                 if (expr_type.IsReferenceType)
 120                                         return new ClassCast (expr, target_type);
 121
 122                                 return new BoxedCast (expr, target_type);
 123                         }
 124
 125                         if (target_type.IsInterface && expr_type.IsConvertibleToInterface (target_type)) {
 126                                 if (expr == null)
 127                                         return EmptyExpression.Null;
 128
 129                                 if (expr_type.IsReferenceType)
 130                                         return new ClassCast (expr, target_type);
 131
 132                                 return new BoxedCast (expr, target_type);
 133                         }
 134
 135                         return null;
 136                 }
 137
 138                 static Expression ExplicitTypeParameterConversionFromT (Expression source, TypeSpec source_type, TypeSpec target_type)
 139                 {
 140                         var target_tp = target_type as TypeParameterSpec;
 141                         if (target_tp != null) {
 142                                 //
 143                                 // From a type parameter U to T, provided T depends on U
 144                                 //
 145                                 if (target_tp.TypeArguments != null && target_tp.HasDependencyOn (source_type)) {
 146                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
 147                                 }
 148                         }
 149
 150                         //
 151                         // From T to any interface-type I provided there is not already an implicit conversion from T to I
 152                         //
 153                         if (target_type.IsInterface)
 154                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type, true);
 155
 156                         return null;
 157                 }
 158
 159                 static Expression ExplicitTypeParameterConversionToT (Expression source, TypeSpec source_type, TypeParameterSpec target_type)
 160                 {
 161                         //
 162                         // From the effective base class C of T to T and from any base class of C to T
 163                         //
 164                         var effective = target_type.GetEffectiveBase ();
 165                         if (TypeSpecComparer.IsEqual (effective, source_type) || TypeSpec.IsBaseClass (effective, source_type, false))
 166                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
 167
 168                         return null;
 169                 }
 170
 171                 public static Expression ImplicitReferenceConversion (Expression expr, TypeSpec target_type, bool explicit_cast)
 172                 {
 173                         TypeSpec expr_type = expr.Type;
 174
 175                         if (expr_type.Kind == MemberKind.TypeParameter)
 176                                 return ImplicitTypeParameterConversion (expr, (TypeParameterSpec) expr.Type, target_type);
 177
 178                         //
 179                         // from the null type to any reference-type.
 180                         //
 181                         NullLiteral nl = expr as NullLiteral;
 182                         if (nl != null) {
 183                                 return nl.ConvertImplicitly (target_type);
 184                         }
 185
 186                         if (ImplicitReferenceConversionExists (expr_type, target_type)) {
 187                                 //
 188                                 // Avoid wrapping implicitly convertible reference type
 189                                 //
 190                                 if (!explicit_cast)
 191                                         return expr;
 192
 193                                 return EmptyCast.Create (expr, target_type);
 194                         }
 195
 196                         return null;
 197                 }
 198
 199                 //
 200                 // Implicit reference conversions
 201                 //
 202                 public static bool ImplicitReferenceConversionExists (TypeSpec expr_type, TypeSpec target_type)
 203                 {
 204                         return ImplicitReferenceConversionExists (expr_type, target_type, true);
 205                 }
 206
 207                 public static bool ImplicitReferenceConversionExists (TypeSpec expr_type, TypeSpec target_type, bool refOnlyTypeParameter)
 208                 {
 209                         // It's here only to speed things up
 210                         if (target_type.IsStruct)
 211                                 return false;
 212
 213                         switch (expr_type.Kind) {
 214                         case MemberKind.TypeParameter:
 215                                 return ImplicitTypeParameterConversion (null, (TypeParameterSpec) expr_type, target_type) != null &&
 216                                         (!refOnlyTypeParameter || TypeSpec.IsReferenceType (expr_type));
 217
 218                         case MemberKind.Class:
 219                                 //
 220                                 // From any class-type to dynamic (+object to speed up common path)
 221                                 //
 222                                 if (target_type.BuiltinType == BuiltinTypeSpec.Type.Object || target_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic)
 223                                         return true;
 224
 225                                 if (target_type.IsClass) {
 226                                         //
 227                                         // Identity conversion, including dynamic erasure
 228                                         //
 229                                         if (TypeSpecComparer.IsEqual (expr_type, target_type))
 230                                                 return true;
 231
 232                                         //
 233                                         // From any class-type S to any class-type T, provided S is derived from T
 234                                         //
 235                                         return TypeSpec.IsBaseClass (expr_type, target_type, true);
 236                                 }
 237
 238                                 //
 239                                 // From any class-type S to any interface-type T, provided S implements T
 240                                 //
 241                                 if (target_type.IsInterface)
 242                                         return expr_type.ImplementsInterface (target_type, true);
 243
 244                                 return false;
 245
 246                         case MemberKind.ArrayType:
 247                                 //
 248                                 // Identity array conversion
 249                                 //
 250                                 if (expr_type == target_type)
 251                                         return true;
 252
 253                                 //
 254                                 // From any array-type to System.Array
 255                                 //
 256                                 switch (target_type.BuiltinType) {
 257                                 case BuiltinTypeSpec.Type.Array:
 258                                 case BuiltinTypeSpec.Type.Object:
 259                                 case BuiltinTypeSpec.Type.Dynamic:
 260                                         return true;
 261                                 }
 262
 263                                 var expr_type_array = (ArrayContainer) expr_type;
 264                                 var target_type_array = target_type as ArrayContainer;
 265
 266                                 //
 267                                 // From an array-type S to an array-type of type T
 268                                 //
 269                                 if (target_type_array != null && expr_type_array.Rank == target_type_array.Rank) {
 270
 271                                         //
 272                                         // Both SE and TE are reference-types. TE check is defered
 273                                         // to ImplicitReferenceConversionExists
 274                                         //
 275                                         TypeSpec expr_element_type = expr_type_array.Element;
 276                                         if (!TypeSpec.IsReferenceType (expr_element_type))
 277                                                 return false;
 278
 279                                         //
 280                                         // An implicit reference conversion exists from SE to TE
 281                                         //
 282                                         return ImplicitReferenceConversionExists (expr_element_type, target_type_array.Element);
 283                                 }
 284
 285                                 //
 286                                 // From any array-type to the interfaces it implements
 287                                 //
 288                                 if (target_type.IsInterface) {
 289                                         if (expr_type.ImplementsInterface (target_type, false))
 290                                                 return true;
 291
 292                                         // from an array-type of type T to IList<T>
 293                                         if (ArrayToIList (expr_type_array, target_type, false))
 294                                                 return true;
 295                                 }
 296
 297                                 return false;
 298
 299                         case MemberKind.Delegate:
 300                                 //
 301                                 // From any delegate-type to System.Delegate (and its base types)
 302                                 //
 303                                 switch (target_type.BuiltinType) {
 304                                 case BuiltinTypeSpec.Type.Delegate:
 305                                 case BuiltinTypeSpec.Type.MulticastDelegate:
 306                                 case BuiltinTypeSpec.Type.Object:
 307                                 case BuiltinTypeSpec.Type.Dynamic:
 308                                         return true;
 309                                 }
 310
 311                                 //
 312                                 // Identity conversion, including dynamic erasure
 313                                 //
 314                                 if (TypeSpecComparer.IsEqual (expr_type, target_type))
 315                                         return true;
 316
 317                                 //
 318                                 // From any delegate-type to the interfaces it implements
 319                                 // From any reference-type to an delegate type if is variance-convertible
 320                                 //
 321                                 return expr_type.ImplementsInterface (target_type, false) || TypeSpecComparer.Variant.IsEqual (expr_type, target_type);
 322
 323                         case MemberKind.Interface:
 324                                 //
 325                                 // Identity conversion, including dynamic erasure
 326                                 //
 327                                 if (TypeSpecComparer.IsEqual (expr_type, target_type))
 328                                         return true;
 329
 330                                 //
 331                                 // From any interface type S to interface-type T
 332                                 // From any reference-type to an interface if is variance-convertible
 333                                 //
 334                                 if (target_type.IsInterface)
 335                                         return TypeSpecComparer.Variant.IsEqual (expr_type, target_type) || expr_type.ImplementsInterface (target_type, true);
 336
 337                                 return target_type.BuiltinType == BuiltinTypeSpec.Type.Object || target_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic;
 338
 339                         case MemberKind.InternalCompilerType:
 340                                 //
 341                                 // from the null literal to any reference-type.
 342                                 //
 343                                 if (expr_type == InternalType.NullLiteral) {
 344                                         // Exlude internal compiler types
 345                                         if (target_type.Kind == MemberKind.InternalCompilerType)
 346                                                 return target_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic;
 347
 348                                         return TypeSpec.IsReferenceType (target_type) || target_type.Kind == MemberKind.PointerType;
 349                                 }
 350
 351                                 //
 352                                 // Implicit dynamic conversion
 353                                 //
 354                                 if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 355                                         switch (target_type.Kind) {
 356                                         case MemberKind.ArrayType:
 357                                         case MemberKind.Class:
 358                                         case MemberKind.Delegate:
 359                                         case MemberKind.Interface:
 360                                         case MemberKind.TypeParameter:
 361                                                 return true;
 362                                         }
 363
 364                                         // dynamic to __arglist
 365                                         if (target_type == InternalType.Arglist)
 366                                                 return true;
 367
 368                                         return false;
 369                                 }
 370
 371                                 break;
 372                         }
 373
 374                         return false;
 375                 }
 376
 377                 public static Expression ImplicitBoxingConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
 378                 {
 379                         switch (target_type.BuiltinType) {
 380                         //
 381                         // From any non-nullable-value-type to the type object and dynamic
 382                         //
 383                         case BuiltinTypeSpec.Type.Object:
 384                         case BuiltinTypeSpec.Type.Dynamic:
 385                         //
 386                         // From any non-nullable-value-type to the type System.ValueType
 387                         //
 388                         case BuiltinTypeSpec.Type.ValueType:
 389                                 //
 390                                 // No ned to check for nullable type as underlying type is always convertible
 391                                 //
 392                                 if (!TypeSpec.IsValueType (expr_type))
 393                                         return null;
 394
 395                                 return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 396
 397                         case BuiltinTypeSpec.Type.Enum:
 398                                 //
 399                                 // From any enum-type to the type System.Enum.
