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                         // From T to a type parameter U
  97                         //
  98                         var ttype = target_type as TypeParameterSpec;
  99                         if (ttype != null) {
 100                                 if (expr_type.IsReferenceType && !ttype.IsReferenceType)
 101                                         return new BoxedCast (expr, target_type);
 102
 103                                 return new ClassCast (expr, target_type);
 104                         }
 105
 106                         //
 107                         // From T to its effective base class C
 108                         // From T to any base class of C
 109                         // From T to any interface implemented by C
 110                         //
 111                         var base_type = expr_type.GetEffectiveBase ();
 112                         if (base_type == target_type || TypeManager.IsSubclassOf (base_type, target_type) || base_type.ImplementsInterface (target_type)) {
 113                                 if (expr_type.IsReferenceType)
 114                                         return new ClassCast (expr, target_type);
 115
 116                                 return new BoxedCast (expr, target_type);
 117                         }
 118
 119                         if (target_type.IsInterface && expr_type.IsConvertibleToInterface (target_type)) {
 120                                 if (expr_type.IsReferenceType)
 121                                         return new ClassCast (expr, target_type);
 122
 123                                 return new BoxedCast (expr, target_type);
 124                         }
 125
 126                         return null;
 127                 }
 128
 129                 static Expression ExplicitTypeParameterConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
 130                 {
 131                         var target_tp = target_type as TypeParameterSpec;
 132                         if (target_tp != null) {
 133                                 if (target_tp.Interfaces != null) {
 134                                         foreach (TypeSpec iface in target_tp.Interfaces) {
 135                                                 if (!TypeManager.IsGenericParameter (iface))
 136                                                         continue;
 137
 138                                                 if (TypeManager.IsSubclassOf (source_type, iface))
 139                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type, true);
 140                                         }
 141                                 }
 142
 143                                 return null;
 144                         }
 145
 146                         if (target_type.IsInterface)
 147                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type, true);
 148
 149                         return null;
 150                 }
 151
 152                 static Expression ImplicitReferenceConversion (Expression expr, TypeSpec target_type, bool explicit_cast)
 153                 {
 154                         TypeSpec expr_type = expr.Type;
 155
 156                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 157                                 // if we are a method group, emit a warning
 158
 159                                 expr.Emit (null);
 160                         }
 161
 162                         if (expr_type == TypeManager.void_type)
 163                                 return null;
 164
 165                         if (expr_type.Kind == MemberKind.TypeParameter)
 166                                 return ImplicitTypeParameterConversion (expr, target_type);
 167
 168                         //
 169                         // from the null type to any reference-type.
 170                         //
 171                         NullLiteral nl = expr as NullLiteral;
 172                         if (nl != null) {
 173                                 return nl.ConvertImplicitly (null, target_type);
 174                         }
 175
 176                         if (ImplicitReferenceConversionExists (expr, target_type)) {
 177                                 //
 178                                 // Avoid wrapping implicitly convertible reference type
 179                                 //
 180                                 if (!explicit_cast)
 181                                         return expr;
 182
 183                                 return EmptyCast.Create (expr, target_type);
 184                         }
 185
 186                         return ImplicitBoxingConversion (expr, expr_type, target_type);
 187                 }
 188
 189                 //
 190                 // 6.1.6 Implicit reference conversions
 191                 //
 192                 public static bool ImplicitReferenceConversionExists (Expression expr, TypeSpec target_type)
 193                 {
 194                         if (TypeManager.IsStruct (target_type))
 195                                 return false;
 196
 197                         TypeSpec expr_type = expr.Type;
 198
 199                         // from the null type to any reference-type.
 200                         if (expr_type == TypeManager.null_type)
 201                                 return target_type != InternalType.AnonymousMethod;
 202
 203                         if (TypeManager.IsGenericParameter (expr_type))
 204                                 return ImplicitTypeParameterConversion (expr, target_type) != null;
 205
 206                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 207                         // with the small distinction that we only probe there
 208                         //
 209                         // Always ensure that the code here and there is in sync
 210
 211                         // from any class-type S to any interface-type T.
 212                         if (target_type.IsInterface) {
 213                                 if (expr_type.ImplementsInterface (target_type)){
 214                                         return !TypeManager.IsValueType (expr_type);
 215                                 }
 216                         }
 217
 218                         //
 219                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 220                         // is an abstract class, and not really a value type, so we apply the same rules.
 221                         //
 222                         if (target_type == TypeManager.object_type || target_type == InternalType.Dynamic) {
 223                                 //
 224                                 // A pointer type cannot be converted to object
 225                                 //
 226                                 if (expr_type.IsPointer)
 227                                         return false;
 228
 229                                 if (TypeManager.IsValueType (expr_type))
 230                                         return false;
 231
 232                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type || expr_type.IsDelegate || expr_type.Kind == MemberKind.ArrayType) {
 233                                         // No mcs internal types are convertible
 234                                         return true; // expr_type.MetaInfo.Module != typeof (Convert).Module;
 235                                 }
 236
 237                                 // From anything to dynamic
 238                                 if (target_type == InternalType.Dynamic)
 239                                         return true;
 240
 241                                 // From dynamic to object
 242                                 if (expr_type == InternalType.Dynamic)
 243                                         return true;
 244
 245                                 return false;
 246                         } else if (target_type == TypeManager.value_type) {
 247                                 return expr_type == TypeManager.enum_type;
 248                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 249                                 //
 250                                 // Special case: enumeration to System.Enum.
 251                                 // System.Enum is not a value type, it is a class, so we need
 252                                 // a boxing conversion
 253                                 //
 254                                 if (target_type == TypeManager.enum_type || TypeManager.IsGenericParameter (expr_type))
 255                                         return false;
 256
 257                                 if (TypeManager.IsValueType (expr_type))
 258                                         return false;
 259
 260                                 // Array type variance conversion
 261                                 //if (target_type.IsArray != expr_type.IsArray)
 262                                 //      return false;
 263
 264                                 return true;
 265                         }
 266
 267                         var expr_type_array = expr_type as ArrayContainer;
 268                         if (expr_type_array != null) {
 269                                 var target_type_array = target_type as ArrayContainer;
 270                                 // from an array-type S to an array-type of type T
 271                                 if (target_type_array != null && expr_type_array.Rank == target_type_array.Rank) {
 272
 273                                         //
 274                                         // Both SE and TE are reference-types
 275                                         //
 276                                         TypeSpec expr_element_type = expr_type_array.Element;
 277                                         if (!TypeManager.IsReferenceType (expr_element_type))
 278                                                 return false;
 279
 280                                         TypeSpec target_element_type = target_type_array.Element;
 281                                         if (!TypeManager.IsReferenceType (target_element_type))
 282                                                 return false;
 283
 284                                         if (MyEmptyExpr == null)
 285                                                 MyEmptyExpr = new EmptyExpression (expr_element_type);
 286                                         else
 287                                                 MyEmptyExpr.SetType (expr_element_type);
 288
 289                                         return ImplicitStandardConversionExists (MyEmptyExpr, target_element_type);
 290                                 }
 291
 292                                 // from an array-type to System.Array
 293                                 if (target_type == TypeManager.array_type)
 294                                         return true;
 295
 296                                 // from an array-type of type T to IList<T>
 297                                 if (ArrayToIList (expr_type_array, target_type, false))
 298                                         return true;
 299
 300                                 return false;
 301                         }
 302
 303                         if (TypeSpecComparer.Variant.IsEqual (expr_type, target_type))
 304                                 return true;
 305
 306                         // from any interface type S to interface-type T.
 307                         if (expr_type.IsInterface && target_type.IsInterface) {
 308                                 return expr_type.ImplementsInterface (target_type);
 309                         }
 310
 311                         // from any delegate type to System.Delegate
 312                         if (target_type == TypeManager.delegate_type &&
 313                                 (expr_type == TypeManager.delegate_type || expr_type.IsDelegate))
 314                                 return true;
 315
 316                         if (TypeManager.IsEqual (expr_type, target_type))
 317                                 return true;
 318
 319                         return false;
 320                 }
 321
 322                 public static Expression ImplicitBoxingConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
 323                 {
 324                         //
 325                         // From any value-type to the type object.
