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 namespace Mono.CSharp {
  14         using System;
  15         using System.Collections;
  16         using System.Diagnostics;
  17         using System.Reflection;
  18         using System.Reflection.Emit;
  19
  20         //
  21         // A container class for all the conversion operations
  22         //
  23         static class Convert {
  24 #if GMCS_SOURCE
  25                 static Type TypeParam_EffectiveBaseType (GenericConstraints gc)
  26                 {
  27                         ArrayList list = new ArrayList ();
  28                         list.Add (gc.EffectiveBaseClass);
  29                         foreach (Type t in gc.InterfaceConstraints) {
  30                                 if (!TypeManager.IsGenericParameter (t))
  31                                         continue;
  32
  33                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  34                                 if (new_gc != null)
  35                                         list.Add (TypeParam_EffectiveBaseType (new_gc));
  36                         }
  37                         return FindMostEncompassedType (list);
  38                 }
  39 #endif
  40
  41                 //
  42                 // From a one-dimensional array-type S[] to System.Collections.IList<T> and base
  43                 // interfaces of this interface, provided there is an implicit reference conversion
  44                 // from S to T.
  45                 //
  46                 static bool Array_To_IList (Type array, Type list, bool isExplicit)
  47                 {
  48 #if GMCS_SOURCE
  49                         if ((array.GetArrayRank () != 1) || !list.IsGenericType)
  50                                 return false;
  51
  52                         Type gt = list.GetGenericTypeDefinition ();
  53                         if ((gt != TypeManager.generic_ilist_type) &&
  54                             (gt != TypeManager.generic_icollection_type) &&
  55                             (gt != TypeManager.generic_ienumerable_type))
  56                                 return false;
  57
  58                         Type element_type = TypeManager.GetElementType (array);
  59                         Type arg_type = TypeManager.GetTypeArguments (list) [0];
  60
  61                         if (element_type == arg_type)
  62                                 return true;
  63
  64                         if (isExplicit)
  65                                 return ExplicitReferenceConversionExists (element_type, arg_type);
  66
  67                         if (MyEmptyExpr == null)
  68                                 MyEmptyExpr = new EmptyExpression ();
  69                         MyEmptyExpr.SetType (TypeManager.GetElementType (array));
  70
  71                         return ImplicitReferenceConversionExists (MyEmptyExpr, arg_type);
  72 #else
  73                         return false;
  74 #endif
  75                 }
  76
  77                 static bool IList_To_Array(Type list, Type array)
  78                 {
  79 # if GMCS_SOURCE
  80                         if (!list.IsGenericType || !array.IsArray || array.GetArrayRank() != 1)
  81                                 return false;
  82
  83                         Type gt = list.GetGenericTypeDefinition();
  84                         if (gt != TypeManager.generic_ilist_type &&
  85                                 gt != TypeManager.generic_icollection_type &&
  86                                 gt != TypeManager.generic_ienumerable_type)
  87                                 return false;
  88
  89                         Type arg_type = TypeManager.GetTypeArguments(list)[0];
  90                         Type element_type = TypeManager.GetElementType(array);
  91
  92                         if (element_type == arg_type)
  93                                 return true;
  94
  95                         if (MyEmptyExpr == null)
  96                                 MyEmptyExpr = new EmptyExpression();
  97                         MyEmptyExpr.SetType(element_type);
  98                         return ImplicitReferenceConversionExists(MyEmptyExpr, arg_type) || ExplicitReferenceConversionExists(element_type, arg_type);
  99 #else
 100                         return false;
 101 #endif
 102                 }
 103
 104                 static Expression ImplicitTypeParameterConversion (Expression expr,
 105                                                                    Type target_type)
 106                 {
 107 #if GMCS_SOURCE
 108                         Type expr_type = expr.Type;
 109
 110                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
 111
 112                         if (gc == null) {
 113                                 if (target_type == TypeManager.object_type)
 114                                         return new BoxedCast (expr, target_type);
 115
 116                                 return null;
 117                         }
 118
 119                         // We're converting from a type parameter which is known to be a reference type.
 120                         Type base_type = TypeParam_EffectiveBaseType (gc);
 121
 122                         if (TypeManager.IsSubclassOf (base_type, target_type))
 123                                 return new ClassCast (expr, target_type);
 124
 125                         if (target_type.IsInterface) {
 126                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 127                                         return new ClassCast (expr, target_type);
 128
 129                                 foreach (Type t in gc.InterfaceConstraints) {
 130                                         if (TypeManager.IsSubclassOf (t, target_type))
 131                                                 return new ClassCast (expr, target_type);
 132                                         if (TypeManager.ImplementsInterface (t, target_type))
 133                                                 return new ClassCast (expr, target_type);
 134                                 }
 135                         }
 136
 137                         foreach (Type t in gc.InterfaceConstraints) {
 138                                 if (!TypeManager.IsGenericParameter (t))
 139                                         continue;
 140                                 if (TypeManager.IsSubclassOf (t, target_type))
 141                                         return new ClassCast (expr, target_type);
 142                                 if (TypeManager.ImplementsInterface (t, target_type))
 143                                         return new ClassCast (expr, target_type);
 144                         }
 145 #endif
 146                         return null;
 147                 }
 148
 149                 static bool ImplicitTypeParameterBoxingConversion (Type expr_type, Type target_type,
 150                                                                    out bool use_class_cast)
 151                 {
 152 #if GMCS_SOURCE
 153                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
 154
 155                         if (gc == null) {
 156                                 use_class_cast = false;
 157                                 return target_type == TypeManager.object_type;
 158                         }
 159
 160                         use_class_cast = true;
 161
 162                         if (!gc.HasReferenceTypeConstraint)
 163                                 return false;
 164
 165                         // We're converting from a type parameter which is known to be a reference type.
 166                         Type base_type = TypeParam_EffectiveBaseType (gc);
 167
 168                         if (TypeManager.IsSubclassOf (base_type, target_type))
 169                                 return true;
 170
 171                         if (target_type.IsInterface) {
 172                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 173                                         return true;
 174
 175                                 foreach (Type t in gc.InterfaceConstraints) {
 176                                         if (TypeManager.IsSubclassOf (t, target_type))
 177                                                 return true;
 178                                         if (TypeManager.ImplementsInterface (t, target_type))
 179                                                 return true;
 180                                 }
 181                         }
 182
 183                         foreach (Type t in gc.InterfaceConstraints) {
 184                                 if (!TypeManager.IsGenericParameter (t))
 185                                         continue;
 186                                 if (TypeManager.IsSubclassOf (t, target_type))
 187                                         return true;
 188                                 if (TypeManager.ImplementsInterface (t, target_type))
 189                                         return true;
 190                         }
 191 #endif
 192
 193                         use_class_cast = false;
 194                         return false;
 195                 }
 196
 197                 static Expression ExplicitTypeParameterConversion (Expression source, Type source_type, Type target_type)
 198                 {
 199 #if GMCS_SOURCE
 200                         if (TypeManager.IsGenericParameter (target_type)) {
 201                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 202                                 if (gc == null)
 203                                         return null;
 204
 205                                 foreach (Type iface in gc.InterfaceConstraints) {
 206                                         if (!TypeManager.IsGenericParameter (iface))
 207                                                 continue;
 208
 209                                         if (TypeManager.IsSubclassOf (source_type, iface))
 210                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
 211                                 }
 212                         }
 213
 214                         if (target_type.IsInterface)
 215                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
 216 #endif
 217                         return null;
 218                 }
 219
 220                 static EmptyExpression MyEmptyExpr;
 221                 static Expression ImplicitReferenceConversion (Expression expr, Type target_type, bool explicit_cast)
 222                 {
 223                         Type expr_type = expr.Type;
 224
 225                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 226                                 // if we are a method group, emit a warning
 227
 228                                 expr.Emit (null);
 229                         }
 230
 231                         if (expr_type == TypeManager.void_type)
 232                                 return null;
 233
 234                         if (TypeManager.IsGenericParameter (expr_type))
 235                                 return ImplicitTypeParameterConversion (expr, target_type);
 236
 237                         //
 238                         // from the null type to any reference-type.