 400                                 //
 401                                 if (expr_type.IsEnum)
 402                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 403
 404                                 break;
 405                         }
 406
 407                         //
 408                         // From a nullable-type to a reference type, if a boxing conversion exists from
 409                         // the underlying type to the reference type
 410                         //
 411                         if (expr_type.IsNullableType) {
 412                                 if (!TypeSpec.IsReferenceType (target_type))
 413                                         return null;
 414
 415                                 var res = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
 416
 417                                 // "cast" underlying type to target type to emit correct InvalidCastException when
 418                                 // underlying hierarchy changes without recompilation
 419                                 if (res != null && expr != null)
 420                                         res = new UnboxCast (res, target_type);
 421
 422                                 return res;
 423                         }
 424
 425                         //
 426                         // A value type has a boxing conversion to an interface type I if it has a boxing conversion
 427                         // to an interface or delegate type I0 and I0 is variance-convertible to I
 428                         //
 429                         if (target_type.IsInterface && TypeSpec.IsValueType (expr_type) && expr_type.ImplementsInterface (target_type, true)) {
 430                                 return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 431                         }
 432
 433                         return null;
 434                 }
 435
 436                 public static Expression ImplicitNulableConversion (ResolveContext ec, Expression expr, TypeSpec target_type)
 437                 {
 438                         TypeSpec expr_type = expr.Type;
 439
 440                         //
 441                         // From null to any nullable type
 442                         //
 443                         if (expr_type == InternalType.NullLiteral)
 444                                 return ec == null ? EmptyExpression.Null : Nullable.LiftedNull.Create (target_type, expr.Location);
 445
 446                         // S -> T?
 447                         TypeSpec t_el = Nullable.NullableInfo.GetUnderlyingType (target_type);
 448
 449                         // S? -> T?
 450                         if (expr_type.IsNullableType)
 451                                 expr_type = Nullable.NullableInfo.GetUnderlyingType (expr_type);
 452
 453                         //
 454                         // Predefined implicit identity or implicit numeric conversion
 455                         // has to exist between underlying type S and underlying type T
 456                         //
 457
 458                         // conversion exists only mode
 459                         if (ec == null) {
 460                                 if (TypeSpecComparer.IsEqual (expr_type, t_el))
 461                                         return EmptyExpression.Null;
 462
 463                                 if (expr is Constant)
 464                                         return ((Constant) expr).ConvertImplicitly (t_el);
 465
 466                                 return ImplicitNumericConversion (null, expr_type, t_el);
 467                         }
 468
 469                         Expression unwrap;
 470                         if (expr_type != expr.Type)
 471                                 unwrap = Nullable.Unwrap.Create (expr);
 472                         else
 473                                 unwrap = expr;
 474
 475                         Expression conv = unwrap;
 476                         if (!TypeSpecComparer.IsEqual (expr_type, t_el)) {
 477                                 if (conv is Constant)
 478                                         conv = ((Constant)conv).ConvertImplicitly (t_el);
 479                                 else
 480                                         conv = ImplicitNumericConversion (conv, expr_type, t_el);
 481
 482                                 if (conv == null)
 483                                         return null;
 484                         }
 485
 486                         if (expr_type != expr.Type)
 487                                 return new Nullable.LiftedConversion (conv, unwrap, target_type).Resolve (ec);
 488
 489                         return Nullable.Wrap.Create (conv, target_type);
 490                 }
 491
 492                 /// <summary>
 493                 ///   Implicit Numeric Conversions.
 494                 ///
 495                 ///   expr is the expression to convert, returns a new expression of type
 496                 ///   target_type or null if an implicit conversion is not possible.
 497                 /// </summary>
 498                 public static Expression ImplicitNumericConversion (Expression expr, TypeSpec target_type)
 499                 {
 500                         return ImplicitNumericConversion (expr, expr.Type, target_type);
 501                 }
 502
 503                 public static bool ImplicitNumericConversionExists (TypeSpec expr_type, TypeSpec target_type)
 504                 {
 505                         return ImplicitNumericConversion (null, expr_type, target_type) != null;
 506                 }
 507
 508                 static Expression ImplicitNumericConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
 509                 {
 510                         switch (expr_type.BuiltinType) {
 511                         case BuiltinTypeSpec.Type.SByte:
 512                                 //
 513                                 // From sbyte to short, int, long, float, double, decimal
 514                                 //
 515                                 switch (target_type.BuiltinType) {
 516                                 case BuiltinTypeSpec.Type.Int:
 517                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 518                                 case BuiltinTypeSpec.Type.Long:
 519                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 520                                 case BuiltinTypeSpec.Type.Double:
 521                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 522                                 case BuiltinTypeSpec.Type.Float:
 523                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 524                                 case BuiltinTypeSpec.Type.Short:
 525                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 526                                 case BuiltinTypeSpec.Type.Decimal:
 527                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 528
 529                                 }
 530
 531                                 break;
 532                         case BuiltinTypeSpec.Type.Byte:
 533                                 //
 534                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 535                                 //
 536                                 switch (target_type.BuiltinType) {
 537                                 case BuiltinTypeSpec.Type.Int:
 538                                 case BuiltinTypeSpec.Type.UInt:
 539                                 case BuiltinTypeSpec.Type.Short:
 540                                 case BuiltinTypeSpec.Type.UShort:
 541                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 542                                 case BuiltinTypeSpec.Type.ULong:
 543                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 544                                 case BuiltinTypeSpec.Type.Long:
 545                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 546                                 case BuiltinTypeSpec.Type.Float:
 547                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 548                                 case BuiltinTypeSpec.Type.Double:
 549                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 550                                 case BuiltinTypeSpec.Type.Decimal:
 551                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 552                                 }
 553                                 break;
 554                         case BuiltinTypeSpec.Type.Short:
 555                                 //
 556                                 // From short to int, long, float, double, decimal
 557                                 //
 558                                 switch (target_type.BuiltinType) {
 559                                 case BuiltinTypeSpec.Type.Int:
 560                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 561                                 case BuiltinTypeSpec.Type.Long:
 562                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 563                                 case BuiltinTypeSpec.Type.Double:
 564                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 565                                 case BuiltinTypeSpec.Type.Float:
 566                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 567                                 case BuiltinTypeSpec.Type.Decimal:
 568                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 569                                 }
 570                                 break;
 571                         case BuiltinTypeSpec.Type.UShort:
 572                                 //
 573                                 // From ushort to int, uint, long, ulong, float, double, decimal
 574                                 //
 575                                 switch (target_type.BuiltinType) {
 576                                 case BuiltinTypeSpec.Type.Int:
 577                                 case BuiltinTypeSpec.Type.UInt:
 578                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 579                                 case BuiltinTypeSpec.Type.ULong:
 580                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 581                                 case BuiltinTypeSpec.Type.Long:
 582                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 583                                 case BuiltinTypeSpec.Type.Double:
 584                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 585                                 case BuiltinTypeSpec.Type.Float:
 586                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 587                                 case BuiltinTypeSpec.Type.Decimal:
 588                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 589                                 }
 590                                 break;
 591                         case BuiltinTypeSpec.Type.Int:
 592                                 //
 593                                 // From int to long, float, double, decimal
 594                                 //
 595                                 switch (target_type.BuiltinType) {
 596                                 case BuiltinTypeSpec.Type.Long:
 597                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 598                                 case BuiltinTypeSpec.Type.Double:
 599                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 600                                 case BuiltinTypeSpec.Type.Float:
 601                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 602                                 case BuiltinTypeSpec.Type.Decimal:
 603                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 604                                 }
 605                                 break;
 606                         case BuiltinTypeSpec.Type.UInt:
 607                                 //
 608                                 // From uint to long, ulong, float, double, decimal
 609                                 //
 610                                 switch (target_type.BuiltinType) {
 611                                 case BuiltinTypeSpec.Type.Long:
 612                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 613                                 case BuiltinTypeSpec.Type.ULong:
 614                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 615                                 case BuiltinTypeSpec.Type.Double:
 616                                         return expr == null ? EmptyExpression.Null : new OpcodeCastDuplex (expr, target_type, OpCodes.Conv_R_Un, OpCodes.Conv_R8);
 617                                 case BuiltinTypeSpec.Type.Float:
 618                                         return expr == null ? EmptyExpression.Null : new OpcodeCastDuplex (expr, target_type, OpCodes.Conv_R_Un, OpCodes.Conv_R4);
 619                                 case BuiltinTypeSpec.Type.Decimal:
 620                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 621                                 }
 622                                 break;
 623                         case BuiltinTypeSpec.Type.Long:
 624                                 //
 625                                 // From long to float, double, decimal
 626                                 //
 627                                 switch (target_type.BuiltinType) {
 628                                 case BuiltinTypeSpec.Type.Double:
 629                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 630                                 case BuiltinTypeSpec.Type.Float:
 631                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 632                                 case BuiltinTypeSpec.Type.Decimal:
 633                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 634                                 }
 635                                 break;
 636                         case BuiltinTypeSpec.Type.ULong:
 637                                 //
 638                                 // From ulong to float, double, decimal
 639                                 //
 640                                 switch (target_type.BuiltinType) {
 641                                 case BuiltinTypeSpec.Type.Double:
 642                                         return expr == null ? EmptyExpression.Null : new OpcodeCastDuplex (expr, target_type, OpCodes.Conv_R_Un, OpCodes.Conv_R8);
 643                                 case BuiltinTypeSpec.Type.Float:
 644                                         return expr == null ? EmptyExpression.Null : new OpcodeCastDuplex (expr, target_type, OpCodes.Conv_R_Un, OpCodes.Conv_R4);
 645                                 case BuiltinTypeSpec.Type.Decimal:
 646                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 647                                 }
 648                                 break;