 326                         //
 327                         if (target_type == TypeManager.object_type || target_type == InternalType.Dynamic) {
 328                                 //
 329                                 // A pointer type cannot be converted to object
 330                                 //
 331                                 if (expr_type.IsPointer)
 332                                         return null;
 333
 334                                 if (!TypeManager.IsValueType (expr_type))
 335                                         return null;
 336
 337                                 return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 338                         }
 339
 340                         //
 341                         // From any value-type to the type System.ValueType.
 342                         //
 343                         if (target_type == TypeManager.value_type) {
 344                                 if (!TypeManager.IsValueType (expr_type))
 345                                         return null;
 346
 347                                 return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 348                         }
 349
 350                         if (target_type == TypeManager.enum_type) {
 351                                 //
 352                                 // From any enum-type to the type System.Enum.
 353                                 //
 354                                 if (TypeManager.IsEnumType (expr_type))
 355                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 356                         }
 357
 358                         //
 359                         // From a nullable-type to a reference type, if a boxing conversion exists from
 360                         // the underlying type to the reference type
 361                         //
 362                         if (TypeManager.IsNullableType (expr_type)) {
 363                                 if (!TypeManager.IsReferenceType (target_type))
 364                                         return null;
 365
 366                                 var res = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
 367
 368                                 // "cast" underlying type to target type to emit correct InvalidCastException when
 369                                 // underlying hierarchy changes without recompilation
 370                                 if (res != null && expr != null)
 371                                         res = new UnboxCast (res, target_type);
 372
 373                                 return res;
 374                         }
 375
 376                         if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 377                                 //
 378                                 // Don't box same type arguments
 379                                 //
 380                                 if (TypeManager.IsGenericParameter (expr_type) && expr_type != target_type)
 381                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 382
 383                                 return null;
 384                         }
 385
 386                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 387                         // with the small distinction that we only probe there
 388                         //
 389                         // Always ensure that the code here and there is in sync
 390
 391                         // from any class-type S to any interface-type T.
 392                         if (target_type.IsInterface) {
 393                                 if (expr_type.ImplementsInterface (target_type) &&
 394                                         (TypeManager.IsGenericParameter (expr_type) || TypeManager.IsValueType (expr_type))) {
 395                                         return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 396                                 }
 397                         }
 398
 399                         return null;
 400                 }
 401
 402                 public static Expression ImplicitNulableConversion (ResolveContext ec, Expression expr, TypeSpec target_type)
 403                 {
 404                         TypeSpec expr_type = expr.Type;
 405
 406                         //
 407                         // From null to any nullable type
 408                         //
 409                         if (expr_type == TypeManager.null_type)
 410                                 return ec == null ? EmptyExpression.Null : Nullable.LiftedNull.Create (target_type, expr.Location);
 411
 412                         // S -> T?
 413                         TypeSpec t_el = Nullable.NullableInfo.GetUnderlyingType (target_type);
 414
 415                         // S? -> T?
 416                         if (TypeManager.IsNullableType (expr_type))
 417                                 expr_type = Nullable.NullableInfo.GetUnderlyingType (expr_type);
 418
 419                         //
 420                         // Predefined implicit identity or implicit numeric conversion
 421                         // has to exist between underlying type S and underlying type T
 422                         //
 423
 424                         // conversion exists only mode
 425                         if (ec == null) {
 426                                 if (expr_type == t_el)
 427                                         return EmptyExpression.Null;
 428
 429                                 if (expr is Constant)
 430                                         return ((Constant) expr).ConvertImplicitly (ec, t_el);
 431
 432                                 return ImplicitNumericConversion (null, expr_type, t_el);
 433                         }
 434
 435                         Expression unwrap;
 436                         if (expr_type != expr.Type)
 437                                 unwrap = Nullable.Unwrap.Create (expr);
 438                         else
 439                                 unwrap = expr;
 440
 441                         Expression conv = unwrap;
 442                         if (expr_type != t_el) {
 443                                 if (conv is Constant)
 444                                         conv = ((Constant)conv).ConvertImplicitly (ec, t_el);
 445                                 else
 446                                         conv = ImplicitNumericConversion (conv, expr_type, t_el);
 447
 448                                 if (conv == null)
 449                                         return null;
 450                         }
 451
 452                         if (expr_type != expr.Type)
 453                                 return new Nullable.Lifted (conv, unwrap, target_type).Resolve (ec);
 454
 455                         return Nullable.Wrap.Create (conv, target_type);
 456                 }
 457
 458                 /// <summary>
 459                 ///   Implicit Numeric Conversions.
 460                 ///
 461                 ///   expr is the expression to convert, returns a new expression of type
 462                 ///   target_type or null if an implicit conversion is not possible.
 463                 /// </summary>
 464                 public static Expression ImplicitNumericConversion (Expression expr, TypeSpec target_type)
 465                 {
 466                         return ImplicitNumericConversion (expr, expr.Type, target_type);
 467                 }
 468
 469                 static Expression ImplicitNumericConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
 470                 {
 471                         if (expr_type == TypeManager.sbyte_type){
 472                                 //
 473                                 // From sbyte to short, int, long, float, double, decimal
 474                                 //
 475                                 if (target_type == TypeManager.int32_type)
 476                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 477                                 if (target_type == TypeManager.int64_type)
 478                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 479                                 if (target_type == TypeManager.double_type)
 480                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 481                                 if (target_type == TypeManager.float_type)
 482                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 483                                 if (target_type == TypeManager.short_type)
 484                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 485                                 if (target_type == TypeManager.decimal_type)
 486                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 487                         } else if (expr_type == TypeManager.byte_type){
 488                                 //
 489                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 490                                 //
 491                                 if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type ||
 492                                     target_type == TypeManager.short_type || target_type == TypeManager.ushort_type)
 493                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 494
 495                                 if (target_type == TypeManager.uint64_type)
 496                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 497                                 if (target_type == TypeManager.int64_type)
 498                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 499                                 if (target_type == TypeManager.float_type)
 500                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 501                                 if (target_type == TypeManager.double_type)
 502                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 503                                 if (target_type == TypeManager.decimal_type)
 504                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 505
 506                         } else if (expr_type == TypeManager.short_type){
 507                                 //
 508                                 // From short to int, long, float, double, decimal
 509                                 //
 510                                 if (target_type == TypeManager.int32_type)
 511                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 512                                 if (target_type == TypeManager.int64_type)
 513                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 514                                 if (target_type == TypeManager.double_type)
 515                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 516                                 if (target_type == TypeManager.float_type)
 517                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 518                                 if (target_type == TypeManager.decimal_type)
 519                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 520
 521                         } else if (expr_type == TypeManager.ushort_type){
 522                                 //
 523                                 // From ushort to int, uint, long, ulong, float, double, decimal
 524                                 //
 525                                 if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type)
 526                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 527
 528                                 if (target_type == TypeManager.uint64_type)
 529                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 530                                 if (target_type == TypeManager.int64_type)
 531                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 532                                 if (target_type == TypeManager.double_type)
 533                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 534                                 if (target_type == TypeManager.float_type)
 535                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 536                                 if (target_type == TypeManager.decimal_type)
 537                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 538                         } else if (expr_type == TypeManager.int32_type){
 539                                 //
 540                                 // From int to long, float, double, decimal
 541                                 //
 542                                 if (target_type == TypeManager.int64_type)
 543                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 544                                 if (target_type == TypeManager.double_type)
 545                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 546                                 if (target_type == TypeManager.float_type)
 547                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 548                                 if (target_type == TypeManager.decimal_type)
 549                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 550                         } else if (expr_type == TypeManager.uint32_type){
 551                                 //
 552                                 // From uint to long, ulong, float, double, decimal
 553                                 //
 554                                 if (target_type == TypeManager.int64_type)
 555                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 556                                 if (target_type == TypeManager.uint64_type)
 557                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 558                                 if (target_type == TypeManager.double_type)
 559                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
 560                                 if (target_type == TypeManager.float_type)
