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 //
  12
  13 using System;
  14 using System.Collections.Generic;
  15 using System.Diagnostics;
  16 using System.Reflection;
  17 using System.Reflection.Emit;
  18
  19 namespace Mono.CSharp {
  20
  21         //
  22         // A container class for all the conversion operations
  23         //
  24         static class Convert {
  25
  26                 static EmptyExpression MyEmptyExpr;
  27
  28                 static Convert ()
  29                 {
  30                         Reset ();
  31                 }
  32
  33                 public static void Reset ()
  34                 {
  35                         MyEmptyExpr = null;
  36                 }
  37
  38                 //
  39                 // From a one-dimensional array-type S[] to System.Collections.IList<T> and base
  40                 // interfaces of this interface, provided there is an implicit reference conversion
  41                 // from S to T.
  42                 //
  43                 static bool ArrayToIList (ArrayContainer array, TypeSpec list, bool isExplicit)
  44                 {
  45                         if (array.Rank != 1 || !list.IsGeneric)
  46                                 return false;
  47
  48                         var open_version = list.GetDefinition ();
  49                         if ((open_version != TypeManager.generic_ilist_type) &&
  50                                 (open_version != TypeManager.generic_icollection_type) &&
  51                                 (open_version != TypeManager.generic_ienumerable_type))
  52                                 return false;
  53
  54                         var arg_type = list.TypeArguments[0];
  55                         if (array.Element == arg_type)
  56                                 return true;
  57
  58                         if (isExplicit)
  59                                 return ExplicitReferenceConversionExists (array.Element, arg_type);
  60
  61                         if (MyEmptyExpr == null)
  62                                 MyEmptyExpr = new EmptyExpression (array.Element);
  63                         else
  64                                 MyEmptyExpr.SetType (array.Element);
  65
  66                         return ImplicitReferenceConversionExists (MyEmptyExpr, arg_type);
  67                 }
  68
  69                 static bool IList_To_Array(TypeSpec list, ArrayContainer array)
  70                 {
  71                         if (array.Rank != 1 || !list.IsGeneric)
  72                                 return false;
  73
  74                         var open_version = list.GetDefinition ();
  75                         if ((open_version != TypeManager.generic_ilist_type) &&
  76                                 (open_version != TypeManager.generic_icollection_type) &&
  77                                 (open_version != TypeManager.generic_ienumerable_type))
  78                                 return false;
  79
  80                         var arg_type = list.TypeArguments[0];
  81                         if (array.Element == arg_type)
  82                                 return true;
  83
  84                         if (MyEmptyExpr == null)
  85                                 MyEmptyExpr = new EmptyExpression (array.Element);
  86                         else
  87                                 MyEmptyExpr.SetType (array.Element);
  88
  89                         return ImplicitReferenceConversionExists (MyEmptyExpr, arg_type) || ExplicitReferenceConversionExists (array.Element, arg_type);
  90                 }
  91
  92                 static Expression ImplicitTypeParameterConversion (Expression expr, TypeSpec target_type)
  93                 {
  94                         var expr_type = (TypeParameterSpec) expr.Type;
  95
  96                         //
  97                         // From T to a type parameter U, provided T depends on U
  98                         //
  99                         var ttype = target_type as TypeParameterSpec;
 100                         if (ttype != null) {
 101                                 if (expr_type.TypeArguments != null) {
 102                                         foreach (var targ in expr_type.TypeArguments) {
 103                                                 if (!TypeSpecComparer.Override.IsEqual (ttype, targ))
 104                                                         continue;
 105
 106                                                 if (expr_type.IsReferenceType && !ttype.IsReferenceType)
 107                                                         return new BoxedCast (expr, target_type);
 108
 109                                                 return new ClassCast (expr, target_type);
 110                                         }
 111                                 }
 112
 113                                 return null;
 114                         }
 115
 116                         //
 117                         // LAMESPEC: From T to dynamic type because it's like T to object
 118                         //
 119                         if (target_type == InternalType.Dynamic) {
 120                                 if (expr_type.IsReferenceType)
 121                                         return new ClassCast (expr, target_type);
 122
 123                                 return new BoxedCast (expr, target_type);
 124                         }
 125
 126                         //
 127                         // From T to its effective base class C
 128                         // From T to any base class of C (it cannot contain dynamic of be of dynamic type)
 129                         // From T to any interface implemented by C
 130                         //
 131                         var base_type = expr_type.GetEffectiveBase ();
 132                         if (base_type == target_type || TypeSpec.IsBaseClass (base_type, target_type, false) || base_type.ImplementsInterface (target_type, true)) {
 133                                 if (expr_type.IsReferenceType)
 134                                         return new ClassCast (expr, target_type);
 135
 136                                 return new BoxedCast (expr, target_type);
 137                         }
 138
 139                         if (target_type.IsInterface && expr_type.IsConvertibleToInterface (target_type)) {
 140                                 if (expr_type.IsReferenceType)
 141                                         return new ClassCast (expr, target_type);
 142
 143                                 return new BoxedCast (expr, target_type);
 144                         }
 145
 146                         return null;
 147                 }
 148
 149                 static Expression ExplicitTypeParameterConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
 150                 {
 151                         var target_tp = target_type as TypeParameterSpec;
 152                         if (target_tp != null) {
 153                                 if (target_tp.TypeArguments != null) {
 154                                         foreach (var targ in target_tp.TypeArguments) {
 155                                                 if (!TypeSpecComparer.Override.IsEqual (source_type, targ))
 156                                                         continue;
 157
 158                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
 159                                         }
 160                                 }
 161 /*
 162                                 if (target_tp.Interfaces != null) {
 163                                         foreach (TypeSpec iface in target_tp.Interfaces) {
 164                                                 if (!TypeManager.IsGenericParameter (iface))
 165                                                         continue;
 166
 167                                                 if (TypeManager.IsSubclassOf (source_type, iface))
 168                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type, true);
 169                                         }
 170                                 }
 171 */
 172                                 return null;
 173                         }
 174
 175                         if (target_type.IsInterface)
 176                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type, true);
 177
 178                         return null;
 179                 }
 180
 181                 static Expression ImplicitReferenceConversion (Expression expr, TypeSpec target_type, bool explicit_cast)
 182                 {
 183                         TypeSpec expr_type = expr.Type;
 184
 185                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 186                                 // if we are a method group, emit a warning
 187
 188                                 expr.Emit (null);
 189                         }
 190
 191                         if (expr_type == TypeManager.void_type)
 192                                 return null;
 193
 194                         if (expr_type.Kind == MemberKind.TypeParameter)
 195                                 return ImplicitTypeParameterConversion (expr, target_type);
 196
 197                         //
 198                         // from the null type to any reference-type.
 199                         //
 200                         NullLiteral nl = expr as NullLiteral;
 201                         if (nl != null) {
 202                                 return nl.ConvertImplicitly (null, target_type);
 203                         }
 204
 205                         if (ImplicitReferenceConversionExists (expr, target_type)) {
 206                                 //
 207                                 // Avoid wrapping implicitly convertible reference type
 208                                 //
 209                                 if (!explicit_cast)
 210                                         return expr;
 211
 212                                 return EmptyCast.Create (expr, target_type);
 213                         }
 214
 215                         return ImplicitBoxingConversion (expr, expr_type, target_type);
 216                 }
 217
 218                 //
 219                 // 6.1.6 Implicit reference conversions
 220                 //
 221                 public static bool ImplicitReferenceConversionExists (Expression expr, TypeSpec target_type)
 222                 {
 223                         if (TypeManager.IsStruct (target_type))
 224                                 return false;
 225
 226                         TypeSpec expr_type = expr.Type;
 227
 228                         // from the null type to any reference-type.
 229                         if (expr_type == InternalType.Null)
 230                                 return target_type != InternalType.AnonymousMethod;
 231
 232                         if (TypeManager.IsGenericParameter (expr_type))
 233                                 return ImplicitTypeParameterConversion (expr, target_type) != null;
 234
 235                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 236                         // with the small distinction that we only probe there
 237                         //
 238                         // Always ensure that the code here and there is in sync
 239
 240                         // from any class-type S to any interface-type T.
 241                         if (target_type.IsInterface) {
 242                                 if (expr_type.ImplementsInterface (target_type, true)){
 243                                         return !TypeManager.IsValueType (expr_type);
 244                                 }
 245                         }
 246
 247                         //
 248                         // Implicit reference conversions (no-boxing) to object or dynamic
 249                         //
 250                         if (target_type == TypeManager.object_type || target_type == InternalType.Dynamic) {
 251                                 switch (expr_type.Kind) {
 252                                 case MemberKind.Class:
 253                                 case MemberKind.Interface:
 254                                 case MemberKind.Delegate:
 255                                 case MemberKind.ArrayType:
 256                                         return true;
 257                                 }
 258
 259                                 return expr_type == InternalType.Dynamic;
 260                         }
 261
 262                         if (target_type == TypeManager.value_type) {
 263                                 return expr_type == TypeManager.enum_type;
 264                         } else if (expr_type == target_type || TypeSpec.IsBaseClass (expr_type, target_type, true)) {
 265                                 //
 266                                 // Special case: enumeration to System.Enum.
