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)) {
 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)){
 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);
 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) &&
 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                                 return false;
 689                         }
 690
 691                         if (TypeManager.IsNullableType (target_type)) {
 692                                 return ImplicitNulableConversion (null, expr, target_type) != null;
 693                         }
 694
 695                         // First numeric conversions
 696                         if (ImplicitNumericConversion (null, expr_type, target_type) != null)
 697                                 return true;
 698
 699                         if (ImplicitReferenceConversionExists (expr, target_type))
 700                                 return true;
 701
 702                         if (ImplicitBoxingConversion (null, expr_type, target_type) != null)
 703                                 return true;
 704
 705                         //
 706                         // Implicit Constant Expression Conversions
 707                         //
 708                         if (expr is IntConstant){
 709                                 int value = ((IntConstant) expr).Value;
 710
 711                                 if (target_type == TypeManager.sbyte_type){
 712                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 713                                                 return true;
 714                                 } else if (target_type == TypeManager.byte_type){
 715                                         if (value >= 0 && value <= Byte.MaxValue)
 716                                                 return true;
 717                                 } else if (target_type == TypeManager.short_type){
 718                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 719                                                 return true;
 720                                 } else if (target_type == TypeManager.ushort_type){
 721                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 722                                                 return true;
 723                                 } else if (target_type == TypeManager.uint32_type){
 724                                         if (value >= 0)
 725                                                 return true;
 726                                 } else if (target_type == TypeManager.uint64_type){
 727                                          //
 728                                          // we can optimize this case: a positive int32
 729                                          // always fits on a uint64.  But we need an opcode
 730                                          // to do it.
 731                                          //
 732                                         if (value >= 0)
 733                                                 return true;
 734                                 }
 735                         }
 736
 737                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 738                                 //
 739                                 // Try the implicit constant expression conversion
 740                                 // from long to ulong, instead of a nice routine,
 741                                 // we just inline it
 742                                 //
 743                                 long v = ((LongConstant) expr).Value;
 744                                 if (v >= 0)
 745                                         return true;
 746                         }
 747
 748                         if (expr is IntegralConstant && TypeManager.IsEnumType (target_type)) {
 749                                 var i = (IntegralConstant) expr;
 750                                 //
 751                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
 752                                 //
 753                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
 754                                 // to be converted to any enum-type and to any nullable-type whose underlying
 755                                 // type is an enum-type
 756                                 //
 757                                 return i.IsZeroInteger;
 758                         }
 759
 760                         //
 761                         // If `expr_type' implements `target_type' (which is an iface)
 762                         // see TryImplicitIntConversion
 763                         //
 764                         if (target_type.IsInterface && expr_type.ImplementsInterface (target_type))
 765                                 return true;
 766
 767                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 768                                 return true;
 769
 770                         // Conversion from __arglist to System.ArgIterator
 771                         if (expr_type == InternalType.Arglist)
 772                                 return target_type == TypeManager.arg_iterator_type;
 773
 774                         return false;
 775                 }
 776
 777                 /// <summary>
 778                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 779                 ///  amongst the methods in the MethodGroupExpr
 780                 /// </summary>
 781                 public static TypeSpec FindMostEncompassedType (IEnumerable<TypeSpec> types)
 782                 {
 783                         TypeSpec best = null;
 784                         EmptyExpression expr = EmptyExpression.Grab ();
 785
 786                         foreach (TypeSpec t in types) {
 787                                 if (best == null) {
 788                                         best = t;
 789                                         continue;
 790                                 }
 791
 792                                 expr.SetType (t);
 793                                 if (ImplicitStandardConversionExists (expr, best))
 794                                         best = t;
 795                         }
 796
 797                         expr.SetType (best);
 798                         foreach (TypeSpec t in types) {
 799                                 if (best == t)
 800                                         continue;
 801                                 if (!ImplicitStandardConversionExists (expr, t)) {
 802                                         best = null;
 803                                         break;
 804                                 }
 805                         }
 806
 807                         EmptyExpression.Release (expr);
 808
 809                         return best;
 810                 }
 811
 812                 /// <summary>
 813                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 814                 ///  amongst the types in the given set
 815                 /// </summary>
 816                 static TypeSpec FindMostEncompassingType (IList<TypeSpec> types)
 817                 {
 818                         TypeSpec best = null;
 819
 820                         if (types.Count == 0)
 821                                 return null;
 822
 823                         if (types.Count == 1)
 824                                 return types [0];
 825
 826                         EmptyExpression expr = EmptyExpression.Grab ();
 827
 828                         foreach (TypeSpec t in types) {
 829                                 if (best == null) {
 830                                         best = t;
 831                                         continue;
 832                                 }
 833
 834                                 expr.SetType (best);
 835                                 if (ImplicitStandardConversionExists (expr, t))
 836                                         best = t;
 837                         }
 838
 839                         foreach (TypeSpec t in types) {
 840                                 if (best == t)
 841                                         continue;
 842                                 expr.SetType (t);
 843                                 if (!ImplicitStandardConversionExists (expr, best)) {
 844                                         best = null;
 845                                         break;
 846                                 }
 847                         }
 848
 849                         EmptyExpression.Release (expr);
 850
 851                         return best;
 852                 }
 853
 854                 /// <summary>
 855                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 856                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 857                 ///   for explicit and implicit conversion operators.