 561                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), 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.int64_type){
 565                                 //
 566                                 // From long/ulong to float, double
 567                                 //
 568                                 if (target_type == TypeManager.double_type)
 569                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 570                                 if (target_type == TypeManager.float_type)
 571                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 572                                 if (target_type == TypeManager.decimal_type)
 573                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 574                         } else if (expr_type == TypeManager.uint64_type){
 575                                 //
 576                                 // From ulong to float, double
 577                                 //
 578                                 if (target_type == TypeManager.double_type)
 579                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
 580                                 if (target_type == TypeManager.float_type)
 581                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
 582                                 if (target_type == TypeManager.decimal_type)
 583                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 584                         } else if (expr_type == TypeManager.char_type){
 585                                 //
 586                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 587                                 //
 588                                 if ((target_type == TypeManager.ushort_type) ||
 589                                     (target_type == TypeManager.int32_type) ||
 590                                     (target_type == TypeManager.uint32_type))
 591                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 592                                 if (target_type == TypeManager.uint64_type)
 593                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 594                                 if (target_type == TypeManager.int64_type)
 595                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 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.double_type)
 599                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 600                                 if (target_type == TypeManager.decimal_type)
 601                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 602                         } else if (expr_type == TypeManager.float_type){
 603                                 //
 604                                 // float to double
 605                                 //
 606                                 if (target_type == TypeManager.double_type)
 607                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 608                         }
 609
 610                         return null;
 611                 }
 612
 613                 /// <summary>
 614                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 615                 ///  implicit user defined conversions - needed for overload resolution
 616                 /// </summary>
 617                 public static bool ImplicitConversionExists (ResolveContext ec, Expression expr, TypeSpec target_type)
 618                 {
 619                         if (ImplicitStandardConversionExists (expr, target_type))
 620                                 return true;
 621
 622                         if (expr.Type == InternalType.AnonymousMethod) {
 623                                 if (!TypeManager.IsDelegateType (target_type) && target_type.GetDefinition () != TypeManager.expression_type)
 624                                         return false;
 625
 626                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 627                                 return ame.ImplicitStandardConversionExists (ec, target_type);
 628                         }
 629
 630                         if (expr.eclass == ExprClass.MethodGroup) {
 631                                 if (target_type.IsDelegate && RootContext.Version != LanguageVersion.ISO_1) {
 632                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 633                                         if (mg != null)
 634                                                 return DelegateCreation.ImplicitStandardConversionExists (ec, mg, target_type);
 635                                 }
 636
 637                                 return false;
 638                         }
 639
 640                         return ImplicitUserConversion (ec, expr, target_type, Location.Null) != null;
 641                 }
 642
 643                 /// <summary>
 644                 ///  Determines if a standard implicit conversion exists from
 645                 ///  expr_type to target_type
 646                 ///
 647                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 648                 /// </summary>
 649                 public static bool ImplicitStandardConversionExists (Expression expr, TypeSpec target_type)
 650                 {
 651                         TypeSpec expr_type = expr.Type;
 652
 653                         if (expr_type == TypeManager.null_type) {
 654                                 NullLiteral nl = expr as NullLiteral;
 655                                 if (nl != null)
 656                                         return nl.ConvertImplicitly (null, target_type) != null;
 657                         }
 658
 659                         if (expr_type == TypeManager.void_type)
 660                                 return false;
 661
 662                         if (TypeManager.IsEqual (expr_type, target_type))
 663                                 return true;
 664
 665                         if (TypeManager.IsNullableType (target_type)) {
 666                                 return ImplicitNulableConversion (null, expr, target_type) != null;
 667                         }
 668
 669                         // First numeric conversions
 670                         if (ImplicitNumericConversion (null, expr_type, target_type) != null)
 671                                 return true;
 672
 673                         if (ImplicitReferenceConversionExists (expr, target_type))
 674                                 return true;
 675
 676                         if (ImplicitBoxingConversion (null, expr_type, target_type) != null)
 677                                 return true;
 678
 679                         //
 680                         // Implicit Constant Expression Conversions
 681                         //
 682                         if (expr is IntConstant){
 683                                 int value = ((IntConstant) expr).Value;
 684
 685                                 if (target_type == TypeManager.sbyte_type){
 686                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 687                                                 return true;
 688                                 } else if (target_type == TypeManager.byte_type){
 689                                         if (value >= 0 && value <= Byte.MaxValue)
 690                                                 return true;
 691                                 } else if (target_type == TypeManager.short_type){
 692                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 693                                                 return true;
 694                                 } else if (target_type == TypeManager.ushort_type){
 695                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 696                                                 return true;
 697                                 } else if (target_type == TypeManager.uint32_type){
 698                                         if (value >= 0)
 699                                                 return true;
 700                                 } else if (target_type == TypeManager.uint64_type){
 701                                          //
 702                                          // we can optimize this case: a positive int32
 703                                          // always fits on a uint64.  But we need an opcode
 704                                          // to do it.
 705                                          //
 706                                         if (value >= 0)
 707                                                 return true;
 708                                 }
 709
 710                                 if (value == 0 && target_type.IsEnum)
 711                                         return true;
 712                         }
 713
 714                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 715                                 //
 716                                 // Try the implicit constant expression conversion
 717                                 // from long to ulong, instead of a nice routine,
 718                                 // we just inline it
 719                                 //
 720                                 long v = ((LongConstant) expr).Value;
 721                                 if (v >= 0)
 722                                         return true;
 723                         }
 724
 725                         //
 726                         // If `expr_type' implements `target_type' (which is an iface)
 727                         // see TryImplicitIntConversion
 728                         //
 729                         if (target_type.IsInterface && expr_type.ImplementsInterface (target_type))
 730                                 return true;
 731
 732                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 733                                 return true;
 734
 735                         // Conversion from __arglist to System.ArgIterator
 736                         if (expr_type == InternalType.Arglist)
 737                                 return target_type == TypeManager.arg_iterator_type;
 738
 739                         return false;
 740                 }
 741
 742                 /// <summary>
 743                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 744                 ///  amongst the methods in the MethodGroupExpr
 745                 /// </summary>
 746                 public static TypeSpec FindMostEncompassedType (IEnumerable<TypeSpec> types)
 747                 {
 748                         TypeSpec best = null;
 749                         EmptyExpression expr = EmptyExpression.Grab ();
 750
 751                         foreach (TypeSpec t in types) {
 752                                 if (best == null) {
 753                                         best = t;
 754                                         continue;
 755                                 }
 756
 757                                 expr.SetType (t);
 758                                 if (ImplicitStandardConversionExists (expr, best))
 759                                         best = t;
 760                         }
 761
 762                         expr.SetType (best);
 763                         foreach (TypeSpec t in types) {
 764                                 if (best == t)
 765                                         continue;
 766                                 if (!ImplicitStandardConversionExists (expr, t)) {
 767                                         best = null;
 768                                         break;
 769                                 }
 770                         }
 771
 772                         EmptyExpression.Release (expr);
 773
 774                         return best;
 775                 }
 776
 777                 /// <summary>
 778                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 779                 ///  amongst the types in the given set
 780                 /// </summary>
 781                 static TypeSpec FindMostEncompassingType (IList<TypeSpec> types)
 782                 {
 783                         TypeSpec best = null;
 784
 785                         if (types.Count == 0)
 786                                 return null;
 787
 788                         if (types.Count == 1)
 789                                 return types [0];
 790
 791                         EmptyExpression expr = EmptyExpression.Grab ();
 792
 793                         foreach (TypeSpec t in types) {
 794                                 if (best == null) {
 795                                         best = t;
 796                                         continue;
 797                                 }
 798
 799                                 expr.SetType (best);
 800                                 if (ImplicitStandardConversionExists (expr, t))
 801                                         best = t;
 802                         }
 803
 804                         foreach (TypeSpec t in types) {
 805                                 if (best == t)
 806                                         continue;
 807                                 expr.SetType (t);
 808                                 if (!ImplicitStandardConversionExists (expr, best)) {
 809                                         best = null;
 810                                         break;
 811                                 }
 812                         }
 813
 814                         EmptyExpression.Release (expr);
 815
 816                         return best;
 817                 }
 818
 819                 /// <summary>
 820                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 821                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 822                 ///   for explicit and implicit conversion operators.