 267                                 // System.Enum is not a value type, it is a class, so we need
 268                                 // a boxing conversion
 269                                 //
 270                                 if (target_type == TypeManager.enum_type || TypeManager.IsGenericParameter (expr_type))
 271                                         return false;
 272
 273                                 if (TypeManager.IsValueType (expr_type))
 274                                         return false;
 275
 276                                 // Array type variance conversion
 277                                 //if (target_type.IsArray != expr_type.IsArray)
 278                                 //      return false;
 279
 280                                 return true;
 281                         }
 282
 283                         var expr_type_array = expr_type as ArrayContainer;
 284                         if (expr_type_array != null) {
 285                                 var target_type_array = target_type as ArrayContainer;
 286                                 // from an array-type S to an array-type of type T
 287                                 if (target_type_array != null && expr_type_array.Rank == target_type_array.Rank) {
 288
 289                                         //
 290                                         // Both SE and TE are reference-types
 291                                         //
 292                                         TypeSpec expr_element_type = expr_type_array.Element;
 293                                         if (!TypeManager.IsReferenceType (expr_element_type))
 294                                                 return false;
 295
 296                                         TypeSpec target_element_type = target_type_array.Element;
 297                                         if (!TypeManager.IsReferenceType (target_element_type))
 298                                                 return false;
 299
 300                                         if (MyEmptyExpr == null)
 301                                                 MyEmptyExpr = new EmptyExpression (expr_element_type);
 302                                         else
 303                                                 MyEmptyExpr.SetType (expr_element_type);
 304
 305                                         return ImplicitStandardConversionExists (MyEmptyExpr, target_element_type);
 306                                 }
 307
 308                                 // from an array-type to System.Array
 309                                 if (target_type == TypeManager.array_type)
 310                                         return true;
 311
 312                                 // from an array-type of type T to IList<T>
 313                                 if (ArrayToIList (expr_type_array, target_type, false))
 314                                         return true;
 315
 316                                 return false;
 317                         }
 318
 319                         if (TypeSpecComparer.Variant.IsEqual (expr_type, target_type))
 320                                 return true;
 321
 322                         // from any interface type S to interface-type T.
 323                         if (expr_type.IsInterface && target_type.IsInterface) {
 324                                 return expr_type.ImplementsInterface (target_type, true);
 325                         }
 326
 327                         // from any delegate type to System.Delegate
 328                         if (target_type == TypeManager.delegate_type &&
 329                                 (expr_type == TypeManager.delegate_type || expr_type.IsDelegate))
 330                                 return true;
 331
 332                         return false;
 333                 }
 334
 335                 public static Expression ImplicitBoxingConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
 336                 {
 337                         //
 338                         // From any value-type to the type object.
 339                         //
 340                         if (target_type == TypeManager.object_type || target_type == InternalType.Dynamic) {
 341                                 //
 342                                 // A pointer type cannot be converted to object
 343                                 //
 344                                 if (expr_type.IsPointer)
 345                                         return null;
 346
 347                                 if (!TypeManager.IsValueType (expr_type))
 348                                         return null;
 349
 350                                 return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 351                         }
 352
 353                         //
 354                         // From any value-type to the type System.ValueType.
 355                         //
 356                         if (target_type == TypeManager.value_type) {
 357                                 if (!TypeManager.IsValueType (expr_type))
 358                                         return null;
 359
 360                                 return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 361                         }
 362
 363                         if (target_type == TypeManager.enum_type) {
 364                                 //
 365                                 // From any enum-type to the type System.Enum.
 366                                 //
 367                                 if (TypeManager.IsEnumType (expr_type))
 368                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 369                         }
 370
 371                         //
 372                         // From a nullable-type to a reference type, if a boxing conversion exists from
 373                         // the underlying type to the reference type
 374                         //
 375                         if (TypeManager.IsNullableType (expr_type)) {
 376                                 if (!TypeManager.IsReferenceType (target_type))
 377                                         return null;
 378
 379                                 var res = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
 380
 381                                 // "cast" underlying type to target type to emit correct InvalidCastException when
 382                                 // underlying hierarchy changes without recompilation
 383                                 if (res != null && expr != null)
 384                                         res = new UnboxCast (res, target_type);
 385
 386                                 return res;
 387                         }
 388
 389                         if (TypeSpec.IsBaseClass (expr_type, target_type, false)) {
 390                                 //
 391                                 // Don't box same type arguments
 392                                 //
 393                                 if (TypeManager.IsGenericParameter (expr_type) && expr_type != target_type)
 394                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 395
 396                                 return null;
 397                         }
 398
 399                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 400                         // with the small distinction that we only probe there
 401                         //
 402                         // Always ensure that the code here and there is in sync
 403
 404                         // from any class-type S to any interface-type T.
 405                         if (target_type.IsInterface) {
 406                                 if (expr_type.ImplementsInterface (target_type, true) &&
 407                                         (TypeManager.IsGenericParameter (expr_type) || TypeManager.IsValueType (expr_type))) {
 408                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 409                                 }
 410                         }
 411
 412                         return null;
 413                 }
 414
 415                 public static Expression ImplicitNulableConversion (ResolveContext ec, Expression expr, TypeSpec target_type)
 416                 {
 417                         TypeSpec expr_type = expr.Type;
 418
 419                         //
 420                         // From null to any nullable type
 421                         //
 422                         if (expr_type == InternalType.Null)
 423                                 return ec == null ? EmptyExpression.Null : Nullable.LiftedNull.Create (target_type, expr.Location);
 424
 425                         // S -> T?
 426                         TypeSpec t_el = Nullable.NullableInfo.GetUnderlyingType (target_type);
 427
 428                         // S? -> T?
 429                         if (TypeManager.IsNullableType (expr_type))
 430                                 expr_type = Nullable.NullableInfo.GetUnderlyingType (expr_type);
 431
 432                         //
 433                         // Predefined implicit identity or implicit numeric conversion
 434                         // has to exist between underlying type S and underlying type T
 435                         //
 436
 437                         // conversion exists only mode
 438                         if (ec == null) {
 439                                 if (expr_type == t_el)
 440                                         return EmptyExpression.Null;
 441
 442                                 if (expr is Constant)
 443                                         return ((Constant) expr).ConvertImplicitly (ec, t_el);
 444
 445                                 return ImplicitNumericConversion (null, expr_type, t_el);
 446                         }
 447
 448                         Expression unwrap;
 449                         if (expr_type != expr.Type)
 450                                 unwrap = Nullable.Unwrap.Create (expr);
 451                         else
 452                                 unwrap = expr;
 453
 454                         Expression conv = unwrap;
 455                         if (expr_type != t_el) {
 456                                 if (conv is Constant)
 457                                         conv = ((Constant)conv).ConvertImplicitly (ec, t_el);
 458                                 else
 459                                         conv = ImplicitNumericConversion (conv, expr_type, t_el);
 460
 461                                 if (conv == null)
 462                                         return null;
 463                         }
 464
 465                         if (expr_type != expr.Type)
 466                                 return new Nullable.Lifted (conv, unwrap, target_type).Resolve (ec);
 467
 468                         return Nullable.Wrap.Create (conv, target_type);
 469                 }
 470
 471                 /// <summary>
 472                 ///   Implicit Numeric Conversions.
 473                 ///
 474                 ///   expr is the expression to convert, returns a new expression of type
 475                 ///   target_type or null if an implicit conversion is not possible.
