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                 static Expression ImplicitTupleLiteralConversion (ResolveContext rc, Expression source, TypeSpec targetType, Location loc)
 683                 {
 684                         var targetTypeArgument = targetType.TypeArguments;
 685                         if (source.Type.Arity != targetTypeArgument.Length)
 686                                 return null;
 687
 688                         var namedTarget = targetType as NamedTupleSpec;
 689                         var tupleLiteral = source as TupleLiteral;
 690                         Expression instance;
 691
 692                         if (tupleLiteral == null && !ExpressionAnalyzer.IsInexpensiveLoad (source)) {
 693                                 var expr_variable = LocalVariable.CreateCompilerGenerated (source.Type, rc.CurrentBlock, loc);
 694                                 source = new CompilerAssign (expr_variable.CreateReferenceExpression (rc, loc), source, loc);
 695                                 instance = expr_variable.CreateReferenceExpression (rc, loc);
 696                         } else {
 697                                 instance = null;
 698                         }
 699
 700                         var converted = new List<Expression> (targetType.Arity);
 701                         for (int i = 0; i < targetType.Arity; ++i) {
 702                                 Expression elementSrc;
 703                                 if (tupleLiteral != null) {
 704                                         elementSrc = tupleLiteral.Elements [i].Expr;
 705
 706                                         if (namedTarget != null) {
 707                                                 var elementSrcName = tupleLiteral.Elements [i].Name;
 708                                                 if (elementSrcName != null && elementSrcName != namedTarget.Elements [i]) {
 709                                                         rc.Report.Warning (8123, 1, loc,
 710                                                                            "The tuple element name `{0}' is ignored because a different name or no name is specified by the target type `{1}'",
 711                                                                            elementSrcName, namedTarget.GetSignatureForErrorWithNames ());
 712                                                 }
 713                                         }
 714                                 } else {
 715                                         elementSrc = new MemberAccess (instance, NamedTupleSpec.GetElementPropertyName (i)).Resolve (rc);
 716                                 }
 717
 718                                 var res = ImplicitConversionStandard (rc, elementSrc, targetTypeArgument [i], loc);
 719                                 if (res == null)
 720                                         return null;
 721
 722                                 converted.Add (res);
 723                         }
 724
 725                         return new TupleLiteralConversion (source, targetType, converted, loc);
 726                 }
 727
 728                 static bool ImplicitTupleLiteralConversionExists (Expression source, TypeSpec targetType)
 729                 {
 730                         if (source.Type.Arity != targetType.Arity)
 731                                 return false;
 732
 733                         var srcTypeArgument = source.Type.TypeArguments;
 734                         var targetTypeArgument = targetType.TypeArguments;
 735
 736                         var tupleLiteralElements = (source as TupleLiteral)?.Elements;
 737
 738                         for (int i = 0; i < targetType.Arity; ++i) {
 739                                 var elementType = srcTypeArgument [i];
 740
 741                                 if (tupleLiteralElements != null) {
 742                                         if (!ImplicitStandardConversionExists (tupleLiteralElements[i].Expr, targetTypeArgument [i])) {
 743                                                 return false;
 744                                         }
 745                                 } else {
 746                                         if (!ImplicitStandardConversionExists (new EmptyExpression (srcTypeArgument [i]), targetTypeArgument [i])) {
 747                                                 return false;
 748                                         }
 749                                 }
 750                         }
 751
 752                         return true;
 753                 }
 754
 755
 756                 //
 757                 // Full version of implicit conversion
 758                 //
 759                 public static bool ImplicitConversionExists (ResolveContext ec, Expression expr, TypeSpec target_type)
 760                 {
 761                         if (ImplicitStandardConversionExists (ec, expr, target_type))
 762                                 return true;
 763
 764                         if (expr.Type == InternalType.AnonymousMethod) {
 765                                 if (!target_type.IsDelegate && !target_type.IsExpressionTreeType)
 766                                         return false;
 767
 768                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 769                                 return ame.ImplicitStandardConversionExists (ec, target_type);
 770                         }
 771
 772                         // Conversion from __arglist to System.ArgIterator
 773                         if (expr.Type == InternalType.Arglist)
 774                                 return target_type == ec.Module.PredefinedTypes.ArgIterator.TypeSpec;
 775
 776                         return UserDefinedConversion (ec, expr, target_type,
 777                                 UserConversionRestriction.ImplicitOnly | UserConversionRestriction.ProbingOnly, Location.Null) != null;
 778                 }
 779
 780                 public static bool ImplicitStandardConversionExists (ResolveContext rc, Expression expr, TypeSpec target_type)
 781                 {
 782                         if (expr.eclass == ExprClass.MethodGroup) {
 783                                 if (target_type.IsDelegate && rc.Module.Compiler.Settings.Version != LanguageVersion.ISO_1) {
 784                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 785                                         if (mg != null)
 786                                                 return DelegateCreation.ImplicitStandardConversionExists (rc, mg, target_type);
 787                                 }
 788
 789                                 return false;
 790                         }
 791
 792                         var interpolated_string = expr as InterpolatedString;
 793                         if (interpolated_string != null) {
 794                                 if (target_type == rc.Module.PredefinedTypes.IFormattable.TypeSpec || target_type == rc.Module.PredefinedTypes.FormattableString.TypeSpec)
 795                                         return true;
 796                         }
 797
 798                         return ImplicitStandardConversionExists (expr, target_type);
 799                 }
 800
 801                 //
 802                 // Implicit standard conversion (only core conversions are used here)
 803                 //
 804                 public static bool ImplicitStandardConversionExists (Expression expr, TypeSpec target_type)
 805                 {
 806                         //
 807                         // Identity conversions
 808                         // Implicit numeric conversions
 809                         // Implicit nullable conversions
 810                         // Implicit reference conversions
 811                         // Boxing conversions
 812                         // Implicit constant expression conversions
 813                         // Implicit conversions involving type parameters
 814                         //
 815
 816                         TypeSpec expr_type = expr.Type;
 817
 818                         if (expr_type == target_type)
 819                                 return true;
 820
 821                         if (expr_type == InternalType.ThrowExpr)
 822                                 return target_type.Kind != MemberKind.InternalCompilerType;
 823
 824                         if (target_type.IsNullableType)
 825                                 return ImplicitNulableConversion (null, expr, target_type) != null;
 826
 827                         if (ImplicitNumericConversion (null, expr_type, target_type) != null)
 828                                 return true;
 829
 830                         if (ImplicitReferenceConversionExists (expr_type, target_type, false))
 831                                 return true;
 832
 833                         if (ImplicitBoxingConversion (null, expr_type, target_type) != null)
 834                                 return true;
 835
 836                         if (expr_type.IsTupleType && target_type.IsTupleType)
 837                                 return ImplicitTupleLiteralConversionExists (expr, target_type);
 838
 839                         //
 840                         // Implicit Constant Expression Conversions
 841                         //
 842                         if (expr is IntConstant){
 843                                 int value = ((IntConstant) expr).Value;
 844                                 switch (target_type.BuiltinType) {
 845                                 case BuiltinTypeSpec.Type.SByte:
 846                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 847                                                 return true;
 848                                         break;
 849                                 case BuiltinTypeSpec.Type.Byte:
 850                                         if (value >= 0 && value <= Byte.MaxValue)
 851                                                 return true;
 852                                         break;
 853                                 case BuiltinTypeSpec.Type.Short:
 854                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 855                                                 return true;
 856                                         break;
 857                                 case BuiltinTypeSpec.Type.UShort:
 858                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 859                                                 return true;
 860                                         break;
 861                                 case BuiltinTypeSpec.Type.UInt:
 862                                         if (value >= 0)
 863                                                 return true;
 864                                         break;
 865                                 case BuiltinTypeSpec.Type.ULong:
 866                                          //
 867                                          // we can optimize this case: a positive int32
 868                                          // always fits on a uint64.  But we need an opcode
 869                                          // to do it.