 823                 /// </summary>
 824                 static TypeSpec FindMostSpecificSource (IList<MethodSpec> list,
 825                                                            Expression source, bool apply_explicit_conv_rules)
 826                 {
 827                         var src_types_set = new List<TypeSpec> ();
 828
 829                         //
 830                         // If any operator converts from S then Sx = S
 831                         //
 832                         TypeSpec source_type = source.Type;
 833                         foreach (var mb in list){
 834                                 TypeSpec param_type = mb.Parameters.Types [0];
 835
 836                                 if (param_type == source_type)
 837                                         return param_type;
 838
 839                                 src_types_set.Add (param_type);
 840                         }
 841
 842                         //
 843                         // Explicit Conv rules
 844                         //
 845                         if (apply_explicit_conv_rules) {
 846                                 var candidate_set = new List<TypeSpec> ();
 847
 848                                 foreach (TypeSpec param_type in src_types_set){
 849                                         if (ImplicitStandardConversionExists (source, param_type))
 850                                                 candidate_set.Add (param_type);
 851                                 }
 852
 853                                 if (candidate_set.Count != 0)
 854                                         return FindMostEncompassedType (candidate_set);
 855                         }
 856
 857                         //
 858                         // Final case
 859                         //
 860                         if (apply_explicit_conv_rules)
 861                                 return FindMostEncompassingType (src_types_set);
 862                         else
 863                                 return FindMostEncompassedType (src_types_set);
 864                 }
 865
 866                 /// <summary>
 867                 ///  Finds the most specific target Tx according to section 13.4.4
 868                 /// </summary>
 869                 static public TypeSpec FindMostSpecificTarget (IList<MethodSpec> list,
 870                                                            TypeSpec target, bool apply_explicit_conv_rules)
 871                 {
 872                         var tgt_types_set = new List<TypeSpec> ();
 873
 874                         //
 875                         // If any operator converts to T then Tx = T
 876                         //
 877                         foreach (var mi in list){
 878                                 TypeSpec ret_type = mi.ReturnType;
 879                                 if (ret_type == target)
 880                                         return ret_type;
 881
 882                                 tgt_types_set.Add (ret_type);
 883                         }
 884
 885                         //
 886                         // Explicit conv rules
 887                         //
 888                         if (apply_explicit_conv_rules) {
 889                                 var candidate_set = new List<TypeSpec> ();
 890
 891                                 EmptyExpression expr = EmptyExpression.Grab ();
 892
 893                                 foreach (TypeSpec ret_type in tgt_types_set){
 894                                         expr.SetType (ret_type);
 895
 896                                         if (ImplicitStandardConversionExists (expr, target))
 897                                                 candidate_set.Add (ret_type);
 898                                 }
 899
 900                                 EmptyExpression.Release (expr);
 901
 902                                 if (candidate_set.Count != 0)
 903                                         return FindMostEncompassingType (candidate_set);
 904                         }
 905
 906                         //
 907                         // Okay, final case !
 908                         //
 909                         if (apply_explicit_conv_rules)
 910                                 return FindMostEncompassedType (tgt_types_set);
 911                         else
 912                                 return FindMostEncompassingType (tgt_types_set);
 913                 }
 914
 915                 /// <summary>
 916                 ///  User-defined Implicit conversions
 917                 /// </summary>
 918                 static public Expression ImplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
 919                 {
 920                         return UserDefinedConversion (ec, source, target, true, loc);
 921                 }
 922
 923                 /// <summary>
 924                 ///  User-defined Explicit conversions
 925                 /// </summary>
 926                 static Expression ExplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
 927                 {
 928                         return UserDefinedConversion (ec, source, target, false, loc);
 929                 }
 930
 931                 static void FindApplicableUserDefinedConversionOperators (MethodSpec[] operators, Expression source, TypeSpec target, bool implicitOnly, ref List<MethodSpec> candidates)
 932                 {
 933                         //
 934                         // LAMESPEC: Undocumented IntPtr/UIntPtr conversions
 935                         // IntPtr -> uint uses int
 936                         // UIntPtr -> long uses ulong
 937                         //
 938                         if (source.Type == TypeManager.intptr_type) {
 939                                 if (target == TypeManager.uint32_type)
 940                                         target = TypeManager.int32_type;
 941                         } else if (source.Type == TypeManager.uintptr_type) {
 942                                 if (target == TypeManager.int64_type)
 943                                         target = TypeManager.uint64_type;
 944                         }
 945
 946                         // For a conversion operator to be applicable, it must be possible
 947                         // to perform a standard conversion from the source type to
 948                         // the operand type of the operator, and it must be possible
 949                         // to perform a standard conversion from the result type of
 950                         // the operator to the target type.
 951
 952                         Expression texpr = null;
 953
 954                         foreach (var op in operators) {
 955                                 var t = op.Parameters.Types[0];
 956                                 if (source.Type != t && !ImplicitStandardConversionExists (source, t)) {
 957                                         if (implicitOnly)
 958                                                 continue;
 959
 960                                         if (!ImplicitStandardConversionExists (new EmptyExpression (t), source.Type))
 961                                                 continue;
 962                                 }
 963
 964                                 t = op.ReturnType;
 965
 966                                 // LAMESPEC: Exclude UIntPtr -> int conversion
 967                                 if (t == TypeManager.uint32_type && source.Type == TypeManager.uintptr_type)
 968                                         continue;
 969
 970                                 if (target != t && !ImplicitStandardConversionExists (new EmptyExpression (t), target)) {
 971                                         if (implicitOnly)
 972                                                 continue;
 973
 974                                         if (texpr == null)
 975                                                 texpr = new EmptyExpression (target);
 976
 977                                         if (!ImplicitStandardConversionExists (texpr, t))
 978                                                 continue;
 979                                 }
 980
 981                                 if (candidates == null)
 982                                         candidates = new List<MethodSpec> ();
 983
 984                                 candidates.Add (op);
 985                         }
 986                 }
 987
 988                 //
 989                 // User-defined conversions
 990                 //
 991                 static Expression UserDefinedConversion (ResolveContext ec, Expression source, TypeSpec target, bool implicitOnly, Location loc)
 992                 {
 993                         List<MethodSpec> candidates = null;
 994
 995                         //
 996                         // If S or T are nullable types, S0 and T0 are their underlying types
 997                         // otherwise S0 and T0 are equal to S and T respectively.