 476                 /// </summary>
 477                 public static Expression ImplicitNumericConversion (Expression expr, TypeSpec target_type)
 478                 {
 479                         return ImplicitNumericConversion (expr, expr.Type, target_type);
 480                 }
 481
 482                 static Expression ImplicitNumericConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
 483                 {
 484                         if (expr_type == TypeManager.sbyte_type){
 485                                 //
 486                                 // From sbyte to short, int, long, float, double, decimal
 487                                 //
 488                                 if (target_type == TypeManager.int32_type)
 489                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 490                                 if (target_type == TypeManager.int64_type)
 491                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 492                                 if (target_type == TypeManager.double_type)
 493                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 494                                 if (target_type == TypeManager.float_type)
 495                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 496                                 if (target_type == TypeManager.short_type)
 497                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 498                                 if (target_type == TypeManager.decimal_type)
 499                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 500                         } else if (expr_type == TypeManager.byte_type){
 501                                 //
 502                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 503                                 //
 504                                 if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type ||
 505                                     target_type == TypeManager.short_type || target_type == TypeManager.ushort_type)
 506                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 507
 508                                 if (target_type == TypeManager.uint64_type)
 509                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 510                                 if (target_type == TypeManager.int64_type)
 511                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 512                                 if (target_type == TypeManager.float_type)
 513                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 514                                 if (target_type == TypeManager.double_type)
 515                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 516                                 if (target_type == TypeManager.decimal_type)
 517                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 518
 519                         } else if (expr_type == TypeManager.short_type){
 520                                 //
 521                                 // From short to int, long, float, double, decimal
 522                                 //
 523                                 if (target_type == TypeManager.int32_type)
 524                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 525                                 if (target_type == TypeManager.int64_type)
 526                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 527                                 if (target_type == TypeManager.double_type)
 528                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 529                                 if (target_type == TypeManager.float_type)
 530                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 531                                 if (target_type == TypeManager.decimal_type)
 532                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 533
 534                         } else if (expr_type == TypeManager.ushort_type){
 535                                 //
 536                                 // From ushort to int, uint, long, ulong, float, double, decimal
 537                                 //
 538                                 if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type)
 539                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 540
 541                                 if (target_type == TypeManager.uint64_type)
 542                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 543                                 if (target_type == TypeManager.int64_type)
 544                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 545                                 if (target_type == TypeManager.double_type)
 546                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 547                                 if (target_type == TypeManager.float_type)
 548                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 549                                 if (target_type == TypeManager.decimal_type)
 550                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 551                         } else if (expr_type == TypeManager.int32_type){
 552                                 //
 553                                 // From int to long, float, double, decimal
 554                                 //
 555                                 if (target_type == TypeManager.int64_type)
 556                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 557                                 if (target_type == TypeManager.double_type)
 558                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 559                                 if (target_type == TypeManager.float_type)
 560                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 561                                 if (target_type == TypeManager.decimal_type)
 562                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 563                         } else if (expr_type == TypeManager.uint32_type){
 564                                 //
 565                                 // From uint to long, ulong, float, double, decimal
 566                                 //
 567                                 if (target_type == TypeManager.int64_type)
 568                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 569                                 if (target_type == TypeManager.uint64_type)
 570                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 571                                 if (target_type == TypeManager.double_type)
 572                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
 573                                 if (target_type == TypeManager.float_type)
 574                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
 575                                 if (target_type == TypeManager.decimal_type)
 576                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 577                         } else if (expr_type == TypeManager.int64_type){
 578                                 //
 579                                 // From long/ulong to float, double
 580                                 //
 581                                 if (target_type == TypeManager.double_type)
 582                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 583                                 if (target_type == TypeManager.float_type)
 584                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 585                                 if (target_type == TypeManager.decimal_type)
 586                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 587                         } else if (expr_type == TypeManager.uint64_type){
 588                                 //
 589                                 // From ulong to float, double
 590                                 //
 591                                 if (target_type == TypeManager.double_type)
 592                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
 593                                 if (target_type == TypeManager.float_type)
 594                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
 595                                 if (target_type == TypeManager.decimal_type)
 596                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 597                         } else if (expr_type == TypeManager.char_type){
 598                                 //
 599                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 600                                 //
 601                                 if ((target_type == TypeManager.ushort_type) ||
 602                                     (target_type == TypeManager.int32_type) ||
 603                                     (target_type == TypeManager.uint32_type))
 604                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 605                                 if (target_type == TypeManager.uint64_type)
 606                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 607                                 if (target_type == TypeManager.int64_type)
 608                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 609                                 if (target_type == TypeManager.float_type)
 610                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 611                                 if (target_type == TypeManager.double_type)
 612                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 613                                 if (target_type == TypeManager.decimal_type)
 614                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 615                         } else if (expr_type == TypeManager.float_type){
 616                                 //
 617                                 // float to double
 618                                 //
 619                                 if (target_type == TypeManager.double_type)
 620                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 621                         }
 622
 623                         return null;
 624                 }
 625
 626                 /// <summary>
 627                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 628                 ///  implicit user defined conversions - needed for overload resolution
 629                 /// </summary>
 630                 public static bool ImplicitConversionExists (ResolveContext ec, Expression expr, TypeSpec target_type)
 631                 {
 632                         if (ImplicitStandardConversionExists (expr, target_type))
 633                                 return true;
 634
 635                         if (expr.Type == InternalType.AnonymousMethod) {
 636                                 if (!TypeManager.IsDelegateType (target_type) && target_type.GetDefinition () != TypeManager.expression_type)
 637                                         return false;
 638
 639                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 640                                 return ame.ImplicitStandardConversionExists (ec, target_type);
 641                         }
 642
 643                         if (expr.eclass == ExprClass.MethodGroup) {
 644                                 if (target_type.IsDelegate && RootContext.Version != LanguageVersion.ISO_1) {
 645                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 646                                         if (mg != null)
 647                                                 return DelegateCreation.ImplicitStandardConversionExists (ec, mg, target_type);
 648                                 }
 649
 650                                 return false;
 651                         }
 652
 653                         return ImplicitUserConversion (ec, expr, target_type, Location.Null) != null;
 654                 }
 655
 656                 /// <summary>
 657                 ///  Determines if a standard implicit conversion exists from
 658                 ///  expr_type to target_type
 659                 ///
 660                 /// </summary>
 661                 public static bool ImplicitStandardConversionExists (Expression expr, TypeSpec target_type)
 662                 {
 663                         TypeSpec expr_type = expr.Type;
 664
 665                         NullLiteral nl = expr as NullLiteral;
 666                         if (nl != null)
 667                                 return nl.ConvertImplicitly (null, target_type) != null;
 668
 669                         if (expr_type == TypeManager.void_type)
 670                                 return false;
 671
 672                         if (expr_type == target_type)
 673                                 return true;
 674
 675                         // Implicit dynamic conversion
 676                         if (expr_type == InternalType.Dynamic) {
 677                                 switch (target_type.Kind) {
 678                                 case MemberKind.ArrayType:
 679                                 case MemberKind.Class:
 680                                 case MemberKind.Struct:
 681                                 case MemberKind.Delegate:
 682                                 case MemberKind.Enum:
 683                                 case MemberKind.Interface:
 684                                 case MemberKind.TypeParameter:
 685                                         return true;
 686                                 }
 687
 688                                 // dynamic to __arglist
 689                                 if (target_type == InternalType.Arglist)
 690                                         return true;
 691
 692                                 return false;
 693                         }
 694
 695                         if (TypeManager.IsNullableType (target_type)) {
 696                                 return ImplicitNulableConversion (null, expr, target_type) != null;
 697                         }
 698
 699                         // First numeric conversions
 700                         if (ImplicitNumericConversion (null, expr_type, target_type) != null)
 701                                 return true;
 702
 703                         if (ImplicitReferenceConversionExists (expr, target_type))
 704                                 return true;
 705
 706                         if (ImplicitBoxingConversion (null, expr_type, target_type) != null)
 707                                 return true;
 708
 709                         //
 710                         // Implicit Constant Expression Conversions
 711                         //
 712                         if (expr is IntConstant){
 713                                 int value = ((IntConstant) expr).Value;
 714
 715                                 if (target_type == TypeManager.sbyte_type){
 716                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 717                                                 return true;
 718                                 } else if (target_type == TypeManager.byte_type){
 719                                         if (value >= 0 && value <= Byte.MaxValue)
 720                                                 return true;
 721                                 } else if (target_type == TypeManager.short_type){
 722                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 723                                                 return true;
 724                                 } else if (target_type == TypeManager.ushort_type){
 725                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 726                                                 return true;
 727                                 } else if (target_type == TypeManager.uint32_type){
 728                                         if (value >= 0)
 729                                                 return true;
 730                                 } else if (target_type == TypeManager.uint64_type){
 731                                          //
 732                                          // we can optimize this case: a positive int32
 733                                          // always fits on a uint64.  But we need an opcode
 734                                          // to do it.