 870                                          //
 871                                         if (value >= 0)
 872                                                 return true;
 873
 874                                         break;
 875                                 }
 876                         }
 877
 878                         if (expr is LongConstant && target_type.BuiltinType == BuiltinTypeSpec.Type.ULong){
 879                                 //
 880                                 // Try the implicit constant expression conversion
 881                                 // from long to ulong, instead of a nice routine,
 882                                 // we just inline it
 883                                 //
 884                                 long v = ((LongConstant) expr).Value;
 885                                 if (v >= 0)
 886                                         return true;
 887                         }
 888
 889                         if (expr is IntegralConstant && target_type.IsEnum) {
 890                                 var i = (IntegralConstant) expr;
 891                                 //
 892                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
 893                                 //
 894                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
 895                                 // to be converted to any enum-type and to any nullable-type whose underlying
 896                                 // type is an enum-type
 897                                 //
 898                                 return i.IsZeroInteger;
 899                         }
 900
 901                         //
 902                         // Implicit dynamic conversion for remaining value types. It should probably
 903                         // go somewhere else
 904                         //
 905                         if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 906                                 switch (target_type.Kind) {
 907                                 case MemberKind.Struct:
 908                                 case MemberKind.Enum:
 909                                         return true;
 910                                 }
 911
 912                                 return false;
 913                         }
 914
 915                         //
 916                         // In an unsafe context implicit conversions is extended to include
 917                         //
 918                         // From any pointer-type to the type void*
 919                         // From the null literal to any pointer-type.
 920                         //
 921                         // LAMESPEC: The specification claims this conversion is allowed in implicit conversion but
 922                         // in reality implicit standard conversion uses it
 923                         //
 924                         if (target_type.IsPointer && expr.Type.IsPointer && ((PointerContainer) target_type).Element.Kind == MemberKind.Void)
 925                                 return true;
 926
 927                         //
 928                         // Struct identity conversion, including dynamic erasure
 929                         //
 930                         if (expr_type.IsStruct && TypeSpecComparer.IsEqual (expr_type, target_type))
 931                                 return true;
 932
 933                         return false;
 934                 }
 935
 936                 /// <summary>
 937                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 938                 ///  amongst the methods in the MethodGroupExpr
 939                 /// </summary>
 940                 public static TypeSpec FindMostEncompassedType (IList<TypeSpec> types)
 941                 {
 942                         TypeSpec best = null;
 943                         EmptyExpression expr;
 944
 945                         foreach (TypeSpec t in types) {
 946                                 if (best == null) {
 947                                         best = t;
 948                                         continue;
 949                                 }
 950
 951                                 expr = new EmptyExpression (t);
 952                                 if (ImplicitStandardConversionExists (expr, best))
 953                                         best = t;
 954                         }
 955
 956                         expr = new EmptyExpression (best);
 957                         foreach (TypeSpec t in types) {
 958                                 if (best == t)
 959                                         continue;
 960                                 if (!ImplicitStandardConversionExists (expr, t)) {
 961                                         best = null;
 962                                         break;
 963                                 }
 964                         }
 965
 966                         return best;
 967                 }
 968
 969                 //
 970                 // Finds the most encompassing type (type into which all other
 971                 // types can convert to) amongst the types in the given set
 972                 //
 973                 static TypeSpec FindMostEncompassingType (IList<TypeSpec> types)
 974                 {
 975                         if (types.Count == 0)
 976                                 return null;
 977
 978                         if (types.Count == 1)
 979                                 return types [0];
 980
 981                         TypeSpec best = null;
 982                         for (int i = 0; i < types.Count; ++i) {
 983                                 int ii = 0;
 984                                 for (; ii < types.Count; ++ii) {
 985                                         if (ii == i)
 986                                                 continue;
 987
 988                                         var expr = new EmptyExpression (types[ii]);
 989                                         if (!ImplicitStandardConversionExists (expr, types [i])) {
 990                                                 ii = 0;
 991                                                 break;
 992                                         }
 993                                 }
 994
 995                                 if (ii == 0)
 996                                         continue;
 997
 998                                 if (best == null) {
 999                                         best = types[i];
1000                                         continue;
1001                                 }
1002
1003                                 // Indicates multiple best types
1004                                 return InternalType.FakeInternalType;
1005                         }
1006
1007                         return best;
1008                 }
1009
1010                 //
1011                 // Finds the most specific source Sx according to the rules of the spec (13.4.4)
1012                 // by making use of FindMostEncomp* methods. Applies the correct rules separately
1013                 // for explicit and implicit conversion operators.
1014                 //
1015                 static TypeSpec FindMostSpecificSource (ResolveContext rc, List<MethodSpec> list, TypeSpec sourceType, Expression source, bool apply_explicit_conv_rules)
1016                 {
1017                         TypeSpec[] src_types_set = null;
1018
1019                         //
1020                         // Try exact match first, if any operator converts from S then Sx = S
1021                         //
1022                         for (int i = 0; i < list.Count; ++i) {
1023                                 TypeSpec param_type = list [i].Parameters.Types [0];
1024
1025                                 if (param_type == sourceType)
1026                                         return param_type;
1027
1028                                 if (src_types_set == null)
1029                                         src_types_set = new TypeSpec [list.Count];
1030
1031                                 src_types_set [i] = param_type;
1032                         }
1033
1034                         //
1035                         // Explicit Conv rules
1036                         //
1037                         if (apply_explicit_conv_rules) {
1038                                 var candidate_set = new List<TypeSpec> ();
1039
1040                                 foreach (TypeSpec param_type in src_types_set){
1041                                         if (ImplicitStandardConversionExists (rc, source, param_type))
1042                                                 candidate_set.Add (param_type);
1043                                 }
1044
1045                                 if (candidate_set.Count != 0) {
1046                                         if (source.eclass == ExprClass.MethodGroup)
1047                                                 return InternalType.FakeInternalType;
1048
1049                                         return FindMostEncompassedType (candidate_set);
1050                                 }
1051                         }
1052
1053                         //
1054                         // Final case
1055                         //
1056                         if (apply_explicit_conv_rules)
1057                                 return FindMostEncompassingType (src_types_set);
1058                         else
1059                                 return FindMostEncompassedType (src_types_set);
1060                 }
1061
1062                 /// <summary>
1063                 ///  Finds the most specific target Tx according to section 13.4.4
1064                 /// </summary>
1065                 static public TypeSpec FindMostSpecificTarget (IList<MethodSpec> list,
1066                                                            TypeSpec target, bool apply_explicit_conv_rules)
1067                 {
1068                         List<TypeSpec> tgt_types_set = null;
1069
1070                         //
1071                         // If any operator converts to T then Tx = T
1072                         //
1073                         foreach (var mi in list){
1074                                 TypeSpec ret_type = mi.ReturnType;
1075                                 if (ret_type == target)
1076                                         return ret_type;
1077
1078                                 if (tgt_types_set == null) {
1079                                         tgt_types_set = new List<TypeSpec> (list.Count);
1080                                 } else if (tgt_types_set.Contains (ret_type)) {
1081                                         continue;
1082                                 }
1083
1084                                 tgt_types_set.Add (ret_type);
1085                         }
1086
1087                         //
1088                         // Explicit conv rules
1089                         //
1090                         if (apply_explicit_conv_rules) {
1091                                 var candidate_set = new List<TypeSpec> ();
1092
1093                                 foreach (TypeSpec ret_type in tgt_types_set) {
1094                                         var expr = new EmptyExpression (ret_type);
1095
1096                                         if (ImplicitStandardConversionExists (expr, target))
1097                                                 candidate_set.Add (ret_type);
1098                                 }
1099
1100                                 if (candidate_set.Count != 0)
1101                                         return FindMostEncompassingType (candidate_set);
1102                         }
1103
1104                         //
1105                         // Okay, final case !