 858                 /// </summary>
 859                 static TypeSpec FindMostSpecificSource (IList<MethodSpec> list,
 860                                                            Expression source, bool apply_explicit_conv_rules)
 861                 {
 862                         var src_types_set = new List<TypeSpec> ();
 863
 864                         //
 865                         // If any operator converts from S then Sx = S
 866                         //
 867                         TypeSpec source_type = source.Type;
 868                         foreach (var mb in list){
 869                                 TypeSpec param_type = mb.Parameters.Types [0];
 870
 871                                 if (param_type == source_type)
 872                                         return param_type;
 873
 874                                 src_types_set.Add (param_type);
 875                         }
 876
 877                         //
 878                         // Explicit Conv rules
 879                         //
 880                         if (apply_explicit_conv_rules) {
 881                                 var candidate_set = new List<TypeSpec> ();
 882
 883                                 foreach (TypeSpec param_type in src_types_set){
 884                                         if (ImplicitStandardConversionExists (source, param_type))
 885                                                 candidate_set.Add (param_type);
 886                                 }
 887
 888                                 if (candidate_set.Count != 0)
 889                                         return FindMostEncompassedType (candidate_set);
 890                         }
 891
 892                         //
 893                         // Final case
 894                         //
 895                         if (apply_explicit_conv_rules)
 896                                 return FindMostEncompassingType (src_types_set);
 897                         else
 898                                 return FindMostEncompassedType (src_types_set);
 899                 }
 900
 901                 /// <summary>
 902                 ///  Finds the most specific target Tx according to section 13.4.4
 903                 /// </summary>
 904                 static public TypeSpec FindMostSpecificTarget (IList<MethodSpec> list,
 905                                                            TypeSpec target, bool apply_explicit_conv_rules)
 906                 {
 907                         var tgt_types_set = new List<TypeSpec> ();
 908
 909                         //
 910                         // If any operator converts to T then Tx = T
 911                         //
 912                         foreach (var mi in list){
 913                                 TypeSpec ret_type = mi.ReturnType;
 914                                 if (ret_type == target)
 915                                         return ret_type;
 916
 917                                 tgt_types_set.Add (ret_type);
 918                         }
 919
 920                         //
 921                         // Explicit conv rules
 922                         //
 923                         if (apply_explicit_conv_rules) {
 924                                 var candidate_set = new List<TypeSpec> ();
 925
 926                                 EmptyExpression expr = EmptyExpression.Grab ();
 927
 928                                 foreach (TypeSpec ret_type in tgt_types_set){
 929                                         expr.SetType (ret_type);
 930
 931                                         if (ImplicitStandardConversionExists (expr, target))
 932                                                 candidate_set.Add (ret_type);
 933                                 }
 934
 935                                 EmptyExpression.Release (expr);
 936
 937                                 if (candidate_set.Count != 0)
 938                                         return FindMostEncompassingType (candidate_set);
 939                         }
 940
 941                         //
 942                         // Okay, final case !
 943                         //
 944                         if (apply_explicit_conv_rules)
 945                                 return FindMostEncompassedType (tgt_types_set);
 946                         else
 947                                 return FindMostEncompassingType (tgt_types_set);
 948                 }
 949
 950                 /// <summary>
 951                 ///  User-defined Implicit conversions
 952                 /// </summary>
 953                 static public Expression ImplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
 954                 {
 955                         return UserDefinedConversion (ec, source, target, true, loc);
 956                 }
 957
 958                 /// <summary>
 959                 ///  User-defined Explicit conversions
 960                 /// </summary>
 961                 static Expression ExplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
 962                 {
 963                         return UserDefinedConversion (ec, source, target, false, loc);
 964                 }
 965
 966                 static void FindApplicableUserDefinedConversionOperators (IList<MemberSpec> operators, Expression source, TypeSpec target, bool implicitOnly, ref List<MethodSpec> candidates)
 967                 {
 968                         //
 969                         // LAMESPEC: Undocumented IntPtr/UIntPtr conversions
 970                         // IntPtr -> uint uses int
 971                         // UIntPtr -> long uses ulong
 972                         //
 973                         if (source.Type == TypeManager.intptr_type) {
 974                                 if (target == TypeManager.uint32_type)
 975                                         target = TypeManager.int32_type;
 976                         } else if (source.Type == TypeManager.uintptr_type) {
 977                                 if (target == TypeManager.int64_type)
 978                                         target = TypeManager.uint64_type;
 979                         }
 980
 981                         // For a conversion operator to be applicable, it must be possible
 982                         // to perform a standard conversion from the source type to
 983                         // the operand type of the operator, and it must be possible
 984                         // to perform a standard conversion from the result type of
 985                         // the operator to the target type.
 986
 987                         Expression texpr = null;
 988
 989                         foreach (MethodSpec op in operators) {
 990
 991                                 // Can be null because MemberCache.GetUserOperator does not resize the array
 992                                 if (op == null)
 993                                         continue;
 994
 995                                 var t = op.Parameters.Types[0];
 996                                 if (source.Type != t && !ImplicitStandardConversionExists (source, t)) {
 997                                         if (implicitOnly)
 998                                                 continue;
 999
1000                                         if (!ImplicitStandardConversionExists (new EmptyExpression (t), source.Type))
1001                                                 continue;
1002                                 }
1003
1004                                 t = op.ReturnType;
1005
1006                                 // LAMESPEC: Exclude UIntPtr -> int conversion
1007                                 if (t == TypeManager.uint32_type && source.Type == TypeManager.uintptr_type)
1008                                         continue;
1009
1010                                 if (target != t && !ImplicitStandardConversionExists (new EmptyExpression (t), target)) {
1011                                         if (implicitOnly)
1012                                                 continue;
1013
1014                                         if (texpr == null)
1015                                                 texpr = new EmptyExpression (target);
1016
1017                                         if (!ImplicitStandardConversionExists (texpr, t))
1018                                                 continue;
1019                                 }
1020
1021                                 if (candidates == null)
1022                                         candidates = new List<MethodSpec> ();
1023
1024                                 candidates.Add (op);
1025                         }
1026                 }
1027
1028                 //
1029                 // User-defined conversions
1030                 //
1031                 static Expression UserDefinedConversion (ResolveContext ec, Expression source, TypeSpec target, bool implicitOnly, Location loc)
1032                 {
1033                         List<MethodSpec> candidates = null;
1034
1035                         //
1036                         // If S or T are nullable types, S0 and T0 are their underlying types
1037                         // otherwise S0 and T0 are equal to S and T respectively.