 735                                          //
 736                                         if (value >= 0)
 737                                                 return true;
 738                                 }
 739                         }
 740
 741                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 742                                 //
 743                                 // Try the implicit constant expression conversion
 744                                 // from long to ulong, instead of a nice routine,
 745                                 // we just inline it
 746                                 //
 747                                 long v = ((LongConstant) expr).Value;
 748                                 if (v >= 0)
 749                                         return true;
 750                         }
 751
 752                         if (expr is IntegralConstant && TypeManager.IsEnumType (target_type)) {
 753                                 var i = (IntegralConstant) expr;
 754                                 //
 755                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
 756                                 //
 757                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
 758                                 // to be converted to any enum-type and to any nullable-type whose underlying
 759                                 // type is an enum-type
 760                                 //
 761                                 return i.IsZeroInteger;
 762                         }
 763
 764                         //
 765                         // If `expr_type' implements `target_type' (which is an iface)
 766                         // see TryImplicitIntConversion
 767                         //
 768                         if (target_type.IsInterface && expr_type.ImplementsInterface (target_type, true))
 769                                 return true;
 770
 771                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 772                                 return true;
 773
 774                         // Conversion from __arglist to System.ArgIterator
 775                         if (expr_type == InternalType.Arglist)
 776                                 return target_type == TypeManager.arg_iterator_type;
 777
 778                         return false;
 779                 }
 780
 781                 /// <summary>
 782                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 783                 ///  amongst the methods in the MethodGroupExpr
 784                 /// </summary>
 785                 public static TypeSpec FindMostEncompassedType (IEnumerable<TypeSpec> types)
 786                 {
 787                         TypeSpec best = null;
 788                         EmptyExpression expr = EmptyExpression.Grab ();
 789
 790                         foreach (TypeSpec t in types) {
 791                                 if (best == null) {
 792                                         best = t;
 793                                         continue;
 794                                 }
 795
 796                                 expr.SetType (t);
 797                                 if (ImplicitStandardConversionExists (expr, best))
 798                                         best = t;
 799                         }
 800
 801                         expr.SetType (best);
 802                         foreach (TypeSpec t in types) {
 803                                 if (best == t)
 804                                         continue;
 805                                 if (!ImplicitStandardConversionExists (expr, t)) {
 806                                         best = null;
 807                                         break;
 808                                 }
 809                         }
 810
 811                         EmptyExpression.Release (expr);
 812
 813                         return best;
 814                 }
 815
 816                 /// <summary>
 817                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 818                 ///  amongst the types in the given set
 819                 /// </summary>
 820                 static TypeSpec FindMostEncompassingType (IList<TypeSpec> types)
 821                 {
 822                         TypeSpec best = null;
 823
 824                         if (types.Count == 0)
 825                                 return null;
 826
 827                         if (types.Count == 1)
 828                                 return types [0];
 829
 830                         EmptyExpression expr = EmptyExpression.Grab ();
 831
 832                         foreach (TypeSpec t in types) {
 833                                 if (best == null) {
 834                                         best = t;
 835                                         continue;
 836                                 }
 837
 838                                 expr.SetType (best);
 839                                 if (ImplicitStandardConversionExists (expr, t))
 840                                         best = t;
 841                         }
 842
 843                         foreach (TypeSpec t in types) {
 844                                 if (best == t)
 845                                         continue;
 846                                 expr.SetType (t);
 847                                 if (!ImplicitStandardConversionExists (expr, best)) {
 848                                         best = null;
 849                                         break;
 850                                 }
 851                         }
 852
 853                         EmptyExpression.Release (expr);
 854
 855                         return best;
 856                 }
 857
 858                 //
 859                 // Finds the most specific source Sx according to the rules of the spec (13.4.4)
 860                 // by making use of FindMostEncomp* methods. Applies the correct rules separately
 861                 // for explicit and implicit conversion operators.
 862                 //
 863                 static TypeSpec FindMostSpecificSource (List<MethodSpec> list, TypeSpec sourceType, Expression source, bool apply_explicit_conv_rules)
 864                 {
 865                         var src_types_set = new TypeSpec [list.Count];
 866
 867                         //
 868                         // Try exact match first, if any operator converts from S then Sx = S
 869                         //
 870                         for (int i = 0; i < src_types_set.Length; ++i) {
 871                                 TypeSpec param_type = list [i].Parameters.Types [0];
 872
 873                                 if (param_type == sourceType)
 874                                         return param_type;
 875
 876                                 src_types_set [i] = param_type;
 877                         }
 878
 879                         //
 880                         // Explicit Conv rules
 881                         //
 882                         if (apply_explicit_conv_rules) {
 883                                 var candidate_set = new List<TypeSpec> ();
 884
 885                                 foreach (TypeSpec param_type in src_types_set){
 886                                         if (ImplicitStandardConversionExists (source, param_type))
 887                                                 candidate_set.Add (param_type);
 888                                 }
 889
 890                                 if (candidate_set.Count != 0)
 891                                         return FindMostEncompassedType (candidate_set);
 892                         }
 893
 894                         //
 895                         // Final case
 896                         //
 897                         if (apply_explicit_conv_rules)
 898                                 return FindMostEncompassingType (src_types_set);
 899                         else
 900                                 return FindMostEncompassedType (src_types_set);
 901                 }
 902
 903                 /// <summary>
 904                 ///  Finds the most specific target Tx according to section 13.4.4
 905                 /// </summary>
 906                 static public TypeSpec FindMostSpecificTarget (IList<MethodSpec> list,
 907                                                            TypeSpec target, bool apply_explicit_conv_rules)
 908                 {
 909                         var tgt_types_set = new List<TypeSpec> ();
 910
 911                         //
 912                         // If any operator converts to T then Tx = T
 913                         //
 914                         foreach (var mi in list){
 915                                 TypeSpec ret_type = mi.ReturnType;
 916                                 if (ret_type == target)
 917                                         return ret_type;
 918
 919                                 tgt_types_set.Add (ret_type);
 920                         }
 921
 922                         //
 923                         // Explicit conv rules
 924                         //
 925                         if (apply_explicit_conv_rules) {
 926                                 var candidate_set = new List<TypeSpec> ();
 927
 928                                 EmptyExpression expr = EmptyExpression.Grab ();
 929
 930                                 foreach (TypeSpec ret_type in tgt_types_set){
 931                                         expr.SetType (ret_type);
 932
 933                                         if (ImplicitStandardConversionExists (expr, target))
 934                                                 candidate_set.Add (ret_type);
 935                                 }
 936
 937                                 EmptyExpression.Release (expr);
 938
 939                                 if (candidate_set.Count != 0)
 940                                         return FindMostEncompassingType (candidate_set);
 941                         }
 942
 943                         //
 944                         // Okay, final case !
 945                         //
 946                         if (apply_explicit_conv_rules)
 947                                 return FindMostEncompassedType (tgt_types_set);
 948                         else
 949                                 return FindMostEncompassingType (tgt_types_set);
 950                 }
 951
 952                 /// <summary>
 953                 ///  User-defined Implicit conversions
 954                 /// </summary>
 955                 static public Expression ImplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
 956                 {
 957                         return UserDefinedConversion (ec, source, target, true, loc);
 958                 }
 959
 960                 /// <summary>
 961                 ///  User-defined Explicit conversions
 962                 /// </summary>
 963                 static Expression ExplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
 964                 {
 965                         return UserDefinedConversion (ec, source, target, false, loc);
 966                 }
 967
 968                 static void FindApplicableUserDefinedConversionOperators (IList<MemberSpec> operators, Expression source, TypeSpec target, bool implicitOnly, ref List<MethodSpec> candidates)
 969                 {
 970                         //
 971                         // LAMESPEC: Undocumented IntPtr/UIntPtr conversions
 972                         // IntPtr -> uint uses int
 973                         // UIntPtr -> long uses ulong
 974                         //
 975                         if (source.Type == TypeManager.intptr_type) {
 976                                 if (target == TypeManager.uint32_type)
 977                                         target = TypeManager.int32_type;
 978                         } else if (source.Type == TypeManager.uintptr_type) {
 979                                 if (target == TypeManager.int64_type)
 980                                         target = TypeManager.uint64_type;
 981                         }
 982
 983                         // Neither A nor B are interface-types
 984                         if (source.Type.IsInterface)
 985                                 return;
 986
 987                         // For a conversion operator to be applicable, it must be possible
 988                         // to perform a standard conversion from the source type to
 989                         // the operand type of the operator, and it must be possible
 990                         // to perform a standard conversion from the result type of
 991                         // the operator to the target type.
 992
 993                         Expression texpr = null;
 994
 995                         foreach (MethodSpec op in operators) {
 996
 997                                 // Can be null because MemberCache.GetUserOperator does not resize the array
 998                                 if (op == null)
 999                                         continue;
1000
1001                                 var t = op.Parameters.Types[0];
1002                                 if (source.Type != t && !ImplicitStandardConversionExists (source, t)) {
1003                                         if (implicitOnly)
1004                                                 continue;
1005
1006                                         if (!ImplicitStandardConversionExists (new EmptyExpression (t), source.Type))
1007                                                 continue;
1008                                 }
1009
1010                                 t = op.ReturnType;
1011
1012                                 // LAMESPEC: Exclude UIntPtr -> int conversion
1013                                 if (t == TypeManager.uint32_type && source.Type == TypeManager.uintptr_type)
1014                                         continue;
1015
1016                                 if (t.IsInterface)
1017                                         continue;
1018
1019                                 if (target != t && !ImplicitStandardConversionExists (new EmptyExpression (t), target)) {
1020                                         if (implicitOnly)
1021                                                 continue;
1022
1023                                         if (texpr == null)
1024                                                 texpr = new EmptyExpression (target);
1025
1026                                         if (!ImplicitStandardConversionExists (texpr, t))
1027                                                 continue;
1028                                 }
1029
1030                                 if (candidates == null)
1031                                         candidates = new List<MethodSpec> ();
1032
1033                                 candidates.Add (op);
1034                         }
1035                 }
1036
1037                 //
1038                 // User-defined conversions
1039                 //
1040                 static Expression UserDefinedConversion (ResolveContext ec, Expression source, TypeSpec target, bool implicitOnly, Location loc)
1041                 {
1042                         List<MethodSpec> candidates = null;
1043
1044                         //
1045                         // If S or T are nullable types, source_type and target_type are their underlying types
1046                         // otherwise source_type and target_type are equal to S and T respectively.