 998                         //
 999                         TypeSpec source_type = source.Type;
1000                         TypeSpec target_type = target;
1001                         Expression unwrap;
1002
1003                         if (TypeManager.IsNullableType (source_type)) {
1004                                 // No implicit conversion S? -> T for non-reference types
1005                                 if (implicitOnly && !TypeManager.IsReferenceType (target_type) && !TypeManager.IsNullableType (target_type))
1006                                         return null;
1007
1008                                 unwrap = source = Nullable.Unwrap.Create (source);
1009                                 source_type = source.Type;
1010                         } else {
1011                                 unwrap = null;
1012                         }
1013
1014                         if (TypeManager.IsNullableType (target_type))
1015                                 target_type = Nullable.NullableInfo.GetUnderlyingType (target_type);
1016
1017                         // Only these containers can contain a user defined implicit or explicit operators
1018                         const MemberKind user_conversion_kinds = MemberKind.Class | MemberKind.Struct | MemberKind.TypeParameter;
1019
1020                         if ((source_type.Kind & user_conversion_kinds) != 0 && source_type != TypeManager.decimal_type) {
1021                                 bool declared_only = source_type.IsStruct;
1022
1023                                 var operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Implicit, declared_only);
1024                                 if (operators != null) {
1025                                         FindApplicableUserDefinedConversionOperators (operators, source, target_type, implicitOnly, ref candidates);
1026                                 }
1027
1028                                 if (!implicitOnly) {
1029                                         operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Explicit, declared_only);
1030                                         if (operators != null) {
1031                                                 FindApplicableUserDefinedConversionOperators (operators, source, target_type, false, ref candidates);
1032                                         }
1033                                 }
1034                         }
1035
1036                         if ((target.Kind & user_conversion_kinds) != 0 && target != TypeManager.decimal_type) {
1037                                 bool declared_only = target.IsStruct || implicitOnly;
1038
1039                                 var operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Implicit, declared_only);
1040                                 if (operators != null) {
1041                                         FindApplicableUserDefinedConversionOperators (operators, source, target_type, implicitOnly, ref candidates);
1042                                 }
1043
1044                                 if (!implicitOnly) {
1045                                         operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Explicit, declared_only);
1046                                         if (operators != null) {
1047                                                 FindApplicableUserDefinedConversionOperators (operators, source, target_type, false, ref candidates);
1048                                         }
1049                                 }
1050                         }
1051
1052                         if (candidates == null)
1053                                 return null;
1054
1055                         //
1056                         // Find the most specific conversion operator
1057                         //
1058                         MethodSpec most_specific_operator;
1059                         TypeSpec s_x, t_x;
1060                         if (candidates.Count == 1) {
1061                                 most_specific_operator = candidates[0];
1062                                 s_x = most_specific_operator.Parameters.Types[0];
1063                                 t_x = most_specific_operator.ReturnType;
1064                         } else {
1065                                 s_x = FindMostSpecificSource (candidates, source, !implicitOnly);
1066                                 if (s_x == null)
1067                                         return null;
1068
1069                                 t_x = FindMostSpecificTarget (candidates, target, !implicitOnly);
1070                                 if (t_x == null)
1071                                         return null;
1072
1073                                 most_specific_operator = candidates[0];
1074
1075                                 for (int i = 1; i < candidates.Count; ++i) {
1076                                         if (candidates[i].ReturnType == t_x && candidates[i].Parameters.Types[0] == s_x) {
1077                                                 most_specific_operator = candidates[i];
1078                                                 break;
1079                                         }
1080                                 }
1081                         }
1082
1083                         //
1084                         // Convert input type when it's different to best operator argument
1085                         //
1086                         if (s_x != source.Type)
1087                                 source = implicitOnly ?
1088                                         ImplicitConversionStandard (ec, source, s_x, loc) :
1089                                         ExplicitConversionStandard (ec, source, s_x, loc);
1090
1091                         source = new UserCast (most_specific_operator, source, loc).Resolve (ec);
1092
1093                         //
1094                         // Convert result type when it's different to best operator return type
1095                         //
1096                         if (t_x != target_type) {
1097                                 //
1098                                 // User operator is of T?, no need to lift it
1099                                 //
1100                                 if (TypeManager.IsNullableType (t_x) && t_x == target)
1101                                         return source;
1102
1103                                 source = implicitOnly ?
1104                                         ImplicitConversionStandard (ec, source, target_type, loc) :
1105                                         ExplicitConversionStandard (ec, source, target_type, loc);
1106                         }
1107
1108                         //
1109                         // Source expression is of nullable type, lift the result in case of it's null
1110                         //
1111                         if (unwrap != null && (TypeManager.IsReferenceType (target) || target_type != target))
1112                                 source = new Nullable.Lifted (source, unwrap, target).Resolve (ec);
1113                         else if (target_type != target)
1114                                 source = Nullable.Wrap.Create (source, target);
1115
1116                         return source;
1117                 }
1118
1119                 /// <summary>
1120                 ///   Converts implicitly the resolved expression `expr' into the
1121                 ///   `target_type'.  It returns a new expression that can be used
1122                 ///   in a context that expects a `target_type'.
1123                 /// </summary>
1124                 static public Expression ImplicitConversion (ResolveContext ec, Expression expr,
1125                                                              TypeSpec target_type, Location loc)
1126                 {
1127                         Expression e;
1128
1129                         if (target_type == null)
1130                                 throw new Exception ("Target type is null");
1131
1132                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1133                         if (e != null)
1134                                 return e;
1135
1136                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1137                         if (e != null)
1138                                 return e;
1139
1140                         return null;
1141                 }
1142
1143
1144                 /// <summary>
1145                 ///   Attempts to apply the `Standard Implicit
1146                 ///   Conversion' rules to the expression `expr' into
1147                 ///   the `target_type'.  It returns a new expression
1148                 ///   that can be used in a context that expects a
1149                 ///   `target_type'.
1150                 ///
1151                 ///   This is different from `ImplicitConversion' in that the
1152                 ///   user defined implicit conversions are excluded.
1153                 /// </summary>
1154                 static public Expression ImplicitConversionStandard (ResolveContext ec, Expression expr,
1155                                                                      TypeSpec target_type, Location loc)
1156                 {
1157                         return ImplicitConversionStandard (ec, expr, target_type, loc, false);
1158                 }
1159
1160                 static Expression ImplicitConversionStandard (ResolveContext ec, Expression expr, TypeSpec target_type, Location loc, bool explicit_cast)
1161                 {
1162                         if (expr.eclass == ExprClass.MethodGroup){
1163                                 if (!TypeManager.IsDelegateType (target_type)){
1164                                         return null;
1165                                 }
1166
1167                                 //
1168                                 // Only allow anonymous method conversions on post ISO_1
1169                                 //
1170                                 if (RootContext.Version != LanguageVersion.ISO_1){
1171                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1172                                         if (mg != null)
1173                                                 return ImplicitDelegateCreation.Create (
1174                                                         ec, mg, target_type, loc);
1175                                 }
1176                         }
1177
1178                         TypeSpec expr_type = expr.Type;
1179                         Expression e;
1180
1181                         if (expr_type.Equals (target_type)) {
1182                                 if (expr_type != TypeManager.null_type && expr_type != InternalType.AnonymousMethod)
1183                                         return expr;
1184                                 return null;
1185                         }
1186
1187                         if (TypeSpecComparer.Variant.IsEqual (expr_type, target_type)) {
1188                                 return expr;
1189                         }
1190
1191                         if (TypeManager.IsNullableType (target_type))
1192                                 return ImplicitNulableConversion (ec, expr, target_type);
1193
1194                         //
1195                         // Attempt to do the implicit constant expression conversions
1196                         //
1197                         Constant c = expr as Constant;
1198                         if (c != null) {
1199                                 try {
1200                                         c = c.ConvertImplicitly (ec, target_type);
1201                                 } catch {
1202                                         Console.WriteLine ("Conversion error happened in line {0}", loc);
1203                                         throw;
1204                                 }
1205                                 if (c != null)
1206                                         return c;
1207                         }
1208
1209                         e = ImplicitNumericConversion (expr, expr_type, target_type);
1210                         if (e != null)
1211                                 return e;
1212
1213                         e = ImplicitReferenceConversion (expr, target_type, explicit_cast);
1214                         if (e != null)
1215                                 return e;
1216
1217                         if (expr is IntConstant && TypeManager.IsEnumType (target_type)){
1218                                 Constant i = (Constant) expr;
1219                                 //
1220                                 // LAMESPEC: Conversion from any 0 constant is allowed
1221                                 //
1222                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
1223                                 // to be converted to any enum-type and to any nullable-type whose underlying
1224                                 // type is an enum-type
1225                                 //
1226                                 if (i.IsDefaultValue)
1227                                         return new EnumConstant (i, target_type).Resolve (ec);
1228                         }
1229
1230                         if (ec.IsUnsafe) {
1231                                 if (expr_type.IsPointer){
1232                                         if (target_type == TypeManager.void_ptr_type)
1233                                                 return EmptyCast.Create (expr, target_type);
1234
1235                                         //
1236                                         // yep, comparing pointer types cant be done with
1237                                         // t1 == t2, we have to compare their element types.