1038                         //
1039                         TypeSpec source_type = source.Type;
1040                         TypeSpec target_type = target;
1041                         Expression unwrap;
1042
1043                         if (TypeManager.IsNullableType (source_type)) {
1044                                 // No implicit conversion S? -> T for non-reference types
1045                                 if (implicitOnly && !TypeManager.IsReferenceType (target_type) && !TypeManager.IsNullableType (target_type))
1046                                         return null;
1047
1048                                 unwrap = source = Nullable.Unwrap.Create (source);
1049                                 source_type = source.Type;
1050                         } else {
1051                                 unwrap = null;
1052                         }
1053
1054                         if (TypeManager.IsNullableType (target_type))
1055                                 target_type = Nullable.NullableInfo.GetUnderlyingType (target_type);
1056
1057                         // Only these containers can contain a user defined implicit or explicit operators
1058                         const MemberKind user_conversion_kinds = MemberKind.Class | MemberKind.Struct | MemberKind.TypeParameter;
1059
1060                         if ((source_type.Kind & user_conversion_kinds) != 0 && source_type != TypeManager.decimal_type) {
1061                                 bool declared_only = source_type.IsStruct;
1062
1063                                 var operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Implicit, declared_only);
1064                                 if (operators != null) {
1065                                         FindApplicableUserDefinedConversionOperators (operators, source, target_type, implicitOnly, ref candidates);
1066                                 }
1067
1068                                 if (!implicitOnly) {
1069                                         operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Explicit, declared_only);
1070                                         if (operators != null) {
1071                                                 FindApplicableUserDefinedConversionOperators (operators, source, target_type, false, ref candidates);
1072                                         }
1073                                 }
1074                         }
1075
1076                         if ((target.Kind & user_conversion_kinds) != 0 && target != TypeManager.decimal_type) {
1077                                 bool declared_only = target.IsStruct || implicitOnly;
1078
1079                                 var operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Implicit, declared_only);
1080                                 if (operators != null) {
1081                                         FindApplicableUserDefinedConversionOperators (operators, source, target_type, implicitOnly, ref candidates);
1082                                 }
1083
1084                                 if (!implicitOnly) {
1085                                         operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Explicit, declared_only);
1086                                         if (operators != null) {
1087                                                 FindApplicableUserDefinedConversionOperators (operators, source, target_type, false, ref candidates);
1088                                         }
1089                                 }
1090                         }
1091
1092                         if (candidates == null)
1093                                 return null;
1094
1095                         //
1096                         // Find the most specific conversion operator
1097                         //
1098                         MethodSpec most_specific_operator;
1099                         TypeSpec s_x, t_x;
1100                         if (candidates.Count == 1) {
1101                                 most_specific_operator = candidates[0];
1102                                 s_x = most_specific_operator.Parameters.Types[0];
1103                                 t_x = most_specific_operator.ReturnType;
1104                         } else {
1105                                 s_x = FindMostSpecificSource (candidates, source, !implicitOnly);
1106                                 if (s_x == null)
1107                                         return null;
1108
1109                                 t_x = FindMostSpecificTarget (candidates, target, !implicitOnly);
1110                                 if (t_x == null)
1111                                         return null;
1112
1113                                 most_specific_operator = candidates[0];
1114
1115                                 for (int i = 1; i < candidates.Count; ++i) {
1116                                         if (candidates[i].ReturnType == t_x && candidates[i].Parameters.Types[0] == s_x) {
1117                                                 most_specific_operator = candidates[i];
1118                                                 break;
1119                                         }
1120                                 }
1121                         }
1122
1123                         //
1124                         // Convert input type when it's different to best operator argument
1125                         //
1126                         if (s_x != source.Type)
1127                                 source = implicitOnly ?
1128                                         ImplicitConversionStandard (ec, source, s_x, loc) :
1129                                         ExplicitConversionStandard (ec, source, s_x, loc);
1130
1131                         source = new UserCast (most_specific_operator, source, loc).Resolve (ec);
1132
1133                         //
1134                         // Convert result type when it's different to best operator return type
1135                         //
1136                         if (t_x != target_type) {
1137                                 //
1138                                 // User operator is of T?, no need to lift it
1139                                 //
1140                                 if (TypeManager.IsNullableType (t_x) && t_x == target)
1141                                         return source;
1142
1143                                 source = implicitOnly ?
1144                                         ImplicitConversionStandard (ec, source, target_type, loc) :
1145                                         ExplicitConversionStandard (ec, source, target_type, loc);
1146                         }
1147
1148                         //
1149                         // Source expression is of nullable type, lift the result in case of it's null
1150                         //
1151                         if (unwrap != null && (TypeManager.IsReferenceType (target) || target_type != target))
1152                                 source = new Nullable.Lifted (source, unwrap, target).Resolve (ec);
1153                         else if (target_type != target)
1154                                 source = Nullable.Wrap.Create (source, target);
1155
1156                         return source;
1157                 }
1158
1159                 /// <summary>
1160                 ///   Converts implicitly the resolved expression `expr' into the
1161                 ///   `target_type'.  It returns a new expression that can be used
1162                 ///   in a context that expects a `target_type'.
1163                 /// </summary>
1164                 static public Expression ImplicitConversion (ResolveContext ec, Expression expr,
1165                                                              TypeSpec target_type, Location loc)
1166                 {
1167                         Expression e;
1168
1169                         if (target_type == null)
1170                                 throw new Exception ("Target type is null");
1171
1172                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1173                         if (e != null)
1174                                 return e;
1175
1176                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1177                         if (e != null)
1178                                 return e;
1179
1180                         return null;
1181                 }
1182
1183
1184                 /// <summary>
1185                 ///   Attempts to apply the `Standard Implicit
1186                 ///   Conversion' rules to the expression `expr' into
1187                 ///   the `target_type'.  It returns a new expression
1188                 ///   that can be used in a context that expects a
1189                 ///   `target_type'.
