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 // (C) 2001, 2002, 2003 Ximian, Inc.
  10 //
  11
  12 namespace Mono.CSharp {
  13         using System;
  14         using System.Collections;
  15         using System.Diagnostics;
  16         using System.Reflection;
  17         using System.Reflection.Emit;
  18
  19         //
  20         // A container class for all the conversion operations
  21         //
  22         public class Convert {
  23 #if GMCS_SOURCE
  24                 static bool TypeParameter_to_Null (Type target_type)
  25                 {
  26                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
  27                         if (gc == null)
  28                                 return false;
  29
  30                         if (gc.HasReferenceTypeConstraint)
  31                                 return true;
  32                         if (gc.HasClassConstraint && !TypeManager.IsValueType (gc.ClassConstraint))
  33                                 return true;
  34
  35                         return false;
  36                 }
  37
  38                 static Type TypeParam_EffectiveBaseType (GenericConstraints gc)
  39                 {
  40                         ArrayList list = new ArrayList ();
  41                         list.Add (gc.EffectiveBaseClass);
  42                         foreach (Type t in gc.InterfaceConstraints) {
  43                                 if (!TypeManager.IsGenericParameter (t))
  44                                         continue;
  45
  46                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  47                                 if (new_gc != null)
  48                                         list.Add (TypeParam_EffectiveBaseType (new_gc));
  49                         }
  50                         return FindMostEncompassedType (list);
  51                 }
  52 #endif
  53
  54                 //
  55                 // From a one-dimensional array-type S[] to System.Collections.IList<S> and base
  56                 // interfaces of this interface.
  57                 //
  58                 // From a one-dimensional array-type S[] to System.Collections.IList<T> and base
  59                 // interfaces of this interface, provided there is an implicit reference conversion
  60                 // from S to T.
  61                 //
  62                 static bool Array_To_IList (Type array, Type list)
  63                 {
  64 #if GMCS_SOURCE
  65                         if (!array.IsArray || (array.GetArrayRank () != 1) || !list.IsGenericType)
  66                                 return false;
  67
  68                         Type gt = list.GetGenericTypeDefinition ();
  69                         if ((gt != TypeManager.generic_ilist_type) &&
  70                             (gt != TypeManager.generic_icollection_type) &&
  71                             (gt != TypeManager.generic_ienumerable_type))
  72                                 return false;
  73
  74                         Type element_type = TypeManager.GetElementType (array);
  75                         Type arg_type = TypeManager.GetTypeArguments (list) [0];
  76
  77                         if (element_type == arg_type)
  78                                 return true;
  79
  80                         if (MyEmptyExpr == null)
  81                                 MyEmptyExpr = new EmptyExpression ();
  82                         MyEmptyExpr.SetType (TypeManager.GetElementType (array));
  83
  84                         return ImplicitReferenceConversionExists (MyEmptyExpr, arg_type);
  85 #else
  86                         return false;
  87 #endif
  88                 }
  89
  90                 static Expression ImplicitTypeParameterConversion (Expression expr,
  91                                                                    Type target_type)
  92                 {
  93 #if GMCS_SOURCE
  94                         Type expr_type = expr.Type;
  95
  96                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
  97
  98                         if (gc == null) {
  99                                 if (target_type == TypeManager.object_type)
 100                                         return new BoxedCast (expr, target_type);
 101
 102                                 return null;
 103                         }
 104
 105                         // We're converting from a type parameter which is known to be a reference type.
 106                         Type base_type = TypeParam_EffectiveBaseType (gc);
 107
 108                         if (TypeManager.IsSubclassOf (base_type, target_type))
 109                                 return new ClassCast (expr, target_type);
 110
 111                         if (target_type.IsInterface) {
 112                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 113                                         return new ClassCast (expr, target_type);
 114
 115                                 foreach (Type t in gc.InterfaceConstraints) {
 116                                         if (TypeManager.IsSubclassOf (t, target_type))
 117                                                 return new ClassCast (expr, target_type);
 118                                         if (TypeManager.ImplementsInterface (t, target_type))
 119                                                 return new ClassCast (expr, target_type);
 120                                 }
 121                         }
 122
 123                         foreach (Type t in gc.InterfaceConstraints) {
 124                                 if (!TypeManager.IsGenericParameter (t))
 125                                         continue;
 126                                 if (TypeManager.IsSubclassOf (t, target_type))
 127                                         return new ClassCast (expr, target_type);
 128                                 if (TypeManager.ImplementsInterface (t, target_type))
 129                                         return new ClassCast (expr, target_type);
 130                         }
 131 #endif
 132                         return null;
 133                 }
 134
 135                 static bool ExplicitTypeParameterConversionExists (Type source_type, Type target_type)
 136                 {
 137 #if GMCS_SOURCE
 138                         if (target_type.IsInterface)
 139                                 return true;
 140
 141                         if (TypeManager.IsGenericParameter (target_type)) {
 142                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 143                                 if (gc == null)
 144                                         return false;
 145
 146                                 foreach (Type iface in gc.InterfaceConstraints) {
 147                                         if (!TypeManager.IsGenericParameter (iface))
 148                                                 continue;
 149
 150                                         if (TypeManager.IsSubclassOf (source_type, iface))
 151                                                 return true;
 152                                 }
 153                         }
 154 #endif
 155                         return false;
 156                 }
 157
 158                 static Expression ExplicitTypeParameterConversion (Expression source, Type target_type)
 159                 {
 160 #if GMCS_SOURCE
 161                         Type source_type = source.Type;
 162
 163                         if (target_type.IsInterface)
 164                                 return new ClassCast (source, target_type);
 165
 166                         if (TypeManager.IsGenericParameter (target_type)) {
 167                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 168                                 if (gc == null)
 169                                         return null;
 170
 171                                 foreach (Type iface in gc.InterfaceConstraints) {
 172                                         if (!TypeManager.IsGenericParameter (iface))
 173                                                 continue;
 174
 175                                         if (TypeManager.IsSubclassOf (source_type, iface))
 176                                                 return new ClassCast (source, target_type);
 177                                 }
 178                         }
 179 #endif
 180                         return null;
 181                 }
 182
 183                 static EmptyExpression MyEmptyExpr;
 184                 static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
 185                 {
 186                         Type expr_type = expr.Type;
 187
 188                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 189                                 // if we are a method group, emit a warning
 190
 191                                 expr.Emit (null);
 192                         }
 193
 194                         if (expr_type == TypeManager.void_type)
 195                                 return null;
 196
 197                         if (TypeManager.IsGenericParameter (expr_type))
 198                                 return ImplicitTypeParameterConversion (expr, target_type);
 199
 200                         //
 201                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 202                         // is an abstract class, and not really a value type, so we apply the same rules.
 203                         //
 204                         if (target_type == TypeManager.object_type) {
 205                                 //
 206                                 // A pointer type cannot be converted to object
 207                                 //
 208                                 if (expr_type.IsPointer)
 209                                         return null;
 210
 211                                 if (TypeManager.IsValueType (expr_type))
 212                                         return new BoxedCast (expr, target_type);
 213                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 214                                         if (expr_type == TypeManager.anonymous_method_type)
 215                                                 return null;
 216                                         return new EmptyCast (expr, target_type);
 217                                 }
 218
 219                                 return null;
 220                         } else if (target_type == TypeManager.value_type) {
 221                                 if (TypeManager.IsValueType (expr_type))
 222                                         return new BoxedCast (expr, target_type);
 223                                 if (expr_type == TypeManager.null_type)
 224                                         return new EmptyConstantCast ((Constant)expr, target_type);
 225
 226                                 return null;
 227                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 228                                 //
 229                                 // Special case: enumeration to System.Enum.
