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                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 249                         // is an abstract class, and not really a value type, so we apply the same rules.
 250                         //
 251                         if (target_type == TypeManager.object_type || target_type == InternalType.Dynamic) {
 252                                 //
 253                                 // A pointer type cannot be converted to object
 254                                 //
 255                                 if (expr_type.IsPointer)
 256                                         return false;
 257
 258                                 if (TypeManager.IsValueType (expr_type))
 259                                         return false;
 260
 261                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type || expr_type.IsDelegate || expr_type.Kind == MemberKind.ArrayType) {
 262                                         // No mcs internal types are convertible
 263                                         return true; // expr_type.MetaInfo.Module != typeof (Convert).Module;
 264                                 }
 265
 266                                 // From anything to dynamic, including dynamic -> dynamic
 267                                 if (target_type == InternalType.Dynamic)
 268                                         return true;
 269
 270                                 // From dynamic to object
 271                                 if (expr_type == InternalType.Dynamic)
 272                                         return true;
 273
 274                                 return false;
 275                         } else if (target_type == TypeManager.value_type) {
 276                                 return expr_type == TypeManager.enum_type;
 277                         } else if (expr_type == target_type || TypeSpec.IsBaseClass (expr_type, target_type, true)) {
 278                                 //
 279                                 // Special case: enumeration to System.Enum.
 280                                 // System.Enum is not a value type, it is a class, so we need
 281                                 // a boxing conversion
 282                                 //
 283                                 if (target_type == TypeManager.enum_type || TypeManager.IsGenericParameter (expr_type))
 284                                         return false;
 285
 286                                 if (TypeManager.IsValueType (expr_type))
 287                                         return false;
 288
 289                                 // Array type variance conversion
 290                                 //if (target_type.IsArray != expr_type.IsArray)
 291                                 //      return false;
 292
 293                                 return true;
 294                         }
 295
 296                         var expr_type_array = expr_type as ArrayContainer;
 297                         if (expr_type_array != null) {
 298                                 var target_type_array = target_type as ArrayContainer;
 299                                 // from an array-type S to an array-type of type T
 300                                 if (target_type_array != null && expr_type_array.Rank == target_type_array.Rank) {
 301
 302                                         //
 303                                         // Both SE and TE are reference-types
 304                                         //
 305                                         TypeSpec expr_element_type = expr_type_array.Element;
 306                                         if (!TypeManager.IsReferenceType (expr_element_type))
 307                                                 return false;
 308
 309                                         TypeSpec target_element_type = target_type_array.Element;
 310                                         if (!TypeManager.IsReferenceType (target_element_type))
 311                                                 return false;
 312
 313                                         if (MyEmptyExpr == null)
 314                                                 MyEmptyExpr = new EmptyExpression (expr_element_type);
 315                                         else
 316                                                 MyEmptyExpr.SetType (expr_element_type);
 317
 318                                         return ImplicitStandardConversionExists (MyEmptyExpr, target_element_type);
 319                                 }
 320
 321                                 // from an array-type to System.Array
 322                                 if (target_type == TypeManager.array_type)
 323                                         return true;
 324
 325                                 // from an array-type of type T to IList<T>
 326                                 if (ArrayToIList (expr_type_array, target_type, false))
 327                                         return true;
 328
 329                                 return false;
 330                         }
 331
 332                         if (TypeSpecComparer.Variant.IsEqual (expr_type, target_type))
 333                                 return true;
 334
 335                         // from any interface type S to interface-type T.
 336                         if (expr_type.IsInterface && target_type.IsInterface) {
 337                                 return expr_type.ImplementsInterface (target_type);
 338                         }
 339
 340                         // from any delegate type to System.Delegate
 341                         if (target_type == TypeManager.delegate_type &&
 342                                 (expr_type == TypeManager.delegate_type || expr_type.IsDelegate))
 343                                 return true;
 344
 345                         return false;
 346                 }
 347
 348                 public static Expression ImplicitBoxingConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
 349                 {
 350                         //
 351                         // From any value-type to the type object.
 352                         //
 353                         if (target_type == TypeManager.object_type || target_type == InternalType.Dynamic) {
 354                                 //
 355                                 // A pointer type cannot be converted to object
 356                                 //
 357                                 if (expr_type.IsPointer)
 358                                         return null;
 359
 360                                 if (!TypeManager.IsValueType (expr_type))
 361                                         return null;
 362
 363                                 return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 364                         }
 365
 366                         //
 367                         // From any value-type to the type System.ValueType.
 368                         //
 369                         if (target_type == TypeManager.value_type) {
 370                                 if (!TypeManager.IsValueType (expr_type))
 371                                         return null;
 372
 373                                 return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 374                         }
 375
 376                         if (target_type == TypeManager.enum_type) {
 377                                 //
 378                                 // From any enum-type to the type System.Enum.
 379                                 //
 380                                 if (TypeManager.IsEnumType (expr_type))
 381                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 382                         }
 383
 384                         //
 385                         // From a nullable-type to a reference type, if a boxing conversion exists from
 386                         // the underlying type to the reference type
 387                         //
 388                         if (TypeManager.IsNullableType (expr_type)) {
 389                                 if (!TypeManager.IsReferenceType (target_type))
 390                                         return null;
 391
 392                                 var res = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
 393
 394                                 // "cast" underlying type to target type to emit correct InvalidCastException when
 395                                 // underlying hierarchy changes without recompilation
 396                                 if (res != null && expr != null)
 397                                         res = new UnboxCast (res, target_type);
 398
 399                                 return res;
 400                         }
 401
 402                         if (TypeSpec.IsBaseClass (expr_type, target_type, false)) {
 403                                 //
 404                                 // Don't box same type arguments
 405                                 //
 406                                 if (TypeManager.IsGenericParameter (expr_type) && expr_type != target_type)
 407                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 408
 409                                 return null;
 410                         }
 411
 412                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 413                         // with the small distinction that we only probe there
 414                         //
 415                         // Always ensure that the code here and there is in sync
 416
 417                         // from any class-type S to any interface-type T.
 418                         if (target_type.IsInterface) {
 419                                 if (expr_type.ImplementsInterface (target_type) &&
 420                                         (TypeManager.IsGenericParameter (expr_type) || TypeManager.IsValueType (expr_type))) {
 421                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 422                                 }
 423                         }
 424
 425                         return null;
 426                 }
 427
 428                 public static Expression ImplicitNulableConversion (ResolveContext ec, Expression expr, TypeSpec target_type)
 429                 {
 430                         TypeSpec expr_type = expr.Type;
 431
 432                         //
 433                         // From null to any nullable type
 434                         //
 435                         if (expr_type == InternalType.Null)
 436                                 return ec == null ? EmptyExpression.Null : Nullable.LiftedNull.Create (target_type, expr.Location);
 437
 438                         // S -> T?
 439                         TypeSpec t_el = Nullable.NullableInfo.GetUnderlyingType (target_type);
 440
 441                         // S? -> T?