1190                 ///
1191                 ///   This is different from `ImplicitConversion' in that the
1192                 ///   user defined implicit conversions are excluded.
1193                 /// </summary>
1194                 static public Expression ImplicitConversionStandard (ResolveContext ec, Expression expr,
1195                                                                      TypeSpec target_type, Location loc)
1196                 {
1197                         return ImplicitConversionStandard (ec, expr, target_type, loc, false);
1198                 }
1199
1200                 static Expression ImplicitConversionStandard (ResolveContext ec, Expression expr, TypeSpec target_type, Location loc, bool explicit_cast)
1201                 {
1202                         if (expr.eclass == ExprClass.MethodGroup){
1203                                 if (!TypeManager.IsDelegateType (target_type)){
1204                                         return null;
1205                                 }
1206
1207                                 //
1208                                 // Only allow anonymous method conversions on post ISO_1
1209                                 //
1210                                 if (RootContext.Version != LanguageVersion.ISO_1){
1211                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1212                                         if (mg != null)
1213                                                 return ImplicitDelegateCreation.Create (
1214                                                         ec, mg, target_type, loc);
1215                                 }
1216                         }
1217
1218                         TypeSpec expr_type = expr.Type;
1219                         Expression e;
1220
1221                         if (expr_type == target_type) {
1222                                 if (expr_type != InternalType.Null && expr_type != InternalType.AnonymousMethod)
1223                                         return expr;
1224                                 return null;
1225                         }
1226
1227                         if (expr_type == InternalType.Dynamic) {
1228                                 switch (target_type.Kind) {
1229                                 case MemberKind.ArrayType:
1230                                 case MemberKind.Class:
1231                                         if (target_type == TypeManager.object_type)
1232                                                 return EmptyCast.Create (expr, target_type);
1233
1234                                         goto case MemberKind.Struct;
1235                                 case MemberKind.Struct:
1236                                 case MemberKind.Delegate:
1237                                 case MemberKind.Enum:
1238                                 case MemberKind.Interface:
1239                                 case MemberKind.TypeParameter:
1240                                         Arguments args = new Arguments (1);
1241                                         args.Add (new Argument (expr));
1242                                         return new DynamicConversion (target_type, 0, args, loc).Resolve (ec);
1243                                 }
1244
1245                                 return null;
1246                         }
1247
1248                         if (TypeManager.IsNullableType (target_type))
1249                                 return ImplicitNulableConversion (ec, expr, target_type);
1250
1251                         //
1252                         // Attempt to do the implicit constant expression conversions
1253                         //
1254                         Constant c = expr as Constant;
1255                         if (c != null) {
1256                                 try {
1257                                         c = c.ConvertImplicitly (ec, target_type);
1258                                 } catch {
1259                                         Console.WriteLine ("Conversion error happened in line {0}", loc);
1260                                         throw;
1261                                 }
1262                                 if (c != null)
1263                                         return c;
1264                         }
1265
1266                         e = ImplicitNumericConversion (expr, expr_type, target_type);
1267                         if (e != null)
1268                                 return e;
1269
1270                         e = ImplicitReferenceConversion (expr, target_type, explicit_cast);
1271                         if (e != null)
1272                                 return e;
1273
1274                         if (expr is IntegralConstant && TypeManager.IsEnumType (target_type)){
1275                                 var i = (IntegralConstant) expr;
1276                                 //
1277                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
1278                                 //
1279                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
1280                                 // to be converted to any enum-type and to any nullable-type whose underlying
1281                                 // type is an enum-type
1282                                 //
1283                                 if (i.IsZeroInteger) {
1284                                         // Recreate 0 literal to remove any collected conversions
1285                                         return new EnumConstant (new IntLiteral (0, i.Location), target_type).Resolve (ec);
1286                                 }
1287                         }
1288
1289                         if (ec.IsUnsafe) {
1290                                 if (expr_type.IsPointer){
1291                                         if (target_type == TypeManager.void_ptr_type)
1292                                                 return EmptyCast.Create (expr, target_type);
1293
1294                                         //
1295                                         // yep, comparing pointer types cant be done with
1296                                         // t1 == t2, we have to compare their element types.
1297                                         //
1298                                         if (target_type.IsPointer){
1299                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1300                                                         return expr;
1301
1302                                                 //return null;
1303                                         }
1304                                 }
1305
1306                                 if (expr_type == InternalType.Null && target_type.IsPointer)
1307                                         return EmptyCast.Create (new NullPointer (loc), target_type);
1308                         }
1309
1310                         if (expr_type == InternalType.AnonymousMethod){
1311                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1312                                 Expression am = ame.Compatible (ec, target_type);
1313                                 if (am != null)
1314                                         return am.Resolve (ec);
1315                         }
1316
1317                         if (expr_type == InternalType.Arglist && target_type == TypeManager.arg_iterator_type)
1318                                 return expr;
1319
1320                         return null;
1321                 }
1322
1323                 /// <summary>
1324                 ///   Attempts to implicitly convert `source' into `target_type', using
1325                 ///   ImplicitConversion.  If there is no implicit conversion, then
1326                 ///   an error is signaled
1327                 /// </summary>
1328                 static public Expression ImplicitConversionRequired (ResolveContext ec, Expression source,
1329                                                                      TypeSpec target_type, Location loc)
1330                 {
1331                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1332                         if (e != null)
1333                                 return e;
1334
1335                         source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
1336                         return null;
1337                 }
1338
1339                 /// <summary>
1340                 ///   Performs the explicit numeric conversions
1341                 ///
1342                 /// There are a few conversions that are not part of the C# standard,
1343                 /// they were interim hacks in the C# compiler that were supposed to
1344                 /// become explicit operators in the UIntPtr class and IntPtr class,
1345                 /// but for historical reasons it did not happen, so the C# compiler
1346                 /// ended up with these special hacks.