1238                                         //
1239                                         if (target_type.IsPointer){
1240                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1241                                                         return expr;
1242
1243                                                 //return null;
1244                                         }
1245                                 }
1246
1247                                 if (expr_type == TypeManager.null_type && target_type.IsPointer)
1248                                         return EmptyCast.Create (new NullPointer (loc), target_type);
1249                         }
1250
1251                         if (expr_type == InternalType.AnonymousMethod){
1252                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1253                                 Expression am = ame.Compatible (ec, target_type);
1254                                 if (am != null)
1255                                         return am.Resolve (ec);
1256                         }
1257
1258                         if (expr_type == InternalType.Arglist && target_type == TypeManager.arg_iterator_type)
1259                                 return expr;
1260
1261                         return null;
1262                 }
1263
1264                 /// <summary>
1265                 ///   Attempts to implicitly convert `source' into `target_type', using
1266                 ///   ImplicitConversion.  If there is no implicit conversion, then
1267                 ///   an error is signaled
1268                 /// </summary>
1269                 static public Expression ImplicitConversionRequired (ResolveContext ec, Expression source,
1270                                                                      TypeSpec target_type, Location loc)
1271                 {
1272                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1273                         if (e != null)
1274                                 return e;
1275
1276                         if (source.Type == InternalType.Dynamic) {
1277                                 Arguments args = new Arguments (1);
1278                                 args.Add (new Argument (source));
1279                                 return new DynamicConversion (target_type, 0, args, loc).Resolve (ec);
1280                         }
1281
1282                         source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
1283                         return null;
1284                 }
1285
1286                 /// <summary>
1287                 ///   Performs the explicit numeric conversions
1288                 ///
1289                 /// There are a few conversions that are not part of the C# standard,
1290                 /// they were interim hacks in the C# compiler that were supposed to
1291                 /// become explicit operators in the UIntPtr class and IntPtr class,
1292                 /// but for historical reasons it did not happen, so the C# compiler
1293                 /// ended up with these special hacks.
1294                 ///
1295                 /// See bug 59800 for details.
1296                 ///
1297                 /// The conversion are:
1298                 ///   UIntPtr->SByte
1299                 ///   UIntPtr->Int16
1300                 ///   UIntPtr->Int32
1301                 ///   IntPtr->UInt64
1302                 ///   UInt64->IntPtr
1303                 ///   SByte->UIntPtr
1304                 ///   Int16->UIntPtr
1305                 ///
1306                 /// </summary>
1307                 public static Expression ExplicitNumericConversion (Expression expr, TypeSpec target_type)
1308                 {
1309                         TypeSpec expr_type = expr.Type;
1310                         TypeSpec real_target_type = target_type;
1311
1312                         if (expr_type == TypeManager.sbyte_type){
1313                                 //
1314                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1315                                 //
1316                                 if (real_target_type == TypeManager.byte_type)
1317                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1318                                 if (real_target_type == TypeManager.ushort_type)
1319                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1320                                 if (real_target_type == TypeManager.uint32_type)
1321                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1322                                 if (real_target_type == TypeManager.uint64_type)
1323                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1324                                 if (real_target_type == TypeManager.char_type)
1325                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1326
1327                                 // One of the built-in conversions that belonged in the class library
1328                                 if (real_target_type == TypeManager.uintptr_type){
1329                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
1330
1331                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1332                                 }
1333                         } else if (expr_type == TypeManager.byte_type){
1334                                 //
1335                                 // From byte to sbyte and char
1336                                 //
1337                                 if (real_target_type == TypeManager.sbyte_type)
1338                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1339                                 if (real_target_type == TypeManager.char_type)
1340                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1341                         } else if (expr_type == TypeManager.short_type){
1342                                 //
1343                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1344                                 //
1345                                 if (real_target_type == TypeManager.sbyte_type)
1346                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1347                                 if (real_target_type == TypeManager.byte_type)
1348                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1349                                 if (real_target_type == TypeManager.ushort_type)
1350                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1351                                 if (real_target_type == TypeManager.uint32_type)
1352                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1353                                 if (real_target_type == TypeManager.uint64_type)
1354                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1355                                 if (real_target_type == TypeManager.char_type)
1356                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1357
1358                                 // One of the built-in conversions that belonged in the class library
1359                                 if (real_target_type == TypeManager.uintptr_type){
1360                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1361
1362                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1363                                 }
1364                         } else if (expr_type == TypeManager.ushort_type){
1365                                 //
1366                                 // From ushort to sbyte, byte, short, char
1367                                 //
1368                                 if (real_target_type == TypeManager.sbyte_type)
1369                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1370                                 if (real_target_type == TypeManager.byte_type)
1371                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1372                                 if (real_target_type == TypeManager.short_type)
1373                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1374                                 if (real_target_type == TypeManager.char_type)
1375                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1376                         } else if (expr_type == TypeManager.int32_type){
1377                                 //
1378                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1379                                 //
1380                                 if (real_target_type == TypeManager.sbyte_type)
1381                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1382                                 if (real_target_type == TypeManager.byte_type)
1383                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1384                                 if (real_target_type == TypeManager.short_type)
1385                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1386                                 if (real_target_type == TypeManager.ushort_type)
1387                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1388                                 if (real_target_type == TypeManager.uint32_type)
1389                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1390                                 if (real_target_type == TypeManager.uint64_type)
1391                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1392                                 if (real_target_type == TypeManager.char_type)
1393                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1394
1395                                 // One of the built-in conversions that belonged in the class library
1396                                 if (real_target_type == TypeManager.uintptr_type){
1397                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1398
1399                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1400                                 }
1401                         } else if (expr_type == TypeManager.uint32_type){
1402                                 //
1403                                 // From uint to sbyte, byte, short, ushort, int, char
1404                                 //
1405                                 if (real_target_type == TypeManager.sbyte_type)
1406                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1407                                 if (real_target_type == TypeManager.byte_type)
1408                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1409                                 if (real_target_type == TypeManager.short_type)
1410                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1411                                 if (real_target_type == TypeManager.ushort_type)
1412                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1413                                 if (real_target_type == TypeManager.int32_type)
1414                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1415                                 if (real_target_type == TypeManager.char_type)
1416                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1417                         } else if (expr_type == TypeManager.int64_type){
1418                                 //
1419                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1420                                 //
1421                                 if (real_target_type == TypeManager.sbyte_type)
1422                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1423                                 if (real_target_type == TypeManager.byte_type)
1424                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1425                                 if (real_target_type == TypeManager.short_type)
1426                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1427                                 if (real_target_type == TypeManager.ushort_type)
1428                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1429                                 if (real_target_type == TypeManager.int32_type)
1430                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1431                                 if (real_target_type == TypeManager.uint32_type)
1432                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1433                                 if (real_target_type == TypeManager.uint64_type)
1434                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1435                                 if (real_target_type == TypeManager.char_type)
1436                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1437                         } else if (expr_type == TypeManager.uint64_type){
1438                                 //
1439                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1440                                 //
1441                                 if (real_target_type == TypeManager.sbyte_type)
1442                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1443                                 if (real_target_type == TypeManager.byte_type)
1444                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1445                                 if (real_target_type == TypeManager.short_type)
1446                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1447                                 if (real_target_type == TypeManager.ushort_type)
1448                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1449                                 if (real_target_type == TypeManager.int32_type)
1450                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1451                                 if (real_target_type == TypeManager.uint32_type)
1452                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1453                                 if (real_target_type == TypeManager.int64_type)
1454                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1455                                 if (real_target_type == TypeManager.char_type)
1456                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1457
1458                                 // One of the built-in conversions that belonged in the class library
1459                                 if (real_target_type == TypeManager.intptr_type){
1460                                         return new OperatorCast (EmptyCast.Create (expr, TypeManager.int64_type),
1461                                                                  TypeManager.intptr_type, true);
1462                                 }
1463                         } else if (expr_type == TypeManager.char_type){
1464                                 //
1465                                 // From char to sbyte, byte, short
1466                                 //
1467                                 if (real_target_type == TypeManager.sbyte_type)
1468                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1469                                 if (real_target_type == TypeManager.byte_type)