 239                         //
 240                         NullLiteral nl = expr as NullLiteral;
 241                         if (nl != null) {
 242                                 return nl.ConvertImplicitly(target_type);
 243                         }
 244
 245                         if (ImplicitReferenceConversionExists (expr, target_type)) {
 246                                 //
 247                                 // Reduce implicit reference conversion to object
 248                                 //
 249                                 if (!explicit_cast && target_type == TypeManager.object_type)
 250                                         return expr;
 251
 252                                 return EmptyCast.Create (expr, target_type);
 253                         }
 254
 255                         bool use_class_cast;
 256                         if (ImplicitBoxingConversionExists (expr, target_type, out use_class_cast)) {
 257                                 if (use_class_cast)
 258                                         return new ClassCast (expr, target_type);
 259                                 else
 260                                         return new BoxedCast (expr, target_type);
 261                         }
 262
 263                         return null;
 264                 }
 265
 266                 //
 267                 // 6.1.6 Implicit reference conversions
 268                 //
 269                 public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
 270                 {
 271                         if (target_type.IsValueType)
 272                                 return false;
 273
 274                         Type expr_type = expr.Type;
 275
 276                         // from the null type to any reference-type.
 277                         if (expr_type == TypeManager.null_type)
 278                                 return target_type != TypeManager.anonymous_method_type;
 279
 280                         if (TypeManager.IsGenericParameter (expr_type))
 281                                 return ImplicitTypeParameterConversion (expr, target_type) != null;
 282
 283                         //
 284                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 285                         // is an abstract class, and not really a value type, so we apply the same rules.
 286                         //
 287                         if (target_type == TypeManager.object_type) {
 288                                 //
 289                                 // A pointer type cannot be converted to object
 290                                 //
 291                                 if (expr_type.IsPointer)
 292                                         return false;
 293
 294                                 if (TypeManager.IsValueType (expr_type))
 295                                         return false;
 296                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 297                                         return expr_type != TypeManager.anonymous_method_type;
 298                                 }
 299
 300                                 return false;
 301                         } else if (target_type == TypeManager.value_type) {
 302                                 return expr_type == TypeManager.enum_type;
 303                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 304                                 //
 305                                 // Special case: enumeration to System.Enum.
 306                                 // System.Enum is not a value type, it is a class, so we need
 307                                 // a boxing conversion
 308                                 //
 309                                 if (target_type == TypeManager.enum_type || TypeManager.IsGenericParameter (expr_type))
 310                                         return false;
 311
 312                                 return true;
 313                         }
 314
 315                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 316                         // with the small distinction that we only probe there
 317                         //
 318                         // Always ensure that the code here and there is in sync
 319
 320                         // from any class-type S to any interface-type T.
 321                         if (target_type.IsInterface) {
 322                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 323                                         return !TypeManager.IsGenericParameter (expr_type) &&
 324                                                 !TypeManager.IsValueType (expr_type);
 325                                 }
 326                         }
 327
 328                         if (expr_type.IsArray) {
 329                                 // from an array-type S to an array-type of type T
 330                                 if (target_type.IsArray && expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 331
 332                                         //
 333                                         // Both SE and TE are reference-types
 334                                         //
 335                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 336                                         if (!TypeManager.IsReferenceType (expr_element_type))
 337                                                 return false;
 338
 339                                         Type target_element_type = TypeManager.GetElementType (target_type);
 340                                         if (!TypeManager.IsReferenceType (target_element_type))
 341                                                 return false;
 342
 343                                         if (MyEmptyExpr == null)
 344                                                 MyEmptyExpr = new EmptyExpression ();
 345
 346                                         MyEmptyExpr.SetType (expr_element_type);
 347
 348                                         return ImplicitStandardConversionExists (MyEmptyExpr, target_element_type);
 349                                 }
 350
 351                                 // from an array-type to System.Array
 352                                 if (target_type == TypeManager.array_type)
 353                                         return true;
 354
 355                                 // from an array-type of type T to IList<T>
 356                                 if (Array_To_IList (expr_type, target_type, false))
 357                                         return true;
 358
 359                                 return false;
 360                         }
 361
 362                         // from any interface type S to interface-type T.
 363                         if (expr_type.IsInterface && target_type.IsInterface) {
 364                                 return TypeManager.ImplementsInterface (expr_type, target_type);
 365                         }
 366
 367                         // from any delegate type to System.Delegate
 368                         if (target_type == TypeManager.delegate_type &&
 369                                 (expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)))
 370                                 return true;
 371
 372                         // from a generic type definition to a generic instance.
 373                         if (TypeManager.IsEqual (expr_type, target_type))
 374                                 return true;
 375
 376                         return false;
 377                 }
 378
 379                 public static bool ImplicitBoxingConversionExists (Expression expr, Type target_type,
 380                                                                    out bool use_class_cast)
 381                 {
 382                         Type expr_type = expr.Type;
 383                         use_class_cast = false;
 384
 385                         //
 386                         // From any value-type to the type object.
 387                         //
 388                         if (target_type == TypeManager.object_type) {
 389                                 //
 390                                 // A pointer type cannot be converted to object
 391                                 //
 392                                 if (expr_type.IsPointer)
 393                                         return false;
 394
 395                                 return TypeManager.IsValueType (expr_type);
 396                         }
 397
 398                         //
 399                         // From any value-type to the type System.ValueType.
 400                         //
 401                         if (target_type == TypeManager.value_type)
 402                                 return TypeManager.IsValueType (expr_type);
 403
 404                         if (target_type == TypeManager.enum_type) {
 405                                 //
 406                                 // From any enum-type to the type System.Enum.
 407                                 //
 408                                 if (expr_type.IsEnum)
 409                                         return true;
 410                                 //
 411                                 // From any nullable-type with an underlying enum-type to the type System.Enum
 412                                 //
 413                                 if (TypeManager.IsNullableType (expr_type))
 414                                         return TypeManager.GetTypeArguments (expr_type) [0].IsEnum;
 415                         }
 416
 417                         if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 418                                 //
 419                                 // Don't box same type arguments
 420                                 //
 421                                 if (TypeManager.IsGenericParameter (expr_type) && expr_type != target_type)
 422                                         return true;
 423
 424                                 return false;
 425                         }
 426
 427                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 428                         // with the small distinction that we only probe there
 429                         //
 430                         // Always ensure that the code here and there is in sync
 431
 432                         // from any class-type S to any interface-type T.
 433                         if (target_type.IsInterface) {
 434                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 435                                         return TypeManager.IsGenericParameter (expr_type) ||
 436                                                 TypeManager.IsValueType (expr_type);
 437                         }
 438
 439                         if (TypeManager.IsGenericParameter (expr_type))
 440                                 return ImplicitTypeParameterBoxingConversion (
 441                                         expr_type, target_type, out use_class_cast);
 442
 443                         return false;
 444                 }
 445
 446                 static Expression ImplicitNulableConversion (EmitContext ec, Expression expr, Type target_type)
 447                 {
 448                         Type expr_type = expr.Type;
 449
 450                         //
 451                         // From null to any nullable type
 452                         //
 453                         if (expr_type == TypeManager.null_type)
 454                                 return ec == null ? EmptyExpression.Null : Nullable.LiftedNull.Create (target_type, expr.Location);
 455
 456                         Type target = TypeManager.GetTypeArguments (target_type)[0];
 457                         Expression e;
 458
 459                         // S? -> T?
 460                         if (TypeManager.IsNullableType (expr_type)) {
 461                                 Type etype = TypeManager.GetTypeArguments (expr_type)[0];
 462
 463                                 if (ec == null)
 464                                         return ImplicitConversionExists (ec, new EmptyExpression (etype), target) ? EmptyExpression.Null : null;
 465
 466                                 Expression unwrap = Nullable.Unwrap.Create (expr);
 467                                 e = ImplicitConversion (ec, unwrap, target, expr.Location);
 468                                 if (e == null)
 469                                         return null;
 470
 471                                 return new Nullable.Lifted (e, unwrap, target_type).Resolve (ec);
 472                         }
 473
 474                         // S -> T?