1347                 ///
1348                 /// See bug 59800 for details.
1349                 ///
1350                 /// The conversion are:
1351                 ///   UIntPtr->SByte
1352                 ///   UIntPtr->Int16
1353                 ///   UIntPtr->Int32
1354                 ///   IntPtr->UInt64
1355                 ///   UInt64->IntPtr
1356                 ///   SByte->UIntPtr
1357                 ///   Int16->UIntPtr
1358                 ///
1359                 /// </summary>
1360                 public static Expression ExplicitNumericConversion (Expression expr, TypeSpec target_type)
1361                 {
1362                         TypeSpec expr_type = expr.Type;
1363                         TypeSpec real_target_type = target_type;
1364
1365                         if (expr_type == TypeManager.sbyte_type){
1366                                 //
1367                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1368                                 //
1369                                 if (real_target_type == TypeManager.byte_type)
1370                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1371                                 if (real_target_type == TypeManager.ushort_type)
1372                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1373                                 if (real_target_type == TypeManager.uint32_type)
1374                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1375                                 if (real_target_type == TypeManager.uint64_type)
1376                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1377                                 if (real_target_type == TypeManager.char_type)
1378                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1379
1380                                 // One of the built-in conversions that belonged in the class library
1381                                 if (real_target_type == TypeManager.uintptr_type){
1382                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
1383
1384                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1385                                 }
1386                         } else if (expr_type == TypeManager.byte_type){
1387                                 //
1388                                 // From byte to sbyte and char
1389                                 //
1390                                 if (real_target_type == TypeManager.sbyte_type)
1391                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1392                                 if (real_target_type == TypeManager.char_type)
1393                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1394                         } else if (expr_type == TypeManager.short_type){
1395                                 //
1396                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1397                                 //
1398                                 if (real_target_type == TypeManager.sbyte_type)
1399                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1400                                 if (real_target_type == TypeManager.byte_type)
1401                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1402                                 if (real_target_type == TypeManager.ushort_type)
1403                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1404                                 if (real_target_type == TypeManager.uint32_type)
1405                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1406                                 if (real_target_type == TypeManager.uint64_type)
1407                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1408                                 if (real_target_type == TypeManager.char_type)
1409                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1410
1411                                 // One of the built-in conversions that belonged in the class library
1412                                 if (real_target_type == TypeManager.uintptr_type){
1413                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1414
1415                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1416                                 }
1417                         } else if (expr_type == TypeManager.ushort_type){
1418                                 //
1419                                 // From ushort to sbyte, byte, short, char
1420                                 //
1421                                 if (real_target_type == TypeManager.sbyte_type)
1422                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1423                                 if (real_target_type == TypeManager.byte_type)
1424                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1425                                 if (real_target_type == TypeManager.short_type)
1426                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1427                                 if (real_target_type == TypeManager.char_type)
1428                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1429                         } else if (expr_type == TypeManager.int32_type){
1430                                 //
1431                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1432                                 //
1433                                 if (real_target_type == TypeManager.sbyte_type)
1434                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1435                                 if (real_target_type == TypeManager.byte_type)
1436                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1437                                 if (real_target_type == TypeManager.short_type)
1438                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1439                                 if (real_target_type == TypeManager.ushort_type)
1440                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1441                                 if (real_target_type == TypeManager.uint32_type)
1442                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1443                                 if (real_target_type == TypeManager.uint64_type)
1444                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1445                                 if (real_target_type == TypeManager.char_type)
1446                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1447
1448                                 // One of the built-in conversions that belonged in the class library
1449                                 if (real_target_type == TypeManager.uintptr_type){
1450                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1451
1452                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1453                                 }
1454                         } else if (expr_type == TypeManager.uint32_type){
1455                                 //
1456                                 // From uint to sbyte, byte, short, ushort, int, char
1457                                 //
1458                                 if (real_target_type == TypeManager.sbyte_type)
1459                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1460                                 if (real_target_type == TypeManager.byte_type)
1461                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1462                                 if (real_target_type == TypeManager.short_type)
1463                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1464                                 if (real_target_type == TypeManager.ushort_type)
1465                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1466                                 if (real_target_type == TypeManager.int32_type)
1467                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1468                                 if (real_target_type == TypeManager.char_type)
1469                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1470                         } else if (expr_type == TypeManager.int64_type){
1471                                 //
1472                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1473                                 //
1474                                 if (real_target_type == TypeManager.sbyte_type)
1475                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1476                                 if (real_target_type == TypeManager.byte_type)
1477                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1478                                 if (real_target_type == TypeManager.short_type)
1479                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1480                                 if (real_target_type == TypeManager.ushort_type)
1481                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1482                                 if (real_target_type == TypeManager.int32_type)
1483                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1484                                 if (real_target_type == TypeManager.uint32_type)
1485                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1486                                 if (real_target_type == TypeManager.uint64_type)
1487                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1488                                 if (real_target_type == TypeManager.char_type)
1489                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1490                         } else if (expr_type == TypeManager.uint64_type){
1491                                 //
1492                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1493                                 //
1494                                 if (real_target_type == TypeManager.sbyte_type)
1495                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1496                                 if (real_target_type == TypeManager.byte_type)
1497                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1498                                 if (real_target_type == TypeManager.short_type)
1499                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1500                                 if (real_target_type == TypeManager.ushort_type)
1501                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1502                                 if (real_target_type == TypeManager.int32_type)
1503                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1504                                 if (real_target_type == TypeManager.uint32_type)
1505                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1506                                 if (real_target_type == TypeManager.int64_type)