1106                         //
1107                         if (apply_explicit_conv_rules)
1108                                 return FindMostEncompassedType (tgt_types_set);
1109                         else
1110                                 return FindMostEncompassingType (tgt_types_set);
1111                 }
1112
1113                 /// <summary>
1114                 ///  User-defined Implicit conversions
1115                 /// </summary>
1116                 static public Expression ImplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
1117                 {
1118                         return UserDefinedConversion (ec, source, target, UserConversionRestriction.ImplicitOnly, loc);
1119                 }
1120
1121                 /// <summary>
1122                 ///  User-defined Explicit conversions
1123                 /// </summary>
1124                 static Expression ExplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
1125                 {
1126                         return UserDefinedConversion (ec, source, target, 0, loc);
1127                 }
1128
1129                 static void FindApplicableUserDefinedConversionOperators (ResolveContext rc, IList<MemberSpec> operators, Expression source, TypeSpec target, UserConversionRestriction restr, ref List<MethodSpec> candidates)
1130                 {
1131                         if (source.Type.IsInterface) {
1132                                 // Neither A nor B are interface-types
1133                                 return;
1134                         }
1135
1136                         // For a conversion operator to be applicable, it must be possible
1137                         // to perform a standard conversion from the source type to
1138                         // the operand type of the operator, and it must be possible
1139                         // to perform a standard conversion from the result type of
1140                         // the operator to the target type.
1141
1142                         Expression texpr = null;
1143
1144                         foreach (MethodSpec op in operators) {
1145
1146                                 // Can be null because MemberCache.GetUserOperator does not resize the array
1147                                 if (op == null)
1148                                         continue;
1149
1150                                 var t = op.Parameters.Types[0];
1151                                 if (source.Type != t && !ImplicitStandardConversionExists (rc, source, t)) {
1152                                         if ((restr & UserConversionRestriction.ImplicitOnly) != 0)
1153                                                 continue;
1154
1155                                         if (!ImplicitStandardConversionExists (new EmptyExpression (t), source.Type))
1156                                                         continue;
1157                                 }
1158
1159                                 if ((restr & UserConversionRestriction.NullableSourceOnly) != 0 && !t.IsNullableType)
1160                                         continue;
1161
1162                                 t = op.ReturnType;
1163
1164                                 if (t.IsInterface)
1165                                         continue;
1166
1167                                 if (target != t) {
1168                                         if (t.IsNullableType)
1169                                                 t = Nullable.NullableInfo.GetUnderlyingType (t);
1170
1171                                         if (!ImplicitStandardConversionExists (new EmptyExpression (t), target)) {
1172                                                 if ((restr & UserConversionRestriction.ImplicitOnly) != 0)
1173                                                         continue;
1174
1175                                                 if (texpr == null)
1176                                                         texpr = new EmptyExpression (target);
1177
1178                                                 if (!ImplicitStandardConversionExists (texpr, t))
1179                                                         continue;
1180                                         }
1181                                 }
1182
1183                                 if (candidates == null)
1184                                         candidates = new List<MethodSpec> ();
1185
1186                                 candidates.Add (op);
1187                         }
1188                 }
1189
1190                 //
1191                 // User-defined conversions
1192                 //
1193                 public static Expression UserDefinedConversion (ResolveContext rc, Expression source, TypeSpec target, UserConversionRestriction restr, Location loc)
1194                 {
1195                         List<MethodSpec> candidates = null;
1196
1197                         //
1198                         // If S or T are nullable types, source_type and target_type are their underlying types
1199                         // otherwise source_type and target_type are equal to S and T respectively.
1200                         //
1201                         TypeSpec source_type = source.Type;
1202                         TypeSpec target_type = target;
1203                         Expression source_type_expr;
1204                         bool nullable_source = false;
1205                         var implicitOnly = (restr & UserConversionRestriction.ImplicitOnly) != 0;
1206
1207                         if (source_type.IsNullableType) {
1208                                 // No unwrapping conversion S? -> T for non-reference types
1209                                 if (implicitOnly && !TypeSpec.IsReferenceType (target_type) && !target_type.IsNullableType) {
1210                                         source_type_expr = source;
1211                                 } else {
1212                                         source_type_expr = Nullable.Unwrap.CreateUnwrapped (source);
1213                                         source_type = source_type_expr.Type;
1214                                         nullable_source = true;
1215                                 }
1216                         } else {
1217                                 source_type_expr = source;
1218                         }
1219
1220                         if (target_type.IsNullableType)
1221                                 target_type = Nullable.NullableInfo.GetUnderlyingType (target_type);
1222
1223                         // Only these containers can contain a user defined implicit or explicit operators
1224                         const MemberKind user_conversion_kinds = MemberKind.Class | MemberKind.Struct | MemberKind.TypeParameter;
1225
1226                         if ((source_type.Kind & user_conversion_kinds) != 0 && source_type.BuiltinType != BuiltinTypeSpec.Type.Decimal) {
1227                                 bool declared_only = source_type.IsStruct;
1228
1229                                 var operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Implicit, declared_only);
1230                                 if (operators != null) {
1231                                         FindApplicableUserDefinedConversionOperators (rc, operators, source_type_expr, target_type, restr, ref candidates);
1232                                 }
1233
1234                                 if (!implicitOnly) {
1235                                         operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Explicit, declared_only);
1236                                         if (operators != null) {
1237                                                 FindApplicableUserDefinedConversionOperators (rc, operators, source_type_expr, target_type, restr, ref candidates);
1238                                         }
1239                                 }
1240                         }
1241
1242                         if ((target.Kind & user_conversion_kinds) != 0 && target_type.BuiltinType != BuiltinTypeSpec.Type.Decimal) {
1243                                 bool declared_only = target.IsStruct || implicitOnly;
1244
1245                                 var operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Implicit, declared_only);
1246                                 if (operators != null) {
1247                                         FindApplicableUserDefinedConversionOperators (rc, operators, source_type_expr, target_type, restr, ref candidates);
1248                                 }
1249
1250                                 if (!implicitOnly) {
1251                                         operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Explicit, declared_only);
1252                                         if (operators != null) {
1253                                                 FindApplicableUserDefinedConversionOperators (rc, operators, source_type_expr, target_type, restr, ref candidates);
1254                                         }
1255                                 }
1256                         }
1257
1258                         if (candidates == null)
1259                                 return null;
1260
1261                         //
1262                         // Find the most specific conversion operator
1263                         //
1264                         MethodSpec most_specific_operator;
1265                         TypeSpec s_x, t_x;
1266                         if (candidates.Count == 1) {
1267                                 most_specific_operator = candidates[0];
1268                                 s_x = most_specific_operator.Parameters.Types[0];
1269                                 t_x = most_specific_operator.ReturnType;
1270                         } else {
1271                                 //
1272                                 // Pass original source type to find the best match against input type and
1273                                 // not the unwrapped expression
1274                                 //
1275                                 s_x = FindMostSpecificSource (rc, candidates, source.Type, source_type_expr, !implicitOnly);
1276                                 if (s_x == null)
1277                                         return null;
1278
1279                                 t_x = FindMostSpecificTarget (candidates, target, !implicitOnly);
1280                                 if (t_x == null)
1281                                         return null;
1282
1283                                 most_specific_operator = null;
1284                                 for (int i = 0; i < candidates.Count; ++i) {
1285                                         if (candidates[i].ReturnType == t_x && candidates[i].Parameters.Types[0] == s_x) {
1286                                                 most_specific_operator = candidates[i];
1287                                                 break;
1288                                         }
1289                                 }
1290
1291                                 if (most_specific_operator == null) {
1292                                         //
1293                                         // Unless running in probing more
1294                                         //
1295                                         if ((restr & UserConversionRestriction.ProbingOnly) == 0) {
1296                                                 MethodSpec ambig_arg = candidates [0];
1297                                                 most_specific_operator = candidates [1];
1298                                                 /*
1299                                                 foreach (var candidate in candidates) {
1300                                                         if (candidate.ReturnType == t_x)
1301                                                                 most_specific_operator = candidate;
1302                                                         else if (candidate.Parameters.Types[0] == s_x)
1303                                                                 ambig_arg = candidate;
1304                                                 }
1305                                                 */
1306                                                 rc.Report.Error (457, loc,
1307                                                         "Ambiguous user defined operators `{0}' and `{1}' when converting from `{2}' to `{3}'",
1308                                                         ambig_arg.GetSignatureForError (), most_specific_operator.GetSignatureForError (),
1309                                                         source.Type.GetSignatureForError (), target.GetSignatureForError ());
1310                                         }
1311
1312                                         return ErrorExpression.Instance;
1313                                 }
1314                         }
1315
1316                         //
1317                         // Convert input type when it's different to best operator argument
1318                         //
1319                         if (s_x != source_type) {
1320                                 var c = source as Constant;
1321                                 if (c != null) {
1322                                         source = c.Reduce (rc, s_x);
1323                                         if (source == null)
1324                                                 c = null;
1325                                 }
1326
1327                                 if (c == null) {
1328                                         source = implicitOnly ?