 475                         if (ec == null)
 476                                 return ImplicitConversionExists (ec, expr, target) ? EmptyExpression.Null : null;
 477
 478                         e = ImplicitConversion (ec, expr, target, expr.Location);
 479                         if (e != null)
 480                                 return Nullable.Wrap.Create (e, target_type);
 481
 482                         return null;
 483                 }
 484
 485                 /// <summary>
 486                 ///   Implicit Numeric Conversions.
 487                 ///
 488                 ///   expr is the expression to convert, returns a new expression of type
 489                 ///   target_type or null if an implicit conversion is not possible.
 490                 /// </summary>
 491                 public static Expression ImplicitNumericConversion (Expression expr, Type target_type)
 492                 {
 493                         return ImplicitNumericConversion (expr, expr.Type, target_type);
 494                 }
 495
 496                 static Expression ImplicitNumericConversion (Expression expr, Type expr_type, Type target_type)
 497                 {
 498                         if (expr_type == TypeManager.sbyte_type){
 499                                 //
 500                                 // From sbyte to short, int, long, float, double, decimal
 501                                 //
 502                                 if (target_type == TypeManager.int32_type)
 503                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 504                                 if (target_type == TypeManager.int64_type)
 505                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 506                                 if (target_type == TypeManager.double_type)
 507                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 508                                 if (target_type == TypeManager.float_type)
 509                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 510                                 if (target_type == TypeManager.short_type)
 511                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 512                                 if (target_type == TypeManager.decimal_type)
 513                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 514                         } else if (expr_type == TypeManager.byte_type){
 515                                 //
 516                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 517                                 //
 518                                 if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type ||
 519                                     target_type == TypeManager.short_type || target_type == TypeManager.ushort_type)
 520                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 521
 522                                 if (target_type == TypeManager.uint64_type)
 523                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 524                                 if (target_type == TypeManager.int64_type)
 525                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 526                                 if (target_type == TypeManager.float_type)
 527                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 528                                 if (target_type == TypeManager.double_type)
 529                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 530                                 if (target_type == TypeManager.decimal_type)
 531                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 532
 533                         } else if (expr_type == TypeManager.short_type){
 534                                 //
 535                                 // From short to int, long, float, double, decimal
 536                                 //
 537                                 if (target_type == TypeManager.int32_type)
 538                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 539                                 if (target_type == TypeManager.int64_type)
 540                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 541                                 if (target_type == TypeManager.double_type)
 542                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 543                                 if (target_type == TypeManager.float_type)
 544                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 545                                 if (target_type == TypeManager.decimal_type)
 546                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 547
 548                         } else if (expr_type == TypeManager.ushort_type){
 549                                 //
 550                                 // From ushort to int, uint, long, ulong, float, double, decimal
 551                                 //
 552                                 if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type)
 553                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 554
 555                                 if (target_type == TypeManager.uint64_type)
 556                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 557                                 if (target_type == TypeManager.int64_type)
 558                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 559                                 if (target_type == TypeManager.double_type)
 560                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 561                                 if (target_type == TypeManager.float_type)
 562                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 563                                 if (target_type == TypeManager.decimal_type)
 564                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 565                         } else if (expr_type == TypeManager.int32_type){
 566                                 //
 567                                 // From int to long, float, double, decimal
 568                                 //
 569                                 if (target_type == TypeManager.int64_type)
 570                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 571                                 if (target_type == TypeManager.double_type)
 572                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 573                                 if (target_type == TypeManager.float_type)
 574                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 575                                 if (target_type == TypeManager.decimal_type)
 576                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 577                         } else if (expr_type == TypeManager.uint32_type){
 578                                 //
 579                                 // From uint to long, ulong, float, double, decimal
 580                                 //
 581                                 if (target_type == TypeManager.int64_type)
 582                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 583                                 if (target_type == TypeManager.uint64_type)
 584                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 585                                 if (target_type == TypeManager.double_type)
 586                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
 587                                 if (target_type == TypeManager.float_type)
 588                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
 589                                 if (target_type == TypeManager.decimal_type)
 590                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 591                         } else if (expr_type == TypeManager.int64_type){
 592                                 //
 593                                 // From long/ulong to float, double
 594                                 //
 595                                 if (target_type == TypeManager.double_type)
 596                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 597                                 if (target_type == TypeManager.float_type)
 598                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 599                                 if (target_type == TypeManager.decimal_type)
 600                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 601                         } else if (expr_type == TypeManager.uint64_type){
 602                                 //
 603                                 // From ulong to float, double
 604                                 //
 605                                 if (target_type == TypeManager.double_type)
 606                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
 607                                 if (target_type == TypeManager.float_type)
 608                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
 609                                 if (target_type == TypeManager.decimal_type)
 610                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 611                         } else if (expr_type == TypeManager.char_type){
 612                                 //
 613                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 614                                 //
 615                                 if ((target_type == TypeManager.ushort_type) ||
 616                                     (target_type == TypeManager.int32_type) ||
 617                                     (target_type == TypeManager.uint32_type))
 618                                         return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
 619                                 if (target_type == TypeManager.uint64_type)
 620                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 621                                 if (target_type == TypeManager.int64_type)
 622                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 623                                 if (target_type == TypeManager.float_type)
 624                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 625                                 if (target_type == TypeManager.double_type)
 626                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 627                                 if (target_type == TypeManager.decimal_type)
 628                                         return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
 629                         } else if (expr_type == TypeManager.float_type){
 630                                 //
 631                                 // float to double
 632                                 //
 633                                 if (target_type == TypeManager.double_type)
 634                                         return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 635                         }
 636
 637                         return null;
 638                 }
 639
 640                 /// <summary>
 641                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 642                 ///  implicit user defined conversions - needed for overload resolution
 643                 /// </summary>
 644                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 645                 {
 646                         if (expr is NullLiteral) {
 647                                 return ((NullLiteral)expr).ConvertImplicitly (target_type) != null;
 648                         }
 649
 650                         if (ImplicitStandardConversionExists (expr, target_type))
 651                                 return true;
 652
 653                         if (expr.Type == TypeManager.anonymous_method_type) {
 654                                 if (!TypeManager.IsDelegateType (target_type) &&
 655                                         TypeManager.DropGenericTypeArguments (target_type) != TypeManager.expression_type)
 656                                         return false;
 657
 658                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 659                                 return ame.ImplicitStandardConversionExists (ec, target_type);
 660                         }
 661
 662                         return ImplicitUserConversion (ec, expr, target_type, Location.Null) != null;
 663                 }
 664
 665                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 666                 {
 667                         return ImplicitUserConversion (ec, new EmptyExpression (source), target, Location.Null) != null;
 668                 }
 669
 670                 /// <summary>
 671                 ///  Determines if a standard implicit conversion exists from
 672                 ///  expr_type to target_type
 673                 ///
 674                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 675                 /// </summary>
 676                 public static bool ImplicitStandardConversionExists (Expression expr, Type target_type)
 677                 {
 678                         Type expr_type = expr.Type;
 679                         if (expr_type == TypeManager.void_type)
 680                                 return false;
 681
 682                         if (expr.eclass == ExprClass.MethodGroup) {
 683                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1) {
 684                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 685                                         if (mg != null) {
 686                                                 return DelegateCreation.ImplicitStandardConversionExists (mg, target_type) != null;
 687                                         }
 688                                 }
 689
 690                                 return false;
 691                         }
 692
 693                         //Console.WriteLine ("Expr is {0}", expr);
 694                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 695                         if (TypeManager.IsEqual (expr_type, target_type))
 696                                 return true;
 697
 698                         if (TypeManager.IsNullableType (target_type))
 699                                 return ImplicitNulableConversion (null, expr, target_type) != null;
 700
 701                         // First numeric conversions
 702                         if (ImplicitNumericConversion (null, expr_type, target_type) != null)
 703                                 return true;
 704
 705                         if (ImplicitReferenceConversionExists (expr, target_type))
 706                                 return true;
 707
 708                         bool use_class_cast;
 709                         if (ImplicitBoxingConversionExists (expr, target_type, out use_class_cast))
 710                                 return true;
 711
 712                         //
 713                         // Implicit Constant Expression Conversions
 714                         //
 715                         if (expr is IntConstant){
 716                                 int value = ((IntConstant) expr).Value;
 717
 718                                 if (target_type == TypeManager.sbyte_type){
 719                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 720                                                 return true;
 721                                 } else if (target_type == TypeManager.byte_type){
 722                                         if (value >= 0 && value <= Byte.MaxValue)
 723                                                 return true;
 724                                 } else if (target_type == TypeManager.short_type){
 725                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 726                                                 return true;
 727                                 } else if (target_type == TypeManager.ushort_type){
 728                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 729                                                 return true;
 730                                 } else if (target_type == TypeManager.uint32_type){
 731                                         if (value >= 0)
 732                                                 return true;
 733                                 } else if (target_type == TypeManager.uint64_type){
 734                                          //
 735                                          // we can optimize this case: a positive int32
 736                                          // always fits on a uint64.  But we need an opcode
 737                                          // to do it.