1507                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1508                                 if (real_target_type == TypeManager.char_type)
1509                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1510
1511                                 // One of the built-in conversions that belonged in the class library
1512                                 if (real_target_type == TypeManager.intptr_type){
1513                                         return new OperatorCast (EmptyCast.Create (expr, TypeManager.int64_type),
1514                                                                  TypeManager.intptr_type, true);
1515                                 }
1516                         } else if (expr_type == TypeManager.char_type){
1517                                 //
1518                                 // From char to sbyte, byte, short
1519                                 //
1520                                 if (real_target_type == TypeManager.sbyte_type)
1521                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1522                                 if (real_target_type == TypeManager.byte_type)
1523                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1524                                 if (real_target_type == TypeManager.short_type)
1525                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1526                         } else if (expr_type == TypeManager.float_type){
1527                                 //
1528                                 // From float to sbyte, byte, short,
1529                                 // ushort, int, uint, long, ulong, char
1530                                 // or decimal
1531                                 //
1532                                 if (real_target_type == TypeManager.sbyte_type)
1533                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1534                                 if (real_target_type == TypeManager.byte_type)
1535                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1536                                 if (real_target_type == TypeManager.short_type)
1537                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1538                                 if (real_target_type == TypeManager.ushort_type)
1539                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1540                                 if (real_target_type == TypeManager.int32_type)
1541                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1542                                 if (real_target_type == TypeManager.uint32_type)
1543                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1544                                 if (real_target_type == TypeManager.int64_type)
1545                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1546                                 if (real_target_type == TypeManager.uint64_type)
1547                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1548                                 if (real_target_type == TypeManager.char_type)
1549                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1550                                 if (real_target_type == TypeManager.decimal_type)
1551                                         return new CastToDecimal (expr, true);
1552                         } else if (expr_type == TypeManager.double_type){
1553                                 //
1554                                 // From double to sbyte, byte, short,
1555                                 // ushort, int, uint, long, ulong,
1556                                 // char, float or decimal
1557                                 //
1558                                 if (real_target_type == TypeManager.sbyte_type)
1559                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1560                                 if (real_target_type == TypeManager.byte_type)
1561                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1562                                 if (real_target_type == TypeManager.short_type)
1563                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1564                                 if (real_target_type == TypeManager.ushort_type)
1565                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1566                                 if (real_target_type == TypeManager.int32_type)
1567                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1568                                 if (real_target_type == TypeManager.uint32_type)
1569                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1570                                 if (real_target_type == TypeManager.int64_type)
1571                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1572                                 if (real_target_type == TypeManager.uint64_type)
1573                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1574                                 if (real_target_type == TypeManager.char_type)
1575                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1576                                 if (real_target_type == TypeManager.float_type)
1577                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1578                                 if (real_target_type == TypeManager.decimal_type)
1579                                         return new CastToDecimal (expr, true);
1580                         } else if (expr_type == TypeManager.uintptr_type){
1581                                 //
1582                                 // Various built-in conversions that belonged in the class library
1583                                 //
1584                                 // from uintptr to sbyte, short, int32
1585                                 //
1586                                 if (real_target_type == TypeManager.sbyte_type){
1587                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1588                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
1589                                 }
1590                                 if (real_target_type == TypeManager.short_type){
1591                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1592                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
1593                                 }
1594                                 if (real_target_type == TypeManager.int32_type){
1595                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.uint32_type, true),
1596                                                               TypeManager.int32_type);
1597                                 }
1598                         } else if (expr_type == TypeManager.intptr_type){
1599                                 if (real_target_type == TypeManager.uint64_type){
1600                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.int64_type, true),
1601                                                               TypeManager.uint64_type);
1602                                 }
1603                         } else if (expr_type == TypeManager.decimal_type) {
1604                                 return new CastFromDecimal (expr, target_type).Resolve ();
1605                         }
1606                         return null;
1607                 }
1608
1609                 /// <summary>
1610                 ///  Returns whether an explicit reference conversion can be performed
1611                 ///  from source_type to target_type
1612                 /// </summary>
1613                 public static bool ExplicitReferenceConversionExists (TypeSpec source_type, TypeSpec target_type)
1614                 {
1615                         Expression e = ExplicitReferenceConversion (null, source_type, target_type);
1616                         if (e == null)
1617                                 return false;
1618
1619                         if (e == EmptyExpression.Null)
1620                                 return true;
1621
1622                         throw new InternalErrorException ("Invalid probing conversion result");
1623                 }
1624
1625                 /// <summary>
1626                 ///   Implements Explicit Reference conversions
1627                 /// </summary>
1628                 static Expression ExplicitReferenceConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
1629                 {
1630                         //
1631                         // From object to a generic parameter
1632                         //
1633                         if (source_type == TypeManager.object_type && TypeManager.IsGenericParameter (target_type))
1634                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1635
1636                         //
1637                         // Explicit type parameter conversion.
1638                         //
1639                         if (source_type.Kind == MemberKind.TypeParameter)
1640                                 return ExplicitTypeParameterConversion (source, source_type, target_type);
1641
1642                         bool target_is_value_type = TypeManager.IsStruct (target_type) || TypeManager.IsEnumType (target_type);
1643
1644                         //
1645                         // Unboxing conversion from System.ValueType to any non-nullable-value-type
1646                         //
1647                         if (source_type == TypeManager.value_type && target_is_value_type)
1648                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1649
1650                         //
1651                         // From object to any reference type or value type (unboxing)
1652                         //
1653                         if (source_type == TypeManager.object_type)
1654                                 return
1655                                         source == null ? EmptyExpression.Null :
1656                                         target_is_value_type ? new UnboxCast (source, target_type) :
1657                                         source is Constant ? (Expression) new EmptyConstantCast ((Constant) source, target_type) :
1658                                         new ClassCast (source, target_type);
1659
1660                         //
1661                         // From any class S to any class-type T, provided S is a base class of T
1662                         //
1663                         if (source_type.Kind == MemberKind.Class && TypeSpec.IsBaseClass (target_type, source_type, true))
1664                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1665
1666                         //
1667                         // From any interface-type S to to any class type T, provided T is not
1668                         // sealed, or provided T implements S.