 442                         if (TypeManager.IsNullableType (expr_type))
 443                                 expr_type = Nullable.NullableInfo.GetUnderlyingType (expr_type);
 444
 445                         //
 446                         // Predefined implicit identity or implicit numeric conversion
 447                         // has to exist between underlying type S and underlying type T
 448                         //
 449
 450                         // conversion exists only mode
 451                         if (ec == null) {
 452                                 if (expr_type == t_el)
 453                                         return EmptyExpression.Null;
 454
 455                                 if (expr is Constant)
 456                                         return ((Constant) expr).ConvertImplicitly (ec, t_el);
 457
 458                                 return ImplicitNumericConversion (null, expr_type, t_el);
 459                         }
 460
 461                         Expression unwrap;
 462                         if (expr_type != expr.Type)
 463                                 unwrap = Nullable.Unwrap.Create (expr);
 464                         else
 465                                 unwrap = expr;
 466
 467                         Expression conv = unwrap;
 468                         if (expr_type != t_el) {
 469                                 if (conv is Constant)
 470                                         conv = ((Constant)conv).ConvertImplicitly (ec, t_el);
 471                                 else
 472                                         conv = ImplicitNumericConversion (conv, expr_type, t_el);
 473
 474                                 if (conv == null)
 475                                         return null;
 476                         }
 477
 478                         if (expr_type != expr.Type)
 479                                 return new Nullable.Lifted (conv, unwrap, target_type).Resolve (ec);
 480
 481                         return Nullable.Wrap.Create (conv, target_type);
 482                 }
 483
 484                 /// <summary>
 485                 ///   Implicit Numeric Conversions.
 486                 ///
 487                 ///   expr is the expression to convert, returns a new expression of type
 488                 ///   target_type or null if an implicit conversion is not possible.
 489                 /// </summary>
 490                 public static Expression ImplicitNumericConversion (Expression expr, TypeSpec target_type)
 491                 {
 492                         return ImplicitNumericConversion (expr, expr.Type, target_type);
 493                 }
 494
 495                 static Expression ImplicitNumericConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
 496                 {
 497                         if (expr_type == TypeManager.sbyte_type){
 498                                 //
 499                                 // From sbyte to short, int, long, float, double, decimal
 500                                 //
 501                                 if (target_type == TypeManager.int32_type)
 502                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 503                                 if (target_type == TypeManager.int64_type)
 504                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 505                                 if (target_type == TypeManager.double_type)
 506                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 507                                 if (target_type == TypeManager.float_type)
 508                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 509                                 if (target_type == TypeManager.short_type)
 510                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 511                                 if (target_type == TypeManager.decimal_type)
 512                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 513                         } else if (expr_type == TypeManager.byte_type){
 514                                 //
 515                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 516                                 //
 517                                 if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type ||
 518                                     target_type == TypeManager.short_type || target_type == TypeManager.ushort_type)
 519                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 520
 521                                 if (target_type == TypeManager.uint64_type)
 522                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 523                                 if (target_type == TypeManager.int64_type)
 524                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 525                                 if (target_type == TypeManager.float_type)
 526                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 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.decimal_type)
 530                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 531
 532                         } else if (expr_type == TypeManager.short_type){
 533                                 //
 534                                 // From short to int, long, float, double, decimal
 535                                 //
 536                                 if (target_type == TypeManager.int32_type)
 537                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 538                                 if (target_type == TypeManager.int64_type)
 539                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 540                                 if (target_type == TypeManager.double_type)
 541                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 542                                 if (target_type == TypeManager.float_type)
 543                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 544                                 if (target_type == TypeManager.decimal_type)
 545                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 546
 547                         } else if (expr_type == TypeManager.ushort_type){
 548                                 //
 549                                 // From ushort to int, uint, long, ulong, float, double, decimal
 550                                 //
 551                                 if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type)
 552                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 553
 554                                 if (target_type == TypeManager.uint64_type)
 555                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 556                                 if (target_type == TypeManager.int64_type)
 557                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 558                                 if (target_type == TypeManager.double_type)
 559                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 560                                 if (target_type == TypeManager.float_type)
 561                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 562                                 if (target_type == TypeManager.decimal_type)
 563                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 564                         } else if (expr_type == TypeManager.int32_type){
 565                                 //
 566                                 // From int to long, float, double, decimal
 567                                 //
 568                                 if (target_type == TypeManager.int64_type)
 569                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 570                                 if (target_type == TypeManager.double_type)
 571                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 572                                 if (target_type == TypeManager.float_type)
 573                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 574                                 if (target_type == TypeManager.decimal_type)
 575                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 576                         } else if (expr_type == TypeManager.uint32_type){
 577                                 //
 578                                 // From uint to long, ulong, float, double, decimal
 579                                 //
 580                                 if (target_type == TypeManager.int64_type)
 581                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 582                                 if (target_type == TypeManager.uint64_type)
 583                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 584                                 if (target_type == TypeManager.double_type)
 585                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
 586                                 if (target_type == TypeManager.float_type)
 587                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
 588                                 if (target_type == TypeManager.decimal_type)
 589                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 590                         } else if (expr_type == TypeManager.int64_type){
 591                                 //
 592                                 // From long/ulong to float, double
 593                                 //
 594                                 if (target_type == TypeManager.double_type)
 595                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 596                                 if (target_type == TypeManager.float_type)
 597                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 598                                 if (target_type == TypeManager.decimal_type)
 599                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 600                         } else if (expr_type == TypeManager.uint64_type){
 601                                 //
 602                                 // From ulong to float, double
 603                                 //
 604                                 if (target_type == TypeManager.double_type)
 605                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
 606                                 if (target_type == TypeManager.float_type)
 607                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
 608                                 if (target_type == TypeManager.decimal_type)
 609                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 610                         } else if (expr_type == TypeManager.char_type){
 611                                 //
 612                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 613                                 //
 614                                 if ((target_type == TypeManager.ushort_type) ||
 615                                     (target_type == TypeManager.int32_type) ||
 616                                     (target_type == TypeManager.uint32_type))
 617                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 618                                 if (target_type == TypeManager.uint64_type)
 619                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 620                                 if (target_type == TypeManager.int64_type)
 621                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 622                                 if (target_type == TypeManager.float_type)
 623                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 624                                 if (target_type == TypeManager.double_type)
 625                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 626                                 if (target_type == TypeManager.decimal_type)
 627                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 628                         } else if (expr_type == TypeManager.float_type){
 629                                 //
 630                                 // float to double
 631                                 //
 632                                 if (target_type == TypeManager.double_type)
 633                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 634                         }
 635
 636                         return null;
 637                 }
 638
 639                 /// <summary>
 640                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 641                 ///  implicit user defined conversions - needed for overload resolution
 642                 /// </summary>
 643                 public static bool ImplicitConversionExists (ResolveContext ec, Expression expr, TypeSpec target_type)
 644                 {
 645                         if (ImplicitStandardConversionExists (expr, target_type))
 646                                 return true;
 647
 648                         if (expr.Type == InternalType.AnonymousMethod) {
 649                                 if (!TypeManager.IsDelegateType (target_type) && target_type.GetDefinition () != TypeManager.expression_type)
 650                                         return false;
 651
 652                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 653                                 return ame.ImplicitStandardConversionExists (ec, target_type);
 654                         }
 655
 656                         if (expr.eclass == ExprClass.MethodGroup) {
 657                                 if (target_type.IsDelegate && RootContext.Version != LanguageVersion.ISO_1) {
 658                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 659                                         if (mg != null)
 660                                                 return DelegateCreation.ImplicitStandardConversionExists (ec, mg, target_type);
 661                                 }
 662
 663                                 return false;
 664                         }
 665
 666                         return ImplicitUserConversion (ec, expr, target_type, Location.Null) != null;
 667                 }
 668
 669                 /// <summary>
 670                 ///  Determines if a standard implicit conversion exists from
 671                 ///  expr_type to target_type
 672                 ///
 673                 /// </summary>
 674                 public static bool ImplicitStandardConversionExists (Expression expr, TypeSpec target_type)
 675                 {
 676                         TypeSpec expr_type = expr.Type;
 677
 678                         NullLiteral nl = expr as NullLiteral;
 679                         if (nl != null)
 680                                 return nl.ConvertImplicitly (null, target_type) != null;
 681
 682                         if (expr_type == TypeManager.void_type)
 683                                 return false;
 684
 685                         if (expr_type == target_type)
 686                                 return true;
 687
 688                         if (TypeManager.IsNullableType (target_type)) {
 689                                 return ImplicitNulableConversion (null, expr, target_type) != null;
 690                         }
 691
 692                         // First numeric conversions
 693                         if (ImplicitNumericConversion (null, expr_type, target_type) != null)
 694                                 return true;
 695
 696                         if (ImplicitReferenceConversionExists (expr, target_type))
 697                                 return true;
 698
 699                         if (ImplicitBoxingConversion (null, expr_type, target_type) != null)
 700                                 return true;
 701
 702                         //
 703                         // Implicit Constant Expression Conversions
 704                         //
 705                         if (expr is IntConstant){
 706                                 int value = ((IntConstant) expr).Value;
 707
 708                                 if (target_type == TypeManager.sbyte_type){
 709                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 710                                                 return true;
 711                                 } else if (target_type == TypeManager.byte_type){
 712                                         if (value >= 0 && value <= Byte.MaxValue)
 713                                                 return true;
 714                                 } else if (target_type == TypeManager.short_type){
 715                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 716                                                 return true;
 717                                 } else if (target_type == TypeManager.ushort_type){
 718                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 719                                                 return true;
 720                                 } else if (target_type == TypeManager.uint32_type){
 721                                         if (value >= 0)
 722                                                 return true;
 723                                 } else if (target_type == TypeManager.uint64_type){
 724                                          //
 725                                          // we can optimize this case: a positive int32
 726                                          // always fits on a uint64.  But we need an opcode
 727                                          // to do it.