 230                                 // System.Enum is not a value type, it is a class, so we need
 231                                 // a boxing conversion
 232                                 //
 233                                 if (expr_type.IsEnum || TypeManager.IsGenericParameter (expr_type))
 234                                         return new BoxedCast (expr, target_type);
 235
 236                                 return new EmptyCast (expr, target_type);
 237                         }
 238
 239                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 240                         // with the small distinction that we only probe there
 241                         //
 242                         // Always ensure that the code here and there is in sync
 243
 244                         // from the null type to any reference-type.
 245                         if (expr_type == TypeManager.null_type) {
 246                                 NullConstant nc = (NullConstant)expr;
 247                                 return nc.ConvertImplicitly(target_type);
 248                         }
 249
 250                         // from any class-type S to any interface-type T.
 251                         if (target_type.IsInterface) {
 252                                 if (target_type != TypeManager.iconvertible_type &&
 253                                     expr_type.IsValueType && (expr is Constant) &&
 254                                     !(expr is IntLiteral || expr is BoolLiteral ||
 255                                       expr is FloatLiteral || expr is DoubleLiteral ||
 256                                       expr is LongLiteral || expr is CharLiteral ||
 257                                       expr is StringLiteral || expr is DecimalLiteral ||
 258                                       expr is UIntLiteral || expr is ULongLiteral)) {
 259                                         return null;
 260                                 }
 261
 262                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 263                                         if (TypeManager.IsGenericParameter (expr_type) || TypeManager.IsValueType (expr_type))
 264                                                 return new BoxedCast (expr, target_type);
 265                                         else
 266                                                 return new EmptyCast (expr, target_type);
 267                                 }
 268                         }
 269
 270                         // from any interface type S to interface-type T.
 271                         if (expr_type.IsInterface && target_type.IsInterface) {
 272                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 273                                         return new EmptyCast (expr, target_type);
 274                                 else
 275                                         return null;
 276                         }
 277
 278                         // from an array-type S to an array-type of type T
 279                         if (expr_type.IsArray && target_type.IsArray) {
 280                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 281
 282                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 283
 284                                         if (MyEmptyExpr == null)
 285                                                 MyEmptyExpr = new EmptyExpression ();
 286
 287                                         MyEmptyExpr.SetType (expr_element_type);
 288                                         Type target_element_type = TypeManager.GetElementType (target_type);
 289
 290                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 291                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 292                                                                                       target_element_type))
 293                                                         return new EmptyCast (expr, target_type);
 294                                 }
 295                         }
 296
 297                         // from an array-type to System.Array
 298                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 299                                 return new EmptyCast (expr, target_type);
 300
 301                         // from an array-type of type T to IList<T>
 302                         if (expr_type.IsArray && Array_To_IList (expr_type, target_type))
 303                                 return new EmptyCast (expr, target_type);
 304
 305                         // from any delegate type to System.Delegate
 306                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 307                             target_type == TypeManager.delegate_type)
 308                                 return new EmptyCast (expr, target_type);
 309
 310                         // from any array-type or delegate type into System.ICloneable.
 311                         if (expr_type.IsArray ||
 312                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 313                                 if (target_type == TypeManager.icloneable_type)
 314                                         return new EmptyCast (expr, target_type);
 315
 316                         // from a generic type definition to a generic instance.
 317                         if (TypeManager.IsEqual (expr_type, target_type))
 318                                 return new EmptyCast (expr, target_type);
 319
 320                         return null;
 321                 }
 322
 323                 //
 324                 // Tests whether an implicit reference conversion exists between expr_type
 325                 // and target_type
 326                 //
 327                 public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
 328                 {
 329                         if (target_type.IsValueType)
 330                                 return false;
 331
 332                         Type expr_type = expr.Type;
 333
 334                         if (TypeManager.IsGenericParameter (expr_type))
 335                                 return ImplicitTypeParameterConversion (expr, target_type) != null;
 336
 337                         //
 338                         // This is the boxed case.
 339                         //
 340                         if (target_type == TypeManager.object_type) {
 341                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 342                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 343                                         if (target_type != TypeManager.anonymous_method_type)
 344                                         return true;
 345
 346                                 return false;
 347                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 348                                 return true;
 349
 350                         // Please remember that all code below actually comes
 351                         // from ImplicitReferenceConversion so make sure code remains in sync
 352
 353                         // from any class-type S to any interface-type T.
 354                         if (target_type.IsInterface) {
 355                                 if (target_type != TypeManager.iconvertible_type &&
 356                                     expr_type.IsValueType && (expr is Constant) &&
 357                                     !(expr is IntLiteral || expr is BoolLiteral ||
 358                                       expr is FloatLiteral || expr is DoubleLiteral ||
 359                                       expr is LongLiteral || expr is CharLiteral ||
 360                                       expr is StringLiteral || expr is DecimalLiteral ||
 361                                       expr is UIntLiteral || expr is ULongLiteral)) {
 362                                         return false;
 363                                 }
 364
 365                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 366                                         return true;
 367                         }
 368
 369                         // from any interface type S to interface-type T.
 370                         if (expr_type.IsInterface && target_type.IsInterface)
 371                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 372                                         return true;
 373
 374                         // from an array-type S to an array-type of type T
 375                         if (expr_type.IsArray && target_type.IsArray) {
 376                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 377
 378                                         Type expr_element_type = expr_type.GetElementType ();
 379
 380                                         if (MyEmptyExpr == null)
 381                                                 MyEmptyExpr = new EmptyExpression ();
 382
 383                                         MyEmptyExpr.SetType (expr_element_type);
 384                                         Type target_element_type = TypeManager.GetElementType (target_type);
 385
 386                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 387                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 388                                                                                       target_element_type))
 389                                                         return true;
 390                                 }
 391                         }
 392
 393                         // from an array-type to System.Array
 394                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 395                                 return true;
 396
 397                         // from an array-type of type T to IList<T>
 398                         if (expr_type.IsArray && Array_To_IList (expr_type, target_type))
 399                                 return true;
 400
 401                         // from any delegate type to System.Delegate
 402                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 403                             target_type == TypeManager.delegate_type)
 404                                 if (target_type.IsAssignableFrom (expr_type))
 405                                         return true;
 406
 407                         // from any array-type or delegate type into System.ICloneable.
 408                         if (expr_type.IsArray ||
 409                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 410                                 if (target_type == TypeManager.icloneable_type)
 411                                         return true;
 412
 413                         // from the null type to any reference-type.
 414                         if (expr_type == TypeManager.null_type){
 415                                 if (target_type.IsPointer)
 416                                         return true;
 417
 418                                 if (!target_type.IsValueType)
 419                                         return true;
 420                         }
 421
 422                         // from a generic type definition to a generic instance.
 423                         if (TypeManager.IsEqual (expr_type, target_type))
 424                                 return true;
 425
 426                         return false;
 427                 }
 428
 429                 /// <summary>
 430                 ///   Implicit Numeric Conversions.
 431                 ///
 432                 ///   expr is the expression to convert, returns a new expression of type
 433                 ///   target_type or null if an implicit conversion is not possible.