1047                         //
1048                         TypeSpec source_type = source.Type;
1049                         TypeSpec target_type = target;
1050                         Expression source_type_expr;
1051
1052                         if (TypeManager.IsNullableType (source_type)) {
1053                                 // No implicit conversion S? -> T for non-reference types
1054                                 if (implicitOnly && !TypeManager.IsReferenceType (target_type) && !TypeManager.IsNullableType (target_type))
1055                                         return null;
1056
1057                                 source_type_expr = Nullable.Unwrap.Create (source);
1058                                 source_type = source_type_expr.Type;
1059                         } else {
1060                                 source_type_expr = source;
1061                         }
1062
1063                         if (TypeManager.IsNullableType (target_type))
1064                                 target_type = Nullable.NullableInfo.GetUnderlyingType (target_type);
1065
1066                         // Only these containers can contain a user defined implicit or explicit operators
1067                         const MemberKind user_conversion_kinds = MemberKind.Class | MemberKind.Struct | MemberKind.TypeParameter;
1068
1069                         if ((source_type.Kind & user_conversion_kinds) != 0 && source_type != TypeManager.decimal_type) {
1070                                 bool declared_only = source_type.IsStruct;
1071
1072                                 var operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Implicit, declared_only);
1073                                 if (operators != null) {
1074                                         FindApplicableUserDefinedConversionOperators (operators, source_type_expr, target_type, implicitOnly, ref candidates);
1075                                 }
1076
1077                                 if (!implicitOnly) {
1078                                         operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Explicit, declared_only);
1079                                         if (operators != null) {
1080                                                 FindApplicableUserDefinedConversionOperators (operators, source_type_expr, target_type, false, ref candidates);
1081                                         }
1082                                 }
1083                         }
1084
1085                         if ((target.Kind & user_conversion_kinds) != 0 && target != TypeManager.decimal_type) {
1086                                 bool declared_only = target.IsStruct || implicitOnly;
1087
1088                                 var operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Implicit, declared_only);
1089                                 if (operators != null) {
1090                                         FindApplicableUserDefinedConversionOperators (operators, source_type_expr, target_type, implicitOnly, ref candidates);
1091                                 }
1092
1093                                 if (!implicitOnly) {
1094                                         operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Explicit, declared_only);
1095                                         if (operators != null) {
1096                                                 FindApplicableUserDefinedConversionOperators (operators, source_type_expr, target_type, false, ref candidates);
1097                                         }
1098                                 }
1099                         }
1100
1101                         if (candidates == null)
1102                                 return null;
1103
1104                         //
1105                         // Find the most specific conversion operator
1106                         //
1107                         MethodSpec most_specific_operator;
1108                         TypeSpec s_x, t_x;
1109                         if (candidates.Count == 1) {
1110                                 most_specific_operator = candidates[0];
1111                                 s_x = most_specific_operator.Parameters.Types[0];
1112                                 t_x = most_specific_operator.ReturnType;
1113                         } else {
1114                                 //
1115                                 // Pass original source type to find best match against input type and
1116                                 // not the unwrapped expression
1117                                 //
1118                                 s_x = FindMostSpecificSource (candidates, source.Type, source_type_expr, !implicitOnly);
1119                                 if (s_x == null)
1120                                         return null;
1121
1122                                 t_x = FindMostSpecificTarget (candidates, target, !implicitOnly);
1123                                 if (t_x == null)
1124                                         return null;
1125
1126                                 most_specific_operator = candidates[0];
1127
1128                                 for (int i = 1; i < candidates.Count; ++i) {
1129                                         if (candidates[i].ReturnType == t_x && candidates[i].Parameters.Types[0] == s_x) {
1130                                                 most_specific_operator = candidates[i];
1131                                                 break;
1132                                         }
1133                                 }
1134                         }
1135
1136                         //
1137                         // Convert input type when it's different to best operator argument
1138                         //
1139                         if (s_x != source_type)
1140                                 source = implicitOnly ?
1141                                         ImplicitConversionStandard (ec, source_type_expr, s_x, loc) :
1142                                         ExplicitConversionStandard (ec, source_type_expr, s_x, loc);
1143                         else {
1144                                 source = source_type_expr;
1145                         }
1146
1147                         source = new UserCast (most_specific_operator, source, loc).Resolve (ec);
1148
1149                         //
1150                         // Convert result type when it's different to best operator return type
1151                         //
1152                         if (t_x != target_type) {
1153                                 //
1154                                 // User operator is of T?, no need to lift it
1155                                 //
1156                                 if (TypeManager.IsNullableType (t_x) && t_x == target)
1157                                         return source;
1158
1159                                 source = implicitOnly ?
1160                                         ImplicitConversionStandard (ec, source, target_type, loc) :
1161                                         ExplicitConversionStandard (ec, source, target_type, loc);
1162                         }
1163
1164                         //
1165                         // Source expression is of nullable type, lift the result in the case it's null and
1166                         // not nullable/lifted user operator is used
1167                         //
1168                         if (source_type_expr is Nullable.Unwrap && !TypeManager.IsNullableType (s_x) && (TypeManager.IsReferenceType (target) || target_type != target))
1169                                 source = new Nullable.Lifted (source, source_type_expr, target).Resolve (ec);
1170                         else if (target_type != target)
1171                                 source = Nullable.Wrap.Create (source, target);
1172
1173                         return source;
1174                 }
1175
1176                 /// <summary>
1177                 ///   Converts implicitly the resolved expression `expr' into the
1178                 ///   `target_type'.  It returns a new expression that can be used
1179                 ///   in a context that expects a `target_type'.
1180                 /// </summary>
1181                 static public Expression ImplicitConversion (ResolveContext ec, Expression expr,
1182                                                              TypeSpec target_type, Location loc)
1183                 {
1184                         Expression e;
1185
1186                         if (target_type == null)
1187                                 throw new Exception ("Target type is null");
1188
1189                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1190                         if (e != null)
1191                                 return e;
1192
1193                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1194                         if (e != null)
1195                                 return e;
1196
1197                         return null;
1198                 }
1199
1200
1201                 /// <summary>
1202                 ///   Attempts to apply the `Standard Implicit
1203                 ///   Conversion' rules to the expression `expr' into
1204                 ///   the `target_type'.  It returns a new expression
1205                 ///   that can be used in a context that expects a
1206                 ///   `target_type'.
1207                 ///
1208                 ///   This is different from `ImplicitConversion' in that the
1209                 ///   user defined implicit conversions are excluded.
1210                 /// </summary>
1211                 static public Expression ImplicitConversionStandard (ResolveContext ec, Expression expr,
1212                                                                      TypeSpec target_type, Location loc)
1213                 {
1214                         return ImplicitConversionStandard (ec, expr, target_type, loc, false);
1215                 }
1216
1217                 static Expression ImplicitConversionStandard (ResolveContext ec, Expression expr, TypeSpec target_type, Location loc, bool explicit_cast)
1218                 {
1219                         if (expr.eclass == ExprClass.MethodGroup){
1220                                 if (!TypeManager.IsDelegateType (target_type)){
1221                                         return null;
1222                                 }
1223
1224                                 //
1225                                 // Only allow anonymous method conversions on post ISO_1
1226                                 //
1227                                 if (RootContext.Version != LanguageVersion.ISO_1){
1228                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1229                                         if (mg != null)
1230                                                 return ImplicitDelegateCreation.Create (
1231                                                         ec, mg, target_type, loc);
1232                                 }
1233                         }
1234
1235                         TypeSpec expr_type = expr.Type;
1236                         Expression e;
1237
1238                         if (expr_type == target_type) {
1239                                 if (expr_type != InternalType.Null && expr_type != InternalType.AnonymousMethod)
1240                                         return expr;
1241                                 return null;
1242                         }
1243
1244                         if (expr_type == InternalType.Dynamic) {
1245                                 switch (target_type.Kind) {
1246                                 case MemberKind.ArrayType:
1247                                 case MemberKind.Class:
1248                                         if (target_type == TypeManager.object_type)
1249                                                 return EmptyCast.Create (expr, target_type);
1250
1251                                         goto case MemberKind.Struct;
1252                                 case MemberKind.Struct:
1253                                 case MemberKind.Delegate:
1254                                 case MemberKind.Enum:
1255                                 case MemberKind.Interface:
1256                                 case MemberKind.TypeParameter:
1257                                         Arguments args = new Arguments (1);
1258                                         args.Add (new Argument (expr));
1259                                         return new DynamicConversion (target_type, explicit_cast ? CSharpBinderFlags.ConvertExplicit : 0, args, loc).Resolve (ec);
1260                                 }
1261
1262                                 return null;
1263                         }
1264
1265                         if (TypeManager.IsNullableType (target_type))
1266                                 return ImplicitNulableConversion (ec, expr, target_type);
1267
1268                         //
1269                         // Attempt to do the implicit constant expression conversions
1270                         //
1271                         Constant c = expr as Constant;
1272                         if (c != null) {
1273                                 try {
1274                                         c = c.ConvertImplicitly (ec, target_type);
1275                                 } catch {
1276                                         Console.WriteLine ("Conversion error happened in line {0}", loc);
1277                                         throw;
1278                                 }
1279                                 if (c != null)
1280                                         return c;
1281                         }
1282
1283                         e = ImplicitNumericConversion (expr, expr_type, target_type);
1284                         if (e != null)
1285                                 return e;
1286
1287                         e = ImplicitReferenceConversion (expr, target_type, explicit_cast);
1288                         if (e != null)
1289                                 return e;
1290
1291                         if (expr is IntegralConstant && TypeManager.IsEnumType (target_type)){
1292                                 var i = (IntegralConstant) expr;
1293                                 //
1294                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
1295                                 //
1296                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
1297                                 // to be converted to any enum-type and to any nullable-type whose underlying
1298                                 // type is an enum-type
1299                                 //
1300                                 if (i.IsZeroInteger) {
1301                                         // Recreate 0 literal to remove any collected conversions
1302                                         return new EnumConstant (new IntLiteral (0, i.Location), target_type).Resolve (ec);
1303                                 }
1304                         }
1305
1306                         if (ec.IsUnsafe) {
1307                                 if (expr_type.IsPointer){
1308                                         if (target_type == TypeManager.void_ptr_type)
1309                                                 return EmptyCast.Create (expr, target_type);
1310
1311                                         //
1312                                         // yep, comparing pointer types cant be done with
1313                                         // t1 == t2, we have to compare their element types.