 728                                          //
 729                                         if (value >= 0)
 730                                                 return true;
 731                                 }
 732                         }
 733
 734                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 735                                 //
 736                                 // Try the implicit constant expression conversion
 737                                 // from long to ulong, instead of a nice routine,
 738                                 // we just inline it
 739                                 //
 740                                 long v = ((LongConstant) expr).Value;
 741                                 if (v >= 0)
 742                                         return true;
 743                         }
 744
 745                         if (expr is IntegralConstant && TypeManager.IsEnumType (target_type)) {
 746                                 var i = (IntegralConstant) expr;
 747                                 //
 748                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
 749                                 //
 750                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
 751                                 // to be converted to any enum-type and to any nullable-type whose underlying
 752                                 // type is an enum-type
 753                                 //
 754                                 return i.IsZeroInteger;
 755                         }
 756
 757                         //
 758                         // If `expr_type' implements `target_type' (which is an iface)
 759                         // see TryImplicitIntConversion
 760                         //
 761                         if (target_type.IsInterface && expr_type.ImplementsInterface (target_type))
 762                                 return true;
 763
 764                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 765                                 return true;
 766
 767                         // Conversion from __arglist to System.ArgIterator
 768                         if (expr_type == InternalType.Arglist)
 769                                 return target_type == TypeManager.arg_iterator_type;
 770
 771                         return false;
 772                 }
 773
 774                 /// <summary>
 775                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 776                 ///  amongst the methods in the MethodGroupExpr
 777                 /// </summary>
 778                 public static TypeSpec FindMostEncompassedType (IEnumerable<TypeSpec> types)
 779                 {
 780                         TypeSpec best = null;
 781                         EmptyExpression expr = EmptyExpression.Grab ();
 782
 783                         foreach (TypeSpec t in types) {
 784                                 if (best == null) {
 785                                         best = t;
 786                                         continue;
 787                                 }
 788
 789                                 expr.SetType (t);
 790                                 if (ImplicitStandardConversionExists (expr, best))
 791                                         best = t;
 792                         }
 793
 794                         expr.SetType (best);
 795                         foreach (TypeSpec t in types) {
 796                                 if (best == t)
 797                                         continue;
 798                                 if (!ImplicitStandardConversionExists (expr, t)) {
 799                                         best = null;
 800                                         break;
 801                                 }
 802                         }
 803
 804                         EmptyExpression.Release (expr);
 805
 806                         return best;
 807                 }
 808
 809                 /// <summary>
 810                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 811                 ///  amongst the types in the given set
 812                 /// </summary>
 813                 static TypeSpec FindMostEncompassingType (IList<TypeSpec> types)
 814                 {
 815                         TypeSpec best = null;
 816
 817                         if (types.Count == 0)
 818                                 return null;
 819
 820                         if (types.Count == 1)
 821                                 return types [0];
 822
 823                         EmptyExpression expr = EmptyExpression.Grab ();
 824
 825                         foreach (TypeSpec t in types) {
 826                                 if (best == null) {
 827                                         best = t;
 828                                         continue;
 829                                 }
 830
 831                                 expr.SetType (best);
 832                                 if (ImplicitStandardConversionExists (expr, t))
 833                                         best = t;
 834                         }
 835
 836                         foreach (TypeSpec t in types) {
 837                                 if (best == t)
 838                                         continue;
 839                                 expr.SetType (t);
 840                                 if (!ImplicitStandardConversionExists (expr, best)) {
 841                                         best = null;
 842                                         break;
 843                                 }
 844                         }
 845
 846                         EmptyExpression.Release (expr);
 847
 848                         return best;
 849                 }
 850
 851                 /// <summary>
 852                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 853                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 854                 ///   for explicit and implicit conversion operators.
 855                 /// </summary>
 856                 static TypeSpec FindMostSpecificSource (IList<MethodSpec> list,
 857                                                            Expression source, bool apply_explicit_conv_rules)
 858                 {
 859                         var src_types_set = new List<TypeSpec> ();
 860
 861                         //
 862                         // If any operator converts from S then Sx = S
 863                         //
 864                         TypeSpec source_type = source.Type;
 865                         foreach (var mb in list){
 866                                 TypeSpec param_type = mb.Parameters.Types [0];
 867
 868                                 if (param_type == source_type)
 869                                         return param_type;
 870
 871                                 src_types_set.Add (param_type);
 872                         }
 873
 874                         //
 875                         // Explicit Conv rules
 876                         //
 877                         if (apply_explicit_conv_rules) {
 878                                 var candidate_set = new List<TypeSpec> ();
 879
 880                                 foreach (TypeSpec param_type in src_types_set){
 881                                         if (ImplicitStandardConversionExists (source, param_type))
 882                                                 candidate_set.Add (param_type);
 883                                 }
 884
 885                                 if (candidate_set.Count != 0)
 886                                         return FindMostEncompassedType (candidate_set);
 887                         }
 888
 889                         //
 890                         // Final case
 891                         //
 892                         if (apply_explicit_conv_rules)
 893                                 return FindMostEncompassingType (src_types_set);
 894                         else
 895                                 return FindMostEncompassedType (src_types_set);
 896                 }
 897
 898                 /// <summary>
 899                 ///  Finds the most specific target Tx according to section 13.4.4
 900                 /// </summary>
 901                 static public TypeSpec FindMostSpecificTarget (IList<MethodSpec> list,
 902                                                            TypeSpec target, bool apply_explicit_conv_rules)
 903                 {
 904                         var tgt_types_set = new List<TypeSpec> ();
 905
 906                         //
 907                         // If any operator converts to T then Tx = T
 908                         //
 909                         foreach (var mi in list){
 910                                 TypeSpec ret_type = mi.ReturnType;
 911                                 if (ret_type == target)
 912                                         return ret_type;
 913
 914                                 tgt_types_set.Add (ret_type);
 915                         }
 916
 917                         //
 918                         // Explicit conv rules
 919                         //
 920                         if (apply_explicit_conv_rules) {
 921                                 var candidate_set = new List<TypeSpec> ();
 922
 923                                 EmptyExpression expr = EmptyExpression.Grab ();
 924
 925                                 foreach (TypeSpec ret_type in tgt_types_set){
 926                                         expr.SetType (ret_type);
 927
 928                                         if (ImplicitStandardConversionExists (expr, target))
 929                                                 candidate_set.Add (ret_type);
 930                                 }
 931
 932                                 EmptyExpression.Release (expr);
 933
 934                                 if (candidate_set.Count != 0)
 935                                         return FindMostEncompassingType (candidate_set);
 936                         }
 937
 938                         //
 939                         // Okay, final case !