1470                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1471                                 if (real_target_type == TypeManager.short_type)
1472                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1473                         } else if (expr_type == TypeManager.float_type){
1474                                 //
1475                                 // From float to sbyte, byte, short,
1476                                 // ushort, int, uint, long, ulong, char
1477                                 // or decimal
1478                                 //
1479                                 if (real_target_type == TypeManager.sbyte_type)
1480                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1481                                 if (real_target_type == TypeManager.byte_type)
1482                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1483                                 if (real_target_type == TypeManager.short_type)
1484                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1485                                 if (real_target_type == TypeManager.ushort_type)
1486                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1487                                 if (real_target_type == TypeManager.int32_type)
1488                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1489                                 if (real_target_type == TypeManager.uint32_type)
1490                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1491                                 if (real_target_type == TypeManager.int64_type)
1492                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1493                                 if (real_target_type == TypeManager.uint64_type)
1494                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1495                                 if (real_target_type == TypeManager.char_type)
1496                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1497                                 if (real_target_type == TypeManager.decimal_type)
1498                                         return new CastToDecimal (expr, true);
1499                         } else if (expr_type == TypeManager.double_type){
1500                                 //
1501                                 // From double to sbyte, byte, short,
1502                                 // ushort, int, uint, long, ulong,
1503                                 // char, float or decimal
1504                                 //
1505                                 if (real_target_type == TypeManager.sbyte_type)
1506                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1507                                 if (real_target_type == TypeManager.byte_type)
1508                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1509                                 if (real_target_type == TypeManager.short_type)
1510                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1511                                 if (real_target_type == TypeManager.ushort_type)
1512                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1513                                 if (real_target_type == TypeManager.int32_type)
1514                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1515                                 if (real_target_type == TypeManager.uint32_type)
1516                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1517                                 if (real_target_type == TypeManager.int64_type)
1518                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1519                                 if (real_target_type == TypeManager.uint64_type)
1520                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1521                                 if (real_target_type == TypeManager.char_type)
1522                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1523                                 if (real_target_type == TypeManager.float_type)
1524                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1525                                 if (real_target_type == TypeManager.decimal_type)
1526                                         return new CastToDecimal (expr, true);
1527                         } else if (expr_type == TypeManager.uintptr_type){
1528                                 //
1529                                 // Various built-in conversions that belonged in the class library
1530                                 //
1531                                 // from uintptr to sbyte, short, int32
1532                                 //
1533                                 if (real_target_type == TypeManager.sbyte_type){
1534                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1535                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
1536                                 }
1537                                 if (real_target_type == TypeManager.short_type){
1538                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1539                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
1540                                 }
1541                                 if (real_target_type == TypeManager.int32_type){
1542                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.uint32_type, true),
1543                                                               TypeManager.int32_type);
1544                                 }
1545                         } else if (expr_type == TypeManager.intptr_type){
1546                                 if (real_target_type == TypeManager.uint64_type){
1547                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.int64_type, true),
1548                                                               TypeManager.uint64_type);
1549                                 }
1550                         } else if (expr_type == TypeManager.decimal_type) {
1551                                 return new CastFromDecimal (expr, target_type).Resolve ();
1552                         }
1553                         return null;
1554                 }
1555
1556                 /// <summary>
1557                 ///  Returns whether an explicit reference conversion can be performed
1558                 ///  from source_type to target_type
1559                 /// </summary>
1560                 public static bool ExplicitReferenceConversionExists (TypeSpec source_type, TypeSpec target_type)
1561                 {
1562                         Expression e = ExplicitReferenceConversion (null, source_type, target_type);
1563                         if (e == null)
1564                                 return false;
1565
1566                         if (e == EmptyExpression.Null)
1567                                 return true;
1568
1569                         throw new InternalErrorException ("Invalid probing conversion result");
1570                 }
1571
1572                 /// <summary>
1573                 ///   Implements Explicit Reference conversions
1574                 /// </summary>
1575                 static Expression ExplicitReferenceConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
1576                 {
1577                         //
1578                         // From object to a generic parameter
1579                         //
1580                         if (source_type == TypeManager.object_type && TypeManager.IsGenericParameter (target_type))
1581                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1582
1583                         //
1584                         // Explicit type parameter conversion.
1585                         //
1586                         if (TypeManager.IsGenericParameter (source_type))
1587                                 return ExplicitTypeParameterConversion (source, source_type, target_type);
1588
1589                         bool target_is_value_type = TypeManager.IsStruct (target_type) || TypeManager.IsEnumType (target_type);
1590
1591                         //
1592                         // Unboxing conversion from System.ValueType to any non-nullable-value-type
1593                         //
1594                         if (source_type == TypeManager.value_type && target_is_value_type)
1595                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1596
1597                         //
1598                         // From object to any reference type or value type (unboxing)
1599                         //
1600                         if (source_type == TypeManager.object_type)
1601                                 return
1602                                         source == null ? EmptyExpression.Null :
1603                                         target_is_value_type ? new UnboxCast (source, target_type) :
1604                                         source is Constant ? (Expression) new EmptyConstantCast ((Constant) source, target_type) :
1605                                         new ClassCast (source, target_type);
1606
1607                         //
1608                         // From any class S to any class-type T, provided S is a base class of T
1609                         //
1610                         if (TypeManager.IsSubclassOf (target_type, source_type))
1611                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1612
1613                         //
1614                         // From any interface-type S to to any class type T, provided T is not
1615                         // sealed, or provided T implements S.
1616                         //
1617                         if (source_type.IsInterface) {
1618                                 if (!target_type.IsSealed || target_type.ImplementsInterface (source_type)) {
1619                                         if (target_type.IsClass)
1620                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1621
1622                                         //
1623                                         // Unboxing conversion from any interface-type to any non-nullable-value-type that
1624                                         // implements the interface-type
1625                                         //
1626                                         return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1627                                 }
1628
1629                                 //
1630                                 // From System.Collections.Generic.IList<T> and its base interfaces to a one-dimensional
1631                                 // array type S[], provided there is an implicit or explicit reference conversion from S to T.
1632                                 //
1633                                 var target_array = target_type as ArrayContainer;
1634                                 if (target_array != null && IList_To_Array (source_type, target_array))
1635                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1636
1637                                 return null;
1638                         }
1639
1640                         var source_array = source_type as ArrayContainer;
1641                         if (source_array != null) {
1642                                 var target_array = target_type as ArrayContainer;
1643                                 if (target_array != null) {
1644                                         //
1645                                         // From System.Array to any array-type
1646                                         //
1647                                         if (source_type == TypeManager.array_type)
1648                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1649
1650                                         //
1651                                         // From an array type S with an element type Se to an array type T with an
1652                                         // element type Te provided all the following are true:
1653                                         //     * S and T differe only in element type, in other words, S and T
1654                                         //       have the same number of dimensions.
1655                                         //     * Both Se and Te are reference types
1656                                         //     * An explicit reference conversions exist from Se to Te
1657                                         //
1658                                         if (source_array.Rank == target_array.Rank) {
1659
1660                                                 source_type = source_array.Element;
1661                                                 if (!TypeManager.IsReferenceType (source_type))
1662                                                         return null;
1663
1664                                                 var target_element = target_array.Element;
1665                                                 if (!TypeManager.IsReferenceType (target_element))
1666                                                         return null;
1667
1668                                                 if (ExplicitReferenceConversionExists (source_type, target_element))
1669                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1670
1671                                                 return null;
1672                                         }
1673                                 }
1674
1675                                 //
1676                                 // From a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its base interfaces,
1677                                 // provided that there is an explicit reference conversion from S to T
1678                                 //
1679                                 if (ArrayToIList (source_array, target_type, true))
1680                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1681
1682                                 return null;
1683                         }
1684
1685                         //
1686                         // From any class type S to any interface T, provides S is not sealed
1687                         // and provided S does not implement T.
1688                         //
1689                         if (target_type.IsInterface && !source_type.IsSealed && !source_type.ImplementsInterface (target_type)) {
1690                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1691                         }
1692
1693                         //
1694                         // From System delegate to any delegate-type
1695                         //
1696                         if (source_type == TypeManager.delegate_type && TypeManager.IsDelegateType (target_type))
1697                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1698
1699                         return null;
1700                 }
1701
1702                 /// <summary>
1703                 ///   Performs an explicit conversion of the expression `expr' whose
1704                 ///   type is expr.Type to `target_type'.