 738                                          //
 739                                         if (value >= 0)
 740                                                 return true;
 741                                 }
 742
 743                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 744                                         return true;
 745                         }
 746
 747                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 748                                 //
 749                                 // Try the implicit constant expression conversion
 750                                 // from long to ulong, instead of a nice routine,
 751                                 // we just inline it
 752                                 //
 753                                 long v = ((LongConstant) expr).Value;
 754                                 if (v >= 0)
 755                                         return true;
 756                         }
 757
 758                         //
 759                         // If `expr_type' implements `target_type' (which is an iface)
 760                         // see TryImplicitIntConversion
 761                         //
 762                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 763                                 return true;
 764
 765                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 766                                 return true;
 767
 768                         return false;
 769                 }
 770
 771                 /// <summary>
 772                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 773                 ///  amongst the methods in the MethodGroupExpr
 774                 /// </summary>
 775                 static Type FindMostEncompassedType (ArrayList types)
 776                 {
 777                         Type best = null;
 778
 779                         if (types.Count == 0)
 780                                 return null;
 781
 782                         if (types.Count == 1)
 783                                 return (Type) types [0];
 784
 785                         EmptyExpression expr = EmptyExpression.Grab ();
 786
 787                         foreach (Type t in types) {
 788                                 if (best == null) {
 789                                         best = t;
 790                                         continue;
 791                                 }
 792
 793                                 expr.SetType (t);
 794                                 if (ImplicitStandardConversionExists (expr, best))
 795                                         best = t;
 796                         }
 797
 798                         expr.SetType (best);
 799                         foreach (Type t in types) {
 800                                 if (best == t)
 801                                         continue;
 802                                 if (!ImplicitStandardConversionExists (expr, t)) {
 803                                         best = null;
 804                                         break;
 805                                 }
 806                         }
 807
 808                         EmptyExpression.Release (expr);
 809
 810                         return best;
 811                 }
 812
 813                 /// <summary>
 814                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 815                 ///  amongst the types in the given set
 816                 /// </summary>
 817                 static Type FindMostEncompassingType (ArrayList types)
 818                 {
 819                         Type best = null;
 820
 821                         if (types.Count == 0)
 822                                 return null;
 823
 824                         if (types.Count == 1)
 825                                 return (Type) types [0];
 826
 827                         EmptyExpression expr = EmptyExpression.Grab ();
 828
 829                         foreach (Type t in types) {
 830                                 if (best == null) {
 831                                         best = t;
 832                                         continue;
 833                                 }
 834
 835                                 expr.SetType (best);
 836                                 if (ImplicitStandardConversionExists (expr, t))
 837                                         best = t;
 838                         }
 839
 840                         foreach (Type t in types) {
 841                                 if (best == t)
 842                                         continue;
 843                                 expr.SetType (t);
 844                                 if (!ImplicitStandardConversionExists (expr, best)) {
 845                                         best = null;
 846                                         break;
 847                                 }
 848                         }
 849
 850                         EmptyExpression.Release (expr);
 851
 852                         return best;
 853                 }
 854
 855                 /// <summary>
 856                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 857                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 858                 ///   for explicit and implicit conversion operators.
 859                 /// </summary>
 860                 static public Type FindMostSpecificSource (IList list,
 861                                                            Expression source, bool apply_explicit_conv_rules)
 862                 {
 863                         ArrayList src_types_set = new ArrayList ();
 864
 865                         //
 866                         // If any operator converts from S then Sx = S
 867                         //
 868                         Type source_type = source.Type;
 869                         foreach (MethodBase mb in list){
 870                                 AParametersCollection pd = TypeManager.GetParameterData (mb);
 871                                 Type param_type = pd.Types [0];
 872
 873                                 if (param_type == source_type)
 874                                         return param_type;
 875
 876                                 src_types_set.Add (param_type);
 877                         }
 878
 879                         //
 880                         // Explicit Conv rules
 881                         //
 882                         if (apply_explicit_conv_rules) {
 883                                 ArrayList candidate_set = new ArrayList ();
 884
 885                                 foreach (Type param_type in src_types_set){
 886                                         if (ImplicitStandardConversionExists (source, param_type))
 887                                                 candidate_set.Add (param_type);
 888                                 }
 889
 890                                 if (candidate_set.Count != 0)
 891                                         return FindMostEncompassedType (candidate_set);
 892                         }
 893
 894                         //
 895                         // Final case
 896                         //
 897                         if (apply_explicit_conv_rules)
 898                                 return FindMostEncompassingType (src_types_set);
 899                         else
 900                                 return FindMostEncompassedType (src_types_set);
 901                 }
 902
 903                 /// <summary>
 904                 ///  Finds the most specific target Tx according to section 13.4.4
 905                 /// </summary>
 906                 static public Type FindMostSpecificTarget (IList list,
 907                                                            Type target, bool apply_explicit_conv_rules)
 908                 {
 909                         ArrayList tgt_types_set = new ArrayList ();
 910
 911                         //
 912                         // If any operator converts to T then Tx = T
 913                         //
 914                         foreach (MethodInfo mi in list){
 915                                 Type ret_type = TypeManager.TypeToCoreType (mi.ReturnType);
 916                                 if (ret_type == target)
 917                                         return ret_type;
 918
 919                                 tgt_types_set.Add (ret_type);
 920                         }
 921
 922                         //
 923                         // Explicit conv rules
 924                         //
 925                         if (apply_explicit_conv_rules) {
 926                                 ArrayList candidate_set = new ArrayList ();
 927
 928                                 EmptyExpression expr = EmptyExpression.Grab ();
 929
 930                                 foreach (Type ret_type in tgt_types_set){
 931                                         expr.SetType (ret_type);
 932
 933                                         if (ImplicitStandardConversionExists (expr, target))
 934                                                 candidate_set.Add (ret_type);
 935                                 }
 936
 937                                 EmptyExpression.Release (expr);
 938
 939                                 if (candidate_set.Count != 0)
 940                                         return FindMostEncompassingType (candidate_set);
 941                         }
 942
 943                         //
 944                         // Okay, final case !