 940                         //
 941                         if (apply_explicit_conv_rules)
 942                                 return FindMostEncompassedType (tgt_types_set);
 943                         else
 944                                 return FindMostEncompassingType (tgt_types_set);
 945                 }
 946
 947                 /// <summary>
 948                 ///  User-defined Implicit conversions
 949                 /// </summary>
 950                 static public Expression ImplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
 951                 {
 952                         return UserDefinedConversion (ec, source, target, true, loc);
 953                 }
 954
 955                 /// <summary>
 956                 ///  User-defined Explicit conversions
 957                 /// </summary>
 958                 static Expression ExplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
 959                 {
 960                         return UserDefinedConversion (ec, source, target, false, loc);
 961                 }
 962
 963                 static void FindApplicableUserDefinedConversionOperators (IList<MemberSpec> operators, Expression source, TypeSpec target, bool implicitOnly, ref List<MethodSpec> candidates)
 964                 {
 965                         //
 966                         // LAMESPEC: Undocumented IntPtr/UIntPtr conversions
 967                         // IntPtr -> uint uses int
 968                         // UIntPtr -> long uses ulong
 969                         //
 970                         if (source.Type == TypeManager.intptr_type) {
 971                                 if (target == TypeManager.uint32_type)
 972                                         target = TypeManager.int32_type;
 973                         } else if (source.Type == TypeManager.uintptr_type) {
 974                                 if (target == TypeManager.int64_type)
 975                                         target = TypeManager.uint64_type;
 976                         }
 977
 978                         // For a conversion operator to be applicable, it must be possible
 979                         // to perform a standard conversion from the source type to
 980                         // the operand type of the operator, and it must be possible
 981                         // to perform a standard conversion from the result type of
 982                         // the operator to the target type.
 983
 984                         Expression texpr = null;
 985
 986                         foreach (MethodSpec op in operators) {
 987
 988                                 // Can be null because MemberCache.GetUserOperator does not resize the array
 989                                 if (op == null)
 990                                         continue;
 991
 992                                 var t = op.Parameters.Types[0];
 993                                 if (source.Type != t && !ImplicitStandardConversionExists (source, t)) {
 994                                         if (implicitOnly)
 995                                                 continue;
 996
 997                                         if (!ImplicitStandardConversionExists (new EmptyExpression (t), source.Type))
 998                                                 continue;
 999                                 }
1000
1001                                 t = op.ReturnType;
1002
1003                                 // LAMESPEC: Exclude UIntPtr -> int conversion
1004                                 if (t == TypeManager.uint32_type && source.Type == TypeManager.uintptr_type)
1005                                         continue;
1006
1007                                 if (target != t && !ImplicitStandardConversionExists (new EmptyExpression (t), target)) {
1008                                         if (implicitOnly)
1009                                                 continue;
1010
1011                                         if (texpr == null)
1012                                                 texpr = new EmptyExpression (target);
1013
1014                                         if (!ImplicitStandardConversionExists (texpr, t))
1015                                                 continue;
1016                                 }
1017
1018                                 if (candidates == null)
1019                                         candidates = new List<MethodSpec> ();
1020
1021                                 candidates.Add (op);
1022                         }
1023                 }
1024
1025                 //
1026                 // User-defined conversions
1027                 //
1028                 static Expression UserDefinedConversion (ResolveContext ec, Expression source, TypeSpec target, bool implicitOnly, Location loc)
1029                 {
1030                         List<MethodSpec> candidates = null;
1031
1032                         //
1033                         // If S or T are nullable types, S0 and T0 are their underlying types
1034                         // otherwise S0 and T0 are equal to S and T respectively.
1035                         //
1036                         TypeSpec source_type = source.Type;
1037                         TypeSpec target_type = target;
1038                         Expression unwrap;
1039
1040                         if (TypeManager.IsNullableType (source_type)) {
1041                                 // No implicit conversion S? -> T for non-reference types
1042                                 if (implicitOnly && !TypeManager.IsReferenceType (target_type) && !TypeManager.IsNullableType (target_type))
1043                                         return null;
1044
1045                                 unwrap = source = Nullable.Unwrap.Create (source);
1046                                 source_type = source.Type;
1047                         } else {
1048                                 unwrap = null;
1049                         }
1050
1051                         if (TypeManager.IsNullableType (target_type))
1052                                 target_type = Nullable.NullableInfo.GetUnderlyingType (target_type);
1053
1054                         // Only these containers can contain a user defined implicit or explicit operators
1055                         const MemberKind user_conversion_kinds = MemberKind.Class | MemberKind.Struct | MemberKind.TypeParameter;
1056
1057                         if ((source_type.Kind & user_conversion_kinds) != 0 && source_type != TypeManager.decimal_type) {
1058                                 bool declared_only = source_type.IsStruct;
1059
1060                                 var operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Implicit, declared_only);
1061                                 if (operators != null) {
1062                                         FindApplicableUserDefinedConversionOperators (operators, source, target_type, implicitOnly, ref candidates);
1063                                 }
1064
1065                                 if (!implicitOnly) {
1066                                         operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Explicit, declared_only);
1067                                         if (operators != null) {
1068                                                 FindApplicableUserDefinedConversionOperators (operators, source, target_type, false, ref candidates);
1069                                         }
1070                                 }
1071                         }
1072
1073                         if ((target.Kind & user_conversion_kinds) != 0 && target != TypeManager.decimal_type) {
1074                                 bool declared_only = target.IsStruct || implicitOnly;
1075
1076                                 var operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Implicit, declared_only);
1077                                 if (operators != null) {
1078                                         FindApplicableUserDefinedConversionOperators (operators, source, target_type, implicitOnly, ref candidates);
1079                                 }
1080
1081                                 if (!implicitOnly) {
1082                                         operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Explicit, declared_only);
1083                                         if (operators != null) {
1084                                                 FindApplicableUserDefinedConversionOperators (operators, source, target_type, false, ref candidates);
1085                                         }
1086                                 }
1087                         }
1088
1089                         if (candidates == null)
1090                                 return null;
1091
1092                         //
1093                         // Find the most specific conversion operator
1094                         //
1095                         MethodSpec most_specific_operator;
1096                         TypeSpec s_x, t_x;
1097                         if (candidates.Count == 1) {
1098                                 most_specific_operator = candidates[0];
1099                                 s_x = most_specific_operator.Parameters.Types[0];
1100                                 t_x = most_specific_operator.ReturnType;
1101                         } else {
1102                                 s_x = FindMostSpecificSource (candidates, source, !implicitOnly);
1103                                 if (s_x == null)
1104                                         return null;
1105
1106                                 t_x = FindMostSpecificTarget (candidates, target, !implicitOnly);
1107                                 if (t_x == null)
1108                                         return null;
1109
1110                                 most_specific_operator = candidates[0];
1111
1112                                 for (int i = 1; i < candidates.Count; ++i) {
1113                                         if (candidates[i].ReturnType == t_x && candidates[i].Parameters.Types[0] == s_x) {
1114                                                 most_specific_operator = candidates[i];
1115                                                 break;
1116                                         }
1117                                 }
1118                         }
1119
1120                         //
1121                         // Convert input type when it's different to best operator argument
1122                         //
1123                         if (s_x != source.Type)
1124                                 source = implicitOnly ?