 434                 /// </summary>
 435                 static public Expression ImplicitNumericConversion (Expression expr,
 436                                                                     Type target_type)
 437                 {
 438                         Type expr_type = expr.Type;
 439
 440                         //
 441                         // Attempt to do the implicit constant expression conversions
 442
 443                         if (expr is Constant){
 444                                 if (expr is IntConstant){
 445                                         Expression e;
 446
 447                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 448
 449                                         if (e != null)
 450                                                 return e;
 451                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 452                                         //
 453                                         // Try the implicit constant expression conversion
 454                                         // from long to ulong, instead of a nice routine,
 455                                         // we just inline it
 456                                         //
 457                                         long v = ((LongConstant) expr).Value;
 458                                         if (v >= 0)
 459                                                 return new ULongConstant ((ulong) v, expr.Location);
 460                                 }
 461                         }
 462
 463                         Type real_target_type = target_type;
 464
 465                         if (expr_type == TypeManager.sbyte_type){
 466                                 //
 467                                 // From sbyte to short, int, long, float, double, decimal
 468                                 //
 469                                 if (real_target_type == TypeManager.int32_type)
 470                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 471                                 if (real_target_type == TypeManager.int64_type)
 472                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 473                                 if (real_target_type == TypeManager.double_type)
 474                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 475                                 if (real_target_type == TypeManager.float_type)
 476                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 477                                 if (real_target_type == TypeManager.short_type)
 478                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 479                                 if (real_target_type == TypeManager.decimal_type)
 480                                         return new CastToDecimal (expr);
 481                         } else if (expr_type == TypeManager.byte_type){
 482                                 //
 483                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 484                                 //
 485                                 if ((real_target_type == TypeManager.short_type) ||
 486                                     (real_target_type == TypeManager.ushort_type) ||
 487                                     (real_target_type == TypeManager.int32_type) ||
 488                                     (real_target_type == TypeManager.uint32_type))
 489                                         return new EmptyCast (expr, target_type);
 490
 491                                 if (real_target_type == TypeManager.uint64_type)
 492                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 493                                 if (real_target_type == TypeManager.int64_type)
 494                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 495                                 if (real_target_type == TypeManager.float_type)
 496                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 497                                 if (real_target_type == TypeManager.double_type)
 498                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 499                                 if (real_target_type == TypeManager.decimal_type)
 500                                         return new CastToDecimal (expr);
 501
 502                         } else if (expr_type == TypeManager.short_type){
 503                                 //
 504                                 // From short to int, long, float, double, decimal
 505                                 //
 506                                 if (real_target_type == TypeManager.int32_type)
 507                                         return new EmptyCast (expr, target_type);
 508                                 if (real_target_type == TypeManager.int64_type)
 509                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 510                                 if (real_target_type == TypeManager.double_type)
 511                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 512                                 if (real_target_type == TypeManager.float_type)
 513                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 514                                 if (real_target_type == TypeManager.decimal_type)
 515                                         return new CastToDecimal (expr);
 516
 517                         } else if (expr_type == TypeManager.ushort_type){
 518                                 //
 519                                 // From ushort to int, uint, long, ulong, float, double, decimal
 520                                 //
 521                                 if (real_target_type == TypeManager.uint32_type)
 522                                         return new EmptyCast (expr, target_type);
 523
 524                                 if (real_target_type == TypeManager.uint64_type)
 525                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 526                                 if (real_target_type == TypeManager.int32_type)
 527                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 528                                 if (real_target_type == TypeManager.int64_type)
 529                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 530                                 if (real_target_type == TypeManager.double_type)
 531                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 532                                 if (real_target_type == TypeManager.float_type)
 533                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 534                                 if (real_target_type == TypeManager.decimal_type)
 535                                         return new CastToDecimal (expr);
 536                         } else if (expr_type == TypeManager.int32_type){
 537                                 //
 538                                 // From int to long, float, double, decimal
 539                                 //
 540                                 if (real_target_type == TypeManager.int64_type)
 541                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 542                                 if (real_target_type == TypeManager.double_type)
 543                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 544                                 if (real_target_type == TypeManager.float_type)
 545                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 546                                 if (real_target_type == TypeManager.decimal_type)
 547                                         return new CastToDecimal (expr);
 548                         } else if (expr_type == TypeManager.uint32_type){
 549                                 //
 550                                 // From uint to long, ulong, float, double, decimal
 551                                 //
 552                                 if (real_target_type == TypeManager.int64_type)
 553                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 554                                 if (real_target_type == TypeManager.uint64_type)
 555                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 556                                 if (real_target_type == TypeManager.double_type)
 557                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 558                                                                OpCodes.Conv_R8);
 559                                 if (real_target_type == TypeManager.float_type)
 560                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 561                                                                OpCodes.Conv_R4);
 562                                 if (real_target_type == TypeManager.decimal_type)
 563                                         return new CastToDecimal (expr);
 564                         } else if (expr_type == TypeManager.int64_type){
 565                                 //
 566                                 // From long/ulong to float, double
 567                                 //
 568                                 if (real_target_type == TypeManager.double_type)
 569                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 570                                 if (real_target_type == TypeManager.float_type)
 571                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 572                                 if (real_target_type == TypeManager.decimal_type)
 573                                         return new CastToDecimal (expr);
 574                         } else if (expr_type == TypeManager.uint64_type){
 575                                 //
 576                                 // From ulong to float, double
 577                                 //
 578                                 if (real_target_type == TypeManager.double_type)
 579                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 580                                                                OpCodes.Conv_R8);
 581                                 if (real_target_type == TypeManager.float_type)
 582                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 583                                                                OpCodes.Conv_R4);
 584                                 if (real_target_type == TypeManager.decimal_type)
 585                                         return new CastToDecimal (expr);
 586                         } else if (expr_type == TypeManager.char_type){
 587                                 //
 588                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 589                                 //
 590                                 if ((real_target_type == TypeManager.ushort_type) ||
 591                                     (real_target_type == TypeManager.int32_type) ||
 592                                     (real_target_type == TypeManager.uint32_type))
 593                                         return new EmptyCast (expr, target_type);
 594                                 if (real_target_type == TypeManager.uint64_type)
 595                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 596                                 if (real_target_type == TypeManager.int64_type)
 597                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 598                                 if (real_target_type == TypeManager.float_type)
 599                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 600                                 if (real_target_type == TypeManager.double_type)
 601                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 602                                 if (real_target_type == TypeManager.decimal_type)
 603                                         return new CastToDecimal (expr);
 604                         } else if (expr_type == TypeManager.float_type){
 605                                 //
 606                                 // float to double
 607                                 //
 608                                 if (real_target_type == TypeManager.double_type)
 609                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 610                         }
 611
 612                         return null;
 613                 }
 614
 615                 /// <summary>
 616                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 617                 ///  implicit user defined conversions - needed for overload resolution
 618                 /// </summary>
 619                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 620                 {
 621 #if GMCS_SOURCE
 622                         if (expr is NullLiteral) {
 623                                 if (TypeManager.IsGenericParameter (target_type))
 624                                         return TypeParameter_to_Null (target_type);
 625
 626                                 if (TypeManager.IsNullableType (target_type))
 627                                         return true;
 628                         }
 629 #endif
 630                         if (ImplicitStandardConversionExists (expr, target_type))
 631                                 return true;
 632
 633                         return ImplicitUserConversion (ec, expr, target_type, Location.Null) != null;
 634                 }
 635
 636                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 637                 {
 638                         return ImplicitUserConversion (ec, new EmptyExpression (source), target, Location.Null) != null;
 639                 }
 640
 641                 /// <summary>
 642                 ///  Determines if a standard implicit conversion exists from
 643                 ///  expr_type to target_type
 644                 ///
 645                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 646                 /// </summary>
 647                 public static bool ImplicitStandardConversionExists (Expression expr, Type target_type)
 648                 {
 649                         Type expr_type = expr.Type;
 650 #if GMCS_SOURCE
 651                         if (TypeManager.IsNullableType (target_type)) {
 652                                 // if implicit standard conversion S -> T exists, S -> T? and S? -> T? also exists
 653                                 target_type = TypeManager.GetTypeArguments (target_type) [0];
 654
 655                                 // S? -> T?