1314                                         //
1315                                         if (target_type.IsPointer){
1316                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1317                                                         return expr;
1318
1319                                                 //return null;
1320                                         }
1321                                 }
1322
1323                                 if (expr_type == InternalType.Null && target_type.IsPointer)
1324                                         return EmptyCast.Create (new NullPointer (loc), target_type);
1325                         }
1326
1327                         if (expr_type == InternalType.AnonymousMethod){
1328                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1329                                 Expression am = ame.Compatible (ec, target_type);
1330                                 if (am != null)
1331                                         return am.Resolve (ec);
1332                         }
1333
1334                         if (expr_type == InternalType.Arglist && target_type == TypeManager.arg_iterator_type)
1335                                 return expr;
1336
1337                         return null;
1338                 }
1339
1340                 /// <summary>
1341                 ///   Attempts to implicitly convert `source' into `target_type', using
1342                 ///   ImplicitConversion.  If there is no implicit conversion, then
1343                 ///   an error is signaled
1344                 /// </summary>
1345                 static public Expression ImplicitConversionRequired (ResolveContext ec, Expression source,
1346                                                                      TypeSpec target_type, Location loc)
1347                 {
1348                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1349                         if (e != null)
1350                                 return e;
1351
1352                         source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
1353                         return null;
1354                 }
1355
1356                 /// <summary>
1357                 ///   Performs the explicit numeric conversions
1358                 ///
1359                 /// There are a few conversions that are not part of the C# standard,
1360                 /// they were interim hacks in the C# compiler that were supposed to
1361                 /// become explicit operators in the UIntPtr class and IntPtr class,
1362                 /// but for historical reasons it did not happen, so the C# compiler
1363                 /// ended up with these special hacks.
1364                 ///
1365                 /// See bug 59800 for details.
1366                 ///
1367                 /// The conversion are:
1368                 ///   UIntPtr->SByte
1369                 ///   UIntPtr->Int16
1370                 ///   UIntPtr->Int32
1371                 ///   IntPtr->UInt64
1372                 ///   UInt64->IntPtr
1373                 ///   SByte->UIntPtr
1374                 ///   Int16->UIntPtr
1375                 ///
1376                 /// </summary>
1377                 public static Expression ExplicitNumericConversion (Expression expr, TypeSpec target_type)
1378                 {
1379                         TypeSpec expr_type = expr.Type;
1380                         TypeSpec real_target_type = target_type;
1381
1382                         if (expr_type == TypeManager.sbyte_type){
1383                                 //
1384                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1385                                 //
1386                                 if (real_target_type == TypeManager.byte_type)
1387                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1388                                 if (real_target_type == TypeManager.ushort_type)
1389                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1390                                 if (real_target_type == TypeManager.uint32_type)
1391                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1392                                 if (real_target_type == TypeManager.uint64_type)
1393                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1394                                 if (real_target_type == TypeManager.char_type)
1395                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1396
1397                                 // One of the built-in conversions that belonged in the class library
1398                                 if (real_target_type == TypeManager.uintptr_type){
1399                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
1400
1401                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1402                                 }
1403                         } else if (expr_type == TypeManager.byte_type){
1404                                 //
1405                                 // From byte to sbyte and char
1406                                 //
1407                                 if (real_target_type == TypeManager.sbyte_type)
1408                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1409                                 if (real_target_type == TypeManager.char_type)
1410                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1411                         } else if (expr_type == TypeManager.short_type){
1412                                 //
1413                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1414                                 //
1415                                 if (real_target_type == TypeManager.sbyte_type)
1416                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1417                                 if (real_target_type == TypeManager.byte_type)
1418                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1419                                 if (real_target_type == TypeManager.ushort_type)
1420                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1421                                 if (real_target_type == TypeManager.uint32_type)
1422                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1423                                 if (real_target_type == TypeManager.uint64_type)
1424                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1425                                 if (real_target_type == TypeManager.char_type)
1426                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1427
1428                                 // One of the built-in conversions that belonged in the class library
1429                                 if (real_target_type == TypeManager.uintptr_type){
1430                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1431
1432                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1433                                 }
1434                         } else if (expr_type == TypeManager.ushort_type){
1435                                 //
1436                                 // From ushort to sbyte, byte, short, char
1437                                 //
1438                                 if (real_target_type == TypeManager.sbyte_type)
1439                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1440                                 if (real_target_type == TypeManager.byte_type)
1441                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1442                                 if (real_target_type == TypeManager.short_type)
1443                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1444                                 if (real_target_type == TypeManager.char_type)
1445                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1446                         } else if (expr_type == TypeManager.int32_type){
1447                                 //
1448                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1449                                 //
1450                                 if (real_target_type == TypeManager.sbyte_type)
1451                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1452                                 if (real_target_type == TypeManager.byte_type)
1453                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1454                                 if (real_target_type == TypeManager.short_type)
1455                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1456                                 if (real_target_type == TypeManager.ushort_type)
1457                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1458                                 if (real_target_type == TypeManager.uint32_type)
1459                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1460                                 if (real_target_type == TypeManager.uint64_type)
1461                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1462                                 if (real_target_type == TypeManager.char_type)
1463                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1464
1465                                 // One of the built-in conversions that belonged in the class library
1466                                 if (real_target_type == TypeManager.uintptr_type){
1467                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1468
1469                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1470                                 }
1471                         } else if (expr_type == TypeManager.uint32_type){
1472                                 //
1473                                 // From uint to sbyte, byte, short, ushort, int, char
1474                                 //
1475                                 if (real_target_type == TypeManager.sbyte_type)
1476                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1477                                 if (real_target_type == TypeManager.byte_type)
1478                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1479                                 if (real_target_type == TypeManager.short_type)
1480                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1481                                 if (real_target_type == TypeManager.ushort_type)
1482                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1483                                 if (real_target_type == TypeManager.int32_type)
1484                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1485                                 if (real_target_type == TypeManager.char_type)
1486                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1487                         } else if (expr_type == TypeManager.int64_type){
1488                                 //
1489                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1490                                 //
1491                                 if (real_target_type == TypeManager.sbyte_type)
1492                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1493                                 if (real_target_type == TypeManager.byte_type)
1494                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1495                                 if (real_target_type == TypeManager.short_type)
1496                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1497                                 if (real_target_type == TypeManager.ushort_type)
1498                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1499                                 if (real_target_type == TypeManager.int32_type)
1500                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1501                                 if (real_target_type == TypeManager.uint32_type)
1502                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1503                                 if (real_target_type == TypeManager.uint64_type)
1504                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1505                                 if (real_target_type == TypeManager.char_type)
1506                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1507                         } else if (expr_type == TypeManager.uint64_type){
1508                                 //
1509                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1510                                 //
1511                                 if (real_target_type == TypeManager.sbyte_type)
1512                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1513                                 if (real_target_type == TypeManager.byte_type)
1514                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1515                                 if (real_target_type == TypeManager.short_type)
1516                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1517                                 if (real_target_type == TypeManager.ushort_type)
1518                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1519                                 if (real_target_type == TypeManager.int32_type)
1520                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1521                                 if (real_target_type == TypeManager.uint32_type)
1522                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1523                                 if (real_target_type == TypeManager.int64_type)
1524                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1525                                 if (real_target_type == TypeManager.char_type)
1526                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1527
1528                                 // One of the built-in conversions that belonged in the class library
1529                                 if (real_target_type == TypeManager.intptr_type){
1530                                         return new OperatorCast (EmptyCast.Create (expr, TypeManager.int64_type),
1531                                                                  TypeManager.intptr_type, true);
1532                                 }
1533                         } else if (expr_type == TypeManager.char_type){
1534                                 //
1535                                 // From char to sbyte, byte, short
1536                                 //
1537                                 if (real_target_type == TypeManager.sbyte_type)
1538                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1539                                 if (real_target_type == TypeManager.byte_type)
1540                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1541                                 if (real_target_type == TypeManager.short_type)
1542                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1543                         } else if (expr_type == TypeManager.float_type){
1544                                 //
1545                                 // From float to sbyte, byte, short,
1546                                 // ushort, int, uint, long, ulong, char
1547                                 // or decimal
1548                                 //
1549                                 if (real_target_type == TypeManager.sbyte_type)
1550                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1551                                 if (real_target_type == TypeManager.byte_type)
1552                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1553                                 if (real_target_type == TypeManager.short_type)
1554                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1555                                 if (real_target_type == TypeManager.ushort_type)
1556                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1557                                 if (real_target_type == TypeManager.int32_type)
1558                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1559                                 if (real_target_type == TypeManager.uint32_type)
1560                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1561                                 if (real_target_type == TypeManager.int64_type)