 945                         //
 946                         if (apply_explicit_conv_rules)
 947                                 return FindMostEncompassedType (tgt_types_set);
 948                         else
 949                                 return FindMostEncompassingType (tgt_types_set);
 950                 }
 951
 952                 /// <summary>
 953                 ///  User-defined Implicit conversions
 954                 /// </summary>
 955                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
 956                                                                  Type target, Location loc)
 957                 {
 958                         Expression expr = UserDefinedConversion (ec, source, target, loc, false);
 959                         if (expr != null && !TypeManager.IsEqual (expr.Type, target))
 960                                 expr = ImplicitConversionStandard (ec, expr, target, loc);
 961
 962                         return expr;
 963                 }
 964
 965                 /// <summary>
 966                 ///  User-defined Explicit conversions
 967                 /// </summary>
 968                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
 969                                                                  Type target, Location loc)
 970                 {
 971                         Expression expr = UserDefinedConversion (ec, source, target, loc, true);
 972                         if (expr != null && !TypeManager.IsEqual (expr.Type, target))
 973                                 expr = ExplicitConversionStandard (ec, expr, target, loc);
 974
 975                         return expr;
 976                 }
 977
 978                 static void AddConversionOperators (ArrayList list,
 979                                                     Expression source, Type target_type,
 980                                                     bool look_for_explicit,
 981                                                     MethodGroupExpr mg)
 982                 {
 983                         if (mg == null)
 984                                 return;
 985
 986                         Type source_type = source.Type;
 987                         EmptyExpression expr = EmptyExpression.Grab ();
 988
 989                         //
 990                         // LAMESPEC: Undocumented IntPtr/UIntPtr conversions
 991                         // IntPtr -> uint uses int
 992                         // UIntPtr -> long uses ulong
 993                         //
 994                         if (source_type == TypeManager.intptr_type) {
 995                                 if (target_type == TypeManager.uint32_type)
 996                                         target_type = TypeManager.int32_type;
 997                         } else if (source_type == TypeManager.uintptr_type) {
 998                                 if (target_type == TypeManager.int64_type)
 999                                         target_type = TypeManager.uint64_type;
1000                         }
1001
1002                         foreach (MethodInfo m in mg.Methods) {
1003                                 AParametersCollection pd = TypeManager.GetParameterData (m);
1004                                 Type return_type = TypeManager.TypeToCoreType (m.ReturnType);
1005                                 Type arg_type = pd.Types [0];
1006
1007                                 if (source_type != arg_type) {
1008                                         if (!ImplicitStandardConversionExists (source, arg_type)) {
1009                                                 if (!look_for_explicit)
1010                                                         continue;
1011                                                 expr.SetType (arg_type);
1012                                                 if (!ImplicitStandardConversionExists (expr, source_type))
1013                                                         continue;
1014                                         }
1015                                 }
1016
1017                                 if (target_type != return_type) {
1018                                         expr.SetType (return_type);
1019                                         if (!ImplicitStandardConversionExists (expr, target_type)) {
1020                                                 if (!look_for_explicit)
1021                                                         continue;
1022                                                 expr.SetType (target_type);
1023                                                 if (!ImplicitStandardConversionExists (expr, return_type))
1024                                                         continue;
1025                                         }
1026                                 }
1027
1028                                 // See LAMESPEC: Exclude IntPtr -> int conversion
1029                                 if (source_type == TypeManager.uintptr_type && return_type == TypeManager.uint32_type)
1030                                         continue;
1031
1032                                 list.Add (m);
1033                         }
1034
1035                         EmptyExpression.Release (expr);
1036                 }
1037
1038                 /// <summary>
1039                 ///   Compute the user-defined conversion operator from source_type to target_type.
1040                 ///   `look_for_explicit' controls whether we should also include the list of explicit operators
1041                 /// </summary>
1042                 static MethodInfo GetConversionOperator (Type container_type, Expression source, Type target_type, bool look_for_explicit)
1043                 {
1044                         ArrayList ops = new ArrayList (4);
1045
1046                         Type source_type = source.Type;
1047
1048                         if (source_type != TypeManager.decimal_type) {
1049                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1050                                         Expression.MethodLookup (container_type, source_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1051                                 if (look_for_explicit) {
1052                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1053                                                 Expression.MethodLookup (
1054                                                         container_type, source_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1055                                 }
1056                         }
1057
1058                         if (target_type != TypeManager.decimal_type) {
1059                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1060                                         Expression.MethodLookup (container_type, target_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1061                                 if (look_for_explicit) {
1062                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1063                                                 Expression.MethodLookup (
1064                                                         container_type, target_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1065                                 }
1066                         }
1067
1068                         if (ops.Count == 0)
1069                                 return null;
1070
1071                         Type most_specific_source = FindMostSpecificSource (ops, source, look_for_explicit);
1072                         if (most_specific_source == null)
1073                                 return null;
1074
1075                         Type most_specific_target = FindMostSpecificTarget (ops, target_type, look_for_explicit);
1076                         if (most_specific_target == null)
1077                                 return null;
1078
1079                         MethodInfo method = null;
1080
1081                         foreach (MethodInfo m in ops) {
1082                                 if (TypeManager.TypeToCoreType (m.ReturnType) != most_specific_target)
1083                                         continue;
1084                                 if (TypeManager.GetParameterData (m).Types [0] != most_specific_source)
1085                                         continue;
1086                                 // Ambiguous: more than one conversion operator satisfies the signature.
1087                                 if (method != null)
1088                                         return null;
1089                                 method = m;
1090                         }
1091
1092                         return method;
1093                 }
1094
1095                 static DoubleHash explicit_conv = new DoubleHash (100);
1096                 static DoubleHash implicit_conv = new DoubleHash (100);
1097
1098                 /// <summary>
1099                 ///   User-defined conversions
1100                 /// </summary>
1101                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1102                                                                 Type target, Location loc,
1103                                                                 bool look_for_explicit)
1104                 {
1105                         Type source_type = source.Type;
1106                         MethodInfo method = null;
1107
1108                         object o;
1109                         DoubleHash hash;
1110                         if (look_for_explicit) {
1111                                 hash = explicit_conv;
1112                         } else {
1113                                 // Implicit user operators cannot convert to interfaces
1114                                 if (target.IsInterface)
1115                                         return null;
1116
1117                                 hash = implicit_conv;
1118                         }
1119
1120                         if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
1121                                 method = (MethodInfo) o;
1122                         } else {
1123                                 method = GetConversionOperator (null, source, target, look_for_explicit);
1124                                 if (!(source is Constant))
1125                                         hash.Insert (source_type, target, method);
1126                         }
1127
1128                         if (method == null)
1129                                 return null;
1130
1131                         Type most_specific_source = TypeManager.GetParameterData (method).Types [0];
1132
1133                         //
1134                         // This will do the conversion to the best match that we
1135                         // found.  Now we need to perform an implict standard conversion
1136                         // if the best match was not the type that we were requested
1137                         // by target.
1138                         //
1139                         if (look_for_explicit)
1140                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1141                         else
1142                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1143
1144                         if (source == null)
1145                                 return null;
1146
1147                         return new UserCast (method, source, loc).DoResolve (ec);
1148                 }
1149
1150                 /// <summary>
1151                 ///   Converts implicitly the resolved expression `expr' into the
1152                 ///   `target_type'.  It returns a new expression that can be used
1153                 ///   in a context that expects a `target_type'.
1154                 /// </summary>
1155                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1156                                                              Type target_type, Location loc)
1157                 {
1158                         Expression e;
1159
1160                         if (target_type == null)
1161                                 throw new Exception ("Target type is null");
1162
1163                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1164                         if (e != null)
1165                                 return e;
1166
1167                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1168                         if (e != null)
1169                                 return e;
1170
1171                         return null;
1172                 }
1173
1174
1175                 /// <summary>
1176                 ///   Attempts to apply the `Standard Implicit
1177                 ///   Conversion' rules to the expression `expr' into
1178                 ///   the `target_type'.  It returns a new expression
1179                 ///   that can be used in a context that expects a
1180                 ///   `target_type'.
1181                 ///
1182                 ///   This is different from `ImplicitConversion' in that the
1183                 ///   user defined implicit conversions are excluded.