 656                                 if (TypeManager.IsNullableType (expr_type)) {
 657                                         EmptyExpression new_expr = EmptyExpression.Grab ();
 658                                         new_expr.SetType (TypeManager.GetTypeArguments (expr_type) [0]);
 659                                         bool retval = ImplicitStandardConversionExists (new_expr, target_type);
 660                                         EmptyExpression.Release (new_expr);
 661                                         return retval;
 662                                 }
 663                         }
 664 #endif
 665                         if (expr_type == TypeManager.void_type)
 666                                 return false;
 667
 668                         //Console.WriteLine ("Expr is {0}", expr);
 669                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 670                         if (TypeManager.IsEqual (expr_type, target_type))
 671                                 return true;
 672
 673
 674                         // First numeric conversions
 675
 676                         if (expr_type == TypeManager.sbyte_type){
 677                                 //
 678                                 // From sbyte to short, int, long, float, double, decimal
 679                                 //
 680                                 if ((target_type == TypeManager.int32_type) ||
 681                                     (target_type == TypeManager.int64_type) ||
 682                                     (target_type == TypeManager.double_type) ||
 683                                     (target_type == TypeManager.float_type)  ||
 684                                     (target_type == TypeManager.short_type) ||
 685                                     (target_type == TypeManager.decimal_type))
 686                                         return true;
 687
 688                         } else if (expr_type == TypeManager.byte_type){
 689                                 //
 690                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 691                                 //
 692                                 if ((target_type == TypeManager.short_type) ||
 693                                     (target_type == TypeManager.ushort_type) ||
 694                                     (target_type == TypeManager.int32_type) ||
 695                                     (target_type == TypeManager.uint32_type) ||
 696                                     (target_type == TypeManager.uint64_type) ||
 697                                     (target_type == TypeManager.int64_type) ||
 698                                     (target_type == TypeManager.float_type) ||
 699                                     (target_type == TypeManager.double_type) ||
 700                                     (target_type == TypeManager.decimal_type))
 701                                         return true;
 702
 703                         } else if (expr_type == TypeManager.short_type){
 704                                 //
 705                                 // From short to int, long, double, float, decimal
 706                                 //
 707                                 if ((target_type == TypeManager.int32_type) ||
 708                                     (target_type == TypeManager.int64_type) ||
 709                                     (target_type == TypeManager.double_type) ||
 710                                     (target_type == TypeManager.float_type) ||
 711                                     (target_type == TypeManager.decimal_type))
 712                                         return true;
 713
 714                         } else if (expr_type == TypeManager.ushort_type){
 715                                 //
 716                                 // From ushort to int, uint, long, ulong, double, float, decimal
 717                                 //
 718                                 if ((target_type == TypeManager.uint32_type) ||
 719                                     (target_type == TypeManager.uint64_type) ||
 720                                     (target_type == TypeManager.int32_type) ||
 721                                     (target_type == TypeManager.int64_type) ||
 722                                     (target_type == TypeManager.double_type) ||
 723                                     (target_type == TypeManager.float_type) ||
 724                                     (target_type == TypeManager.decimal_type))
 725                                         return true;
 726
 727                         } else if (expr_type == TypeManager.int32_type){
 728                                 //
 729                                 // From int to long, double, float, decimal
 730                                 //
 731                                 if ((target_type == TypeManager.int64_type) ||
 732                                     (target_type == TypeManager.double_type) ||
 733                                     (target_type == TypeManager.float_type) ||
 734                                     (target_type == TypeManager.decimal_type))
 735                                         return true;
 736
 737                         } else if (expr_type == TypeManager.uint32_type){
 738                                 //
 739                                 // From uint to long, ulong, double, float, decimal
 740                                 //
 741                                 if ((target_type == TypeManager.int64_type) ||
 742                                     (target_type == TypeManager.uint64_type) ||
 743                                     (target_type == TypeManager.double_type) ||
 744                                     (target_type == TypeManager.float_type) ||
 745                                     (target_type == TypeManager.decimal_type))
 746                                         return true;
 747
 748                         } else if ((expr_type == TypeManager.uint64_type) ||
 749                                    (expr_type == TypeManager.int64_type)) {
 750                                 //
 751                                 // From long/ulong to double, float, decimal
 752                                 //
 753                                 if ((target_type == TypeManager.double_type) ||
 754                                     (target_type == TypeManager.float_type) ||
 755                                     (target_type == TypeManager.decimal_type))
 756                                         return true;
 757
 758                         } else if (expr_type == TypeManager.char_type){
 759                                 //
 760                                 // From char to ushort, int, uint, ulong, long, float, double, decimal
 761                                 //
 762                                 if ((target_type == TypeManager.ushort_type) ||
 763                                     (target_type == TypeManager.int32_type) ||
 764                                     (target_type == TypeManager.uint32_type) ||
 765                                     (target_type == TypeManager.uint64_type) ||
 766                                     (target_type == TypeManager.int64_type) ||
 767                                     (target_type == TypeManager.float_type) ||
 768                                     (target_type == TypeManager.double_type) ||
 769                                     (target_type == TypeManager.decimal_type))
 770                                         return true;
 771
 772                         } else if (expr_type == TypeManager.float_type){
 773                                 //
 774                                 // float to double
 775                                 //
 776                                 if (target_type == TypeManager.double_type)
 777                                         return true;
 778                         }
 779
 780                         if (expr.eclass == ExprClass.MethodGroup){
 781                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
 782                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 783                                         if (mg != null){
 784                                                 return DelegateCreation.ImplicitStandardConversionExists (mg, target_type) != null;
 785                                         }
 786                                 }
 787                         }
 788
 789                         if (ImplicitReferenceConversionExists (expr, target_type))
 790                                 return true;
 791
 792                         //
 793                         // Implicit Constant Expression Conversions
 794                         //
 795                         if (expr is IntConstant){
 796                                 int value = ((IntConstant) expr).Value;
 797
 798                                 if (target_type == TypeManager.sbyte_type){
 799                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 800                                                 return true;
 801                                 } else if (target_type == TypeManager.byte_type){
 802                                         if (value >= 0 && value <= Byte.MaxValue)
 803                                                 return true;
 804                                 } else if (target_type == TypeManager.short_type){
 805                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 806                                                 return true;
 807                                 } else if (target_type == TypeManager.ushort_type){
 808                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 809                                                 return true;
 810                                 } else if (target_type == TypeManager.uint32_type){
 811                                         if (value >= 0)
 812                                                 return true;
 813                                 } else if (target_type == TypeManager.uint64_type){
 814                                          //
 815                                          // we can optimize this case: a positive int32
 816                                          // always fits on a uint64.  But we need an opcode
 817                                          // to do it.