1329                                                 ImplicitConversionStandard (rc, source_type_expr, s_x, loc) :
1330                                                 ExplicitConversionStandard (rc, source_type_expr, s_x, loc);
1331                                 }
1332                         } else {
1333                                 source = source_type_expr;
1334                         }
1335
1336                         source = new UserCast (most_specific_operator, source, loc).Resolve (rc);
1337
1338                         //
1339                         // Convert result type when it's different to best operator return type
1340                         //
1341                         if (t_x != target_type) {
1342                                 //
1343                                 // User operator is of T?
1344                                 //
1345                                 if (t_x.IsNullableType && (target.IsNullableType || !implicitOnly)) {
1346                                         //
1347                                         // User operator return type does not match target type we need
1348                                         // yet another conversion. This should happen for promoted numeric
1349                                         // types only
1350                                         //
1351                                         if (t_x != target) {
1352                                                 var unwrap = Nullable.Unwrap.CreateUnwrapped (source);
1353
1354                                                 source = implicitOnly ?
1355                                                         ImplicitConversionStandard (rc, unwrap, target_type, loc) :
1356                                                         ExplicitConversionStandard (rc, unwrap, target_type, loc);
1357
1358                                                 if (source == null)
1359                                                         return null;
1360
1361                                                 if (target.IsNullableType)
1362                                                         source = new Nullable.LiftedConversion (source, unwrap, target).Resolve (rc);
1363                                         }
1364                                 } else {
1365                                         source = implicitOnly ?
1366                                                 ImplicitConversionStandard (rc, source, target_type, loc) :
1367                                                 ExplicitConversionStandard (rc, source, target_type, loc);
1368
1369                                         if (source == null)
1370                                                 return null;
1371                                 }
1372                         }
1373
1374
1375                         //
1376                         // Source expression is of nullable type and underlying conversion returns
1377                         // only non-nullable type we need to lift it manually
1378                         //
1379                         if (nullable_source && !s_x.IsNullableType)
1380                                 return new Nullable.LiftedConversion (source, source_type_expr, target).Resolve (rc);
1381
1382                         //
1383                         // Target is of nullable type but source type is not, wrap the result expression
1384                         //
1385                         if (target.IsNullableType && !t_x.IsNullableType)
1386                                 source = Nullable.Wrap.Create (source, target);
1387
1388                         return source;
1389                 }
1390
1391                 /// <summary>
1392                 ///   Converts implicitly the resolved expression `expr' into the
1393                 ///   `target_type'.  It returns a new expression that can be used
1394                 ///   in a context that expects a `target_type'.
1395                 /// </summary>
1396                 static public Expression ImplicitConversion (ResolveContext ec, Expression expr,
1397                                                              TypeSpec target_type, Location loc)
1398                 {
1399                         Expression e;
1400
1401                         if (target_type == null)
1402                                 throw new Exception ("Target type is null");
1403
1404                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1405                         if (e != null)
1406                                 return e;
1407
1408                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1409                         if (e != null)
1410                                 return e;
1411
1412                         return null;
1413                 }
1414
1415
1416                 /// <summary>
1417                 ///   Attempts to apply the `Standard Implicit
1418                 ///   Conversion' rules to the expression `expr' into
1419                 ///   the `target_type'.  It returns a new expression
1420                 ///   that can be used in a context that expects a
1421                 ///   `target_type'.
1422                 ///
1423                 ///   This is different from `ImplicitConversion' in that the
1424                 ///   user defined implicit conversions are excluded.
1425                 /// </summary>
1426                 static public Expression ImplicitConversionStandard (ResolveContext ec, Expression expr,
1427                                                                      TypeSpec target_type, Location loc)
1428                 {
1429                         return ImplicitConversionStandard (ec, expr, target_type, loc, false);
1430                 }
1431
1432                 static Expression ImplicitConversionStandard (ResolveContext ec, Expression expr, TypeSpec target_type, Location loc, bool explicit_cast)
1433                 {
1434                         if (expr.eclass == ExprClass.MethodGroup){
1435                                 if (!target_type.IsDelegate){
1436                                         return null;
1437                                 }
1438
1439                                 //
1440                                 // Only allow anonymous method conversions on post ISO_1
1441                                 //
1442                                 if (ec.Module.Compiler.Settings.Version != LanguageVersion.ISO_1){
1443                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1444                                         if (mg != null)
1445                                                 return new ImplicitDelegateCreation (target_type, mg, loc).Resolve (ec);
1446                                 }
1447                         }
1448
1449                         TypeSpec expr_type = expr.Type;
1450                         Expression e;
1451
1452                         if (expr_type == target_type) {
1453                                 if (expr_type != InternalType.NullLiteral && expr_type != InternalType.AnonymousMethod && expr_type != InternalType.ThrowExpr)
1454                                         return expr;
1455                                 return null;
1456                         }
1457
1458                         if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
1459                                 switch (target_type.Kind) {
1460                                 case MemberKind.ArrayType:
1461                                 case MemberKind.Class:
1462                                         if (target_type.BuiltinType == BuiltinTypeSpec.Type.Object)
1463                                                 return EmptyCast.Create (expr, target_type);
1464
1465                                         goto case MemberKind.Struct;
1466                                 case MemberKind.Struct:
1467                                 case MemberKind.Delegate:
1468                                 case MemberKind.Enum:
1469                                 case MemberKind.Interface:
1470                                 case MemberKind.TypeParameter:
1471                                         Arguments args = new Arguments (1);
1472                                         args.Add (new Argument (expr));
1473                                         return new DynamicConversion (target_type, explicit_cast ? CSharpBinderFlags.ConvertExplicit : 0, args, loc).Resolve (ec);
1474                                 }
1475
1476                                 return null;
1477                         }
1478
1479                         if (expr_type == InternalType.ThrowExpr) {
1480                                 return target_type.Kind == MemberKind.InternalCompilerType ? null : EmptyCast.Create (expr, target_type);
1481                         }
1482
1483                         if (target_type.IsNullableType)
1484                                 return ImplicitNulableConversion (ec, expr, target_type);
1485
1486                         //
1487                         // Attempt to do the implicit constant expression conversions
1488                         //
1489                         Constant c = expr as Constant;
1490                         if (c != null) {
1491                                 try {
1492                                         c = c.ConvertImplicitly (target_type);
1493                                 } catch {
1494                                         throw new InternalErrorException ("Conversion error", loc);
1495                                 }
1496                                 if (c != null)
1497                                         return c;
1498                         }
1499
1500                         if (expr_type.IsTupleType) {
1501                                 if (target_type.IsTupleType)
1502                                         return ImplicitTupleLiteralConversion (ec, expr, target_type, loc);
1503
1504                                 if (expr is TupleLiteral && TupleLiteral.ContainsNoTypeElement (expr_type))
1505                                         return null;
1506                         }
1507
1508                         e = ImplicitNumericConversion (expr, expr_type, target_type);
1509                         if (e != null)
1510                                 return e;
1511
1512                         e = ImplicitReferenceConversion (expr, target_type, explicit_cast);
1513                         if (e != null)
1514                                 return e;
1515
1516                         e = ImplicitBoxingConversion (expr, expr_type, target_type);
1517                         if (e != null)
1518                                 return e;
1519
1520                         if (expr is IntegralConstant && target_type.IsEnum){
1521                                 var i = (IntegralConstant) expr;
1522                                 //
1523                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
1524                                 //
1525                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
1526                                 // to be converted to any enum-type and to any nullable-type whose underlying
1527                                 // type is an enum-type
1528                                 //
1529                                 if (i.IsZeroInteger) {
1530                                         // Recreate 0 literal to remove any collected conversions
1531                                         return new EnumConstant (new IntLiteral (ec.BuiltinTypes, 0, i.Location), target_type);
1532                                 }
1533                         }
1534
1535                         var target_pc = target_type as PointerContainer;
1536                         if (target_pc != null) {
1537                                 if (expr_type.IsPointer) {
1538                                         //
1539                                         // Pointer types are same when they have same element types
1540                                         //
1541                                         if (expr_type == target_pc)
1542                                                 return expr;
1543
1544                                         if (target_pc.Element.Kind == MemberKind.Void)
1545                                                 return EmptyCast.Create (expr, target_type);
1546
1547                                                 //return null;
1548                                 }
1549
1550                                 if (expr_type == InternalType.NullLiteral)
1551                                         return new NullPointer (target_type, loc);
1552                         }
1553
1554                         if (expr_type == InternalType.AnonymousMethod){
1555                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1556                                 Expression am = ame.Compatible (ec, target_type);
1557                                 if (am != null)
1558                                         return am.Resolve (ec);
1559
1560                                 // Avoid CS1503 after CS1661
1561                                 return ErrorExpression.Instance;
1562                         }
1563
1564                         if (expr_type == InternalType.Arglist && target_type == ec.Module.PredefinedTypes.ArgIterator.TypeSpec)