1562                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1563                                 if (real_target_type == TypeManager.uint64_type)
1564                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1565                                 if (real_target_type == TypeManager.char_type)
1566                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1567                                 if (real_target_type == TypeManager.decimal_type)
1568                                         return new CastToDecimal (expr, true);
1569                         } else if (expr_type == TypeManager.double_type){
1570                                 //
1571                                 // From double to sbyte, byte, short,
1572                                 // ushort, int, uint, long, ulong,
1573                                 // char, float or decimal
1574                                 //
1575                                 if (real_target_type == TypeManager.sbyte_type)
1576                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1577                                 if (real_target_type == TypeManager.byte_type)
1578                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1579                                 if (real_target_type == TypeManager.short_type)
1580                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1581                                 if (real_target_type == TypeManager.ushort_type)
1582                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1583                                 if (real_target_type == TypeManager.int32_type)
1584                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1585                                 if (real_target_type == TypeManager.uint32_type)
1586                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1587                                 if (real_target_type == TypeManager.int64_type)
1588                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1589                                 if (real_target_type == TypeManager.uint64_type)
1590                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1591                                 if (real_target_type == TypeManager.char_type)
1592                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1593                                 if (real_target_type == TypeManager.float_type)
1594                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1595                                 if (real_target_type == TypeManager.decimal_type)
1596                                         return new CastToDecimal (expr, true);
1597                         } else if (expr_type == TypeManager.uintptr_type){
1598                                 //
1599                                 // Various built-in conversions that belonged in the class library
1600                                 //
1601                                 // from uintptr to sbyte, short, int32
1602                                 //
1603                                 if (real_target_type == TypeManager.sbyte_type){
1604                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1605                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
1606                                 }
1607                                 if (real_target_type == TypeManager.short_type){
1608                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1609                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
1610                                 }
1611                                 if (real_target_type == TypeManager.int32_type){
1612                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.uint32_type, true),
1613                                                               TypeManager.int32_type);
1614                                 }
1615                         } else if (expr_type == TypeManager.intptr_type){
1616                                 if (real_target_type == TypeManager.uint64_type){
1617                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.int64_type, true),
1618                                                               TypeManager.uint64_type);
1619                                 }
1620                         } else if (expr_type == TypeManager.decimal_type) {
1621                                 return new CastFromDecimal (expr, target_type).Resolve ();
1622                         }
1623                         return null;
1624                 }
1625
1626                 /// <summary>
1627                 ///  Returns whether an explicit reference conversion can be performed
1628                 ///  from source_type to target_type
1629                 /// </summary>
1630                 public static bool ExplicitReferenceConversionExists (TypeSpec source_type, TypeSpec target_type)
1631                 {
1632                         Expression e = ExplicitReferenceConversion (null, source_type, target_type);
1633                         if (e == null)
1634                                 return false;
1635
1636                         if (e == EmptyExpression.Null)
1637                                 return true;
1638
1639                         throw new InternalErrorException ("Invalid probing conversion result");
1640                 }
1641
1642                 /// <summary>
1643                 ///   Implements Explicit Reference conversions
1644                 /// </summary>
1645                 static Expression ExplicitReferenceConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
1646                 {
1647                         //
1648                         // From object to a generic parameter
1649                         //
1650                         if (source_type == TypeManager.object_type && TypeManager.IsGenericParameter (target_type))
1651                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1652
1653                         //
1654                         // Explicit type parameter conversion.
1655                         //
1656                         if (source_type.Kind == MemberKind.TypeParameter)
1657                                 return ExplicitTypeParameterConversion (source, source_type, target_type);
1658
1659                         bool target_is_value_type = TypeManager.IsStruct (target_type) || TypeManager.IsEnumType (target_type);
1660
1661                         //
1662                         // Unboxing conversion from System.ValueType to any non-nullable-value-type
1663                         //
1664                         if (source_type == TypeManager.value_type && target_is_value_type)
1665                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1666
1667                         //
1668                         // From object or dynamic to any reference type or value type (unboxing)
1669                         //
1670                         if (source_type == TypeManager.object_type || source_type == InternalType.Dynamic)
1671                                 return
1672                                         source == null ? EmptyExpression.Null :
1673                                         target_is_value_type ? new UnboxCast (source, target_type) :
1674                                         source is Constant ? (Expression) new EmptyConstantCast ((Constant) source, target_type) :
1675                                         new ClassCast (source, target_type);
1676
1677                         //
1678                         // From any class S to any class-type T, provided S is a base class of T
1679                         //
1680                         if (source_type.Kind == MemberKind.Class && TypeSpec.IsBaseClass (target_type, source_type, true))
1681                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1682
1683                         //
1684                         // From any interface-type S to to any class type T, provided T is not
1685                         // sealed, or provided T implements S.
1686                         //
1687                         if (source_type.IsInterface) {
1688                                 if (!target_type.IsSealed || target_type.ImplementsInterface (source_type, true)) {
1689                                         if (target_type.IsClass)
1690                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1691
1692                                         //
1693                                         // Unboxing conversion from any interface-type to any non-nullable-value-type that
1694                                         // implements the interface-type
1695                                         //
1696                                         return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1697                                 }
1698
1699                                 //
1700                                 // From System.Collections.Generic.IList<T> and its base interfaces to a one-dimensional
1701                                 // array type S[], provided there is an implicit or explicit reference conversion from S to T.
1702                                 //
1703                                 var target_array = target_type as ArrayContainer;
1704                                 if (target_array != null && IList_To_Array (source_type, target_array))
1705                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1706
1707                                 return null;
1708                         }
1709
1710                         var source_array = source_type as ArrayContainer;
1711                         if (source_array != null) {
1712                                 var target_array = target_type as ArrayContainer;
1713                                 if (target_array != null) {
1714                                         //
1715                                         // From System.Array to any array-type
1716                                         //
1717                                         if (source_type == TypeManager.array_type)
1718                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1719
1720                                         //
1721                                         // From an array type S with an element type Se to an array type T with an
1722                                         // element type Te provided all the following are true:
1723                                         //     * S and T differe only in element type, in other words, S and T
1724                                         //       have the same number of dimensions.
1725                                         //     * Both Se and Te are reference types
1726                                         //     * An explicit reference conversions exist from Se to Te
1727                                         //
1728                                         if (source_array.Rank == target_array.Rank) {
1729
1730                                                 source_type = source_array.Element;
1731                                                 if (!TypeManager.IsReferenceType (source_type))
1732                                                         return null;
1733
1734                                                 var target_element = target_array.Element;
1735                                                 if (!TypeManager.IsReferenceType (target_element))
1736                                                         return null;
1737
1738                                                 if (ExplicitReferenceConversionExists (source_type, target_element))
1739                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1740
1741                                                 return null;
1742                                         }
1743                                 }
1744
1745                                 //
1746                                 // From a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its base interfaces,
1747                                 // provided that there is an explicit reference conversion from S to T
1748                                 //
1749                                 if (ArrayToIList (source_array, target_type, true))
1750                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1751
1752                                 return null;
1753                         }
1754
1755                         //
1756                         // From any class type S to any interface T, provides S is not sealed
1757                         // and provided S does not implement T.
1758                         //
1759                         if (target_type.IsInterface && !source_type.IsSealed && !source_type.ImplementsInterface (target_type, true)) {
1760                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1761                         }
1762
1763                         //
1764                         // From System delegate to any delegate-type
1765                         //
1766                         if (source_type == TypeManager.delegate_type && TypeManager.IsDelegateType (target_type))
1767                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1768
1769                         //
1770                         // From variant generic delegate to same variant generic delegate type
1771                         //
1772                         if (source_type.IsDelegate && target_type.IsDelegate && source_type.MemberDefinition == target_type.MemberDefinition) {
1773                                 var tparams = source_type.MemberDefinition.TypeParameters;
1774                                 var targs_src = source_type.TypeArguments;
1775                                 var targs_dst = target_type.TypeArguments;
1776                                 int i;
1777                                 for (i = 0; i < tparams.Length; ++i) {
1778                                         //
1779                                         // If TP is invariant, types have to be identical
1780                                         //
1781                                         if (TypeSpecComparer.IsEqual (targs_src[i], targs_dst[i]))
1782                                                 continue;
1783
1784                                         if (tparams[i].Variance == Variance.Covariant) {
1785                                                 //
1786                                                 //If TP is covariant, an implicit or explicit identity or reference conversion is required
1787                                                 //
1788                                                 if (ImplicitReferenceConversionExists (new EmptyExpression (targs_src[i]), targs_dst[i]))
1789                                                         continue;
1790
1791                                                 if (ExplicitReferenceConversionExists (targs_src[i], targs_dst[i]))
1792                                                         continue;
1793
1794                                         } else if (tparams[i].Variance == Variance.Contravariant) {
1795                                                 //
1796                                                 //If TP is contravariant, both are either identical or reference types
1797                                                 //
1798                                                 if (TypeManager.IsReferenceType (targs_src[i]) && TypeManager.IsReferenceType (targs_dst[i]))
1799                                                         continue;
1800                                         }
1801
1802                                         break;
1803                                 }
1804
1805                                 if (i == tparams.Length)
1806                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1807                         }
1808
1809                         return null;
1810                 }
1811
1812                 /// <summary>
1813                 ///   Performs an explicit conversion of the expression `expr' whose
1814                 ///   type is expr.Type to `target_type'.