1125                                         ImplicitConversionStandard (ec, source, s_x, loc) :
1126                                         ExplicitConversionStandard (ec, source, s_x, loc);
1127
1128                         source = new UserCast (most_specific_operator, source, loc).Resolve (ec);
1129
1130                         //
1131                         // Convert result type when it's different to best operator return type
1132                         //
1133                         if (t_x != target_type) {
1134                                 //
1135                                 // User operator is of T?, no need to lift it
1136                                 //
1137                                 if (TypeManager.IsNullableType (t_x) && t_x == target)
1138                                         return source;
1139
1140                                 source = implicitOnly ?
1141                                         ImplicitConversionStandard (ec, source, target_type, loc) :
1142                                         ExplicitConversionStandard (ec, source, target_type, loc);
1143                         }
1144
1145                         //
1146                         // Source expression is of nullable type, lift the result in case of it's null
1147                         //
1148                         if (unwrap != null && (TypeManager.IsReferenceType (target) || target_type != target))
1149                                 source = new Nullable.Lifted (source, unwrap, target).Resolve (ec);
1150                         else if (target_type != target)
1151                                 source = Nullable.Wrap.Create (source, target);
1152
1153                         return source;
1154                 }
1155
1156                 /// <summary>
1157                 ///   Converts implicitly the resolved expression `expr' into the
1158                 ///   `target_type'.  It returns a new expression that can be used
1159                 ///   in a context that expects a `target_type'.
1160                 /// </summary>
1161                 static public Expression ImplicitConversion (ResolveContext ec, Expression expr,
1162                                                              TypeSpec target_type, Location loc)
1163                 {
1164                         Expression e;
1165
1166                         if (target_type == null)
1167                                 throw new Exception ("Target type is null");
1168
1169                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1170                         if (e != null)
1171                                 return e;
1172
1173                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1174                         if (e != null)
1175                                 return e;
1176
1177                         return null;
1178                 }
1179
1180
1181                 /// <summary>
1182                 ///   Attempts to apply the `Standard Implicit
1183                 ///   Conversion' rules to the expression `expr' into
1184                 ///   the `target_type'.  It returns a new expression
1185                 ///   that can be used in a context that expects a
1186                 ///   `target_type'.
1187                 ///
1188                 ///   This is different from `ImplicitConversion' in that the
1189                 ///   user defined implicit conversions are excluded.
1190                 /// </summary>
1191                 static public Expression ImplicitConversionStandard (ResolveContext ec, Expression expr,
1192                                                                      TypeSpec target_type, Location loc)
1193                 {
1194                         return ImplicitConversionStandard (ec, expr, target_type, loc, false);
1195                 }
1196
1197                 static Expression ImplicitConversionStandard (ResolveContext ec, Expression expr, TypeSpec target_type, Location loc, bool explicit_cast)
1198                 {
1199                         if (expr.eclass == ExprClass.MethodGroup){
1200                                 if (!TypeManager.IsDelegateType (target_type)){
1201                                         return null;
1202                                 }
1203
1204                                 //
1205                                 // Only allow anonymous method conversions on post ISO_1
1206                                 //
1207                                 if (RootContext.Version != LanguageVersion.ISO_1){
1208                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1209                                         if (mg != null)
1210                                                 return ImplicitDelegateCreation.Create (
1211                                                         ec, mg, target_type, loc);
1212                                 }
1213                         }
1214
1215                         TypeSpec expr_type = expr.Type;
1216                         Expression e;
1217
1218                         if (expr_type == target_type) {
1219                                 if (expr_type != InternalType.Null && expr_type != InternalType.AnonymousMethod)
1220                                         return expr;
1221                                 return null;
1222                         }
1223
1224                         if (TypeManager.IsNullableType (target_type))
1225                                 return ImplicitNulableConversion (ec, expr, target_type);
1226
1227                         //
1228                         // Attempt to do the implicit constant expression conversions
1229                         //
1230                         Constant c = expr as Constant;
1231                         if (c != null) {
1232                                 try {
1233                                         c = c.ConvertImplicitly (ec, target_type);
1234                                 } catch {
1235                                         Console.WriteLine ("Conversion error happened in line {0}", loc);
1236                                         throw;
1237                                 }
1238                                 if (c != null)
1239                                         return c;
1240                         }
1241
1242                         e = ImplicitNumericConversion (expr, expr_type, target_type);
1243                         if (e != null)
1244                                 return e;
1245
1246                         e = ImplicitReferenceConversion (expr, target_type, explicit_cast);
1247                         if (e != null)
1248                                 return e;
1249
1250                         if (expr is IntegralConstant && TypeManager.IsEnumType (target_type)){
1251                                 var i = (IntegralConstant) expr;
1252                                 //
1253                                 // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
1254                                 //
1255                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
1256                                 // to be converted to any enum-type and to any nullable-type whose underlying
1257                                 // type is an enum-type
1258                                 //
1259                                 if (i.IsZeroInteger) {
1260                                         // Recreate 0 literal to remove any collected conversions
1261                                         return new EnumConstant (new IntLiteral (0, i.Location), target_type).Resolve (ec);
1262                                 }
1263                         }
1264
1265                         if (ec.IsUnsafe) {
1266                                 if (expr_type.IsPointer){
1267                                         if (target_type == TypeManager.void_ptr_type)
1268                                                 return EmptyCast.Create (expr, target_type);
1269
1270                                         //
1271                                         // yep, comparing pointer types cant be done with
1272                                         // t1 == t2, we have to compare their element types.
1273                                         //
1274                                         if (target_type.IsPointer){
1275                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1276                                                         return expr;
1277
1278                                                 //return null;
1279                                         }
1280                                 }
1281
1282                                 if (expr_type == InternalType.Null && target_type.IsPointer)
1283                                         return EmptyCast.Create (new NullPointer (loc), target_type);
1284                         }
1285
1286                         if (expr_type == InternalType.AnonymousMethod){
1287                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1288                                 Expression am = ame.Compatible (ec, target_type);
1289                                 if (am != null)
1290                                         return am.Resolve (ec);
1291                         }
1292
1293                         if (expr_type == InternalType.Arglist && target_type == TypeManager.arg_iterator_type)
1294                                 return expr;
1295
1296                         return null;
1297                 }
1298
1299                 /// <summary>
1300                 ///   Attempts to implicitly convert `source' into `target_type', using
1301                 ///   ImplicitConversion.  If there is no implicit conversion, then
1302                 ///   an error is signaled
1303                 /// </summary>
1304                 static public Expression ImplicitConversionRequired (ResolveContext ec, Expression source,
1305                                                                      TypeSpec target_type, Location loc)
1306                 {
1307                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1308                         if (e != null)
1309                                 return e;
1310
1311                         if (source.Type == InternalType.Dynamic) {
1312                                 Arguments args = new Arguments (1);
1313                                 args.Add (new Argument (source));
1314                                 return new DynamicConversion (target_type, 0, args, loc).Resolve (ec);
1315                         }
1316
1317                         source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
1318                         return null;
1319                 }
1320
1321                 /// <summary>
1322                 ///   Performs the explicit numeric conversions
1323                 ///
1324                 /// There are a few conversions that are not part of the C# standard,
1325                 /// they were interim hacks in the C# compiler that were supposed to
1326                 /// become explicit operators in the UIntPtr class and IntPtr class,
1327                 /// but for historical reasons it did not happen, so the C# compiler
1328                 /// ended up with these special hacks.