1565                                 return expr;
1566
1567                         //
1568                         // dynamic erasure conversion on value types
1569                         //
1570                         if (expr_type.IsStruct && TypeSpecComparer.IsEqual (expr_type, target_type))
1571                                 return expr_type == target_type ? expr : EmptyCast.Create (expr, target_type);
1572
1573                         var interpolated_string = expr as InterpolatedString;
1574                         if (interpolated_string != null) {
1575                                 if (target_type == ec.Module.PredefinedTypes.IFormattable.TypeSpec || target_type == ec.Module.PredefinedTypes.FormattableString.TypeSpec)
1576                                         return interpolated_string.ConvertTo (ec, target_type);
1577                         }
1578
1579                         return null;
1580                 }
1581
1582                 /// <summary>
1583                 ///   Attempts to implicitly convert `source' into `target_type', using
1584                 ///   ImplicitConversion.  If there is no implicit conversion, then
1585                 ///   an error is signaled
1586                 /// </summary>
1587                 public static Expression ImplicitConversionRequired (ResolveContext ec, Expression source,
1588                                                                      TypeSpec target_type, Location loc)
1589                 {
1590                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1591                         if (e != null)
1592                                 return e;
1593
1594                         if (target_type != InternalType.ErrorType)
1595                                 source.Error_ValueCannotBeConverted (ec, target_type, false);
1596
1597                         return null;
1598                 }
1599
1600                 /// <summary>
1601                 ///   Performs the explicit numeric conversions
1602                 ///
1603                 /// There are a few conversions that are not part of the C# standard,
1604                 /// they were interim hacks in the C# compiler that were supposed to
1605                 /// become explicit operators in the UIntPtr class and IntPtr class,
1606                 /// but for historical reasons it did not happen, so the C# compiler
1607                 /// ended up with these special hacks.
1608                 ///
1609                 /// See bug 59800 for details.
1610                 ///
1611                 /// The conversion are:
1612                 ///   UIntPtr->SByte
1613                 ///   UIntPtr->Int16
1614                 ///   UIntPtr->Int32
1615                 ///   IntPtr->UInt64
1616                 ///   UInt64->IntPtr
1617                 ///   SByte->UIntPtr
1618                 ///   Int16->UIntPtr
1619                 ///
1620                 /// </summary>
1621                 public static Expression ExplicitNumericConversion (ResolveContext rc, Expression expr, TypeSpec target_type)
1622                 {
1623                         // Not all predefined explicit numeric conversion are
1624                         // defined here, for some of them (mostly IntPtr/UIntPtr) we
1625                         // defer to user-operator handling which is now perfect but
1626                         // works for now
1627                         //
1628                         // LAMESPEC: Undocumented IntPtr/UIntPtr conversions
1629                         // IntPtr -> uint uses int
1630                         // UIntPtr -> long uses ulong
1631                         //
1632
1633                         switch (expr.Type.BuiltinType) {
1634                         case BuiltinTypeSpec.Type.SByte:
1635                                 //
1636                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1637                                 //
1638                                 switch (target_type.BuiltinType) {
1639                                 case BuiltinTypeSpec.Type.Byte:
1640                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1641                                 case BuiltinTypeSpec.Type.UShort:
1642                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1643                                 case BuiltinTypeSpec.Type.UInt:
1644                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1645                                 case BuiltinTypeSpec.Type.ULong:
1646                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1647                                 case BuiltinTypeSpec.Type.Char:
1648                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1649
1650                                 // One of the built-in conversions that belonged in the class library
1651                                 case BuiltinTypeSpec.Type.UIntPtr:
1652                                         return new OperatorCast (new ConvCast (expr, rc.BuiltinTypes.ULong, ConvCast.Mode.I1_U8), target_type, target_type, true);
1653                                 }
1654                                 break;
1655                         case BuiltinTypeSpec.Type.Byte:
1656                                 //
1657                                 // From byte to sbyte and char
1658                                 //
1659                                 switch (target_type.BuiltinType) {
1660                                 case BuiltinTypeSpec.Type.SByte:
1661                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1662                                 case BuiltinTypeSpec.Type.Char:
1663                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1664                                 }
1665                                 break;
1666                         case BuiltinTypeSpec.Type.Short:
1667                                 //
1668                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1669                                 //
1670                                 switch (target_type.BuiltinType) {
1671                                 case BuiltinTypeSpec.Type.SByte:
1672                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1673                                 case BuiltinTypeSpec.Type.Byte:
1674                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1675                                 case BuiltinTypeSpec.Type.UShort:
1676                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1677                                 case BuiltinTypeSpec.Type.UInt:
1678                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1679                                 case BuiltinTypeSpec.Type.ULong:
1680                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1681                                 case BuiltinTypeSpec.Type.Char:
1682                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1683
1684                                 // One of the built-in conversions that belonged in the class library
1685                                 case BuiltinTypeSpec.Type.UIntPtr:
1686                                         return new OperatorCast (new ConvCast (expr, rc.BuiltinTypes.ULong, ConvCast.Mode.I2_U8), target_type, target_type, true);
1687                                 }
1688                                 break;
1689                         case BuiltinTypeSpec.Type.UShort:
1690                                 //
1691                                 // From ushort to sbyte, byte, short, char
1692                                 //
1693                                 switch (target_type.BuiltinType) {
1694                                 case BuiltinTypeSpec.Type.SByte:
1695                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1696                                 case BuiltinTypeSpec.Type.Byte:
1697                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1698                                 case BuiltinTypeSpec.Type.Short:
1699                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1700                                 case BuiltinTypeSpec.Type.Char:
1701                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1702                                 }
1703                                 break;
1704                         case BuiltinTypeSpec.Type.Int:
1705                                 //
1706                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1707                                 //
1708                                 switch (target_type.BuiltinType) {
1709                                 case BuiltinTypeSpec.Type.SByte:
1710                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1711                                 case BuiltinTypeSpec.Type.Byte:
1712                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1713                                 case BuiltinTypeSpec.Type.Short:
1714                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1715                                 case BuiltinTypeSpec.Type.UShort:
1716                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1717                                 case BuiltinTypeSpec.Type.UInt:
1718                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1719                                 case BuiltinTypeSpec.Type.ULong:
1720                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1721                                 case BuiltinTypeSpec.Type.Char:
1722                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1723
1724                                 // One of the built-in conversions that belonged in the class library
1725                                 case BuiltinTypeSpec.Type.UIntPtr:
1726                                         return new OperatorCast (new ConvCast (expr, rc.BuiltinTypes.ULong, ConvCast.Mode.I2_U8), target_type, target_type, true);
1727                                 }
1728                                 break;
1729                         case BuiltinTypeSpec.Type.UInt:
1730                                 //
1731                                 // From uint to sbyte, byte, short, ushort, int, char
1732                                 //
1733                                 switch (target_type.BuiltinType) {
1734                                 case BuiltinTypeSpec.Type.SByte:
1735                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1736                                 case BuiltinTypeSpec.Type.Byte:
1737                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1738                                 case BuiltinTypeSpec.Type.Short:
1739                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1740                                 case BuiltinTypeSpec.Type.UShort:
1741                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1742                                 case BuiltinTypeSpec.Type.Int:
1743                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1744                                 case BuiltinTypeSpec.Type.Char:
1745                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1746                                 }
1747                                 break;
1748                         case BuiltinTypeSpec.Type.Long:
1749                                 //
1750                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1751                                 //
1752                                 switch (target_type.BuiltinType) {
1753                                 case BuiltinTypeSpec.Type.SByte:
1754                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1755                                 case BuiltinTypeSpec.Type.Byte:
1756                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1757                                 case BuiltinTypeSpec.Type.Short:
1758                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1759                                 case BuiltinTypeSpec.Type.UShort:
1760                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1761                                 case BuiltinTypeSpec.Type.Int:
1762                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1763                                 case BuiltinTypeSpec.Type.UInt:
1764                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1765                                 case BuiltinTypeSpec.Type.ULong:
1766                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1767                                 case BuiltinTypeSpec.Type.Char:
1768                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1769                                 }
1770                                 break;
1771                         case BuiltinTypeSpec.Type.ULong:
1772                                 //
1773                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1774                                 //
1775                                 switch (target_type.BuiltinType) {
1776                                 case BuiltinTypeSpec.Type.SByte:
1777                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1778                                 case BuiltinTypeSpec.Type.Byte:
1779                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1780                                 case BuiltinTypeSpec.Type.Short:
1781                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1782                                 case BuiltinTypeSpec.Type.UShort:
1783                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1784                                 case BuiltinTypeSpec.Type.Int:
1785                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1786                                 case BuiltinTypeSpec.Type.UInt:
1787                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1788                                 case BuiltinTypeSpec.Type.Long:
1789                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1790                                 case BuiltinTypeSpec.Type.Char:
1791                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1792
1793                                 // One of the built-in conversions that belonged in the class library
1794                                 case BuiltinTypeSpec.Type.IntPtr:
1795                                         return new OperatorCast (EmptyCast.Create (expr, rc.BuiltinTypes.Long), target_type, true);
1796                                 }
1797                                 break;
1798                         case BuiltinTypeSpec.Type.Char:
1799                                 //
1800                                 // From char to sbyte, byte, short
1801                                 //
1802                                 switch (target_type.BuiltinType) {
1803                                 case BuiltinTypeSpec.Type.SByte:
1804                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1805                                 case BuiltinTypeSpec.Type.Byte:
1806                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1807                                 case BuiltinTypeSpec.Type.Short:
1808                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1809                                 }
1810                                 break;
1811                         case BuiltinTypeSpec.Type.Float:
1812                                 //
1813                                 // From float to sbyte, byte, short,
1814                                 // ushort, int, uint, long, ulong, char
1815                                 // or decimal
1816                                 //
1817                                 switch (target_type.BuiltinType) {
1818                                 case BuiltinTypeSpec.Type.SByte:
1819                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1820                                 case BuiltinTypeSpec.Type.Byte:
1821                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1822                                 case BuiltinTypeSpec.Type.Short:
1823                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1824                                 case BuiltinTypeSpec.Type.UShort:
1825                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1826                                 case BuiltinTypeSpec.Type.Int:
1827                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1828                                 case BuiltinTypeSpec.Type.UInt:
1829                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1830                                 case BuiltinTypeSpec.Type.Long:
1831                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1832                                 case BuiltinTypeSpec.Type.ULong:
1833                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1834                                 case BuiltinTypeSpec.Type.Char:
1835                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1836                                 case BuiltinTypeSpec.Type.Decimal:
1837                                         return new OperatorCast (expr, target_type, true);
1838                                 }
1839                                 break;
1840                         case BuiltinTypeSpec.Type.Double:
1841                                 //
1842                                 // From double to sbyte, byte, short,
1843                                 // ushort, int, uint, long, ulong,
1844                                 // char, float or decimal
1845                                 //
1846                                 switch (target_type.BuiltinType) {
1847                                 case BuiltinTypeSpec.Type.SByte:
1848                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1849                                 case BuiltinTypeSpec.Type.Byte:
1850                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1851                                 case BuiltinTypeSpec.Type.Short:
1852                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1853                                 case BuiltinTypeSpec.Type.UShort:
1854                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1855                                 case BuiltinTypeSpec.Type.Int:
1856                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1857                                 case BuiltinTypeSpec.Type.UInt:
1858                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1859                                 case BuiltinTypeSpec.Type.Long:
1860                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1861                                 case BuiltinTypeSpec.Type.ULong:
1862                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1863                                 case BuiltinTypeSpec.Type.Char:
1864                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1865                                 case BuiltinTypeSpec.Type.Float:
1866                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1867                                 case BuiltinTypeSpec.Type.Decimal:
1868                                         return new OperatorCast (expr, target_type, true);
1869                                 }
1870                                 break;
1871                         case BuiltinTypeSpec.Type.UIntPtr:
1872                                 //
1873                                 // Various built-in conversions that belonged in the class library
1874                                 //
1875                                 // from uintptr to sbyte, short, int32
1876                                 //
1877                                 switch (target_type.BuiltinType) {
1878                                 case BuiltinTypeSpec.Type.SByte:
1879                                         return new ConvCast (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.UInt, true), target_type, ConvCast.Mode.U4_I1);
1880                                 case BuiltinTypeSpec.Type.Short:
1881                                         return new ConvCast (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.UInt, true), target_type, ConvCast.Mode.U4_I2);
1882                                 case BuiltinTypeSpec.Type.Int:
1883                                         return EmptyCast.Create (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.UInt, true), target_type);
1884                                 case BuiltinTypeSpec.Type.UInt:
1885                                         return new OperatorCast (expr, expr.Type, target_type, true);
1886                                 case BuiltinTypeSpec.Type.Long:
1887                                         return EmptyCast.Create (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.ULong, true), target_type);
1888                                 }
1889                                 break;
1890                         case BuiltinTypeSpec.Type.IntPtr:
1891                                 if (target_type.BuiltinType == BuiltinTypeSpec.Type.UInt)
1892                                         return EmptyCast.Create (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.Int, true), target_type);
1893                                 if (target_type.BuiltinType == BuiltinTypeSpec.Type.ULong)
1894                                         return EmptyCast.Create (new OperatorCast (expr, expr.Type, rc.BuiltinTypes.Long, true), target_type);
1895
1896                                 break;
1897                         case BuiltinTypeSpec.Type.Decimal:
1898                                 // From decimal to sbyte, byte, short,
1899                                 // ushort, int, uint, long, ulong, char,
1900                                 // float, or double
1901                                 switch (target_type.BuiltinType) {
1902                                 case BuiltinTypeSpec.Type.SByte:
1903                                 case BuiltinTypeSpec.Type.Byte:
1904                                 case BuiltinTypeSpec.Type.Short:
1905                                 case BuiltinTypeSpec.Type.UShort:
1906                                 case BuiltinTypeSpec.Type.Int:
1907                                 case BuiltinTypeSpec.Type.UInt:
1908                                 case BuiltinTypeSpec.Type.Long:
1909                                 case BuiltinTypeSpec.Type.ULong:
1910                                 case BuiltinTypeSpec.Type.Char:
1911                                 case BuiltinTypeSpec.Type.Float:
1912                                 case BuiltinTypeSpec.Type.Double:
1913                                         return new OperatorCast (expr, expr.Type, target_type, true);
1914                                 }
1915
1916                                 break;
1917                         }
1918
1919                         return null;
1920                 }
1921
1922                 /// <summary>
1923                 ///  Returns whether an explicit reference conversion can be performed
1924                 ///  from source_type to target_type
1925                 /// </summary>
1926                 public static bool ExplicitReferenceConversionExists (TypeSpec source_type, TypeSpec target_type)
1927                 {
1928                         Expression e = ExplicitReferenceConversion (null, source_type, target_type);
1929                         if (e == null)
1930                                 return false;
1931
1932                         if (e == EmptyExpression.Null)
1933                                 return true;
1934
1935                         throw new InternalErrorException ("Invalid probing conversion result");
1936                 }
1937
1938                 /// <summary>
1939                 ///   Implements Explicit Reference conversions
1940                 /// </summary>
1941                 static Expression ExplicitReferenceConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
1942                 {
1943                         //
1944                         // From object to a generic parameter
1945                         //
1946                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.Object && TypeManager.IsGenericParameter (target_type))
1947                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1948
1949                         //
1950                         // Explicit type parameter conversion from T
1951                         //
1952                         if (source_type.Kind == MemberKind.TypeParameter)
1953                                 return ExplicitTypeParameterConversionFromT (source, source_type, target_type);
1954
1955                         bool target_is_value_type = target_type.Kind == MemberKind.Struct || target_type.Kind == MemberKind.Enum;
1956
1957                         //
1958                         // Unboxing conversion from System.ValueType to any non-nullable-value-type
1959                         //
1960                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.ValueType && target_is_value_type)
1961                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1962
1963                         //
1964                         // From object or dynamic to any reference type or value type (unboxing)
1965                         //
1966                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.Object || source_type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
1967                                 if (target_type.IsPointer)
1968                                         return null;
1969
1970                                 return
1971                                         source == null ? EmptyExpression.Null :
1972                                         target_is_value_type ? new UnboxCast (source, target_type) :
1973                                         source is Constant ? (Expression) new EmptyConstantCast ((Constant) source, target_type) :
1974                                         new ClassCast (source, target_type);
1975                         }
1976
1977                         //
1978                         // From any class S to any class-type T, provided S is a base class of T
1979                         //
1980                         if (source_type.Kind == MemberKind.Class && TypeSpec.IsBaseClass (target_type, source_type, true))
1981                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1982
1983                         //
1984                         // From any interface-type S to to any class type T, provided T is not
1985                         // sealed, or provided T implements S.