 818                                          //
 819                                         if (value >= 0)
 820                                                 return true;
 821                                 }
 822
 823                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 824                                         return true;
 825                         }
 826
 827                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 828                                 //
 829                                 // Try the implicit constant expression conversion
 830                                 // from long to ulong, instead of a nice routine,
 831                                 // we just inline it
 832                                 //
 833                                 long v = ((LongConstant) expr).Value;
 834                                 if (v >= 0)
 835                                         return true;
 836                         }
 837
 838                         if ((target_type == TypeManager.enum_type ||
 839                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 840                              expr is IntLiteral){
 841                                 IntLiteral i = (IntLiteral) expr;
 842
 843                                 if (i.Value == 0)
 844                                         return true;
 845                         }
 846
 847                         //
 848                         // If `expr_type' implements `target_type' (which is an iface)
 849                         // see TryImplicitIntConversion
 850                         //
 851                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 852                                 return true;
 853
 854                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 855                                 return true;
 856
 857                         if (expr_type == TypeManager.anonymous_method_type){
 858                                 if (!TypeManager.IsDelegateType (target_type))
 859                                         return false;
 860
 861                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 862                                 return ame.ImplicitStandardConversionExists (target_type);
 863                         }
 864
 865                         return false;
 866                 }
 867
 868                 /// <summary>
 869                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 870                 ///  amongst the methods in the MethodGroupExpr
 871                 /// </summary>
 872                 static Type FindMostEncompassedType (ArrayList types)
 873                 {
 874                         Type best = null;
 875
 876                         if (types.Count == 0)
 877                                 return null;
 878
 879                         if (types.Count == 1)
 880                                 return (Type) types [0];
 881
 882                         EmptyExpression expr = EmptyExpression.Grab ();
 883
 884                         foreach (Type t in types) {
 885                                 if (best == null) {
 886                                         best = t;
 887                                         continue;
 888                                 }
 889
 890                                 expr.SetType (t);
 891                                 if (ImplicitStandardConversionExists (expr, best))
 892                                         best = t;
 893                         }
 894
 895                         expr.SetType (best);
 896                         foreach (Type t in types) {
 897                                 if (best == t)
 898                                         continue;
 899                                 if (!ImplicitStandardConversionExists (expr, t)) {
 900                                         best = null;
 901                                         break;
 902                                 }
 903                         }
 904
 905                         EmptyExpression.Release (expr);
 906
 907                         return best;
 908                 }
 909
 910                 /// <summary>
 911                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 912                 ///  amongst the types in the given set
 913                 /// </summary>
 914                 static Type FindMostEncompassingType (ArrayList types)
 915                 {
 916                         Type best = null;
 917
 918                         if (types.Count == 0)
 919                                 return null;
 920
 921                         if (types.Count == 1)
 922                                 return (Type) types [0];
 923
 924                         EmptyExpression expr = EmptyExpression.Grab ();
 925
 926                         foreach (Type t in types) {
 927                                 if (best == null) {
 928                                         best = t;
 929                                         continue;
 930                                 }
 931
 932                                 expr.SetType (best);
 933                                 if (ImplicitStandardConversionExists (expr, t))
 934                                         best = t;
 935                         }
 936
 937                         foreach (Type t in types) {
 938                                 if (best == t)
 939                                         continue;
 940                                 expr.SetType (t);
 941                                 if (!ImplicitStandardConversionExists (expr, best)) {
 942                                         best = null;
 943                                         break;
 944                                 }
 945                         }
 946
 947                         EmptyExpression.Release (expr);
 948
 949                         return best;
 950                 }
 951
 952                 /// <summary>
 953                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 954                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 955                 ///   for explicit and implicit conversion operators.
 956                 /// </summary>
 957                 static public Type FindMostSpecificSource (IList list,
 958                                                            Expression source, bool apply_explicit_conv_rules)
 959                 {
 960                         ArrayList src_types_set = new ArrayList ();
 961
 962                         //
 963                         // If any operator converts from S then Sx = S
 964                         //
 965                         Type source_type = source.Type;
 966                         foreach (MethodBase mb in list){
 967                                 ParameterData pd = TypeManager.GetParameterData (mb);
 968                                 Type param_type = pd.ParameterType (0);
 969
 970                                 if (param_type == source_type)
 971                                         return param_type;
 972
 973                                 src_types_set.Add (param_type);
 974                         }
 975
 976                         //
 977                         // Explicit Conv rules
 978                         //
 979                         if (apply_explicit_conv_rules) {
 980                                 ArrayList candidate_set = new ArrayList ();
 981
 982                                 foreach (Type param_type in src_types_set){
 983                                         if (ImplicitStandardConversionExists (source, param_type))
 984                                                 candidate_set.Add (param_type);
 985                                 }
 986
 987                                 if (candidate_set.Count != 0)
 988                                         return FindMostEncompassedType (candidate_set);
 989                         }
 990
 991                         //
 992                         // Final case
 993                         //
 994                         if (apply_explicit_conv_rules)
 995                                 return FindMostEncompassingType (src_types_set);
 996                         else
 997                                 return FindMostEncompassedType (src_types_set);
 998                 }
 999
1000                 /// <summary>
1001                 ///  Finds the most specific target Tx according to section 13.4.4
1002                 /// </summary>
1003                 static public Type FindMostSpecificTarget (IList list,
1004                                                            Type target, bool apply_explicit_conv_rules)
1005                 {
1006                         ArrayList tgt_types_set = new ArrayList ();
1007
1008                         //
1009                         // If any operator converts to T then Tx = T
1010                         //
1011                         foreach (MethodInfo mi in list){
1012                                 Type ret_type = mi.ReturnType;
1013                                 if (ret_type == target)
1014                                         return ret_type;
1015
1016                                 tgt_types_set.Add (ret_type);
1017                         }
1018
1019                         //
1020                         // Explicit conv rules
1021                         //
1022                         if (apply_explicit_conv_rules) {
1023                                 ArrayList candidate_set = new ArrayList ();
1024
1025                                 EmptyExpression expr = EmptyExpression.Grab ();
1026
1027                                 foreach (Type ret_type in tgt_types_set){
1028                                         expr.SetType (ret_type);
1029
1030                                         if (ImplicitStandardConversionExists (expr, target))
1031                                                 candidate_set.Add (ret_type);
1032                                 }
1033
1034                                 EmptyExpression.Release (expr);
1035
1036                                 if (candidate_set.Count != 0)
1037                                         return FindMostEncompassingType (candidate_set);
1038                         }
1039
1040                         //
1041                         // Okay, final case !
1042                         //
1043                         if (apply_explicit_conv_rules)
1044                                 return FindMostEncompassedType (tgt_types_set);
1045                         else
1046                                 return FindMostEncompassingType (tgt_types_set);
1047                 }
1048
1049                 /// <summary>
1050                 ///  User-defined Implicit conversions
1051                 /// </summary>
1052                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
1053                                                                  Type target, Location loc)
1054                 {
1055                         return UserDefinedConversion (ec, source, target, loc, false);
1056                 }
1057
1058                 /// <summary>
1059                 ///  User-defined Explicit conversions
1060                 /// </summary>
1061                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1062                                                                  Type target, Location loc)
1063                 {
1064                         return UserDefinedConversion (ec, source, target, loc, true);
1065                 }
1066
1067                 static void AddConversionOperators (ArrayList list,
1068                                                     Expression source, Type target_type,
1069                                                     bool look_for_explicit,
1070                                                     MethodGroupExpr mg)
1071                 {
1072                         if (mg == null)
1073                                 return;
1074
1075                         Type source_type = source.Type;
1076                         EmptyExpression expr = EmptyExpression.Grab ();
1077                         foreach (MethodInfo m in mg.Methods) {
1078                                 ParameterData pd = TypeManager.GetParameterData (m);
1079                                 Type return_type = m.ReturnType;
1080                                 Type arg_type = pd.ParameterType (0);
1081
1082                                 if (source_type != arg_type) {
1083                                         if (!ImplicitStandardConversionExists (source, arg_type)) {
1084                                                 if (!look_for_explicit)
1085                                                         continue;
1086                                                 expr.SetType (arg_type);
1087                                                 if (!ImplicitStandardConversionExists (expr, source_type))
1088                                                         continue;
1089                                         }
1090                                 }
1091
1092                                 if (target_type != return_type) {
1093                                         expr.SetType (return_type);
1094                                         if (!ImplicitStandardConversionExists (expr, target_type)) {
1095                                                 if (!look_for_explicit)
1096                                                         continue;
1097                                                 expr.SetType (target_type);
1098                                                 if (!ImplicitStandardConversionExists (expr, return_type))
1099                                                         continue;
1100                                         }
1101                                 }
1102
1103                                 list.Add (m);
1104                         }
1105
1106                         EmptyExpression.Release (expr);
1107                 }
1108
1109                 /// <summary>
1110                 ///   Compute the user-defined conversion operator from source_type to target_type.