 649                         case BuiltinTypeSpec.Type.Char:
 650                                 //
 651                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 652                                 //
 653                                 switch (target_type.BuiltinType) {
 654                                 case BuiltinTypeSpec.Type.UShort:
 655                                 case BuiltinTypeSpec.Type.Int:
 656                                 case BuiltinTypeSpec.Type.UInt:
 657                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 658                                 case BuiltinTypeSpec.Type.ULong:
 659                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 660                                 case BuiltinTypeSpec.Type.Long:
 661                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 662                                 case BuiltinTypeSpec.Type.Float:
 663                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 664                                 case BuiltinTypeSpec.Type.Double:
 665                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 666                                 case BuiltinTypeSpec.Type.Decimal:
 667                                         return expr == null ? EmptyExpression.Null : new OperatorCast (expr, target_type);
 668                                 }
 669                                 break;
 670                         case BuiltinTypeSpec.Type.Float:
 671                                 //
 672                                 // float to double
 673                                 //
 674                                 if (target_type.BuiltinType == BuiltinTypeSpec.Type.Double)
 675                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 676                                 break;
 677                         }
 678
 679                         return null;
 680                 }
 681
 682                 //
 683                 // Full version of implicit conversion
 684                 //
 685                 public static bool ImplicitConversionExists (ResolveContext ec, Expression expr, TypeSpec target_type)
 686                 {
 687                         if (ImplicitStandardConversionExists (ec, expr, target_type))
 688                                 return true;
 689
 690                         if (expr.Type == InternalType.AnonymousMethod) {
 691                                 if (!target_type.IsDelegate && !target_type.IsExpressionTreeType)
 692                                         return false;
 693
 694                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 695                                 return ame.ImplicitStandardConversionExists (ec, target_type);
 696                         }
 697
 698                         // Conversion from __arglist to System.ArgIterator
 699                         if (expr.Type == InternalType.Arglist)
 700                                 return target_type == ec.Module.PredefinedTypes.ArgIterator.TypeSpec;
 701
 702                         return UserDefinedConversion (ec, expr, target_type,
 703                                 UserConversionRestriction.ImplicitOnly | UserConversionRestriction.ProbingOnly, Location.Null) != null;
 704                 }
 705
 706                 public static bool ImplicitStandardConversionExists (ResolveContext rc, Expression expr, TypeSpec target_type)
 707                 {
 708                         if (expr.eclass == ExprClass.MethodGroup) {
 709                                 if (target_type.IsDelegate && rc.Module.Compiler.Settings.Version != LanguageVersion.ISO_1) {
 710                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 711                                         if (mg != null)
 712                                                 return DelegateCreation.ImplicitStandardConversionExists (rc, mg, target_type);
 713                                 }
 714
 715                                 return false;
 716                         }
 717
 718                         return ImplicitStandardConversionExists (expr, target_type);
 719                 }
 720
 721                 //
 722                 // Implicit standard conversion (only core conversions are used here)
 723                 //
 724                 public static bool ImplicitStandardConversionExists (Expression expr, TypeSpec target_type)
 725                 {
 726                         //
 727                         // Identity conversions
 728                         // Implicit numeric conversions
 729                         // Implicit nullable conversions
 730                         // Implicit reference conversions
 731                         // Boxing conversions
 732                         // Implicit constant expression conversions
 733                         // Implicit conversions involving type parameters
 734                         //
 735
 736                         TypeSpec expr_type = expr.Type;
 737
 738                         if (expr_type == target_type)
 739                                 return true;
 740
 741                         if (target_type.IsNullableType)
 742                                 return ImplicitNulableConversion (null, expr, target_type) != null;
 743
 744                         if (ImplicitNumericConversion (null, expr_type, target_type) != null)
 745                                 return true;
 746
 747                         if (ImplicitReferenceConversionExists (expr_type, target_type, false))
 748                                 return true;
 749
 750                         if (ImplicitBoxingConversion (null, expr_type, target_type) != null)
 751                                 return true;
 752
 753                         //
 754                         // Implicit Constant Expression Conversions
 755                         //
 756                         if (expr is IntConstant){
 757                                 int value = ((IntConstant) expr).Value;
 758                                 switch (target_type.BuiltinType) {
 759                                 case BuiltinTypeSpec.Type.SByte:
 760                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 761                                                 return true;
 762                                         break;
 763                                 case BuiltinTypeSpec.Type.Byte:
 764                                         if (value >= 0 && value <= Byte.MaxValue)
 765                                                 return true;
 766                                         break;
 767                                 case BuiltinTypeSpec.Type.Short:
 768                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 769                                                 return true;
 770                                         break;
 771                                 case BuiltinTypeSpec.Type.UShort:
 772                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 773                                                 return true;
 774                                         break;
 775                                 case BuiltinTypeSpec.Type.UInt:
 776                                         if (value >= 0)
 777                                                 return true;
 778                                         break;
 779                                 case BuiltinTypeSpec.Type.ULong:
 780                                          //
 781                                          // we can optimize this case: a positive int32
 782                                          // always fits on a uint64.  But we need an opcode
 783                                          // to do it.
 784                                          //
 785                                         if (value >= 0)
 786                                                 return true;
 787
 788                                         break;
 789                                 }
 790                         }
 791
 792                         if (expr is LongConstant && target_type.BuiltinType == BuiltinTypeSpec.Type.ULong){
 793                                 //
 794                                 // Try the implicit constant expression conversion
 795                                 // from long to ulong, instead of a nice routine,
 796                                 // we just inline it
 797                                 //
 798                                 long v = ((LongConstant) expr).Value;
 799                                 if (v >= 0)
 800                                         return true;
 801                         }
 802
 803                         if (expr is IntegralConstant && target_type.IsEnum) {
 804                                 var i = (IntegralConstant) expr;
 805                                 //
 806                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
 807                                 //
 808                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
 809                                 // to be converted to any enum-type and to any nullable-type whose underlying
 810                                 // type is an enum-type
 811                                 //
 812                                 return i.IsZeroInteger;
 813                         }
 814
 815                         //
 816                         // Implicit dynamic conversion for remaining value types. It should probably
 817                         // go somewhere else
 818                         //
 819                         if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 820                                 switch (target_type.Kind) {
 821                                 case MemberKind.Struct:
 822                                 case MemberKind.Enum:
 823                                         return true;
 824                                 }
 825
 826                                 return false;
 827                         }
 828
 829                         //
 830                         // In an unsafe context implicit conversions is extended to include
 831                         //
 832                         // From any pointer-type to the type void*
 833                         // From the null literal to any pointer-type.
 834                         //
 835                         // LAMESPEC: The specification claims this conversion is allowed in implicit conversion but
 836                         // in reality implicit standard conversion uses it
 837                         //
 838                         if (target_type.IsPointer && expr.Type.IsPointer && ((PointerContainer) target_type).Element.Kind == MemberKind.Void)
 839                                 return true;
 840
 841                         //
 842                         // Struct identity conversion, including dynamic erasure
 843                         //
 844                         if (expr_type.IsStruct && TypeSpecComparer.IsEqual (expr_type, target_type))
 845                                 return true;
 846
 847                         return false;
 848                 }
 849
 850                 /// <summary>
 851                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 852                 ///  amongst the methods in the MethodGroupExpr
 853                 /// </summary>
 854                 public static TypeSpec FindMostEncompassedType (IList<TypeSpec> types)
 855                 {
 856                         TypeSpec best = null;
 857                         EmptyExpression expr;
 858
 859                         foreach (TypeSpec t in types) {
 860                                 if (best == null) {
 861                                         best = t;
 862                                         continue;
 863                                 }
 864
 865                                 expr = new EmptyExpression (t);
 866                                 if (ImplicitStandardConversionExists (expr, best))
 867                                         best = t;
 868                         }
 869
 870                         expr = new EmptyExpression (best);
 871                         foreach (TypeSpec t in types) {
 872                                 if (best == t)
 873                                         continue;
 874                                 if (!ImplicitStandardConversionExists (expr, t)) {
 875                                         best = null;
 876                                         break;
 877                                 }
 878                         }
 879
 880                         return best;
 881                 }
 882
 883                 //
 884                 // Finds the most encompassing type (type into which all other
 885                 // types can convert to) amongst the types in the given set
 886                 //
 887                 static TypeSpec FindMostEncompassingType (IList<TypeSpec> types)
 888                 {
 889                         if (types.Count == 0)
 890                                 return null;
 891
 892                         if (types.Count == 1)
 893                                 return types [0];
 894
 895                         TypeSpec best = null;
 896                         for (int i = 0; i < types.Count; ++i) {
 897                                 int ii = 0;
 898                                 for (; ii < types.Count; ++ii) {
 899                                         if (ii == i)
 900                                                 continue;
 901
 902                                         var expr = new EmptyExpression (types[ii]);
 903                                         if (!ImplicitStandardConversionExists (expr, types [i])) {
 904                                                 ii = 0;
 905                                                 break;
 906                                         }
 907                                 }
 908
 909                                 if (ii == 0)
 910                                         continue;
 911
 912                                 if (best == null) {
 913                                         best = types[i];
 914                                         continue;
 915                                 }
 916
 917                                 // Indicates multiple best types
 918                                 return InternalType.FakeInternalType;
 919                         }
 920
 921                         return best;
 922                 }
 923
 924                 //
 925                 // Finds the most specific source Sx according to the rules of the spec (13.4.4)
 926                 // by making use of FindMostEncomp* methods. Applies the correct rules separately
 927                 // for explicit and implicit conversion operators.