1184                 /// </summary>
1185                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1186                                                                      Type target_type, Location loc)
1187                 {
1188                         return ImplicitConversionStandard (ec, expr, target_type, loc, false);
1189                 }
1190
1191                 static Expression ImplicitConversionStandard (EmitContext ec, Expression expr, Type target_type, Location loc, bool explicit_cast)
1192                 {
1193                         if (expr.eclass == ExprClass.MethodGroup){
1194                                 if (!TypeManager.IsDelegateType (target_type)){
1195                                         return null;
1196                                 }
1197
1198                                 //
1199                                 // Only allow anonymous method conversions on post ISO_1
1200                                 //
1201                                 if (RootContext.Version != LanguageVersion.ISO_1){
1202                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1203                                         if (mg != null)
1204                                                 return ImplicitDelegateCreation.Create (
1205                                                         ec, mg, target_type, loc);
1206                                 }
1207                         }
1208
1209                         Type expr_type = expr.Type;
1210                         Expression e;
1211
1212                         if (expr_type.Equals (target_type)) {
1213                                 if (expr_type != TypeManager.null_type && expr_type != TypeManager.anonymous_method_type)
1214                                         return expr;
1215                                 return null;
1216                         }
1217
1218                         if (TypeManager.IsNullableType (target_type))
1219                                 return ImplicitNulableConversion (ec, expr, target_type);
1220
1221                         //
1222                         // Attempt to do the implicit constant expression conversions
1223                         //
1224                         Constant c = expr as Constant;
1225                         if (c != null) {
1226                                 //
1227                                 // If `target_type' is an interface and the type of `ic' implements the interface
1228                                 // e.g. target_type is IComparable, IConvertible, IFormattable
1229                                 //
1230                                 if (c.Type == TypeManager.int32_type && target_type.IsInterface && target_type.IsAssignableFrom (c.Type))
1231                                         return new BoxedCast (c, target_type);
1232
1233                                 try {
1234                                         c = c.ConvertImplicitly (target_type);
1235                                 } catch {
1236                                         Console.WriteLine ("Conversion error happened in line {0}", loc);
1237                                         throw;
1238                                 }
1239                                 if (c != null)
1240                                         return c;
1241                         }
1242
1243                         e = ImplicitNumericConversion (expr, expr_type, target_type);
1244                         if (e != null)
1245                                 return e;
1246
1247                         e = ImplicitReferenceConversion (expr, target_type, explicit_cast);
1248                         if (e != null)
1249                                 return e;
1250
1251                         if (expr is IntConstant && TypeManager.IsEnumType (target_type)){
1252                                 Constant i = (Constant) expr;
1253                                 //
1254                                 // LAMESPEC: Conversion from any 0 constant is allowed
1255                                 //
1256                                 // An implicit enumeration conversion permits the decimal-integer-literal 0
1257                                 // to be converted to any enum-type and to any nullable-type whose underlying
1258                                 // type is an enum-type
1259                                 //
1260                                 if (i.IsDefaultValue)
1261                                         return new EnumConstant (i, target_type);
1262                         }
1263
1264                         if (ec.InUnsafe) {
1265                                 if (expr_type.IsPointer){
1266                                         if (target_type == TypeManager.void_ptr_type)
1267                                                 return EmptyCast.Create (expr, target_type);
1268
1269                                         //
1270                                         // yep, comparing pointer types cant be done with
1271                                         // t1 == t2, we have to compare their element types.
1272                                         //
1273                                         if (target_type.IsPointer){
1274                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1275                                                         return expr;
1276
1277                                                 //return null;
1278                                         }
1279                                 }
1280
1281                                 if (expr_type == TypeManager.null_type && target_type.IsPointer)
1282                                         return EmptyCast.Create (new NullPointer (loc), target_type);
1283                         }
1284
1285                         if (expr_type == TypeManager.anonymous_method_type){
1286                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1287                                 Expression am = ame.Compatible (ec, target_type);
1288                                 if (am != null)
1289                                         return am.DoResolve (ec);
1290                         }
1291
1292                         return null;
1293                 }
1294
1295                 /// <summary>
1296                 ///   Attempts to implicitly convert `source' into `target_type', using
1297                 ///   ImplicitConversion.  If there is no implicit conversion, then
1298                 ///   an error is signaled
1299                 /// </summary>
1300                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1301                                                                      Type target_type, Location loc)
1302                 {
1303                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1304                         if (e != null)
1305                                 return e;
1306
1307                         source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
1308                         return null;
1309                 }
1310
1311                 /// <summary>
1312                 ///   Performs the explicit numeric conversions
1313                 ///
1314                 /// There are a few conversions that are not part of the C# standard,
1315                 /// they were interim hacks in the C# compiler that were supposed to
1316                 /// become explicit operators in the UIntPtr class and IntPtr class,
1317                 /// but for historical reasons it did not happen, so the C# compiler
1318                 /// ended up with these special hacks.
1319                 ///
1320                 /// See bug 59800 for details.
1321                 ///
1322                 /// The conversion are:
1323                 ///   UIntPtr->SByte
1324                 ///   UIntPtr->Int16
1325                 ///   UIntPtr->Int32
1326                 ///   IntPtr->UInt64
1327                 ///   UInt64->IntPtr
1328                 ///   SByte->UIntPtr
1329                 ///   Int16->UIntPtr
1330                 ///
1331                 /// </summary>
1332                 public static Expression ExplicitNumericConversion (Expression expr, Type target_type)
1333                 {
1334                         Type expr_type = expr.Type;
1335                         Type real_target_type = target_type;
1336
1337                         if (expr_type == TypeManager.sbyte_type){
1338                                 //
1339                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1340                                 //
1341                                 if (real_target_type == TypeManager.byte_type)
1342                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1343                                 if (real_target_type == TypeManager.ushort_type)
1344                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1345                                 if (real_target_type == TypeManager.uint32_type)
1346                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1347                                 if (real_target_type == TypeManager.uint64_type)
1348                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1349                                 if (real_target_type == TypeManager.char_type)
1350                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1351
1352                                 // One of the built-in conversions that belonged in the class library
1353                                 if (real_target_type == TypeManager.uintptr_type){
1354                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
1355
1356                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1357                                 }
1358                         } else if (expr_type == TypeManager.byte_type){
1359                                 //
1360                                 // From byte to sbyte and char
1361                                 //
1362                                 if (real_target_type == TypeManager.sbyte_type)
1363                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1364                                 if (real_target_type == TypeManager.char_type)
1365                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1366                         } else if (expr_type == TypeManager.short_type){
1367                                 //
1368                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1369                                 //
1370                                 if (real_target_type == TypeManager.sbyte_type)
1371                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1372                                 if (real_target_type == TypeManager.byte_type)
1373                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1374                                 if (real_target_type == TypeManager.ushort_type)
1375                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1376                                 if (real_target_type == TypeManager.uint32_type)
1377                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1378                                 if (real_target_type == TypeManager.uint64_type)
1379                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1380                                 if (real_target_type == TypeManager.char_type)
1381                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1382
1383                                 // One of the built-in conversions that belonged in the class library
1384                                 if (real_target_type == TypeManager.uintptr_type){
1385                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1386
1387                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1388                                 }
1389                         } else if (expr_type == TypeManager.ushort_type){
1390                                 //
1391                                 // From ushort to sbyte, byte, short, char
1392                                 //
1393                                 if (real_target_type == TypeManager.sbyte_type)
1394                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1395                                 if (real_target_type == TypeManager.byte_type)
1396                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1397                                 if (real_target_type == TypeManager.short_type)
1398                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1399                                 if (real_target_type == TypeManager.char_type)
1400                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1401                         } else if (expr_type == TypeManager.int32_type){
1402                                 //
1403                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1404                                 //
1405                                 if (real_target_type == TypeManager.sbyte_type)
1406                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1407                                 if (real_target_type == TypeManager.byte_type)
1408                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1409                                 if (real_target_type == TypeManager.short_type)
1410                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1411                                 if (real_target_type == TypeManager.ushort_type)
1412                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1413                                 if (real_target_type == TypeManager.uint32_type)
1414                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1415                                 if (real_target_type == TypeManager.uint64_type)
1416                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1417                                 if (real_target_type == TypeManager.char_type)
1418                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1419
1420                                 // One of the built-in conversions that belonged in the class library
1421                                 if (real_target_type == TypeManager.uintptr_type){
1422                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1423
1424                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1425                                 }
1426                         } else if (expr_type == TypeManager.uint32_type){
1427                                 //
1428                                 // From uint to sbyte, byte, short, ushort, int, char
1429                                 //
1430                                 if (real_target_type == TypeManager.sbyte_type)
1431                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1432                                 if (real_target_type == TypeManager.byte_type)
1433                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1434                                 if (real_target_type == TypeManager.short_type)
1435                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1436                                 if (real_target_type == TypeManager.ushort_type)
1437                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1438                                 if (real_target_type == TypeManager.int32_type)
1439                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1440                                 if (real_target_type == TypeManager.char_type)
1441                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1442                         } else if (expr_type == TypeManager.int64_type){