1986                         //
1987                         // This also covers Explicit conversions involving type parameters
1988                         // section From any interface type to T
1989                         //
1990                         if (source_type.Kind == MemberKind.Interface) {
1991                                 if (!target_type.IsSealed || target_type.ImplementsInterface (source_type, true)) {
1992                                         if (source == null)
1993                                                 return EmptyExpression.Null;
1994
1995                                         //
1996                                         // Unboxing conversion from any interface-type to any non-nullable-value-type that
1997                                         // implements the interface-type
1998                                         //
1999                                         return target_is_value_type ? new UnboxCast (source, target_type) : (Expression) new ClassCast (source, target_type);
2000                                 }
2001
2002                                 //
2003                                 // From System.Collections.Generic.IList<T> and its base interfaces to a one-dimensional
2004                                 // array type S[], provided there is an implicit or explicit reference conversion from S to T.
2005                                 //
2006                                 var target_array = target_type as ArrayContainer;
2007                                 if (target_array != null && IList_To_Array (source_type, target_array))
2008                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
2009
2010                                 return null;
2011                         }
2012
2013                         var source_array = source_type as ArrayContainer;
2014                         if (source_array != null) {
2015                                 var target_array = target_type as ArrayContainer;
2016                                 if (target_array != null) {
2017                                         //
2018                                         // From System.Array to any array-type
2019                                         //
2020                                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.Array)
2021                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
2022
2023                                         //
2024                                         // From an array type S with an element type Se to an array type T with an
2025                                         // element type Te provided all the following are true:
2026                                         //     * S and T differe only in element type, in other words, S and T
2027                                         //       have the same number of dimensions.
2028                                         //     * Both Se and Te are reference types
2029                                         //     * An explicit reference conversions exist from Se to Te
2030                                         //
2031                                         if (source_array.Rank == target_array.Rank) {
2032
2033                                                 source_type = source_array.Element;
2034                                                 var target_element = target_array.Element;
2035
2036                                                 //
2037                                                 // LAMESPEC: Type parameters are special cased somehow but
2038                                                 // only when both source and target elements are type parameters
2039                                                 //
2040                                                 if ((source_type.Kind & target_element.Kind & MemberKind.TypeParameter) == MemberKind.TypeParameter) {
2041                                                         //
2042                                                         // Conversion is allowed unless source element type has struct constrain
2043                                                         //
2044                                                         if (TypeSpec.IsValueType (source_type))
2045                                                                 return null;
2046                                                 } else {
2047                                                         if (!TypeSpec.IsReferenceType (source_type))
2048                                                                 return null;
2049                                                 }
2050
2051                                                 if (!TypeSpec.IsReferenceType (target_element))
2052                                                         return null;
2053
2054                                                 if (ExplicitReferenceConversionExists (source_type, target_element))
2055                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
2056
2057                                                 return null;
2058                                         }
2059                                 }
2060
2061                                 //
2062                                 // From a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its base interfaces,
2063                                 // provided that there is an explicit reference conversion from S to T
2064                                 //
2065                                 if (ArrayToIList (source_array, target_type, true))
2066                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
2067
2068                                 return null;
2069                         }
2070
2071                         //
2072                         // From any class type S to any interface T, provides S is not sealed
2073                         // and provided S does not implement T.
2074                         //
2075                         if (target_type.IsInterface && !source_type.IsSealed && !source_type.ImplementsInterface (target_type, true)) {
2076                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
2077                         }
2078
2079                         //
2080                         // From System delegate to any delegate-type
2081                         //
2082                         if (source_type.BuiltinType == BuiltinTypeSpec.Type.Delegate && target_type.IsDelegate)
2083                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
2084
2085                         //
2086                         // From variant generic delegate to same variant generic delegate type
2087                         //
2088                         if (source_type.IsDelegate && target_type.IsDelegate && source_type.MemberDefinition == target_type.MemberDefinition) {
2089                                 var tparams = source_type.MemberDefinition.TypeParameters;
2090                                 var targs_src = source_type.TypeArguments;
2091                                 var targs_dst = target_type.TypeArguments;
2092                                 int i;
2093                                 for (i = 0; i < tparams.Length; ++i) {
2094                                         //
2095                                         // If TP is invariant, types have to be identical
2096                                         //
2097                                         if (TypeSpecComparer.IsEqual (targs_src[i], targs_dst[i]))
2098                                                 continue;
2099
2100                                         if (tparams[i].Variance == Variance.Covariant) {
2101                                                 //
2102                                                 //If TP is covariant, an implicit or explicit identity or reference conversion is required
2103                                                 //
2104                                                 if (ImplicitReferenceConversionExists (targs_src[i], targs_dst[i]))
2105                                                         continue;
2106
2107                                                 if (ExplicitReferenceConversionExists (targs_src[i], targs_dst[i]))
2108                                                         continue;
2109
2110                                         } else if (tparams[i].Variance == Variance.Contravariant) {
2111                                                 //
2112                                                 //If TP is contravariant, both are either identical or reference types
2113                                                 //
2114                                                 if (TypeSpec.IsReferenceType (targs_src[i]) && TypeSpec.IsReferenceType (targs_dst[i]))
2115                                                         continue;
2116                                         }
2117
2118                                         break;
2119                                 }
2120
2121                                 if (i == tparams.Length)
2122                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
2123                         }
2124
2125                         var tps = target_type as TypeParameterSpec;
2126                         if (tps != null)
2127                                 return ExplicitTypeParameterConversionToT (source, source_type, tps);
2128
2129                         return null;
2130                 }
2131
2132                 /// <summary>
2133                 ///   Performs an explicit conversion of the expression `expr' whose
2134                 ///   type is expr.Type to `target_type'.