 928                 //
 929                 static TypeSpec FindMostSpecificSource (ResolveContext rc, List<MethodSpec> list, TypeSpec sourceType, Expression source, bool apply_explicit_conv_rules)
 930                 {
 931                         TypeSpec[] src_types_set = null;
 932
 933                         //
 934                         // Try exact match first, if any operator converts from S then Sx = S
 935                         //
 936                         for (int i = 0; i < list.Count; ++i) {
 937                                 TypeSpec param_type = list [i].Parameters.Types [0];
 938
 939                                 if (param_type == sourceType)
 940                                         return param_type;
 941
 942                                 if (src_types_set == null)
 943                                         src_types_set = new TypeSpec [list.Count];
 944
 945                                 src_types_set [i] = param_type;
 946                         }
 947
 948                         //
 949                         // Explicit Conv rules
 950                         //
 951                         if (apply_explicit_conv_rules) {
 952                                 var candidate_set = new List<TypeSpec> ();
 953
 954                                 foreach (TypeSpec param_type in src_types_set){
 955                                         if (ImplicitStandardConversionExists (rc, source, param_type))
 956                                                 candidate_set.Add (param_type);
 957                                 }
 958
 959                                 if (candidate_set.Count != 0) {
 960                                         if (source.eclass == ExprClass.MethodGroup)
 961                                                 return InternalType.FakeInternalType;
 962
 963                                         return FindMostEncompassedType (candidate_set);
 964                                 }
 965                         }
 966
 967                         //
 968                         // Final case
 969                         //
 970                         if (apply_explicit_conv_rules)
 971                                 return FindMostEncompassingType (src_types_set);
 972                         else
 973                                 return FindMostEncompassedType (src_types_set);
 974                 }
 975
 976                 /// <summary>
 977                 ///  Finds the most specific target Tx according to section 13.4.4
 978                 /// </summary>
 979                 static public TypeSpec FindMostSpecificTarget (IList<MethodSpec> list,
 980                                                            TypeSpec target, bool apply_explicit_conv_rules)
 981                 {
 982                         List<TypeSpec> tgt_types_set = null;
 983
 984                         //
 985                         // If any operator converts to T then Tx = T
 986                         //
 987                         foreach (var mi in list){
 988                                 TypeSpec ret_type = mi.ReturnType;
 989                                 if (ret_type == target)
 990                                         return ret_type;
 991
 992                                 if (tgt_types_set == null) {
 993                                         tgt_types_set = new List<TypeSpec> (list.Count);
 994                                 } else if (tgt_types_set.Contains (ret_type)) {
 995                                         continue;
 996                                 }
 997
 998                                 tgt_types_set.Add (ret_type);
 999                         }
1000
1001                         //
1002                         // Explicit conv rules
1003                         //
1004                         if (apply_explicit_conv_rules) {
1005                                 var candidate_set = new List<TypeSpec> ();
1006
1007                                 foreach (TypeSpec ret_type in tgt_types_set) {
1008                                         var expr = new EmptyExpression (ret_type);
1009
1010                                         if (ImplicitStandardConversionExists (expr, target))
1011                                                 candidate_set.Add (ret_type);
1012                                 }
1013
1014                                 if (candidate_set.Count != 0)
1015                                         return FindMostEncompassingType (candidate_set);
1016                         }
1017
1018                         //
1019                         // Okay, final case !
1020                         //
1021                         if (apply_explicit_conv_rules)
1022                                 return FindMostEncompassedType (tgt_types_set);
1023                         else
1024                                 return FindMostEncompassingType (tgt_types_set);
1025                 }
1026
1027                 /// <summary>
1028                 ///  User-defined Implicit conversions
1029                 /// </summary>
1030                 static public Expression ImplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
1031                 {
1032                         return UserDefinedConversion (ec, source, target, UserConversionRestriction.ImplicitOnly, loc);
1033                 }
1034
1035                 /// <summary>
1036                 ///  User-defined Explicit conversions
1037                 /// </summary>
1038                 static Expression ExplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
1039                 {
1040                         return UserDefinedConversion (ec, source, target, 0, loc);
1041                 }
1042
1043                 static void FindApplicableUserDefinedConversionOperators (ResolveContext rc, IList<MemberSpec> operators, Expression source, TypeSpec target, UserConversionRestriction restr, ref List<MethodSpec> candidates)
1044                 {
1045                         if (source.Type.IsInterface) {
1046                                 // Neither A nor B are interface-types
1047                                 return;
1048                         }
1049
1050                         // For a conversion operator to be applicable, it must be possible
1051                         // to perform a standard conversion from the source type to
1052                         // the operand type of the operator, and it must be possible
1053                         // to perform a standard conversion from the result type of
1054                         // the operator to the target type.
1055
1056                         Expression texpr = null;
1057
1058                         foreach (MethodSpec op in operators) {
1059
1060                                 // Can be null because MemberCache.GetUserOperator does not resize the array
1061                                 if (op == null)
1062                                         continue;
1063
1064                                 var t = op.Parameters.Types[0];
1065                                 if (source.Type != t && !ImplicitStandardConversionExists (rc, source, t)) {
1066                                         if ((restr & UserConversionRestriction.ImplicitOnly) != 0)
1067                                                 continue;
1068
1069                                         if (!ImplicitStandardConversionExists (new EmptyExpression (t), source.Type))
1070                                                         continue;
1071                                 }
1072
1073                                 if ((restr & UserConversionRestriction.NullableSourceOnly) != 0 && !t.IsNullableType)
1074                                         continue;
1075
1076                                 t = op.ReturnType;
1077
1078                                 if (t.IsInterface)
1079                                         continue;
1080
1081                                 if (target != t) {
1082                                         if (t.IsNullableType)
1083                                                 t = Nullable.NullableInfo.GetUnderlyingType (t);
1084
1085                                         if (!ImplicitStandardConversionExists (new EmptyExpression (t), target)) {
1086                                                 if ((restr & UserConversionRestriction.ImplicitOnly) != 0)
1087                                                         continue;
1088
1089                                                 if (texpr == null)
1090                                                         texpr = new EmptyExpression (target);
1091
1092                                                 if (!ImplicitStandardConversionExists (texpr, t))
1093                                                         continue;
1094                                         }
1095                                 }
1096
1097                                 if (candidates == null)
1098                                         candidates = new List<MethodSpec> ();
1099
1100                                 candidates.Add (op);
1101                         }
1102                 }
1103
1104                 //
1105                 // User-defined conversions
1106                 //
1107                 public static Expression UserDefinedConversion (ResolveContext rc, Expression source, TypeSpec target, UserConversionRestriction restr, Location loc)
1108                 {
1109                         List<MethodSpec> candidates = null;
1110
1111                         //
1112                         // If S or T are nullable types, source_type and target_type are their underlying types
1113                         // otherwise source_type and target_type are equal to S and T respectively.
1114                         //
1115                         TypeSpec source_type = source.Type;
1116                         TypeSpec target_type = target;
1117                         Expression source_type_expr;
1118                         bool nullable_source = false;
1119                         var implicitOnly = (restr & UserConversionRestriction.ImplicitOnly) != 0;
1120
1121                         if (source_type.IsNullableType) {
1122                                 // No unwrapping conversion S? -> T for non-reference types
1123                                 if (implicitOnly && !TypeSpec.IsReferenceType (target_type) && !target_type.IsNullableType) {
1124                                         source_type_expr = source;
1125                                 } else {
1126                                         source_type_expr = Nullable.Unwrap.CreateUnwrapped (source);
1127                                         source_type = source_type_expr.Type;
1128                                         nullable_source = true;
1129                                 }
1130                         } else {
1131                                 source_type_expr = source;
1132                         }
1133
1134                         if (target_type.IsNullableType)
1135                                 target_type = Nullable.NullableInfo.GetUnderlyingType (target_type);
1136
1137                         // Only these containers can contain a user defined implicit or explicit operators
1138                         const MemberKind user_conversion_kinds = MemberKind.Class | MemberKind.Struct | MemberKind.TypeParameter;
1139
1140                         if ((source_type.Kind & user_conversion_kinds) != 0 && source_type.BuiltinType != BuiltinTypeSpec.Type.Decimal) {
1141                                 bool declared_only = source_type.IsStruct;
1142
1143                                 var operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Implicit, declared_only);
1144                                 if (operators != null) {
1145                                         FindApplicableUserDefinedConversionOperators (rc, operators, source_type_expr, target_type, restr, ref candidates);
1146                                 }
1147
1148                                 if (!implicitOnly) {
1149                                         operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Explicit, declared_only);
1150                                         if (operators != null) {
1151                                                 FindApplicableUserDefinedConversionOperators (rc, operators, source_type_expr, target_type, restr, ref candidates);
1152                                         }
1153                                 }
1154                         }
1155
1156                         if ((target.Kind & user_conversion_kinds) != 0 && target_type.BuiltinType != BuiltinTypeSpec.Type.Decimal) {
1157                                 bool declared_only = target.IsStruct || implicitOnly;
1158
1159                                 var operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Implicit, declared_only);
1160                                 if (operators != null) {
1161                                         FindApplicableUserDefinedConversionOperators (rc, operators, source_type_expr, target_type, restr, ref candidates);
1162                                 }
1163
1164                                 if (!implicitOnly) {
1165                                         operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Explicit, declared_only);
1166                                         if (operators != null) {
1167                                                 FindApplicableUserDefinedConversionOperators (rc, operators, source_type_expr, target_type, restr, ref candidates);
1168                                         }
1169                                 }
1170                         }
1171
1172                         if (candidates == null)
1173                                 return null;
1174
1175                         //
1176                         // Find the most specific conversion operator
1177                         //
1178                         MethodSpec most_specific_operator;
1179                         TypeSpec s_x, t_x;
1180                         if (candidates.Count == 1) {
1181                                 most_specific_operator = candidates[0];
1182                                 s_x = most_specific_operator.Parameters.Types[0];
1183                                 t_x = most_specific_operator.ReturnType;
1184                         } else {
1185                                 //
1186                                 // Pass original source type to find the best match against input type and
1187                                 // not the unwrapped expression
1188                                 //
1189                                 s_x = FindMostSpecificSource (rc, candidates, source.Type, source_type_expr, !implicitOnly);
1190                                 if (s_x == null)
1191                                         return null;
1192
1193                                 t_x = FindMostSpecificTarget (candidates, target, !implicitOnly);
1194                                 if (t_x == null)
1195                                         return null;
1196
1197                                 most_specific_operator = null;
1198                                 for (int i = 0; i < candidates.Count; ++i) {
1199                                         if (candidates[i].ReturnType == t_x && candidates[i].Parameters.Types[0] == s_x) {
1200                                                 most_specific_operator = candidates[i];
1201                                                 break;
1202                                         }
1203                                 }
1204
1205                                 if (most_specific_operator == null) {
1206                                         //
1207                                         // Unless running in probing more
1208                                         //
1209                                         if ((restr & UserConversionRestriction.ProbingOnly) == 0) {
1210                                                 MethodSpec ambig_arg = candidates [0];
1211                                                 most_specific_operator = candidates [1];
1212                                                 /*
1213                                                 foreach (var candidate in candidates) {
1214                                                         if (candidate.ReturnType == t_x)
1215                                                                 most_specific_operator = candidate;
1216                                                         else if (candidate.Parameters.Types[0] == s_x)
1217                                                                 ambig_arg = candidate;
1218                                                 }
1219                                                 */
1220                                                 rc.Report.Error (457, loc,
1221                                                         "Ambiguous user defined operators `{0}' and `{1}' when converting from `{2}' to `{3}'",
1222                                                         ambig_arg.GetSignatureForError (), most_specific_operator.GetSignatureForError (),
1223                                                         source.Type.GetSignatureForError (), target.GetSignatureForError ());
1224                                         }
1225
1226                                         return ErrorExpression.Instance;
1227                                 }
1228                         }
1229
1230                         //
1231                         // Convert input type when it's different to best operator argument
1232                         //
1233                         if (s_x != source_type) {
1234                                 var c = source as Constant;
1235                                 if (c != null) {
1236                                         source = c.Reduce (rc, s_x);
1237                                         if (source == null)
1238                                                 c = null;
1239                                 }
1240
1241                                 if (c == null) {
1242                                         source = implicitOnly ?