1111                 ///   `look_for_explicit' controls whether we should also include the list of explicit operators
1112                 /// </summary>
1113                 static MethodInfo GetConversionOperator (Type container_type, Expression source, Type target_type, bool look_for_explicit)
1114                 {
1115                         ArrayList ops = new ArrayList (4);
1116
1117                         Type source_type = source.Type;
1118
1119                         if (source_type != TypeManager.decimal_type) {
1120                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1121                                         Expression.MethodLookup (container_type, source_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1122                                 if (look_for_explicit) {
1123                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1124                                                 Expression.MethodLookup (
1125                                                         container_type, source_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1126                                 }
1127                         }
1128
1129                         if (target_type != TypeManager.decimal_type) {
1130                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1131                                         Expression.MethodLookup (container_type, target_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1132                                 if (look_for_explicit) {
1133                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1134                                                 Expression.MethodLookup (
1135                                                         container_type, target_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1136                                 }
1137                         }
1138
1139                         if (ops.Count == 0)
1140                                 return null;
1141
1142                         Type most_specific_source = FindMostSpecificSource (ops, source, look_for_explicit);
1143                         if (most_specific_source == null)
1144                                 return null;
1145
1146                         Type most_specific_target = FindMostSpecificTarget (ops, target_type, look_for_explicit);
1147                         if (most_specific_target == null)
1148                                 return null;
1149
1150                         MethodInfo method = null;
1151
1152                         foreach (MethodInfo m in ops) {
1153                                 if (m.ReturnType != most_specific_target)
1154                                         continue;
1155                                 if (TypeManager.GetParameterData (m).ParameterType (0) != most_specific_source)
1156                                         continue;
1157                                 // Ambiguous: more than one conversion operator satisfies the signature.
1158                                 if (method != null)
1159                                         return null;
1160                                 method = m;
1161                         }
1162
1163                         return method;
1164                 }
1165
1166                 static DoubleHash explicit_conv = new DoubleHash (100);
1167                 static DoubleHash implicit_conv = new DoubleHash (100);
1168
1169                 /// <summary>
1170                 ///   User-defined conversions
1171                 /// </summary>
1172                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1173                                                                 Type target, Location loc,
1174                                                                 bool look_for_explicit)
1175                 {
1176                         Type source_type = source.Type;
1177                         MethodInfo method = null;
1178
1179                         object o;
1180                         DoubleHash hash = look_for_explicit ? explicit_conv : implicit_conv;
1181
1182                         if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
1183                                 method = (MethodInfo) o;
1184                         } else {
1185                                 method = GetConversionOperator (null, source, target, look_for_explicit);
1186                                 if (!(source is Constant))
1187                                         hash.Insert (source_type, target, method);
1188                         }
1189
1190                         if (method == null)
1191                                 return null;
1192
1193                         Type most_specific_source = TypeManager.GetParameterData (method).ParameterType (0);
1194
1195                         //
1196                         // This will do the conversion to the best match that we
1197                         // found.  Now we need to perform an implict standard conversion
1198                         // if the best match was not the type that we were requested
1199                         // by target.
1200                         //
1201                         if (look_for_explicit)
1202                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1203                         else
1204                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1205
1206                         if (source == null)
1207                                 return null;
1208
1209                         Expression e;
1210                         e =  new UserCast (method, source, loc);
1211                         if (e.Type != target){
1212                                 if (!look_for_explicit)
1213                                         e = ImplicitConversionStandard (ec, e, target, loc);
1214                                 else
1215                                         e = ExplicitConversionStandard (ec, e, target, loc);
1216                         }
1217
1218                         return e;
1219                 }
1220
1221                 /// <summary>
1222                 ///   Converts implicitly the resolved expression `expr' into the
1223                 ///   `target_type'.  It returns a new expression that can be used
1224                 ///   in a context that expects a `target_type'.
1225                 /// </summary>
1226                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1227                                                              Type target_type, Location loc)
1228                 {
1229                         Expression e;
1230
1231                         if (target_type == null)
1232                                 throw new Exception ("Target type is null");
1233
1234                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1235                         if (e != null)
1236                                 return e;
1237
1238                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1239                         if (e != null)
1240                                 return e;
1241
1242                         return null;
1243                 }
1244
1245
1246                 /// <summary>
1247                 ///   Attempts to apply the `Standard Implicit
1248                 ///   Conversion' rules to the expression `expr' into
1249                 ///   the `target_type'.  It returns a new expression
1250                 ///   that can be used in a context that expects a
1251                 ///   `target_type'.
1252                 ///
1253                 ///   This is different from `ImplicitConversion' in that the
1254                 ///   user defined implicit conversions are excluded.
1255                 /// </summary>
1256                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1257                                                                      Type target_type, Location loc)
1258                 {
1259                         Type expr_type = expr.Type;
1260                         Expression e;
1261 #if GMCS_SOURCE
1262                         // TODO: refactor to be a part of constant infrastructure
1263                         if (expr is NullLiteral) {
1264                             if (TypeManager.IsNullableType (target_type))
1265                                 return new Nullable.NullableLiteral (target_type, loc);
1266                         }
1267
1268                         if (TypeManager.IsNullableType (target_type)) {
1269                                 Type target = TypeManager.GetTypeArguments (target_type) [0];
1270
1271                                 if (TypeManager.IsNullableType (expr.Type)) {
1272                                         e = new Nullable.LiftedConversion (
1273                                                 expr, target_type, false, false, loc).Resolve (ec);
1274                                         if (e != null)
1275                                                 return e;
1276                                 } else {
1277                                         e = ImplicitConversion (ec, expr, target, loc);
1278                                         if (e != null)
1279                                                 return Nullable.Wrap.Create (e, ec);
1280                                 }
1281                         }
1282 #endif
1283                         if (expr.eclass == ExprClass.MethodGroup){
1284                                 if (!TypeManager.IsDelegateType (target_type)){
1285                                         return null;
1286                                 }
1287
1288                                 //
1289                                 // Only allow anonymous method conversions on post ISO_1
1290                                 //
1291                                 if (RootContext.Version != LanguageVersion.ISO_1){
1292                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1293                                         if (mg != null)
1294                                                 return ImplicitDelegateCreation.Create (
1295                                                         ec, mg, target_type, loc);
1296                                 }
1297                         }
1298
1299                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1300                                 return expr;
1301
1302                         e = ImplicitNumericConversion (expr, target_type);
1303                         if (e != null)
1304                                 return e;
1305
1306                         e = ImplicitReferenceConversion (expr, target_type);
1307                         if (e != null)
1308                                 return e;
1309
1310                         if (TypeManager.IsEnumType (target_type) && expr is IntLiteral){
1311                                 IntLiteral i = (IntLiteral) expr;
1312
1313                                 if (i.Value == 0)
1314                                         return new EnumConstant ((Constant) expr, target_type);
1315                         }
1316
1317                         if (ec.InUnsafe) {
1318                                 if (expr_type.IsPointer){
1319                                         if (target_type == TypeManager.void_ptr_type)
1320                                                 return new EmptyCast (expr, target_type);
1321
1322                                         //
1323                                         // yep, comparing pointer types cant be done with
1324                                         // t1 == t2, we have to compare their element types.