2135                 /// </summary>
2136                 static public Expression ExplicitConversionCore (ResolveContext ec, Expression expr,
2137                                                                  TypeSpec target_type, Location loc)
2138                 {
2139                         TypeSpec expr_type = expr.Type;
2140
2141                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
2142                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc, true);
2143                         if (ne != null)
2144                                 return ne;
2145
2146                         if (expr_type.IsEnum) {
2147                                 TypeSpec real_target = target_type.IsEnum ? EnumSpec.GetUnderlyingType (target_type) : target_type;
2148                                 Expression underlying = EmptyCast.Create (expr, EnumSpec.GetUnderlyingType (expr_type));
2149                                 if (underlying.Type == real_target)
2150                                         ne = underlying;
2151
2152                                 if (ne == null)
2153                                         ne = ImplicitNumericConversion (underlying, real_target);
2154
2155                                 if (ne == null)
2156                                         ne = ExplicitNumericConversion (ec, underlying, real_target);
2157
2158                                 //
2159                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
2160                                 //
2161                                 if (ne == null && (real_target.BuiltinType == BuiltinTypeSpec.Type.IntPtr || real_target.BuiltinType == BuiltinTypeSpec.Type.UIntPtr))
2162                                         ne = ExplicitUserConversion (ec, underlying, real_target, loc);
2163
2164                                 return ne != null ? EmptyCast.Create (ne, target_type) : null;
2165                         }
2166
2167                         if (target_type.IsEnum) {
2168                                 //
2169                                 // System.Enum can be unboxed to any enum-type
2170                                 //
2171                                 if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Enum)
2172                                         return new UnboxCast (expr, target_type);
2173
2174                                 TypeSpec real_target = target_type.IsEnum ? EnumSpec.GetUnderlyingType (target_type) : target_type;
2175
2176                                 if (expr_type == real_target)
2177                                         return EmptyCast.Create (expr, target_type);
2178
2179                                 Constant c = expr as Constant;
2180                                 if (c != null) {
2181                                         c = c.TryReduce (ec, real_target);
2182                                         if (c != null)
2183                                                 return c;
2184                                 } else {
2185                                         ne = ImplicitNumericConversion (expr, real_target);
2186                                         if (ne != null)
2187                                                 return EmptyCast.Create (ne, target_type);
2188
2189                                         ne = ExplicitNumericConversion (ec, expr, real_target);
2190                                         if (ne != null)
2191                                                 return EmptyCast.Create (ne, target_type);
2192
2193                                         //
2194                                         // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
2195                                         //
2196                                         if (expr_type.BuiltinType == BuiltinTypeSpec.Type.IntPtr || expr_type.BuiltinType == BuiltinTypeSpec.Type.UIntPtr) {
2197                                                 ne = ExplicitUserConversion (ec, expr, real_target, loc);
2198                                                 if (ne != null)
2199                                                         return ExplicitConversionCore (ec, ne, target_type, loc);
2200                                         }
2201                                 }
2202                         } else {
2203                                 ne = ExplicitNumericConversion (ec, expr, target_type);
2204                                 if (ne != null)
2205                                         return ne;
2206                         }
2207
2208                         //
2209                         // Skip the ExplicitReferenceConversion because we can not convert
2210                         // from Null to a ValueType, and ExplicitReference wont check against
2211                         // null literal explicitly
2212                         //
2213                         if (expr_type != InternalType.NullLiteral) {
2214                                 ne = ExplicitReferenceConversion (expr, expr_type, target_type);
2215                                 if (ne != null)
2216                                         return ne;
2217                         }
2218
2219                         if (ec.IsUnsafe){
2220                                 ne = ExplicitUnsafe (expr, target_type);
2221                                 if (ne != null)
2222                                         return ne;
2223                         }
2224
2225                         return null;
2226                 }
2227
2228                 public static Expression ExplicitUnsafe (Expression expr, TypeSpec target_type)
2229                 {
2230                         TypeSpec expr_type = expr.Type;
2231
2232                         if (target_type.IsPointer){
2233                                 if (expr_type.IsPointer)
2234                                         return EmptyCast.Create (expr, target_type);
2235
2236                                 switch (expr_type.BuiltinType) {
2237                                 case BuiltinTypeSpec.Type.SByte:
2238                                 case BuiltinTypeSpec.Type.Short:
2239                                 case BuiltinTypeSpec.Type.Int:
2240                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
2241
2242                                 case BuiltinTypeSpec.Type.UShort:
2243                                 case BuiltinTypeSpec.Type.UInt:
2244                                 case BuiltinTypeSpec.Type.Byte:
2245                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
2246
2247                                 case BuiltinTypeSpec.Type.Long:
2248                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I);
2249
2250                                 case BuiltinTypeSpec.Type.ULong:
2251                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I);
2252                                 }
2253                         }
2254
2255                         if (expr_type.IsPointer){
2256                                 switch (target_type.BuiltinType) {
2257                                 case BuiltinTypeSpec.Type.SByte:
2258                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
2259                                 case BuiltinTypeSpec.Type.Byte:
2260                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
2261                                 case BuiltinTypeSpec.Type.Short:
2262                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
2263                                 case BuiltinTypeSpec.Type.UShort:
2264                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
2265                                 case BuiltinTypeSpec.Type.Int:
2266                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
2267                                 case BuiltinTypeSpec.Type.UInt:
2268                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
2269                                 case BuiltinTypeSpec.Type.Long:
2270                                         return new ConvCast (expr, target_type, ConvCast.Mode.I_I8);
2271                                 case BuiltinTypeSpec.Type.ULong:
2272                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
2273                                 }
2274                         }
2275                         return null;
2276                 }
2277
2278                 /// <summary>
2279                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
2280                 /// </summary>
2281                 static public Expression ExplicitConversionStandard (ResolveContext ec, Expression expr,
2282                                                                      TypeSpec target_type, Location l)
2283                 {
2284                         int errors = ec.Report.Errors;
2285                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
2286                         if (ec.Report.Errors > errors)
2287                                 return null;
2288
2289                         if (ne != null)
2290                                 return ne;
2291
2292                         ne = ExplicitNumericConversion (ec, expr, target_type);
2293                         if (ne != null)
2294                                 return ne;
2295
2296                         ne = ExplicitReferenceConversion (expr, expr.Type, target_type);
2297                         if (ne != null)
2298                                 return ne;
2299
2300                         if (ec.IsUnsafe && expr.Type.IsPointer && target_type.IsPointer && ((PointerContainer)expr.Type).Element.Kind == MemberKind.Void)
2301                                 return EmptyCast.Create (expr, target_type);
2302
2303                         expr.Error_ValueCannotBeConverted (ec, target_type, true);
2304                         return null;
2305                 }
2306
2307                 /// <summary>
2308                 ///   Performs an explicit conversion of the expression `expr' whose
2309                 ///   type is expr.Type to `target_type'.
2310                 /// </summary>
2311                 static public Expression ExplicitConversion (ResolveContext ec, Expression expr,
2312                         TypeSpec target_type, Location loc)
2313                 {
2314                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
2315                         if (e != null) {
2316                                 //
2317                                 // Don't eliminate explicit precission casts
2318                                 //
2319                                 if (e == expr) {
2320                                         if (target_type.BuiltinType == BuiltinTypeSpec.Type.Float)
2321                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
2322
2323                                         if (target_type.BuiltinType == BuiltinTypeSpec.Type.Double)
2324                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
2325                                 }
2326
2327                                 return e;
2328                         }
2329
2330                         TypeSpec expr_type = expr.Type;
2331                         if (target_type.IsNullableType) {
2332                                 TypeSpec target;
2333
2334                                 if (expr_type.IsNullableType) {
2335                                         target = Nullable.NullableInfo.GetUnderlyingType (target_type);
2336                                         Expression unwrap = Nullable.Unwrap.Create (expr);
2337                                         e = ExplicitConversion (ec, unwrap, target, expr.Location);
2338                                         if (e == null)
2339                                                 return null;
2340
2341                                         return new Nullable.LiftedConversion (e, unwrap, target_type).Resolve (ec);
2342                                 }
2343                                 if (expr_type.BuiltinType == BuiltinTypeSpec.Type.Object) {
2344                                         return new UnboxCast (expr, target_type);
2345                                 }
2346
2347                                 target = TypeManager.GetTypeArguments (target_type) [0];
2348                                 e = ExplicitConversionCore (ec, expr, target, loc);
2349                                 if (e != null)
2350                                         return TypeSpec.IsReferenceType (expr.Type) ? new UnboxCast (expr, target_type) : Nullable.Wrap.Create (e, target_type);
2351                         } else if (expr_type.IsNullableType) {
2352                                 e = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
2353                                 if (e != null)
2354                                         return e;
2355
2356                                 e = Nullable.Unwrap.Create (expr, false);
2357                                 e = ExplicitConversionCore (ec, e, target_type, loc);
2358                                 if (e != null)
2359                                         return EmptyCast.Create (e, target_type);
2360                         }
2361
2362                         e = ExplicitUserConversion (ec, expr, target_type, loc);
2363
2364                         if (e != null)
2365                                 return e;
2366
2367                         expr.Error_ValueCannotBeConverted (ec, target_type, true);
2368                         return null;
2369                 }
2370         }
2371 }