1243                                                 ImplicitConversionStandard (rc, source_type_expr, s_x, loc) :
1244                                                 ExplicitConversionStandard (rc, source_type_expr, s_x, loc);
1245                                 }
1246                         } else {
1247                                 source = source_type_expr;
1248                         }
1249
1250                         source = new UserCast (most_specific_operator, source, loc).Resolve (rc);
1251
1252                         //
1253                         // Convert result type when it's different to best operator return type
1254                         //
1255                         if (t_x != target_type) {
1256                                 //
1257                                 // User operator is of T?
1258                                 //
1259                                 if (t_x.IsNullableType && (target.IsNullableType || !implicitOnly)) {
1260                                         //
1261                                         // User operator return type does not match target type we need
1262                                         // yet another conversion. This should happen for promoted numeric
1263                                         // types only
1264                                         //
1265                                         if (t_x != target) {
1266                                                 var unwrap = Nullable.Unwrap.CreateUnwrapped (source);
1267
1268                                                 source = implicitOnly ?
1269                                                         ImplicitConversionStandard (rc, unwrap, target_type, loc) :
1270                                                         ExplicitConversionStandard (rc, unwrap, target_type, loc);
1271
1272                                                 if (source == null)
1273                                                         return null;
1274
1275                                                 if (target.IsNullableType)
1276                                                         source = new Nullable.LiftedConversion (source, unwrap, target).Resolve (rc);
1277                                         }
1278                                 } else {
1279                                         source = implicitOnly ?
1280                                                 ImplicitConversionStandard (rc, source, target_type, loc) :
1281                                                 ExplicitConversionStandard (rc, source, target_type, loc);
1282
1283                                         if (source == null)
1284                                                 return null;
1285                                 }
1286                         }
1287
1288
1289                         //
1290                         // Source expression is of nullable type and underlying conversion returns
1291                         // only non-nullable type we need to lift it manually
1292                         //
1293                         if (nullable_source && !s_x.IsNullableType)
1294                                 return new Nullable.LiftedConversion (source, source_type_expr, target).Resolve (rc);
1295
1296                         //
1297                         // Target is of nullable type but source type is not, wrap the result expression
1298                         //
1299                         if (target.IsNullableType && !t_x.IsNullableType)
1300                                 source = Nullable.Wrap.Create (source, target);
1301
1302                         return source;
1303                 }
1304
1305                 /// <summary>
1306                 ///   Converts implicitly the resolved expression `expr' into the
1307                 ///   `target_type'.  It returns a new expression that can be used
1308                 ///   in a context that expects a `target_type'.
1309                 /// </summary>
1310                 static public Expression ImplicitConversion (ResolveContext ec, Expression expr,
1311                                                              TypeSpec target_type, Location loc)
1312                 {
1313                         Expression e;
1314
1315                         if (target_type == null)
1316                                 throw new Exception ("Target type is null");
1317
1318                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1319                         if (e != null)
1320                                 return e;
1321
1322                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1323                         if (e != null)
1324                                 return e;
1325
1326                         return null;
1327                 }
1328
1329
1330                 /// <summary>
1331                 ///   Attempts to apply the `Standard Implicit
1332                 ///   Conversion' rules to the expression `expr' into
1333                 ///   the `target_type'.  It returns a new expression
1334                 ///   that can be used in a context that expects a
1335                 ///   `target_type'.
1336                 ///
1337                 ///   This is different from `ImplicitConversion' in that the
1338                 ///   user defined implicit conversions are excluded.
1339                 /// </summary>
1340                 static public Expression ImplicitConversionStandard (ResolveContext ec, Expression expr,
1341                                                                      TypeSpec target_type, Location loc)
1342                 {
1343                         return ImplicitConversionStandard (ec, expr, target_type, loc, false);
1344                 }
1345
1346                 static Expression ImplicitConversionStandard (ResolveContext ec, Expression expr, TypeSpec target_type, Location loc, bool explicit_cast)
1347                 {
1348                         if (expr.eclass == ExprClass.MethodGroup){
1349                                 if (!target_type.IsDelegate){
1350                                         return null;
1351                                 }
1352
1353                                 //
1354                                 // Only allow anonymous method conversions on post ISO_1
1355                                 //
1356                                 if (ec.Module.Compiler.Settings.Version != LanguageVersion.ISO_1){
1357                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1358                                         if (mg != null)
1359                                                 return new ImplicitDelegateCreation (target_type, mg, loc).Resolve (ec);
1360                                 }
1361                         }
1362
1363                         TypeSpec expr_type = expr.Type;
1364                         Expression e;
1365
1366                         if (expr_type == target_type) {
1367                                 if (expr_type != InternalType.NullLiteral && expr_type != InternalType.AnonymousMethod)
1368                                         return expr;
1369                                 return null;
1370                         }
1371
1372                         if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
1373                                 switch (target_type.Kind) {
1374                                 case MemberKind.ArrayType:
1375                                 case MemberKind.Class:
1376                                         if (target_type.BuiltinType == BuiltinTypeSpec.Type.Object)
1377                                                 return EmptyCast.Create (expr, target_type);
1378
1379                                         goto case MemberKind.Struct;
1380                                 case MemberKind.Struct:
1381                                 case MemberKind.Delegate:
1382                                 case MemberKind.Enum:
1383                                 case MemberKind.Interface:
1384                                 case MemberKind.TypeParameter:
1385                                         Arguments args = new Arguments (1);
1386                                         args.Add (new Argument (expr));
1387                                         return new DynamicConversion (target_type, explicit_cast ? CSharpBinderFlags.ConvertExplicit : 0, args, loc).Resolve (ec);
1388                                 }
1389
1390                                 return null;
1391                         }
1392
1393                         if (target_type.IsNullableType)
1394                                 return ImplicitNulableConversion (ec, expr, target_type);
1395
1396                         //
1397                         // Attempt to do the implicit constant expression conversions
1398                         //
1399                         Constant c = expr as Constant;
1400                         if (c != null) {
1401                                 try {
1402                                         c = c.ConvertImplicitly (target_type);
1403                                 } catch {
1404                                         throw new InternalErrorException ("Conversion error", loc);
1405                                 }
1406                                 if (c != null)
1407                                         return c;
1408                         }
1409
1410                         e = ImplicitNumericConversion (expr, expr_type, target_type);
1411                         if (e != null)
1412                                 return e;
1413
1414                         e = ImplicitReferenceConversion (expr, target_type, explicit_cast);
1415                         if (e != null)
1416                                 return e;
1417
1418                         e = ImplicitBoxingConversion (expr, expr_type, target_type);
1419                         if (e != null)
1420                                 return e;
1421
1422                         if (expr is IntegralConstant && target_type.IsEnum){
1423                                 var i = (IntegralConstant) expr;
1424                                 //
1425                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
1426                                 //
1427                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
1428                                 // to be converted to any enum-type and to any nullable-type whose underlying
1429                                 // type is an enum-type
1430                                 //
1431                                 if (i.IsZeroInteger) {
1432                                         // Recreate 0 literal to remove any collected conversions
1433                                         return new EnumConstant (new IntLiteral (ec.BuiltinTypes, 0, i.Location), target_type);
1434                                 }
1435                         }
1436
1437                         var target_pc = target_type as PointerContainer;
1438                         if (target_pc != null) {
1439                                 if (expr_type.IsPointer) {
1440                                         //
1441                                         // Pointer types are same when they have same element types
1442                                         //
1443                                         if (expr_type == target_pc)
1444                                                 return expr;
1445
1446                                         if (target_pc.Element.Kind == MemberKind.Void)
1447                                                 return EmptyCast.Create (expr, target_type);
1448
1449                                                 //return null;
1450                                 }
1451
1452                                 if (expr_type == InternalType.NullLiteral)
1453                                         return new NullPointer (target_type, loc);
1454                         }
1455
1456                         if (expr_type == InternalType.AnonymousMethod){
1457                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1458                                 Expression am = ame.Compatible (ec, target_type);
1459                                 if (am != null)
1460                                         return am.Resolve (ec);
1461
1462                                 // Avoid CS1503 after CS1661
1463                                 return ErrorExpression.Instance;
1464                         }
1465
1466                         if (expr_type == InternalType.Arglist && target_type == ec.Module.PredefinedTypes.ArgIterator.TypeSpec)
1467                                 return expr;
1468
1469                         //
1470                         // dynamic erasure conversion on value types
1471                         //
1472                         if (expr_type.IsStruct && TypeSpecComparer.IsEqual (expr_type, target_type))
1473                                 return expr_type == target_type ? expr : EmptyCast.Create (expr, target_type);
1474
1475                         var interpolated_string = expr as InterpolatedString;
1476                         if (interpolated_string != null) {
1477                                 if (target_type == ec.Module.PredefinedTypes.IFormattable.TypeSpec || target_type == ec.Module.PredefinedTypes.FormattableString.TypeSpec)
1478                                         return interpolated_string.ConvertTo (ec, target_type);
1479                         }
1480
1481                         return null;
1482                 }
1483
1484                 /// <summary>
1485                 ///   Attempts to implicitly convert `source' into `target_type', using
1486                 ///   ImplicitConversion.  If there is no implicit conversion, then
1487                 ///   an error is signaled
1488                 /// </summary>
1489                 static public Expression ImplicitConversionRequired (ResolveContext ec, Expression source,
1490                                                                      TypeSpec target_type, Location loc)
1491                 {
1492                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1493                         if (e != null)
1494                                 return e;
1495
1496                         source.Error_ValueCannotBeConverted (ec, target_type, false);
1497
1498                         return null;
1499                 }
1500
1501                 /// <summary>
1502                 ///   Performs the explicit numeric conversions
1503                 ///
1504                 /// There are a few conversions that are not part of the C# standard,
1505                 /// they were interim hacks in the C# compiler that were supposed to
1506                 /// become explicit operators in the UIntPtr class and IntPtr class,
1507                 /// but for historical reasons it did not happen, so the C# compiler
1508                 /// ended up with these special hacks.