1329                 ///
1330                 /// See bug 59800 for details.
1331                 ///
1332                 /// The conversion are:
1333                 ///   UIntPtr->SByte
1334                 ///   UIntPtr->Int16
1335                 ///   UIntPtr->Int32
1336                 ///   IntPtr->UInt64
1337                 ///   UInt64->IntPtr
1338                 ///   SByte->UIntPtr
1339                 ///   Int16->UIntPtr
1340                 ///
1341                 /// </summary>
1342                 public static Expression ExplicitNumericConversion (Expression expr, TypeSpec target_type)
1343                 {
1344                         TypeSpec expr_type = expr.Type;
1345                         TypeSpec real_target_type = target_type;
1346
1347                         if (expr_type == TypeManager.sbyte_type){
1348                                 //
1349                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1350                                 //
1351                                 if (real_target_type == TypeManager.byte_type)
1352                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1353                                 if (real_target_type == TypeManager.ushort_type)
1354                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1355                                 if (real_target_type == TypeManager.uint32_type)
1356                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1357                                 if (real_target_type == TypeManager.uint64_type)
1358                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1359                                 if (real_target_type == TypeManager.char_type)
1360                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1361
1362                                 // One of the built-in conversions that belonged in the class library
1363                                 if (real_target_type == TypeManager.uintptr_type){
1364                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
1365
1366                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1367                                 }
1368                         } else if (expr_type == TypeManager.byte_type){
1369                                 //
1370                                 // From byte to sbyte and char
1371                                 //
1372                                 if (real_target_type == TypeManager.sbyte_type)
1373                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1374                                 if (real_target_type == TypeManager.char_type)
1375                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1376                         } else if (expr_type == TypeManager.short_type){
1377                                 //
1378                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1379                                 //
1380                                 if (real_target_type == TypeManager.sbyte_type)
1381                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1382                                 if (real_target_type == TypeManager.byte_type)
1383                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1384                                 if (real_target_type == TypeManager.ushort_type)
1385                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1386                                 if (real_target_type == TypeManager.uint32_type)
1387                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1388                                 if (real_target_type == TypeManager.uint64_type)
1389                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1390                                 if (real_target_type == TypeManager.char_type)
1391                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1392
1393                                 // One of the built-in conversions that belonged in the class library
1394                                 if (real_target_type == TypeManager.uintptr_type){
1395                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1396
1397                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1398                                 }
1399                         } else if (expr_type == TypeManager.ushort_type){
1400                                 //
1401                                 // From ushort to sbyte, byte, short, char
1402                                 //
1403                                 if (real_target_type == TypeManager.sbyte_type)
1404                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1405                                 if (real_target_type == TypeManager.byte_type)
1406                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1407                                 if (real_target_type == TypeManager.short_type)
1408                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1409                                 if (real_target_type == TypeManager.char_type)
1410                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1411                         } else if (expr_type == TypeManager.int32_type){
1412                                 //
1413                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1414                                 //
1415                                 if (real_target_type == TypeManager.sbyte_type)
1416                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1417                                 if (real_target_type == TypeManager.byte_type)
1418                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1419                                 if (real_target_type == TypeManager.short_type)
1420                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1421                                 if (real_target_type == TypeManager.ushort_type)
1422                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1423                                 if (real_target_type == TypeManager.uint32_type)
1424                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1425                                 if (real_target_type == TypeManager.uint64_type)
1426                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1427                                 if (real_target_type == TypeManager.char_type)
1428                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1429
1430                                 // One of the built-in conversions that belonged in the class library
1431                                 if (real_target_type == TypeManager.uintptr_type){
1432                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1433
1434                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1435                                 }
1436                         } else if (expr_type == TypeManager.uint32_type){
1437                                 //
1438                                 // From uint to sbyte, byte, short, ushort, int, char
1439                                 //
1440                                 if (real_target_type == TypeManager.sbyte_type)
1441                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1442                                 if (real_target_type == TypeManager.byte_type)
1443                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1444                                 if (real_target_type == TypeManager.short_type)
1445                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1446                                 if (real_target_type == TypeManager.ushort_type)
1447                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1448                                 if (real_target_type == TypeManager.int32_type)
1449                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1450                                 if (real_target_type == TypeManager.char_type)
1451                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1452                         } else if (expr_type == TypeManager.int64_type){
1453                                 //
1454                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1455                                 //
1456                                 if (real_target_type == TypeManager.sbyte_type)
1457                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1458                                 if (real_target_type == TypeManager.byte_type)
1459                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1460                                 if (real_target_type == TypeManager.short_type)
1461                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1462                                 if (real_target_type == TypeManager.ushort_type)
1463                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1464                                 if (real_target_type == TypeManager.int32_type)
1465                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1466                                 if (real_target_type == TypeManager.uint32_type)
1467                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1468                                 if (real_target_type == TypeManager.uint64_type)
1469                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1470                                 if (real_target_type == TypeManager.char_type)
1471                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1472                         } else if (expr_type == TypeManager.uint64_type){
1473                                 //
1474                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1475                                 //
1476                                 if (real_target_type == TypeManager.sbyte_type)
1477                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1478                                 if (real_target_type == TypeManager.byte_type)
1479                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1480                                 if (real_target_type == TypeManager.short_type)
1481                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1482                                 if (real_target_type == TypeManager.ushort_type)
1483                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1484                                 if (real_target_type == TypeManager.int32_type)
1485                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1486                                 if (real_target_type == TypeManager.uint32_type)
1487                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1488                                 if (real_target_type == TypeManager.int64_type)
1489                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1490                                 if (real_target_type == TypeManager.char_type)
1491                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1492
1493                                 // One of the built-in conversions that belonged in the class library
1494                                 if (real_target_type == TypeManager.intptr_type){
1495                                         return new OperatorCast (EmptyCast.Create (expr, TypeManager.int64_type),
1496                                                                  TypeManager.intptr_type, true);
1497                                 }
1498                         } else if (expr_type == TypeManager.char_type){
1499                                 //
1500                                 // From char to sbyte, byte, short
1501                                 //
1502                                 if (real_target_type == TypeManager.sbyte_type)
1503                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1504                                 if (real_target_type == TypeManager.byte_type)
1505                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1506                                 if (real_target_type == TypeManager.short_type)
1507                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1508                         } else if (expr_type == TypeManager.float_type){
1509                                 //
1510                                 // From float to sbyte, byte, short,
1511                                 // ushort, int, uint, long, ulong, char
1512                                 // or decimal
1513                                 //
1514                                 if (real_target_type == TypeManager.sbyte_type)
1515                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1516                                 if (real_target_type == TypeManager.byte_type)
1517                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1518                                 if (real_target_type == TypeManager.short_type)
1519                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1520                                 if (real_target_type == TypeManager.ushort_type)
1521                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1522                                 if (real_target_type == TypeManager.int32_type)
1523                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1524                                 if (real_target_type == TypeManager.uint32_type)
1525                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1526                                 if (real_target_type == TypeManager.int64_type)