1669                         //
1670                         if (source_type.IsInterface) {
1671                                 if (!target_type.IsSealed || target_type.ImplementsInterface (source_type)) {
1672                                         if (target_type.IsClass)
1673                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1674
1675                                         //
1676                                         // Unboxing conversion from any interface-type to any non-nullable-value-type that
1677                                         // implements the interface-type
1678                                         //
1679                                         return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1680                                 }
1681
1682                                 //
1683                                 // From System.Collections.Generic.IList<T> and its base interfaces to a one-dimensional
1684                                 // array type S[], provided there is an implicit or explicit reference conversion from S to T.
1685                                 //
1686                                 var target_array = target_type as ArrayContainer;
1687                                 if (target_array != null && IList_To_Array (source_type, target_array))
1688                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1689
1690                                 return null;
1691                         }
1692
1693                         var source_array = source_type as ArrayContainer;
1694                         if (source_array != null) {
1695                                 var target_array = target_type as ArrayContainer;
1696                                 if (target_array != null) {
1697                                         //
1698                                         // From System.Array to any array-type
1699                                         //
1700                                         if (source_type == TypeManager.array_type)
1701                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1702
1703                                         //
1704                                         // From an array type S with an element type Se to an array type T with an
1705                                         // element type Te provided all the following are true:
1706                                         //     * S and T differe only in element type, in other words, S and T
1707                                         //       have the same number of dimensions.
1708                                         //     * Both Se and Te are reference types
1709                                         //     * An explicit reference conversions exist from Se to Te
1710                                         //
1711                                         if (source_array.Rank == target_array.Rank) {
1712
1713                                                 source_type = source_array.Element;
1714                                                 if (!TypeManager.IsReferenceType (source_type))
1715                                                         return null;
1716
1717                                                 var target_element = target_array.Element;
1718                                                 if (!TypeManager.IsReferenceType (target_element))
1719                                                         return null;
1720
1721                                                 if (ExplicitReferenceConversionExists (source_type, target_element))
1722                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1723
1724                                                 return null;
1725                                         }
1726                                 }
1727
1728                                 //
1729                                 // From a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its base interfaces,
1730                                 // provided that there is an explicit reference conversion from S to T
1731                                 //
1732                                 if (ArrayToIList (source_array, target_type, true))
1733                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1734
1735                                 return null;
1736                         }
1737
1738                         //
1739                         // From any class type S to any interface T, provides S is not sealed
1740                         // and provided S does not implement T.
1741                         //
1742                         if (target_type.IsInterface && !source_type.IsSealed && !source_type.ImplementsInterface (target_type)) {
1743                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1744                         }
1745
1746                         //
1747                         // From System delegate to any delegate-type
1748                         //
1749                         if (source_type == TypeManager.delegate_type && TypeManager.IsDelegateType (target_type))
1750                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1751
1752                         return null;
1753                 }
1754
1755                 /// <summary>
1756                 ///   Performs an explicit conversion of the expression `expr' whose
1757                 ///   type is expr.Type to `target_type'.
1758                 /// </summary>
1759                 static public Expression ExplicitConversionCore (ResolveContext ec, Expression expr,
1760                                                                  TypeSpec target_type, Location loc)
1761                 {
1762                         TypeSpec expr_type = expr.Type;
1763
1764                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1765                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc, true);
1766                         if (ne != null)
1767                                 return ne;
1768
1769                         if (TypeManager.IsEnumType (expr_type)) {
1770                                 TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
1771                                 Expression underlying = EmptyCast.Create (expr, EnumSpec.GetUnderlyingType (expr_type));
1772                                 if (underlying.Type == real_target)
1773                                         ne = underlying;
1774
1775                                 if (ne == null)
1776                                         ne = ImplicitNumericConversion (underlying, real_target);
1777
1778                                 if (ne == null)
1779                                         ne = ExplicitNumericConversion (underlying, real_target);
1780
1781                                 //
1782                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1783                                 //
1784                                 if (ne == null && (real_target == TypeManager.intptr_type || real_target == TypeManager.uintptr_type))
1785                                         ne = ExplicitUserConversion (ec, underlying, real_target, loc);
1786
1787                                 return ne != null ? EmptyCast.Create (ne, target_type) : null;
1788                         }
1789
1790                         if (TypeManager.IsEnumType (target_type)) {
1791                                 //
1792                                 // System.Enum can be unboxed to any enum-type
1793                                 //
1794                                 if (expr_type == TypeManager.enum_type)
1795                                         return new UnboxCast (expr, target_type);
1796
1797                                 TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
1798
1799                                 if (expr_type == real_target)
1800                                         return EmptyCast.Create (expr, target_type);
1801
1802                                 ne = ImplicitNumericConversion (expr, real_target);
1803                                 if (ne != null)
1804                                         return EmptyCast.Create (ne, target_type);
1805
1806                                 ne = ExplicitNumericConversion (expr, real_target);
1807                                 if (ne != null)
1808                                         return EmptyCast.Create (ne, target_type);
1809
1810                                 //
1811                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1812                                 //
1813                                 if (expr_type == TypeManager.intptr_type || expr_type == TypeManager.uintptr_type) {
1814                                         ne = ExplicitUserConversion (ec, expr, real_target, loc);
1815                                         if (ne != null)
1816                                                 return ExplicitConversionCore (ec, ne, target_type, loc);
1817                                 }