1509                 ///
1510                 /// See bug 59800 for details.
1511                 ///
1512                 /// The conversion are:
1513                 ///   UIntPtr->SByte
1514                 ///   UIntPtr->Int16
1515                 ///   UIntPtr->Int32
1516                 ///   IntPtr->UInt64
1517                 ///   UInt64->IntPtr
1518                 ///   SByte->UIntPtr
1519                 ///   Int16->UIntPtr
1520                 ///
1521                 /// </summary>
1522                 public static Expression ExplicitNumericConversion (ResolveContext rc, Expression expr, TypeSpec target_type)
1523                 {
1524                         // Not all predefined explicit numeric conversion are
1525                         // defined here, for some of them (mostly IntPtr/UIntPtr) we
1526                         // defer to user-operator handling which is now perfect but
1527                         // works for now
1528                         //
1529                         // LAMESPEC: Undocumented IntPtr/UIntPtr conversions
1530                         // IntPtr -> uint uses int
1531                         // UIntPtr -> long uses ulong
1532                         //
1533
1534                         switch (expr.Type.BuiltinType) {
1535                         case BuiltinTypeSpec.Type.SByte:
1536                                 //
1537                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1538                                 //
1539                                 switch (target_type.BuiltinType) {
1540                                 case BuiltinTypeSpec.Type.Byte:
1541                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1542                                 case BuiltinTypeSpec.Type.UShort:
1543                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1544                                 case BuiltinTypeSpec.Type.UInt:
1545                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1546                                 case BuiltinTypeSpec.Type.ULong:
1547                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1548                                 case BuiltinTypeSpec.Type.Char:
1549                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1550
1551                                 // One of the built-in conversions that belonged in the class library
1552                                 case BuiltinTypeSpec.Type.UIntPtr:
1553                                         return new OperatorCast (new ConvCast (expr, rc.BuiltinTypes.ULong, ConvCast.Mode.I1_U8), target_type, target_type, true);
1554                                 }
1555                                 break;
1556                         case BuiltinTypeSpec.Type.Byte:
1557                                 //
1558                                 // From byte to sbyte and char
1559                                 //
1560                                 switch (target_type.BuiltinType) {
1561                                 case BuiltinTypeSpec.Type.SByte:
1562                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1563                                 case BuiltinTypeSpec.Type.Char:
1564                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1565                                 }
1566                                 break;
1567                         case BuiltinTypeSpec.Type.Short:
1568                                 //
1569                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1570                                 //
1571                                 switch (target_type.BuiltinType) {
1572                                 case BuiltinTypeSpec.Type.SByte:
1573                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1574                                 case BuiltinTypeSpec.Type.Byte:
1575                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1576                                 case BuiltinTypeSpec.Type.UShort:
1577                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1578                                 case BuiltinTypeSpec.Type.UInt:
1579                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1580                                 case BuiltinTypeSpec.Type.ULong:
1581                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1582                                 case BuiltinTypeSpec.Type.Char:
1583                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1584
1585                                 // One of the built-in conversions that belonged in the class library
1586                                 case BuiltinTypeSpec.Type.UIntPtr:
1587                                         return new OperatorCast (new ConvCast (expr, rc.BuiltinTypes.ULong, ConvCast.Mode.I2_U8), target_type, target_type, true);
1588                                 }
1589                                 break;
1590                         case BuiltinTypeSpec.Type.UShort:
1591                                 //
1592                                 // From ushort to sbyte, byte, short, char
1593                                 //
1594                                 switch (target_type.BuiltinType) {
1595                                 case BuiltinTypeSpec.Type.SByte:
1596                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1597                                 case BuiltinTypeSpec.Type.Byte:
1598                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1599                                 case BuiltinTypeSpec.Type.Short:
1600                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1601                                 case BuiltinTypeSpec.Type.Char:
1602                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1603                                 }
1604                                 break;
1605                         case BuiltinTypeSpec.Type.Int:
1606                                 //
1607                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1608                                 //
1609                                 switch (target_type.BuiltinType) {
1610                                 case BuiltinTypeSpec.Type.SByte:
1611                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1612                                 case BuiltinTypeSpec.Type.Byte:
1613                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1614                                 case BuiltinTypeSpec.Type.Short:
1615                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1616                                 case BuiltinTypeSpec.Type.UShort:
1617                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1618                                 case BuiltinTypeSpec.Type.UInt:
1619                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1620                                 case BuiltinTypeSpec.Type.ULong:
1621                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1622                                 case BuiltinTypeSpec.Type.Char:
1623                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1624
1625                                 // One of the built-in conversions that belonged in the class library
1626                                 case BuiltinTypeSpec.Type.UIntPtr:
1627                                         return new OperatorCast (new ConvCast (expr, rc.BuiltinTypes.ULong, ConvCast.Mode.I2_U8), target_type, target_type, true);
1628                                 }
1629                                 break;
1630                         case BuiltinTypeSpec.Type.UInt:
1631                                 //
1632                                 // From uint to sbyte, byte, short, ushort, int, char
1633                                 //
1634                                 switch (target_type.BuiltinType) {
1635                                 case BuiltinTypeSpec.Type.SByte:
1636                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1637                                 case BuiltinTypeSpec.Type.Byte:
1638                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1639                                 case BuiltinTypeSpec.Type.Short:
1640                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1641                                 case BuiltinTypeSpec.Type.UShort:
1642                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1643                                 case BuiltinTypeSpec.Type.Int:
1644                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1645                                 case BuiltinTypeSpec.Type.Char:
1646                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1647                                 }
1648                                 break;
1649                         case BuiltinTypeSpec.Type.Long:
1650                                 //
1651                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1652                                 //
1653                                 switch (target_type.BuiltinType) {
1654                                 case BuiltinTypeSpec.Type.SByte:
1655                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1656                                 case BuiltinTypeSpec.Type.Byte:
1657                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1658                                 case BuiltinTypeSpec.Type.Short:
1659                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1660                                 case BuiltinTypeSpec.Type.UShort:
1661                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1662                                 case BuiltinTypeSpec.Type.Int:
1663                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1664                                 case BuiltinTypeSpec.Type.UInt:
1665                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1666                                 case BuiltinTypeSpec.Type.ULong:
1667                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1668                                 case BuiltinTypeSpec.Type.Char:
1669                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1670                                 }
1671                                 break;
1672                         case BuiltinTypeSpec.Type.ULong:
1673                                 //
1674                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1675                                 //
1676                                 switch (target_type.BuiltinType) {
1677                                 case BuiltinTypeSpec.Type.SByte:
1678                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1679                                 case BuiltinTypeSpec.Type.Byte:
1680                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1681                                 case BuiltinTypeSpec.Type.Short:
1682                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1683                                 case BuiltinTypeSpec.Type.UShort:
1684                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1685                                 case BuiltinTypeSpec.Type.Int:
1686                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1687                                 case BuiltinTypeSpec.Type.UInt:
1688                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1689                                 case BuiltinTypeSpec.Type.Long:
1690                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1691                                 case BuiltinTypeSpec.Type.Char:
1692                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1693
1694                                 // One of the built-in conversions that belonged in the class library
1695                                 case BuiltinTypeSpec.Type.IntPtr:
1696                                         return new OperatorCast (EmptyCast.Create (expr, rc.BuiltinTypes.Long), target_type, true);
1697                                 }
1698                                 break;
1699                         case BuiltinTypeSpec.Type.Char:
1700                                 //
1701                                 // From char to sbyte, byte, short
1702                                 //
1703                                 switch (target_type.BuiltinType) {
1704                                 case BuiltinTypeSpec.Type.SByte:
1705                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1706                                 case BuiltinTypeSpec.Type.Byte:
1707                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1708                                 case BuiltinTypeSpec.Type.Short:
1709                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1710                                 }
1711                                 break;
1712                         case BuiltinTypeSpec.Type.Float:
1713                                 //
1714                                 // From float to sbyte, byte, short,
1715                                 // ushort, int, uint, long, ulong, char
1716                                 // or decimal
1717                                 //
1718                                 switch (target_type.BuiltinType) {
1719                                 case BuiltinTypeSpec.Type.SByte:
1720                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1721                                 case BuiltinTypeSpec.Type.Byte:
1722                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1723                                 case BuiltinTypeSpec.Type.Short:
1724                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1725                                 case BuiltinTypeSpec.Type.UShort:
1726                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1727                                 case BuiltinTypeSpec.Type.Int:
1728                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1729                                 case BuiltinTypeSpec.Type.UInt:
1730                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1731                                 case BuiltinTypeSpec.Type.Long:
1732                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1733                                 case BuiltinTypeSpec.Type.ULong:
1734                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1735                                 case BuiltinTypeSpec.Type.Char:
1736                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1737                                 case BuiltinTypeSpec.Type.Decimal:
1738                                         return new OperatorCast (expr, target_type, true);
1739                                 }
1740                                 break;
1741                         case BuiltinTypeSpec.Type.Double:
1742                                 //
1743                                 // From double to sbyte, byte, short,
1744                                 // ushort, int, uint, long, ulong,
1745                                 // char, float or decimal
1746                                 //
1747                                 switch (target_type.BuiltinType) {
1748                                 case BuiltinTypeSpec.Type.SByte:
1749                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1750                                 case BuiltinTypeSpec.Type.Byte:
1751                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1752                                 case BuiltinTypeSpec.Type.Short:
1753                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1754                                 case BuiltinTypeSpec.Type.UShort:
1755                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1756                                 case BuiltinTypeSpec.Type.Int:
1757                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1758                                 case BuiltinTypeSpec.Type.UInt:
1759                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1760                                 case BuiltinTypeSpec.Type.Long:
1761                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1762                                 case BuiltinTypeSpec.Type.ULong:
1763                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1764                                 case BuiltinTypeSpec.Type.Char:
1765                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1766                                 case BuiltinTypeSpec.Type.Float:
1767                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1768                                 case BuiltinTypeSpec.Type.Decimal:
1769                                         return new OperatorCast (expr, target_type, true);
1770                                 }
1771                                 break;
1772                         case BuiltinTypeSpec.Type.UIntPtr:
1773                                 //
1774                                 // Various built-in conversions that belonged in the class library
1775                                 //
1776                                 // from uintptr to sbyte, short, int32
1777                                 //
1778                                 switch (target_type.BuiltinType) {
1779                                 case BuiltinTypeSpec.Type.SByte:
1780                                         return new ConvCast (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.UInt, true), target_type, ConvCast.Mode.U4_I1);
1781                                 case BuiltinTypeSpec.Type.Short:
1782                                         return new ConvCast (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.UInt, true), target_type, ConvCast.Mode.U4_I2);
1783                                 case BuiltinTypeSpec.Type.Int:
1784                                         return EmptyCast.Create (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.UInt, true), target_type);
1785                                 case BuiltinTypeSpec.Type.UInt:
1786                                         return new OperatorCast (expr, expr.Type, target_type, true);
1787                                 case BuiltinTypeSpec.Type.Long:
1788                                         return EmptyCast.Create (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.ULong, true), target_type);
1789                                 }
1790                                 break;
1791                         case BuiltinTypeSpec.Type.IntPtr:
1792                                 if (target_type.BuiltinType == BuiltinTypeSpec.Type.UInt)
1793                                         return EmptyCast.Create (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.Int, true), target_type);
1794                                 if (target_type.BuiltinType == BuiltinTypeSpec.Type.ULong)
1795                                         return EmptyCast.Create (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.Long, true), target_type);
1796
1797                                 break;
1798                         case BuiltinTypeSpec.Type.Decimal:
1799                                 // From decimal to sbyte, byte, short,
1800                                 // ushort, int, uint, long, ulong, char,
1801                                 // float, or double
1802                                 switch (target_type.BuiltinType) {
1803                                 case BuiltinTypeSpec.Type.SByte:
1804                                 case BuiltinTypeSpec.Type.Byte:
1805                                 case BuiltinTypeSpec.Type.Short:
1806                                 case BuiltinTypeSpec.Type.UShort:
1807                                 case BuiltinTypeSpec.Type.Int:
1808                                 case BuiltinTypeSpec.Type.UInt:
1809                                 case BuiltinTypeSpec.Type.Long:
1810                                 case BuiltinTypeSpec.Type.ULong:
1811                                 case BuiltinTypeSpec.Type.Char:
1812                                 case BuiltinTypeSpec.Type.Float:
1813                                 case BuiltinTypeSpec.Type.Double:
1814                                         return new OperatorCast (expr, expr.Type, target_type, true);
1815                                 }
1816
1817                                 break;
1818                         }
1819
1820                         return null;
1821                 }
1822
1823                 /// <summary>
1824                 ///  Returns whether an explicit reference conversion can be performed
1825                 ///  from source_type to target_type
1826                 /// </summary>
1827                 public static bool ExplicitReferenceConversionExists (TypeSpec source_type, TypeSpec target_type)
1828                 {
1829                         Expression e = ExplicitReferenceConversion (null, source_type, target_type);
1830                         if (e == null)
1831                                 return false;
1832
1833                         if (e == EmptyExpression.Null)
1834                                 return true;
1835
1836                         throw new InternalErrorException ("Invalid probing conversion result");
1837                 }
1838
1839                 /// <summary>
1840                 ///   Implements Explicit Reference conversions
1841                 /// </summary>
1842                 static Expression ExplicitReferenceConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
1843                 {
1844                         //
1845                         // From object to a generic parameter
1846                         //
1847                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.Object && TypeManager.IsGenericParameter (target_type))
1848                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1849
1850                         //
1851                         // Explicit type parameter conversion from T
1852                         //
1853                         if (source_type.Kind == MemberKind.TypeParameter)
1854                                 return ExplicitTypeParameterConversionFromT (source, source_type, target_type);
1855
1856                         bool target_is_value_type = target_type.Kind == MemberKind.Struct || target_type.Kind == MemberKind.Enum;
1857
1858                         //
1859                         // Unboxing conversion from System.ValueType to any non-nullable-value-type
1860                         //
1861                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.ValueType && target_is_value_type)
1862                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1863
1864                         //
1865                         // From object or dynamic to any reference type or value type (unboxing)
1866                         //
1867                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.Object || source_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
1868                                 if (target_type.IsPointer)
1869                                         return null;
1870
1871                                 return
1872                                         source == null ? EmptyExpression.Null :
1873                                         target_is_value_type ? new UnboxCast (source, target_type) :
1874                                         source is Constant ? (Expression) new EmptyConstantCast ((Constant) source, target_type) :
1875                                         new ClassCast (source, target_type);
1876                         }
1877
1878                         //
1879                         // From any class S to any class-type T, provided S is a base class of T
1880                         //
1881                         if (source_type.Kind == MemberKind.Class && TypeSpec.IsBaseClass (target_type, source_type, true))
1882                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1883
1884                         //
1885                         // From any interface-type S to to any class type T, provided T is not
1886                         // sealed, or provided T implements S.
1887                         //
1888                         // This also covers Explicit conversions involving type parameters
1889                         // section From any interface type to T
1890                         //
1891                         if (source_type.Kind == MemberKind.Interface) {
1892                                 if (!target_type.IsSealed || target_type.ImplementsInterface (source_type, true)) {
1893                                         if (source == null)
1894                                                 return EmptyExpression.Null;
1895
1896                                         //
1897                                         // Unboxing conversion from any interface-type to any non-nullable-value-type that
1898                                         // implements the interface-type
1899                                         //
1900                                         return target_is_value_type ? new UnboxCast (source, target_type) : (Expression) new ClassCast (source, target_type);
1901                                 }
1902
1903                                 //
1904                                 // From System.Collections.Generic.IList<T> and its base interfaces to a one-dimensional
1905                                 // array type S[], provided there is an implicit or explicit reference conversion from S to T.
1906                                 //
1907                                 var target_array = target_type as ArrayContainer;
1908                                 if (target_array != null && IList_To_Array (source_type, target_array))
1909                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1910
1911                                 return null;
1912                         }
1913
1914                         var source_array = source_type as ArrayContainer;
1915                         if (source_array != null) {
1916                                 var target_array = target_type as ArrayContainer;
1917                                 if (target_array != null) {
1918                                         //
1919                                         // From System.Array to any array-type
1920                                         //
1921                                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.Array)
1922                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1923
1924                                         //
1925                                         // From an array type S with an element type Se to an array type T with an
1926                                         // element type Te provided all the following are true:
1927                                         //     * S and T differe only in element type, in other words, S and T
1928                                         //       have the same number of dimensions.
1929                                         //     * Both Se and Te are reference types
1930                                         //     * An explicit reference conversions exist from Se to Te
1931                                         //
1932                                         if (source_array.Rank == target_array.Rank) {
1933
1934                                                 source_type = source_array.Element;
1935                                                 var target_element = target_array.Element;
1936
1937                                                 //
1938                                                 // LAMESPEC: Type parameters are special cased somehow but
1939                                                 // only when both source and target elements are type parameters
1940                                                 //
1941                                                 if ((source_type.Kind & target_element.Kind & MemberKind.TypeParameter) == MemberKind.TypeParameter) {
1942                                                         //
1943                                                         // Conversion is allowed unless source element type has struct constrain
1944                                                         //
1945                                                         if (TypeSpec.IsValueType (source_type))
1946                                                                 return null;
1947                                                 } else {
1948                                                         if (!TypeSpec.IsReferenceType (source_type))
1949                                                                 return null;
1950                                                 }
1951
1952                                                 if (!TypeSpec.IsReferenceType (target_element))
1953                                                         return null;
1954
1955                                                 if (ExplicitReferenceConversionExists (source_type, target_element))
1956                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1957
1958                                                 return null;
1959                                         }
1960                                 }
1961
1962                                 //
1963                                 // From a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its base interfaces,
1964                                 // provided that there is an explicit reference conversion from S to T
1965                                 //
1966                                 if (ArrayToIList (source_array, target_type, true))
1967                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1968
1969                                 return null;
1970                         }
1971
1972                         //
1973                         // From any class type S to any interface T, provides S is not sealed
1974                         // and provided S does not implement T.
1975                         //
1976                         if (target_type.IsInterface && !source_type.IsSealed && !source_type.ImplementsInterface (target_type, true)) {
1977                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1978                         }
1979
1980                         //
1981                         // From System delegate to any delegate-type
1982                         //
1983                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.Delegate && target_type.IsDelegate)
1984                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1985
1986                         //
1987                         // From variant generic delegate to same variant generic delegate type
1988                         //
1989                         if (source_type.IsDelegate && target_type.IsDelegate && source_type.MemberDefinition == target_type.MemberDefinition) {
1990                                 var tparams = source_type.MemberDefinition.TypeParameters;
1991                                 var targs_src = source_type.TypeArguments;
1992                                 var targs_dst = target_type.TypeArguments;
1993                                 int i;
1994                                 for (i = 0; i < tparams.Length; ++i) {
1995                                         //
1996                                         // If TP is invariant, types have to be identical
1997                                         //
1998                                         if (TypeSpecComparer.IsEqual (targs_src[i], targs_dst[i]))
1999                                                 continue;
2000
2001                                         if (tparams[i].Variance == Variance.Covariant) {
2002                                                 //
2003                                                 //If TP is covariant, an implicit or explicit identity or reference conversion is required
2004                                                 //
2005                                                 if (ImplicitReferenceConversionExists (targs_src[i], targs_dst[i]))
2006                                                         continue;
2007
2008                                                 if (ExplicitReferenceConversionExists (targs_src[i], targs_dst[i]))
2009                                                         continue;
2010
2011                                         } else if (tparams[i].Variance == Variance.Contravariant) {
2012                                                 //
2013                                                 //If TP is contravariant, both are either identical or reference types
2014                                                 //
2015                                                 if (TypeSpec.IsReferenceType (targs_src[i]) && TypeSpec.IsReferenceType (targs_dst[i]))
2016                                                         continue;
2017                                         }
2018
2019                                         break;
2020                                 }
2021
2022                                 if (i == tparams.Length)
2023                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
2024                         }
2025
2026                         var tps = target_type as TypeParameterSpec;
2027                         if (tps != null)
2028                                 return ExplicitTypeParameterConversionToT (source, source_type, tps);
2029
2030                         return null;
2031                 }
2032
2033                 /// <summary>
2034                 ///   Performs an explicit conversion of the expression `expr' whose
2035                 ///   type is expr.Type to `target_type'.