1815                 /// </summary>
1816                 static public Expression ExplicitConversionCore (ResolveContext ec, Expression expr,
1817                                                                  TypeSpec target_type, Location loc)
1818                 {
1819                         TypeSpec expr_type = expr.Type;
1820
1821                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1822                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc, true);
1823                         if (ne != null)
1824                                 return ne;
1825
1826                         if (TypeManager.IsEnumType (expr_type)) {
1827                                 TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
1828                                 Expression underlying = EmptyCast.Create (expr, EnumSpec.GetUnderlyingType (expr_type));
1829                                 if (underlying.Type == real_target)
1830                                         ne = underlying;
1831
1832                                 if (ne == null)
1833                                         ne = ImplicitNumericConversion (underlying, real_target);
1834
1835                                 if (ne == null)
1836                                         ne = ExplicitNumericConversion (underlying, real_target);
1837
1838                                 //
1839                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1840                                 //
1841                                 if (ne == null && (real_target == TypeManager.intptr_type || real_target == TypeManager.uintptr_type))
1842                                         ne = ExplicitUserConversion (ec, underlying, real_target, loc);
1843
1844                                 return ne != null ? EmptyCast.Create (ne, target_type) : null;
1845                         }
1846
1847                         if (TypeManager.IsEnumType (target_type)) {
1848                                 //
1849                                 // System.Enum can be unboxed to any enum-type
1850                                 //
1851                                 if (expr_type == TypeManager.enum_type)
1852                                         return new UnboxCast (expr, target_type);
1853
1854                                 TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
1855
1856                                 if (expr_type == real_target)
1857                                         return EmptyCast.Create (expr, target_type);
1858
1859                                 ne = ImplicitNumericConversion (expr, real_target);
1860                                 if (ne != null)
1861                                         return EmptyCast.Create (ne, target_type);
1862
1863                                 ne = ExplicitNumericConversion (expr, real_target);
1864                                 if (ne != null)
1865                                         return EmptyCast.Create (ne, target_type);
1866
1867                                 //
1868                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1869                                 //
1870                                 if (expr_type == TypeManager.intptr_type || expr_type == TypeManager.uintptr_type) {
1871                                         ne = ExplicitUserConversion (ec, expr, real_target, loc);
1872                                         if (ne != null)
1873                                                 return ExplicitConversionCore (ec, ne, target_type, loc);
1874                                 }
1875                         } else {
1876                                 ne = ExplicitNumericConversion (expr, target_type);
1877                                 if (ne != null)
1878                                         return ne;
1879                         }
1880
1881                         //
1882                         // Skip the ExplicitReferenceConversion because we can not convert
1883                         // from Null to a ValueType, and ExplicitReference wont check against
1884                         // null literal explicitly
1885                         //
1886                         if (expr_type != InternalType.Null) {
1887                                 ne = ExplicitReferenceConversion (expr, expr_type, target_type);
1888                                 if (ne != null)
1889                                         return ne;
1890                         }
1891
1892                         if (ec.IsUnsafe){
1893                                 ne = ExplicitUnsafe (expr, target_type);
1894                                 if (ne != null)
1895                                         return ne;
1896                         }
1897
1898                         return null;
1899                 }
1900
1901                 public static Expression ExplicitUnsafe (Expression expr, TypeSpec target_type)
1902                 {
1903                         TypeSpec expr_type = expr.Type;
1904
1905                         if (target_type.IsPointer){
1906                                 if (expr_type.IsPointer)
1907                                         return EmptyCast.Create (expr, target_type);
1908
1909                                 if (expr_type == TypeManager.sbyte_type ||
1910                                         expr_type == TypeManager.short_type ||
1911                                         expr_type == TypeManager.int32_type)
1912                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1913
1914                                 if (expr_type == TypeManager.ushort_type ||
1915                                         expr_type == TypeManager.uint32_type ||
1916                                         expr_type == TypeManager.byte_type)
1917                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1918
1919                                 if (expr_type == TypeManager.int64_type)
1920                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I);
1921
1922                                 if (expr_type == TypeManager.uint64_type)
1923                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I);
1924                         }
1925
1926                         if (expr_type.IsPointer){
1927                                 if (target_type == TypeManager.sbyte_type)
1928                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1929                                 if (target_type == TypeManager.byte_type)
1930                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1931                                 if (target_type == TypeManager.short_type)
1932                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1933                                 if (target_type == TypeManager.ushort_type)
1934                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1935                                 if (target_type == TypeManager.int32_type)
1936                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1937                                 if (target_type == TypeManager.uint32_type)
1938                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1939                                 if (target_type == TypeManager.int64_type)
1940                                         return new ConvCast (expr, target_type, ConvCast.Mode.I_I8);
1941                                 if (target_type == TypeManager.uint64_type)
1942                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1943                         }
1944                         return null;
1945                 }
1946
1947                 /// <summary>
1948                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1949                 /// </summary>
1950                 static public Expression ExplicitConversionStandard (ResolveContext ec, Expression expr,
1951                                                                      TypeSpec target_type, Location l)
1952                 {
1953                         int errors = ec.Report.Errors;
1954                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1955                         if (ec.Report.Errors > errors)
1956                                 return null;
1957
1958                         if (ne != null)
1959                                 return ne;
1960
1961                         ne = ExplicitNumericConversion (expr, target_type);
1962                         if (ne != null)
1963                                 return ne;
1964
1965                         ne = ExplicitReferenceConversion (expr, expr.Type, target_type);
1966                         if (ne != null)
1967                                 return ne;
1968
1969                         if (ec.IsUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
1970                                 return EmptyCast.Create (expr, target_type);
1971
1972                         expr.Error_ValueCannotBeConverted (ec, l, target_type, true);
1973                         return null;
1974                 }
1975
1976                 /// <summary>
1977                 ///   Performs an explicit conversion of the expression `expr' whose
1978                 ///   type is expr.Type to `target_type'.
1979                 /// </summary>
1980                 static public Expression ExplicitConversion (ResolveContext ec, Expression expr,
1981                         TypeSpec target_type, Location loc)
1982                 {
1983                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
1984                         if (e != null) {
1985                                 //
1986                                 // Don't eliminate explicit precission casts
1987                                 //
1988                                 if (e == expr) {
1989                                         if (target_type == TypeManager.float_type)
1990                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
1991
1992                                         if (target_type == TypeManager.double_type)
1993                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
1994                                 }
1995
1996                                 return e;
1997                         }
1998
1999                         TypeSpec expr_type = expr.Type;
2000                         if (TypeManager.IsNullableType (target_type)) {
2001                                 if (TypeManager.IsNullableType (expr_type)) {
2002                                         TypeSpec target = Nullable.NullableInfo.GetUnderlyingType (target_type);
2003                                         Expression unwrap = Nullable.Unwrap.Create (expr);
2004                                         e = ExplicitConversion (ec, unwrap, target, expr.Location);
2005                                         if (e == null)
2006                                                 return null;
2007
2008                                         return new Nullable.Lifted (e, unwrap, target_type).Resolve (ec);
2009                                 } else if (expr_type == TypeManager.object_type) {
2010                                         return new UnboxCast (expr, target_type);
2011                                 } else {
2012                                         TypeSpec target = TypeManager.GetTypeArguments (target_type) [0];
2013
2014                                         e = ExplicitConversionCore (ec, expr, target, loc);
2015                                         if (e != null)
2016                                                 return Nullable.Wrap.Create (e, target_type);
2017                                 }
2018                         } else if (TypeManager.IsNullableType (expr_type)) {
2019                                 e = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
2020                                 if (e != null)
2021                                         return e;
2022
2023                                 e = Nullable.Unwrap.Create (expr, false);
2024                                 e = ExplicitConversionCore (ec, e, target_type, loc);
2025                                 if (e != null)
2026                                         return EmptyCast.Create (e, target_type);
2027                         }
2028
2029                         e = ExplicitUserConversion (ec, expr, target_type, loc);
2030                         if (e != null)
2031                                 return e;
2032
2033                         expr.Error_ValueCannotBeConverted (ec, loc, target_type, true);
2034                         return null;
2035                 }
2036         }
2037 }