1325                                         //
1326                                         if (target_type.IsPointer){
1327                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1328                                                         return expr;
1329
1330                                                 //return null;
1331                                         }
1332                                 }
1333
1334                                 if (expr_type == TypeManager.null_type && target_type.IsPointer)
1335                                         return new EmptyCast (NullPointer.Null, target_type);
1336                         }
1337
1338                         if (expr_type == TypeManager.anonymous_method_type){
1339                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1340
1341                                 int errors = Report.Errors;
1342
1343                                 Expression conv = ame.Compatible (ec, target_type);
1344                                 if (conv != null)
1345                                         return conv;
1346
1347                                 //
1348                                 // We return something instead of null, to avoid
1349                                 // the duplicate error, since am.Compatible would have
1350                                 // reported that already
1351                                 //
1352                                 if (errors != Report.Errors)
1353                                         return new EmptyCast (expr, target_type);
1354                         }
1355
1356                         return null;
1357                 }
1358
1359                 /// <summary>
1360                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1361                 ///   into a different data type using casts (See Implicit Constant
1362                 ///   Expression Conversions)
1363                 /// </summary>
1364                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1365                 {
1366                         int value = ic.Value;
1367
1368                         if (target_type == TypeManager.sbyte_type){
1369                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1370                                         return new SByteConstant ((sbyte) value, ic.Location);
1371                         } else if (target_type == TypeManager.byte_type){
1372                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1373                                         return new ByteConstant ((byte) value, ic.Location);
1374                         } else if (target_type == TypeManager.short_type){
1375                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1376                                         return new ShortConstant ((short) value, ic.Location);
1377                         } else if (target_type == TypeManager.ushort_type){
1378                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1379                                         return new UShortConstant ((ushort) value, ic.Location);
1380                         } else if (target_type == TypeManager.uint32_type){
1381                                 if (value >= 0)
1382                                         return new UIntConstant ((uint) value, ic.Location);
1383                         } else if (target_type == TypeManager.uint64_type){
1384                                 //
1385                                 // we can optimize this case: a positive int32
1386                                 // always fits on a uint64.  But we need an opcode
1387                                 // to do it.
1388                                 //
1389                                 if (value >= 0)
1390                                         return new ULongConstant ((ulong) value, ic.Location);
1391                         } else if (target_type == TypeManager.double_type)
1392                                 return new DoubleConstant ((double) value, ic.Location);
1393                         else if (target_type == TypeManager.float_type)
1394                                 return new FloatConstant ((float) value, ic.Location);
1395
1396                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1397                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1398                                 Constant e = (Constant) ic;
1399
1400                                 //
1401                                 // Possibly, we need to create a different 0 literal before passing
1402                                 // to EnumConstant
1403                                 //
1404                                 if (underlying == TypeManager.int64_type)
1405                                         e = new LongLiteral (0, ic.Location);
1406                                 else if (underlying == TypeManager.uint64_type)
1407                                         e = new ULongLiteral (0, ic.Location);
1408
1409                                 return new EnumConstant (e, target_type);
1410                         }
1411
1412                         //
1413                         // If `target_type' is an interface and the type of `ic' implements the interface
1414                         // e.g. target_type is IComparable, IConvertible, IFormattable
1415                         //
1416                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1417                                 return new BoxedCast (ic, target_type);
1418
1419                         return null;
1420                 }
1421
1422                 /// <summary>
1423                 ///   Attempts to implicitly convert `source' into `target_type', using
1424                 ///   ImplicitConversion.  If there is no implicit conversion, then
1425                 ///   an error is signaled
1426                 /// </summary>
1427                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1428                                                                      Type target_type, Location loc)
1429                 {
1430                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1431                         if (e != null)
1432                                 return e;
1433
1434                         source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
1435                         return null;
1436                 }
1437
1438                 /// <summary>
1439                 ///   Performs the explicit numeric conversions
1440                 ///
1441                 /// There are a few conversions that are not part of the C# standard,
1442                 /// they were interim hacks in the C# compiler that were supposed to
1443                 /// become explicit operators in the UIntPtr class and IntPtr class,
1444                 /// but for historical reasons it did not happen, so the C# compiler
1445                 /// ended up with these special hacks.
1446                 ///
1447                 /// See bug 59800 for details.
1448                 ///
1449                 /// The conversion are:
1450                 ///   UIntPtr->SByte
1451                 ///   UIntPtr->Int16
1452                 ///   UIntPtr->Int32
1453                 ///   IntPtr->UInt64
1454                 ///   UInt64->IntPtr
1455                 ///   SByte->UIntPtr
1456                 ///   Int16->UIntPtr
1457                 ///
1458                 /// </summary>
1459                 public static Expression ExplicitNumericConversion (Expression expr, Type target_type)
1460                 {
1461                         Type expr_type = expr.Type;
1462                         Type real_target_type = target_type;
1463
1464                         if (expr_type == TypeManager.sbyte_type){
1465                                 //
1466                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1467                                 //
1468                                 if (real_target_type == TypeManager.byte_type)
1469                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1470                                 if (real_target_type == TypeManager.ushort_type)
1471                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1472                                 if (real_target_type == TypeManager.uint32_type)
1473                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1474                                 if (real_target_type == TypeManager.uint64_type)
1475                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1476                                 if (real_target_type == TypeManager.char_type)
1477                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1478
1479                                 // One of the built-in conversions that belonged in the class library
1480                                 if (real_target_type == TypeManager.uintptr_type){
1481                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
1482
1483                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1484                                 }
1485                         } else if (expr_type == TypeManager.byte_type){
1486                                 //
1487                                 // From byte to sbyte and char
1488                                 //
1489                                 if (real_target_type == TypeManager.sbyte_type)
1490                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1491                                 if (real_target_type == TypeManager.char_type)
1492                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1493                         } else if (expr_type == TypeManager.short_type){
1494                                 //
1495                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1496                                 //
1497                                 if (real_target_type == TypeManager.sbyte_type)
1498                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1499                                 if (real_target_type == TypeManager.byte_type)
1500                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1501                                 if (real_target_type == TypeManager.ushort_type)
1502                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1503                                 if (real_target_type == TypeManager.uint32_type)
1504                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1505                                 if (real_target_type == TypeManager.uint64_type)
1506                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1507                                 if (real_target_type == TypeManager.char_type)
1508                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1509
1510                                 // One of the built-in conversions that belonged in the class library
1511                                 if (real_target_type == TypeManager.uintptr_type){
1512                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1513
1514                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1515                                 }
1516                         } else if (expr_type == TypeManager.ushort_type){
1517                                 //
1518                                 // From ushort to sbyte, byte, short, char
1519                                 //
1520                                 if (real_target_type == TypeManager.sbyte_type)
1521                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1522                                 if (real_target_type == TypeManager.byte_type)
1523                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1524                                 if (real_target_type == TypeManager.short_type)
1525                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1526                                 if (real_target_type == TypeManager.char_type)
1527                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1528                         } else if (expr_type == TypeManager.int32_type){
1529                                 //
1530                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1531                                 //
1532                                 if (real_target_type == TypeManager.sbyte_type)
1533                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1534                                 if (real_target_type == TypeManager.byte_type)
1535                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1536                                 if (real_target_type == TypeManager.short_type)
1537                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1538                                 if (real_target_type == TypeManager.ushort_type)
1539                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1540                                 if (real_target_type == TypeManager.uint32_type)
1541                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1542                                 if (real_target_type == TypeManager.uint64_type)