1527                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1528                                 if (real_target_type == TypeManager.uint64_type)
1529                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1530                                 if (real_target_type == TypeManager.char_type)
1531                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1532                                 if (real_target_type == TypeManager.decimal_type)
1533                                         return new CastToDecimal (expr, true);
1534                         } else if (expr_type == TypeManager.double_type){
1535                                 //
1536                                 // From double to sbyte, byte, short,
1537                                 // ushort, int, uint, long, ulong,
1538                                 // char, float or decimal
1539                                 //
1540                                 if (real_target_type == TypeManager.sbyte_type)
1541                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1542                                 if (real_target_type == TypeManager.byte_type)
1543                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1544                                 if (real_target_type == TypeManager.short_type)
1545                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1546                                 if (real_target_type == TypeManager.ushort_type)
1547                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1548                                 if (real_target_type == TypeManager.int32_type)
1549                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1550                                 if (real_target_type == TypeManager.uint32_type)
1551                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1552                                 if (real_target_type == TypeManager.int64_type)
1553                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1554                                 if (real_target_type == TypeManager.uint64_type)
1555                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1556                                 if (real_target_type == TypeManager.char_type)
1557                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1558                                 if (real_target_type == TypeManager.float_type)
1559                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1560                                 if (real_target_type == TypeManager.decimal_type)
1561                                         return new CastToDecimal (expr, true);
1562                         } else if (expr_type == TypeManager.uintptr_type){
1563                                 //
1564                                 // Various built-in conversions that belonged in the class library
1565                                 //
1566                                 // from uintptr to sbyte, short, int32
1567                                 //
1568                                 if (real_target_type == TypeManager.sbyte_type){
1569                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1570                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
1571                                 }
1572                                 if (real_target_type == TypeManager.short_type){
1573                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1574                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
1575                                 }
1576                                 if (real_target_type == TypeManager.int32_type){
1577                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.uint32_type, true),
1578                                                               TypeManager.int32_type);
1579                                 }
1580                         } else if (expr_type == TypeManager.intptr_type){
1581                                 if (real_target_type == TypeManager.uint64_type){
1582                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.int64_type, true),
1583                                                               TypeManager.uint64_type);
1584                                 }
1585                         } else if (expr_type == TypeManager.decimal_type) {
1586                                 return new CastFromDecimal (expr, target_type).Resolve ();
1587                         }
1588                         return null;
1589                 }
1590
1591                 /// <summary>
1592                 ///  Returns whether an explicit reference conversion can be performed
1593                 ///  from source_type to target_type
1594                 /// </summary>
1595                 public static bool ExplicitReferenceConversionExists (TypeSpec source_type, TypeSpec target_type)
1596                 {
1597                         Expression e = ExplicitReferenceConversion (null, source_type, target_type);
1598                         if (e == null)
1599                                 return false;
1600
1601                         if (e == EmptyExpression.Null)
1602                                 return true;
1603
1604                         throw new InternalErrorException ("Invalid probing conversion result");
1605                 }
1606
1607                 /// <summary>
1608                 ///   Implements Explicit Reference conversions
1609                 /// </summary>
1610                 static Expression ExplicitReferenceConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
1611                 {
1612                         //
1613                         // From object to a generic parameter
1614                         //
1615                         if (source_type == TypeManager.object_type && TypeManager.IsGenericParameter (target_type))
1616                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1617
1618                         //
1619                         // Explicit type parameter conversion.
1620                         //
1621                         if (source_type.Kind == MemberKind.TypeParameter)
1622                                 return ExplicitTypeParameterConversion (source, source_type, target_type);
1623
1624                         bool target_is_value_type = TypeManager.IsStruct (target_type) || TypeManager.IsEnumType (target_type);
1625
1626                         //
1627                         // Unboxing conversion from System.ValueType to any non-nullable-value-type
1628                         //
1629                         if (source_type == TypeManager.value_type && target_is_value_type)
1630                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1631
1632                         //
1633                         // From object to any reference type or value type (unboxing)
1634                         //
1635                         if (source_type == TypeManager.object_type)
1636                                 return
1637                                         source == null ? EmptyExpression.Null :
1638                                         target_is_value_type ? new UnboxCast (source, target_type) :
1639                                         source is Constant ? (Expression) new EmptyConstantCast ((Constant) source, target_type) :
1640                                         new ClassCast (source, target_type);
1641
1642                         //
1643                         // From any class S to any class-type T, provided S is a base class of T
1644                         //
1645                         if (source_type.Kind == MemberKind.Class && TypeSpec.IsBaseClass (target_type, source_type, true))
1646                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1647
1648                         //
1649                         // From any interface-type S to to any class type T, provided T is not
1650                         // sealed, or provided T implements S.
1651                         //
1652                         if (source_type.IsInterface) {
1653                                 if (!target_type.IsSealed || target_type.ImplementsInterface (source_type)) {
1654                                         if (target_type.IsClass)
1655                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1656
1657                                         //
1658                                         // Unboxing conversion from any interface-type to any non-nullable-value-type that
1659                                         // implements the interface-type
1660                                         //
1661                                         return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1662                                 }
1663
1664                                 //
1665                                 // From System.Collections.Generic.IList<T> and its base interfaces to a one-dimensional
1666                                 // array type S[], provided there is an implicit or explicit reference conversion from S to T.
1667                                 //
1668                                 var target_array = target_type as ArrayContainer;
1669                                 if (target_array != null && IList_To_Array (source_type, target_array))
1670                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1671
1672                                 return null;
1673                         }
1674
1675                         var source_array = source_type as ArrayContainer;
1676                         if (source_array != null) {
1677                                 var target_array = target_type as ArrayContainer;
1678                                 if (target_array != null) {
1679                                         //
1680                                         // From System.Array to any array-type
1681                                         //
1682                                         if (source_type == TypeManager.array_type)
1683                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1684
1685                                         //
1686                                         // From an array type S with an element type Se to an array type T with an
1687                                         // element type Te provided all the following are true:
1688                                         //     * S and T differe only in element type, in other words, S and T
1689                                         //       have the same number of dimensions.
1690                                         //     * Both Se and Te are reference types
1691                                         //     * An explicit reference conversions exist from Se to Te
1692                                         //
1693                                         if (source_array.Rank == target_array.Rank) {
1694
1695                                                 source_type = source_array.Element;
1696                                                 if (!TypeManager.IsReferenceType (source_type))
1697                                                         return null;
1698
1699                                                 var target_element = target_array.Element;
1700                                                 if (!TypeManager.IsReferenceType (target_element))
1701                                                         return null;
1702
1703                                                 if (ExplicitReferenceConversionExists (source_type, target_element))
1704                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1705
1706                                                 return null;
1707                                         }
1708                                 }
1709
1710                                 //
1711                                 // From a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its base interfaces,
1712                                 // provided that there is an explicit reference conversion from S to T
1713                                 //
1714                                 if (ArrayToIList (source_array, target_type, true))
1715                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1716
1717                                 return null;
1718                         }
1719
1720                         //
1721                         // From any class type S to any interface T, provides S is not sealed
1722                         // and provided S does not implement T.
1723                         //
1724                         if (target_type.IsInterface && !source_type.IsSealed && !source_type.ImplementsInterface (target_type)) {
1725                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1726                         }
1727
1728                         //
1729                         // From System delegate to any delegate-type
1730                         //
1731                         if (source_type == TypeManager.delegate_type && TypeManager.IsDelegateType (target_type))
1732                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1733
1734                         return null;
1735                 }
1736
1737                 /// <summary>
1738                 ///   Performs an explicit conversion of the expression `expr' whose
1739                 ///   type is expr.Type to `target_type'.