1443                                 //
1444                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1445                                 //
1446                                 if (real_target_type == TypeManager.sbyte_type)
1447                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1448                                 if (real_target_type == TypeManager.byte_type)
1449                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1450                                 if (real_target_type == TypeManager.short_type)
1451                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1452                                 if (real_target_type == TypeManager.ushort_type)
1453                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1454                                 if (real_target_type == TypeManager.int32_type)
1455                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1456                                 if (real_target_type == TypeManager.uint32_type)
1457                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1458                                 if (real_target_type == TypeManager.uint64_type)
1459                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1460                                 if (real_target_type == TypeManager.char_type)
1461                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1462                         } else if (expr_type == TypeManager.uint64_type){
1463                                 //
1464                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1465                                 //
1466                                 if (real_target_type == TypeManager.sbyte_type)
1467                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1468                                 if (real_target_type == TypeManager.byte_type)
1469                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1470                                 if (real_target_type == TypeManager.short_type)
1471                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1472                                 if (real_target_type == TypeManager.ushort_type)
1473                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1474                                 if (real_target_type == TypeManager.int32_type)
1475                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1476                                 if (real_target_type == TypeManager.uint32_type)
1477                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1478                                 if (real_target_type == TypeManager.int64_type)
1479                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1480                                 if (real_target_type == TypeManager.char_type)
1481                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1482
1483                                 // One of the built-in conversions that belonged in the class library
1484                                 if (real_target_type == TypeManager.intptr_type){
1485                                         return new OperatorCast (EmptyCast.Create (expr, TypeManager.int64_type),
1486                                                                  TypeManager.intptr_type, true);
1487                                 }
1488                         } else if (expr_type == TypeManager.char_type){
1489                                 //
1490                                 // From char to sbyte, byte, short
1491                                 //
1492                                 if (real_target_type == TypeManager.sbyte_type)
1493                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1494                                 if (real_target_type == TypeManager.byte_type)
1495                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1496                                 if (real_target_type == TypeManager.short_type)
1497                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1498                         } else if (expr_type == TypeManager.float_type){
1499                                 //
1500                                 // From float to sbyte, byte, short,
1501                                 // ushort, int, uint, long, ulong, char
1502                                 // or decimal
1503                                 //
1504                                 if (real_target_type == TypeManager.sbyte_type)
1505                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1506                                 if (real_target_type == TypeManager.byte_type)
1507                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1508                                 if (real_target_type == TypeManager.short_type)
1509                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1510                                 if (real_target_type == TypeManager.ushort_type)
1511                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1512                                 if (real_target_type == TypeManager.int32_type)
1513                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1514                                 if (real_target_type == TypeManager.uint32_type)
1515                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1516                                 if (real_target_type == TypeManager.int64_type)
1517                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1518                                 if (real_target_type == TypeManager.uint64_type)
1519                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1520                                 if (real_target_type == TypeManager.char_type)
1521                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1522                                 if (real_target_type == TypeManager.decimal_type)
1523                                         return new CastToDecimal (expr, true);
1524                         } else if (expr_type == TypeManager.double_type){
1525                                 //
1526                                 // From double to sbyte, byte, short,
1527                                 // ushort, int, uint, long, ulong,
1528                                 // char, float or decimal
1529                                 //
1530                                 if (real_target_type == TypeManager.sbyte_type)
1531                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1532                                 if (real_target_type == TypeManager.byte_type)
1533                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1534                                 if (real_target_type == TypeManager.short_type)
1535                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1536                                 if (real_target_type == TypeManager.ushort_type)
1537                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1538                                 if (real_target_type == TypeManager.int32_type)
1539                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1540                                 if (real_target_type == TypeManager.uint32_type)
1541                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1542                                 if (real_target_type == TypeManager.int64_type)
1543                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1544                                 if (real_target_type == TypeManager.uint64_type)
1545                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1546                                 if (real_target_type == TypeManager.char_type)
1547                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1548                                 if (real_target_type == TypeManager.float_type)
1549                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1550                                 if (real_target_type == TypeManager.decimal_type)
1551                                         return new CastToDecimal (expr, true);
1552                         } else if (expr_type == TypeManager.uintptr_type){
1553                                 //
1554                                 // Various built-in conversions that belonged in the class library
1555                                 //
1556                                 // from uintptr to sbyte, short, int32
1557                                 //
1558                                 if (real_target_type == TypeManager.sbyte_type){
1559                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1560                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
1561                                 }
1562                                 if (real_target_type == TypeManager.short_type){
1563                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1564                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
1565                                 }
1566                                 if (real_target_type == TypeManager.int32_type){
1567                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.uint32_type, true),
1568                                                               TypeManager.int32_type);
1569                                 }
1570                         } else if (expr_type == TypeManager.intptr_type){
1571                                 if (real_target_type == TypeManager.uint64_type){
1572                                         return EmptyCast.Create (new OperatorCast (expr, TypeManager.int64_type, true),
1573                                                               TypeManager.uint64_type);
1574                                 }
1575                         } else if (expr_type == TypeManager.decimal_type) {
1576                                 return new CastFromDecimal (expr, target_type).Resolve ();
1577                         }
1578                         return null;
1579                 }
1580
1581                 /// <summary>
1582                 ///  Returns whether an explicit reference conversion can be performed
1583                 ///  from source_type to target_type
1584                 /// </summary>
1585                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1586                 {
1587                         Expression e = ExplicitReferenceConversion (null, source_type, target_type);
1588                         if (e == null)
1589                                 return false;
1590
1591                         if (e == EmptyExpression.Null)
1592                                 return true;
1593
1594                         throw new InternalErrorException ("Invalid probing conversion result");
1595                 }
1596
1597                 /// <summary>
1598                 ///   Implements Explicit Reference conversions
1599                 /// </summary>
1600                 static Expression ExplicitReferenceConversion (Expression source, Type source_type, Type target_type)
1601                 {
1602                         bool target_is_value_type = target_type.IsValueType;
1603
1604                         //
1605                         // From object to a generic parameter
1606                         //
1607                         if (source_type == TypeManager.object_type && TypeManager.IsGenericParameter (target_type))
1608                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1609
1610                         //
1611                         // Explicit type parameter conversion.
1612                         //
1613                         if (TypeManager.IsGenericParameter (source_type))
1614                                 return ExplicitTypeParameterConversion (source, source_type, target_type);
1615
1616                         //
1617                         // From object to any reference type
1618                         //
1619                         if (source_type == TypeManager.object_type && !target_is_value_type)
1620                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1621
1622                         //
1623                         // Unboxing conversion.
1624                         //
1625                         if (((source_type == TypeManager.enum_type &&
1626                                 !(source is TypeCast)) ||
1627                                 source_type == TypeManager.value_type) && target_is_value_type)
1628                                 return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1629
1630                         //
1631                         // From any class S to any class-type T, provided S is a base class of T
1632                         //
1633                         if (TypeManager.IsSubclassOf (target_type, source_type))
1634                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1635
1636                         //
1637                         // From any class type S to any interface T, provides S is not sealed
1638                         // and provided S does not implement T.
1639                         //
1640                         if (target_type.IsInterface && !source_type.IsSealed &&
1641                                 !TypeManager.ImplementsInterface (source_type, target_type)) {
1642                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1643                         }
1644
1645                         //
1646                         // From any interface-type S to to any class type T, provided T is not
1647                         // sealed, or provided T implements S.
1648                         //
1649                         if (source_type.IsInterface) {
1650                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1651                                         if (target_type.IsClass)
1652                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1653
1654                                         return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
1655                                 }
1656
1657                                 //
1658                                 // From System.Collecitons.Generic.IList<T> and its base interfaces to a one-dimensional
1659                                 // array type S[], provided there is an implicit or explicit reference conversion from S to T.
1660                                 //
1661                                 if (IList_To_Array (source_type, target_type))
1662                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1663
1664                                 return null;
1665                         }
1666
1667                         if (source_type.IsArray) {
1668                                 if (target_type.IsArray) {
1669                                         //
1670                                         // From System.Array to any array-type
1671                                         //
1672                                         if (source_type == TypeManager.array_type)
1673                                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1674
1675                                         //
1676                                         // From an array type S with an element type Se to an array type T with an
1677                                         // element type Te provided all the following are true:
1678                                         //     * S and T differe only in element type, in other words, S and T
1679                                         //       have the same number of dimensions.