2036                 /// </summary>
2037                 static public Expression ExplicitConversionCore (ResolveContext ec, Expression expr,
2038                                                                  TypeSpec target_type, Location loc)
2039                 {
2040                         TypeSpec expr_type = expr.Type;
2041
2042                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
2043                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc, true);
2044                         if (ne != null)
2045                                 return ne;
2046
2047                         if (expr_type.IsEnum) {
2048                                 TypeSpec real_target = target_type.IsEnum ? EnumSpec.GetUnderlyingType (target_type) : target_type;
2049                                 Expression underlying = EmptyCast.Create (expr, EnumSpec.GetUnderlyingType (expr_type));
2050                                 if (underlying.Type == real_target)
2051                                         ne = underlying;
2052
2053                                 if (ne == null)
2054                                         ne = ImplicitNumericConversion (underlying, real_target);
2055
2056                                 if (ne == null)
2057                                         ne = ExplicitNumericConversion (ec, underlying, real_target);
2058
2059                                 //
2060                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
2061                                 //
2062                                 if (ne == null && (real_target.BuiltinType == BuiltinTypeSpec.Type.IntPtr || real_target.BuiltinType == BuiltinTypeSpec.Type.UIntPtr))
2063                                         ne = ExplicitUserConversion (ec, underlying, real_target, loc);
2064
2065                                 return ne != null ? EmptyCast.Create (ne, target_type) : null;
2066                         }
2067
2068                         if (target_type.IsEnum) {
2069                                 //
2070                                 // System.Enum can be unboxed to any enum-type
2071                                 //
2072                                 if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Enum)
2073                                         return new UnboxCast (expr, target_type);
2074
2075                                 TypeSpec real_target = target_type.IsEnum ? EnumSpec.GetUnderlyingType (target_type) : target_type;
2076
2077                                 if (expr_type == real_target)
2078                                         return EmptyCast.Create (expr, target_type);
2079
2080                                 Constant c = expr as Constant;
2081                                 if (c != null) {
2082                                         c = c.TryReduce (ec, real_target);
2083                                         if (c != null)
2084                                                 return c;
2085                                 } else {
2086                                         ne = ImplicitNumericConversion (expr, real_target);
2087                                         if (ne != null)
2088                                                 return EmptyCast.Create (ne, target_type);
2089
2090                                         ne = ExplicitNumericConversion (ec, expr, real_target);
2091                                         if (ne != null)
2092                                                 return EmptyCast.Create (ne, target_type);
2093
2094                                         //
2095                                         // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
2096                                         //
2097                                         if (expr_type.BuiltinType == BuiltinTypeSpec.Type.IntPtr || expr_type.BuiltinType == BuiltinTypeSpec.Type.UIntPtr) {
2098                                                 ne = ExplicitUserConversion (ec, expr, real_target, loc);
2099                                                 if (ne != null)
2100                                                         return ExplicitConversionCore (ec, ne, target_type, loc);
2101                                         }
2102                                 }
2103                         } else {
2104                                 ne = ExplicitNumericConversion (ec, expr, target_type);
2105                                 if (ne != null)
2106                                         return ne;
2107                         }
2108
2109                         //
2110                         // Skip the ExplicitReferenceConversion because we can not convert
2111                         // from Null to a ValueType, and ExplicitReference wont check against
2112                         // null literal explicitly
2113                         //
2114                         if (expr_type != InternalType.NullLiteral) {
2115                                 ne = ExplicitReferenceConversion (expr, expr_type, target_type);
2116                                 if (ne != null)
2117                                         return ne;
2118                         }
2119
2120                         if (ec.IsUnsafe){
2121                                 ne = ExplicitUnsafe (expr, target_type);
2122                                 if (ne != null)
2123                                         return ne;
2124                         }
2125
2126                         return null;
2127                 }
2128
2129                 public static Expression ExplicitUnsafe (Expression expr, TypeSpec target_type)
2130                 {
2131                         TypeSpec expr_type = expr.Type;
2132
2133                         if (target_type.IsPointer){
2134                                 if (expr_type.IsPointer)
2135                                         return EmptyCast.Create (expr, target_type);
2136
2137                                 switch (expr_type.BuiltinType) {
2138                                 case BuiltinTypeSpec.Type.SByte:
2139                                 case BuiltinTypeSpec.Type.Short:
2140                                 case BuiltinTypeSpec.Type.Int:
2141                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
2142
2143                                 case BuiltinTypeSpec.Type.UShort:
2144                                 case BuiltinTypeSpec.Type.UInt:
2145                                 case BuiltinTypeSpec.Type.Byte:
2146                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
2147
2148                                 case BuiltinTypeSpec.Type.Long:
2149                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I);
2150
2151                                 case BuiltinTypeSpec.Type.ULong:
2152                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I);
2153                                 }
2154                         }
2155
2156                         if (expr_type.IsPointer){
2157                                 switch (target_type.BuiltinType) {
2158                                 case BuiltinTypeSpec.Type.SByte:
2159                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
2160                                 case BuiltinTypeSpec.Type.Byte:
2161                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
2162                                 case BuiltinTypeSpec.Type.Short:
2163                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
2164                                 case BuiltinTypeSpec.Type.UShort:
2165                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
2166                                 case BuiltinTypeSpec.Type.Int:
2167                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
2168                                 case BuiltinTypeSpec.Type.UInt:
2169                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
2170                                 case BuiltinTypeSpec.Type.Long:
2171                                         return new ConvCast (expr, target_type, ConvCast.Mode.I_I8);
2172                                 case BuiltinTypeSpec.Type.ULong:
2173                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
2174                                 }
2175                         }
2176                         return null;
2177                 }
2178
2179                 /// <summary>
2180                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
2181                 /// </summary>
2182                 static public Expression ExplicitConversionStandard (ResolveContext ec, Expression expr,
2183                                                                      TypeSpec target_type, Location l)
2184                 {
2185                         int errors = ec.Report.Errors;
2186                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
2187                         if (ec.Report.Errors > errors)
2188                                 return null;
2189
2190                         if (ne != null)
2191                                 return ne;
2192
2193                         ne = ExplicitNumericConversion (ec, expr, target_type);
2194                         if (ne != null)
2195                                 return ne;
2196
2197                         ne = ExplicitReferenceConversion (expr, expr.Type, target_type);
2198                         if (ne != null)
2199                                 return ne;
2200
2201                         if (ec.IsUnsafe && expr.Type.IsPointer && target_type.IsPointer && ((PointerContainer)expr.Type).Element.Kind == MemberKind.Void)
2202                                 return EmptyCast.Create (expr, target_type);
2203
2204                         expr.Error_ValueCannotBeConverted (ec, target_type, true);
2205                         return null;
2206                 }
2207
2208                 /// <summary>
2209                 ///   Performs an explicit conversion of the expression `expr' whose
2210                 ///   type is expr.Type to `target_type'.
2211                 /// </summary>
2212                 static public Expression ExplicitConversion (ResolveContext ec, Expression expr,
2213                         TypeSpec target_type, Location loc)
2214                 {
2215                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
2216                         if (e != null) {
2217                                 //
2218                                 // Don't eliminate explicit precission casts
2219                                 //
2220                                 if (e == expr) {
2221                                         if (target_type.BuiltinType == BuiltinTypeSpec.Type.Float)
2222                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
2223
2224                                         if (target_type.BuiltinType == BuiltinTypeSpec.Type.Double)
2225                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
2226                                 }
2227
2228                                 return e;
2229                         }
2230
2231                         TypeSpec expr_type = expr.Type;
2232                         if (target_type.IsNullableType) {
2233                                 TypeSpec target;
2234
2235                                 if (expr_type.IsNullableType) {
2236                                         target = Nullable.NullableInfo.GetUnderlyingType (target_type);
2237                                         Expression unwrap = Nullable.Unwrap.Create (expr);
2238                                         e = ExplicitConversion (ec, unwrap, target, expr.Location);
2239                                         if (e == null)
2240                                                 return null;
2241
2242                                         return new Nullable.LiftedConversion (e, unwrap, target_type).Resolve (ec);
2243                                 }
2244                                 if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Object) {
2245                                         return new UnboxCast (expr, target_type);
2246                                 }
2247
2248                                 target = TypeManager.GetTypeArguments (target_type) [0];
2249                                 e = ExplicitConversionCore (ec, expr, target, loc);
2250                                 if (e != null)
2251                                         return TypeSpec.IsReferenceType (expr.Type) ? new UnboxCast (expr, target_type) : Nullable.Wrap.Create (e, target_type);
2252                         } else if (expr_type.IsNullableType) {
2253                                 e = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
2254                                 if (e != null)
2255                                         return e;
2256
2257                                 e = Nullable.Unwrap.Create (expr, false);
2258                                 e = ExplicitConversionCore (ec, e, target_type, loc);
2259                                 if (e != null)
2260                                         return EmptyCast.Create (e, target_type);
2261                         }
2262
2263                         e = ExplicitUserConversion (ec, expr, target_type, loc);
2264
2265                         if (e != null)
2266                                 return e;
2267
2268                         expr.Error_ValueCannotBeConverted (ec, target_type, true);
2269                         return null;
2270                 }
2271         }
2272 }