1740                 /// </summary>
1741                 static public Expression ExplicitConversionCore (ResolveContext ec, Expression expr,
1742                                                                  TypeSpec target_type, Location loc)
1743                 {
1744                         TypeSpec expr_type = expr.Type;
1745
1746                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1747                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc, true);
1748                         if (ne != null)
1749                                 return ne;
1750
1751                         if (TypeManager.IsEnumType (expr_type)) {
1752                                 TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
1753                                 Expression underlying = EmptyCast.Create (expr, EnumSpec.GetUnderlyingType (expr_type));
1754                                 if (underlying.Type == real_target)
1755                                         ne = underlying;
1756
1757                                 if (ne == null)
1758                                         ne = ImplicitNumericConversion (underlying, real_target);
1759
1760                                 if (ne == null)
1761                                         ne = ExplicitNumericConversion (underlying, real_target);
1762
1763                                 //
1764                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1765                                 //
1766                                 if (ne == null && (real_target == TypeManager.intptr_type || real_target == TypeManager.uintptr_type))
1767                                         ne = ExplicitUserConversion (ec, underlying, real_target, loc);
1768
1769                                 return ne != null ? EmptyCast.Create (ne, target_type) : null;
1770                         }
1771
1772                         if (TypeManager.IsEnumType (target_type)) {
1773                                 //
1774                                 // System.Enum can be unboxed to any enum-type
1775                                 //
1776                                 if (expr_type == TypeManager.enum_type)
1777                                         return new UnboxCast (expr, target_type);
1778
1779                                 TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
1780
1781                                 if (expr_type == real_target)
1782                                         return EmptyCast.Create (expr, target_type);
1783
1784                                 ne = ImplicitNumericConversion (expr, real_target);
1785                                 if (ne != null)
1786                                         return EmptyCast.Create (ne, target_type);
1787
1788                                 ne = ExplicitNumericConversion (expr, real_target);
1789                                 if (ne != null)
1790                                         return EmptyCast.Create (ne, target_type);
1791
1792                                 //
1793                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1794                                 //
1795                                 if (expr_type == TypeManager.intptr_type || expr_type == TypeManager.uintptr_type) {
1796                                         ne = ExplicitUserConversion (ec, expr, real_target, loc);
1797                                         if (ne != null)
1798                                                 return ExplicitConversionCore (ec, ne, target_type, loc);
1799                                 }
1800                         } else {
1801                                 ne = ExplicitNumericConversion (expr, target_type);
1802                                 if (ne != null)
1803                                         return ne;
1804                         }
1805
1806                         //
1807                         // Skip the ExplicitReferenceConversion because we can not convert
1808                         // from Null to a ValueType, and ExplicitReference wont check against
1809                         // null literal explicitly
1810                         //
1811                         if (expr_type != InternalType.Null) {
1812                                 ne = ExplicitReferenceConversion (expr, expr_type, target_type);
1813                                 if (ne != null)
1814                                         return ne;
1815                         }
1816
1817                         if (ec.IsUnsafe){
1818                                 ne = ExplicitUnsafe (expr, target_type);
1819                                 if (ne != null)
1820                                         return ne;
1821                         }
1822
1823                         return null;
1824                 }
1825
1826                 public static Expression ExplicitUnsafe (Expression expr, TypeSpec target_type)
1827                 {
1828                         TypeSpec expr_type = expr.Type;
1829
1830                         if (target_type.IsPointer){
1831                                 if (expr_type.IsPointer)
1832                                         return EmptyCast.Create (expr, target_type);
1833
1834                                 if (expr_type == TypeManager.sbyte_type ||
1835                                         expr_type == TypeManager.short_type ||
1836                                         expr_type == TypeManager.int32_type)
1837                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1838
1839                                 if (expr_type == TypeManager.ushort_type ||
1840                                         expr_type == TypeManager.uint32_type ||
1841                                         expr_type == TypeManager.byte_type)
1842                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1843
1844                                 if (expr_type == TypeManager.int64_type)
1845                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I);
1846
1847                                 if (expr_type == TypeManager.uint64_type)
1848                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I);
1849                         }
1850
1851                         if (expr_type.IsPointer){
1852                                 if (target_type == TypeManager.sbyte_type)
1853                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1854                                 if (target_type == TypeManager.byte_type)
1855                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1856                                 if (target_type == TypeManager.short_type)
1857                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1858                                 if (target_type == TypeManager.ushort_type)
1859                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1860                                 if (target_type == TypeManager.int32_type)
1861                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1862                                 if (target_type == TypeManager.uint32_type)
1863                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1864                                 if (target_type == TypeManager.int64_type)
1865                                         return new ConvCast (expr, target_type, ConvCast.Mode.I_I8);
1866                                 if (target_type == TypeManager.uint64_type)
1867                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1868                         }
1869                         return null;
1870                 }
1871
1872                 /// <summary>
1873                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1874                 /// </summary>
1875                 static public Expression ExplicitConversionStandard (ResolveContext ec, Expression expr,
1876                                                                      TypeSpec target_type, Location l)
1877                 {
1878                         int errors = ec.Report.Errors;
1879                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1880                         if (ec.Report.Errors > errors)
1881                                 return null;
1882
1883                         if (ne != null)
1884                                 return ne;
1885
1886                         ne = ExplicitNumericConversion (expr, target_type);
1887                         if (ne != null)
1888                                 return ne;
1889
1890                         ne = ExplicitReferenceConversion (expr, expr.Type, target_type);
1891                         if (ne != null)
1892                                 return ne;
1893
1894                         if (ec.IsUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
1895                                 return EmptyCast.Create (expr, target_type);
1896
1897                         expr.Error_ValueCannotBeConverted (ec, l, target_type, true);
1898                         return null;
1899                 }
1900
1901                 /// <summary>
1902                 ///   Performs an explicit conversion of the expression `expr' whose
1903                 ///   type is expr.Type to `target_type'.
1904                 /// </summary>
1905                 static public Expression ExplicitConversion (ResolveContext ec, Expression expr,
1906                         TypeSpec target_type, Location loc)
1907                 {
1908                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
1909                         if (e != null) {
1910                                 //
1911                                 // Don't eliminate explicit precission casts
1912                                 //
1913                                 if (e == expr) {
1914                                         if (target_type == TypeManager.float_type)
1915                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
1916
1917                                         if (target_type == TypeManager.double_type)
1918                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
1919                                 }
1920
1921                                 return e;
1922                         }
1923
1924                         TypeSpec expr_type = expr.Type;
1925                         if (TypeManager.IsNullableType (target_type)) {
1926                                 if (TypeManager.IsNullableType (expr_type)) {
1927                                         TypeSpec target = Nullable.NullableInfo.GetUnderlyingType (target_type);
1928                                         Expression unwrap = Nullable.Unwrap.Create (expr);
1929                                         e = ExplicitConversion (ec, unwrap, target, expr.Location);
1930                                         if (e == null)
1931                                                 return null;
1932
1933                                         return new Nullable.Lifted (e, unwrap, target_type).Resolve (ec);
1934                                 } else if (expr_type == TypeManager.object_type) {
1935                                         return new UnboxCast (expr, target_type);
1936                                 } else {
1937                                         TypeSpec target = TypeManager.GetTypeArguments (target_type) [0];
1938
1939                                         e = ExplicitConversionCore (ec, expr, target, loc);
1940                                         if (e != null)
1941                                                 return Nullable.Wrap.Create (e, target_type);
1942                                 }
1943                         } else if (TypeManager.IsNullableType (expr_type)) {
1944                                 e = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
1945                                 if (e != null)
1946                                         return e;
1947
1948                                 e = Nullable.Unwrap.Create (expr, false);
1949                                 e = ExplicitConversionCore (ec, e, target_type, loc);
1950                                 if (e != null)
1951                                         return EmptyCast.Create (e, target_type);
1952                         }
1953
1954                         e = ExplicitUserConversion (ec, expr, target_type, loc);
1955                         if (e != null)
1956                                 return e;
1957
1958                         expr.Error_ValueCannotBeConverted (ec, loc, target_type, true);
1959                         return null;
1960                 }
1961         }
1962 }