1680                                         //     * Both Se and Te are reference types
1681                                         //     * An explicit reference conversions exist from Se to Te
1682                                         //
1683                                         if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1684
1685                                                 source_type = TypeManager.GetElementType (source_type);
1686                                                 if (!TypeManager.IsReferenceType (source_type))
1687                                                         return null;
1688
1689                                                 Type target_type_element = TypeManager.GetElementType (target_type);
1690                                                 if (!TypeManager.IsReferenceType (target_type_element))
1691                                                         return null;
1692
1693                                                 if (ExplicitReferenceConversionExists (source_type, target_type_element))
1694                                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1695
1696                                                 return null;
1697                                         }
1698                                 }
1699
1700                                 //
1701                                 // From a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its base interfaces,
1702                                 // provided that there is an explicit reference conversion from S to T
1703                                 //
1704                                 if (Array_To_IList (source_type, target_type, true))
1705                                         return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1706
1707                                 return null;
1708                         }
1709
1710                         //
1711                         // From System delegate to any delegate-type
1712                         //
1713                         if (source_type == TypeManager.delegate_type && TypeManager.IsDelegateType (target_type))
1714                                 return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
1715
1716                         return null;
1717                 }
1718
1719                 /// <summary>
1720                 ///   Performs an explicit conversion of the expression `expr' whose
1721                 ///   type is expr.Type to `target_type'.
1722                 /// </summary>
1723                 static public Expression ExplicitConversionCore (EmitContext ec, Expression expr,
1724                                                                  Type target_type, Location loc)
1725                 {
1726                         Type expr_type = expr.Type;
1727
1728                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1729                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc, true);
1730                         if (ne != null)
1731                                 return ne;
1732
1733                         //
1734                         // Unboxing conversions; only object types can be convertible to enum
1735                         //
1736                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1737                                 return new UnboxCast (expr, target_type);
1738
1739                         if (TypeManager.IsEnumType (expr_type)) {
1740                                 Expression underlying = EmptyCast.Create (expr, TypeManager.GetEnumUnderlyingType (expr_type));
1741                                 expr = ExplicitConversionCore (ec, underlying, target_type, loc);
1742                                 if (expr != null)
1743                                         return expr;
1744
1745                                 return ExplicitUserConversion (ec, underlying, target_type, loc);
1746                         }
1747
1748                         if (TypeManager.IsEnumType (target_type)){
1749                                 if (expr_type == TypeManager.enum_type)
1750                                         return new UnboxCast (expr, target_type);
1751
1752                                 Expression ce = ExplicitConversionCore (ec, expr, TypeManager.GetEnumUnderlyingType (target_type), loc);
1753                                 if (ce != null)
1754                                         return EmptyCast.Create (ce, target_type);
1755
1756                                 //
1757                                 // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
1758                                 //
1759                                 if (expr_type == TypeManager.intptr_type || expr_type == TypeManager.uintptr_type) {
1760                                         ne = ExplicitUserConversion (ec, expr, TypeManager.GetEnumUnderlyingType (target_type), loc);
1761                                         if (ne != null)
1762                                                 return ExplicitConversionCore (ec, ne, target_type, loc);
1763                                 }
1764
1765                                 return null;
1766                         }
1767
1768                         ne = ExplicitNumericConversion (expr, target_type);
1769                         if (ne != null)
1770                                 return ne;
1771
1772                         //
1773                         // Skip the ExplicitReferenceConversion because we can not convert
1774                         // from Null to a ValueType, and ExplicitReference wont check against
1775                         // null literal explicitly
1776                         //
1777                         if (expr_type != TypeManager.null_type){
1778                                 ne = ExplicitReferenceConversion (expr, expr_type, target_type);
1779                                 if (ne != null)
1780                                         return ne;
1781                         }
1782
1783                         if (ec.InUnsafe){
1784                                 ne = ExplicitUnsafe (expr, target_type);
1785                                 if (ne != null)
1786                                         return ne;
1787                         }
1788
1789                         return null;
1790                 }
1791
1792                 public static Expression ExplicitUnsafe (Expression expr, Type target_type)
1793                 {
1794                         Type expr_type = expr.Type;
1795
1796                         if (target_type.IsPointer){
1797                                 if (expr_type.IsPointer)
1798                                         return EmptyCast.Create (expr, target_type);
1799
1800                                 if (expr_type == TypeManager.sbyte_type ||
1801                                         expr_type == TypeManager.short_type ||
1802                                         expr_type == TypeManager.int32_type)
1803                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1804
1805                                 if (expr_type == TypeManager.ushort_type ||
1806                                         expr_type == TypeManager.uint32_type ||
1807                                         expr_type == TypeManager.uint64_type || expr_type == TypeManager.int64_type ||
1808                                         expr_type == TypeManager.byte_type)
1809                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1810                         }
1811
1812                         if (expr_type.IsPointer){
1813                                 if (target_type == TypeManager.sbyte_type)
1814                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1815                                 else if (target_type == TypeManager.byte_type)
1816                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1817                                 else if (target_type == TypeManager.short_type)
1818                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1819                                 else if (target_type == TypeManager.ushort_type)
1820                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1821                                 else if (target_type == TypeManager.int32_type)
1822                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1823                                 else if (target_type == TypeManager.uint32_type)
1824                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1825                                 else if (target_type == TypeManager.uint64_type || target_type == TypeManager.int64_type)
1826                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1827                         }
1828                         return null;
1829                 }
1830
1831                 /// <summary>
1832                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1833                 /// </summary>
1834                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1835                                                                      Type target_type, Location l)
1836                 {
1837                         int errors = Report.Errors;
1838                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1839                         if (Report.Errors > errors)
1840                                 return null;
1841
1842                         if (ne != null)
1843                                 return ne;
1844
1845                         ne = ExplicitNumericConversion (expr, target_type);
1846                         if (ne != null)
1847                                 return ne;
1848
1849                         ne = ExplicitReferenceConversion (expr, expr.Type, target_type);
1850                         if (ne != null)
1851                                 return ne;
1852
1853                         if (ec.InUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
1854                                 return EmptyCast.Create (expr, target_type);
1855
1856                         expr.Error_ValueCannotBeConverted (ec, l, target_type, true);
1857                         return null;
1858                 }
1859
1860                 /// <summary>
1861                 ///   Performs an explicit conversion of the expression `expr' whose
1862                 ///   type is expr.Type to `target_type'.
1863                 /// </summary>
1864                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1865                         Type target_type, Location loc)
1866                 {
1867                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
1868                         if (e != null)
1869                                 return e;
1870
1871 #if GMCS_SOURCE
1872                         Type expr_type = expr.Type;
1873                         if (TypeManager.IsNullableType (target_type)) {
1874                                 if (TypeManager.IsNullableType (expr_type)) {
1875                                         Type target = TypeManager.GetTypeArguments (target_type)[0];
1876                                         Expression unwrap = Nullable.Unwrap.Create (expr);
1877                                         e = ExplicitConversion (ec, unwrap, target, expr.Location);
1878                                         if (e == null)
1879                                                 return null;
1880
1881                                         return new Nullable.Lifted (e, unwrap, target_type).Resolve (ec);
1882                                 } else if (expr_type == TypeManager.object_type) {
1883                                         return new UnboxCast (expr, target_type);
1884                                 } else {
1885                                         Type target = TypeManager.GetTypeArguments (target_type) [0];
1886
1887                                         e = ExplicitConversionCore (ec, expr, target, loc);
1888                                         if (e != null)
1889                                                 return Nullable.Wrap.Create (e, target_type);
1890                                 }
1891                         } else if (TypeManager.IsNullableType (expr_type)) {
1892                                 e = Nullable.Unwrap.Create (expr, ec);
1893
1894                                 bool use_class_cast;
1895                                 if (ImplicitBoxingConversionExists (e, target_type, out use_class_cast))
1896                                         return new BoxedCast (expr, target_type);
1897
1898                                 e = ExplicitConversion (ec, e, target_type, loc);
1899                                 if (e != null)
1900                                         e = EmptyCast.Create (e, target_type);
1901                                 return e;
1902                         }
1903 #endif
1904
1905                         e = ExplicitUserConversion (ec, expr, target_type, loc);
1906                         if (e != null)
1907                                 return e;
1908
1909                         expr.Error_ValueCannotBeConverted (ec, loc, target_type, true);
1910                         return null;
1911                 }
1912         }
1913 }