1818                         } else {
1819                                 ne = ExplicitNumericConversion (expr, target_type);
1820                                 if (ne != null)
1821                                         return ne;
1822                         }
1823
1824                         //
1825                         // Skip the ExplicitReferenceConversion because we can not convert
1826                         // from Null to a ValueType, and ExplicitReference wont check against
1827                         // null literal explicitly
1828                         //
1829                         if (expr_type != InternalType.Null) {
1830                                 ne = ExplicitReferenceConversion (expr, expr_type, target_type);
1831                                 if (ne != null)
1832                                         return ne;
1833                         }
1834
1835                         if (ec.IsUnsafe){
1836                                 ne = ExplicitUnsafe (expr, target_type);
1837                                 if (ne != null)
1838                                         return ne;
1839                         }
1840
1841                         return null;
1842                 }
1843
1844                 public static Expression ExplicitUnsafe (Expression expr, TypeSpec target_type)
1845                 {
1846                         TypeSpec expr_type = expr.Type;
1847
1848                         if (target_type.IsPointer){
1849                                 if (expr_type.IsPointer)
1850                                         return EmptyCast.Create (expr, target_type);
1851
1852                                 if (expr_type == TypeManager.sbyte_type ||
1853                                         expr_type == TypeManager.short_type ||
1854                                         expr_type == TypeManager.int32_type)
1855                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1856
1857                                 if (expr_type == TypeManager.ushort_type ||
1858                                         expr_type == TypeManager.uint32_type ||
1859                                         expr_type == TypeManager.byte_type)
1860                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1861
1862                                 if (expr_type == TypeManager.int64_type)
1863                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I);
1864
1865                                 if (expr_type == TypeManager.uint64_type)
1866                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I);
1867                         }
1868
1869                         if (expr_type.IsPointer){
1870                                 if (target_type == TypeManager.sbyte_type)
1871                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1872                                 if (target_type == TypeManager.byte_type)
1873                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1874                                 if (target_type == TypeManager.short_type)
1875                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1876                                 if (target_type == TypeManager.ushort_type)
1877                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1878                                 if (target_type == TypeManager.int32_type)
1879                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1880                                 if (target_type == TypeManager.uint32_type)
1881                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1882                                 if (target_type == TypeManager.int64_type)
1883                                         return new ConvCast (expr, target_type, ConvCast.Mode.I_I8);
1884                                 if (target_type == TypeManager.uint64_type)
1885                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1886                         }
1887                         return null;
1888                 }
1889
1890                 /// <summary>
1891                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1892                 /// </summary>
1893                 static public Expression ExplicitConversionStandard (ResolveContext ec, Expression expr,
1894                                                                      TypeSpec target_type, Location l)
1895                 {
1896                         int errors = ec.Report.Errors;
1897                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1898                         if (ec.Report.Errors > errors)
1899                                 return null;
1900
1901                         if (ne != null)
1902                                 return ne;
1903
1904                         ne = ExplicitNumericConversion (expr, target_type);
1905                         if (ne != null)
1906                                 return ne;
1907
1908                         ne = ExplicitReferenceConversion (expr, expr.Type, target_type);
1909                         if (ne != null)
1910                                 return ne;
1911
1912                         if (ec.IsUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
1913                                 return EmptyCast.Create (expr, target_type);
1914
1915                         expr.Error_ValueCannotBeConverted (ec, l, target_type, true);
1916                         return null;
1917                 }
1918
1919                 /// <summary>
1920                 ///   Performs an explicit conversion of the expression `expr' whose
1921                 ///   type is expr.Type to `target_type'.
1922                 /// </summary>
1923                 static public Expression ExplicitConversion (ResolveContext ec, Expression expr,
1924                         TypeSpec target_type, Location loc)
1925                 {
1926                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
1927                         if (e != null) {
1928                                 //
1929                                 // Don't eliminate explicit precission casts
1930                                 //
1931                                 if (e == expr) {
1932                                         if (target_type == TypeManager.float_type)
1933                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
1934
1935                                         if (target_type == TypeManager.double_type)
1936                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
1937                                 }
1938
1939                                 return e;
1940                         }
1941
1942                         TypeSpec expr_type = expr.Type;
1943                         if (TypeManager.IsNullableType (target_type)) {
1944                                 if (TypeManager.IsNullableType (expr_type)) {
1945                                         TypeSpec target = Nullable.NullableInfo.GetUnderlyingType (target_type);
1946                                         Expression unwrap = Nullable.Unwrap.Create (expr);
1947                                         e = ExplicitConversion (ec, unwrap, target, expr.Location);
1948                                         if (e == null)
1949                                                 return null;
1950
1951                                         return new Nullable.Lifted (e, unwrap, target_type).Resolve (ec);
1952                                 } else if (expr_type == TypeManager.object_type) {
1953                                         return new UnboxCast (expr, target_type);
1954                                 } else {
1955                                         TypeSpec target = TypeManager.GetTypeArguments (target_type) [0];
1956
1957                                         e = ExplicitConversionCore (ec, expr, target, loc);
1958                                         if (e != null)
1959                                                 return Nullable.Wrap.Create (e, target_type);
1960                                 }
1961                         } else if (TypeManager.IsNullableType (expr_type)) {
1962                                 e = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
1963                                 if (e != null)
1964                                         return e;
1965
1966                                 e = Nullable.Unwrap.Create (expr, false);
1967                                 e = ExplicitConversionCore (ec, e, target_type, loc);
1968                                 if (e != null)
1969                                         return EmptyCast.Create (e, target_type);
1970                         }
1971
1972                         e = ExplicitUserConversion (ec, expr, target_type, loc);
1973                         if (e != null)
1974                                 return e;
1975
1976                         expr.Error_ValueCannotBeConverted (ec, loc, target_type, true);
1977                         return null;
1978                 }
1979         }
1980 }