1705                 /// </summary>
1706                 static public Expression ExplicitConversionCore (ResolveContext ec, Expression expr,
1707                                                                  TypeSpec target_type, Location loc)
1708                 {
1709                         TypeSpec expr_type = expr.Type;
1710
1711                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1712                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc, true);
1713                         if (ne != null)
1714                                 return ne;
1715
1716                         if (TypeManager.IsEnumType (expr_type)) {
1717                                 TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
1718                                 Expression underlying = EmptyCast.Create (expr, EnumSpec.GetUnderlyingType (expr_type));
1719                                 if (underlying.Type == real_target)
1720                                         ne = underlying;
1721
1722                                 if (ne == null)
1723                                         ne = ImplicitNumericConversion (underlying, real_target);
1724
1725                                 if (ne == null)
1726                                         ne = ExplicitNumericConversion (underlying, real_target);
1727
1728                                 //
1729                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1730                                 //
1731                                 if (ne == null && (real_target == TypeManager.intptr_type || real_target == TypeManager.uintptr_type))
1732                                         ne = ExplicitUserConversion (ec, underlying, real_target, loc);
1733
1734                                 return ne != null ? EmptyCast.Create (ne, target_type) : null;
1735                         }
1736
1737                         if (TypeManager.IsEnumType (target_type)) {
1738                                 //
1739                                 // System.Enum can be unboxed to any enum-type
1740                                 //
1741                                 if (expr_type == TypeManager.enum_type)
1742                                         return new UnboxCast (expr, target_type);
1743
1744                                 TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
1745
1746                                 if (expr_type == real_target)
1747                                         return EmptyCast.Create (expr, target_type);
1748
1749                                 ne = ImplicitNumericConversion (expr, real_target);
1750                                 if (ne != null)
1751                                         return EmptyCast.Create (ne, target_type);
1752
1753                                 ne = ExplicitNumericConversion (expr, real_target);
1754                                 if (ne != null)
1755                                         return EmptyCast.Create (ne, target_type);
1756
1757                                 //
1758                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1759                                 //
1760                                 if (expr_type == TypeManager.intptr_type || expr_type == TypeManager.uintptr_type) {
1761                                         ne = ExplicitUserConversion (ec, expr, real_target, loc);
1762                                         if (ne != null)
1763                                                 return ExplicitConversionCore (ec, ne, target_type, loc);
1764                                 }
1765                         } else {
1766                                 ne = ExplicitNumericConversion (expr, target_type);
1767                                 if (ne != null)
1768                                         return ne;
1769                         }
1770
1771                         //
1772                         // Skip the ExplicitReferenceConversion because we can not convert
1773                         // from Null to a ValueType, and ExplicitReference wont check against
1774                         // null literal explicitly
1775                         //
1776                         if (expr_type != TypeManager.null_type){
1777                                 ne = ExplicitReferenceConversion (expr, expr_type, target_type);
1778                                 if (ne != null)
1779                                         return ne;
1780                         }
1781
1782                         if (ec.IsUnsafe){
1783                                 ne = ExplicitUnsafe (expr, target_type);
1784                                 if (ne != null)
1785                                         return ne;
1786                         }
1787
1788                         return null;
1789                 }
1790
1791                 public static Expression ExplicitUnsafe (Expression expr, TypeSpec target_type)
1792                 {
1793                         TypeSpec expr_type = expr.Type;
1794
1795                         if (target_type.IsPointer){
1796                                 if (expr_type.IsPointer)
1797                                         return EmptyCast.Create (expr, target_type);
1798
1799                                 if (expr_type == TypeManager.sbyte_type ||
1800                                         expr_type == TypeManager.short_type ||
1801                                         expr_type == TypeManager.int32_type)
1802                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1803
1804                                 if (expr_type == TypeManager.ushort_type ||
1805                                         expr_type == TypeManager.uint32_type ||
1806                                         expr_type == TypeManager.byte_type)
1807                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1808
1809                                 if (expr_type == TypeManager.int64_type)
1810                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I);
1811
1812                                 if (expr_type == TypeManager.uint64_type)
1813                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I);
1814                         }
1815
1816                         if (expr_type.IsPointer){
1817                                 if (target_type == TypeManager.sbyte_type)
1818                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1819                                 if (target_type == TypeManager.byte_type)
1820                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1821                                 if (target_type == TypeManager.short_type)
1822                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1823                                 if (target_type == TypeManager.ushort_type)
1824                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1825                                 if (target_type == TypeManager.int32_type)
1826                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1827                                 if (target_type == TypeManager.uint32_type)
1828                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1829                                 if (target_type == TypeManager.int64_type)
1830                                         return new ConvCast (expr, target_type, ConvCast.Mode.I_I8);
1831                                 if (target_type == TypeManager.uint64_type)
1832                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1833                         }
1834                         return null;
1835                 }
1836
1837                 /// <summary>
1838                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1839                 /// </summary>
1840                 static public Expression ExplicitConversionStandard (ResolveContext ec, Expression expr,
1841                                                                      TypeSpec target_type, Location l)
1842                 {
1843                         int errors = ec.Report.Errors;
1844                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1845                         if (ec.Report.Errors > errors)
1846                                 return null;
1847
1848                         if (ne != null)
1849                                 return ne;
1850
1851                         ne = ExplicitNumericConversion (expr, target_type);
1852                         if (ne != null)
1853                                 return ne;
1854
1855                         ne = ExplicitReferenceConversion (expr, expr.Type, target_type);
1856                         if (ne != null)
1857                                 return ne;
1858
1859                         if (ec.IsUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
1860                                 return EmptyCast.Create (expr, target_type);
1861
1862                         expr.Error_ValueCannotBeConverted (ec, l, target_type, true);
1863                         return null;
1864                 }
1865
1866                 /// <summary>
1867                 ///   Performs an explicit conversion of the expression `expr' whose
1868                 ///   type is expr.Type to `target_type'.
1869                 /// </summary>
1870                 static public Expression ExplicitConversion (ResolveContext ec, Expression expr,
1871                         TypeSpec target_type, Location loc)
1872                 {
1873                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
1874                         if (e != null) {
1875                                 //
1876                                 // Don't eliminate explicit precission casts
1877                                 //
1878                                 if (e == expr) {
1879                                         if (target_type == TypeManager.float_type)
1880                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
1881
1882                                         if (target_type == TypeManager.double_type)
1883                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
1884                                 }
1885
1886                                 return e;
1887                         }
1888
1889                         TypeSpec expr_type = expr.Type;
1890                         if (TypeManager.IsNullableType (target_type)) {
1891                                 if (TypeManager.IsNullableType (expr_type)) {
1892                                         TypeSpec target = Nullable.NullableInfo.GetUnderlyingType (target_type);
1893                                         Expression unwrap = Nullable.Unwrap.Create (expr);
1894                                         e = ExplicitConversion (ec, unwrap, target, expr.Location);
1895                                         if (e == null)
1896                                                 return null;
1897
1898                                         return new Nullable.Lifted (e, unwrap, target_type).Resolve (ec);
1899                                 } else if (expr_type == TypeManager.object_type) {
1900                                         return new UnboxCast (expr, target_type);
1901                                 } else {
1902                                         TypeSpec target = TypeManager.GetTypeArguments (target_type) [0];
1903
1904                                         e = ExplicitConversionCore (ec, expr, target, loc);
1905                                         if (e != null)
1906                                                 return Nullable.Wrap.Create (e, target_type);
1907                                 }
1908                         } else if (TypeManager.IsNullableType (expr_type)) {
1909                                 e = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
1910                                 if (e != null)
1911                                         return e;
1912
1913                                 e = Nullable.Unwrap.Create (expr, false);
1914                                 e = ExplicitConversionCore (ec, e, target_type, loc);
1915                                 if (e != null)
1916                                         return EmptyCast.Create (e, target_type);
1917                         }
1918
1919                         e = ExplicitUserConversion (ec, expr, target_type, loc);
1920                         if (e != null)
1921                                 return e;
1922
1923                         expr.Error_ValueCannotBeConverted (ec, loc, target_type, true);
1924                         return null;
1925                 }
1926         }
1927 }