1543                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1544                                 if (real_target_type == TypeManager.char_type)
1545                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1546
1547                                 // One of the built-in conversions that belonged in the class library
1548                                 if (real_target_type == TypeManager.uintptr_type){
1549                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1550
1551                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1552                                 }
1553                         } else if (expr_type == TypeManager.uint32_type){
1554                                 //
1555                                 // From uint to sbyte, byte, short, ushort, int, char
1556                                 //
1557                                 if (real_target_type == TypeManager.sbyte_type)
1558                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1559                                 if (real_target_type == TypeManager.byte_type)
1560                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1561                                 if (real_target_type == TypeManager.short_type)
1562                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1563                                 if (real_target_type == TypeManager.ushort_type)
1564                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1565                                 if (real_target_type == TypeManager.int32_type)
1566                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1567                                 if (real_target_type == TypeManager.char_type)
1568                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1569                         } else if (expr_type == TypeManager.int64_type){
1570                                 //
1571                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1572                                 //
1573                                 if (real_target_type == TypeManager.sbyte_type)
1574                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1575                                 if (real_target_type == TypeManager.byte_type)
1576                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1577                                 if (real_target_type == TypeManager.short_type)
1578                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1579                                 if (real_target_type == TypeManager.ushort_type)
1580                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1581                                 if (real_target_type == TypeManager.int32_type)
1582                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1583                                 if (real_target_type == TypeManager.uint32_type)
1584                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1585                                 if (real_target_type == TypeManager.uint64_type)
1586                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1587                                 if (real_target_type == TypeManager.char_type)
1588                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1589                         } else if (expr_type == TypeManager.uint64_type){
1590                                 //
1591                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1592                                 //
1593                                 if (real_target_type == TypeManager.sbyte_type)
1594                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1595                                 if (real_target_type == TypeManager.byte_type)
1596                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1597                                 if (real_target_type == TypeManager.short_type)
1598                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1599                                 if (real_target_type == TypeManager.ushort_type)
1600                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1601                                 if (real_target_type == TypeManager.int32_type)
1602                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1603                                 if (real_target_type == TypeManager.uint32_type)
1604                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1605                                 if (real_target_type == TypeManager.int64_type)
1606                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1607                                 if (real_target_type == TypeManager.char_type)
1608                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1609
1610                                 // One of the built-in conversions that belonged in the class library
1611                                 if (real_target_type == TypeManager.intptr_type){
1612                                         return new OperatorCast (new EmptyCast (expr, TypeManager.int64_type),
1613                                                                  TypeManager.intptr_type, true);
1614                                 }
1615                         } else if (expr_type == TypeManager.char_type){
1616                                 //
1617                                 // From char to sbyte, byte, short
1618                                 //
1619                                 if (real_target_type == TypeManager.sbyte_type)
1620                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1621                                 if (real_target_type == TypeManager.byte_type)
1622                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1623                                 if (real_target_type == TypeManager.short_type)
1624                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1625                         } else if (expr_type == TypeManager.float_type){
1626                                 //
1627                                 // From float to sbyte, byte, short,
1628                                 // ushort, int, uint, long, ulong, char
1629                                 // or decimal
1630                                 //
1631                                 if (real_target_type == TypeManager.sbyte_type)
1632                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1633                                 if (real_target_type == TypeManager.byte_type)
1634                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1635                                 if (real_target_type == TypeManager.short_type)
1636                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1637                                 if (real_target_type == TypeManager.ushort_type)
1638                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1639                                 if (real_target_type == TypeManager.int32_type)
1640                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1641                                 if (real_target_type == TypeManager.uint32_type)
1642                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1643                                 if (real_target_type == TypeManager.int64_type)
1644                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1645                                 if (real_target_type == TypeManager.uint64_type)
1646                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1647                                 if (real_target_type == TypeManager.char_type)
1648                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1649                                 if (real_target_type == TypeManager.decimal_type)
1650                                         return new CastToDecimal (expr, true);
1651                         } else if (expr_type == TypeManager.double_type){
1652                                 //
1653                                 // From double to sbyte, byte, short,
1654                                 // ushort, int, uint, long, ulong,
1655                                 // char, float or decimal
1656                                 //
1657                                 if (real_target_type == TypeManager.sbyte_type)
1658                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1659                                 if (real_target_type == TypeManager.byte_type)
1660                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1661                                 if (real_target_type == TypeManager.short_type)
1662                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1663                                 if (real_target_type == TypeManager.ushort_type)
1664                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1665                                 if (real_target_type == TypeManager.int32_type)
1666                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1667                                 if (real_target_type == TypeManager.uint32_type)
1668                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1669                                 if (real_target_type == TypeManager.int64_type)
1670                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1671                                 if (real_target_type == TypeManager.uint64_type)
1672                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1673                                 if (real_target_type == TypeManager.char_type)
1674                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1675                                 if (real_target_type == TypeManager.float_type)
1676                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1677                                 if (real_target_type == TypeManager.decimal_type)
1678                                         return new CastToDecimal (expr, true);
1679                         } else if (expr_type == TypeManager.uintptr_type){
1680                                 //
1681                                 // Various built-in conversions that belonged in the class library
1682                                 //
1683                                 // from uintptr to sbyte, short, int32
1684                                 //
1685                                 if (real_target_type == TypeManager.sbyte_type){
1686                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1687                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
1688                                 }
1689                                 if (real_target_type == TypeManager.short_type){
1690                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1691                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
1692                                 }
1693                                 if (real_target_type == TypeManager.int32_type){
1694                                         return new EmptyCast (new OperatorCast (expr, TypeManager.uint32_type, true),
1695                                                               TypeManager.int32_type);
1696                                 }
1697                         } else if (expr_type == TypeManager.intptr_type){
1698                                 if (real_target_type == TypeManager.uint64_type){
1699                                         return new EmptyCast (new OperatorCast (expr, TypeManager.int64_type, true),
1700                                                               TypeManager.uint64_type);
1701                                 }
1702                         } else if (expr_type == TypeManager.decimal_type) {
1703                                 return new CastFromDecimal (expr, target_type).Resolve ();
1704                         }
1705                         return null;
1706                 }
1707
1708                 /// <summary>
1709                 ///  Returns whether an explicit reference conversion can be performed
1710                 ///  from source_type to target_type
1711                 /// </summary>
1712                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1713                 {
1714                         bool target_is_type_param = TypeManager.IsGenericParameter (target_type);
1715                         bool target_is_value_type = target_type.IsValueType;
1716
1717                         if (source_type == target_type)
1718                                 return true;
1719
1720                         //
1721                         // From generic parameter to any type
1722                         //
1723                         if (TypeManager.IsGenericParameter (source_type))
1724                                 return ExplicitTypeParameterConversionExists (source_type, target_type);
1725
1726                         //
1727                         // From object to a generic parameter
1728                         //
1729                         if (source_type == TypeManager.object_type && target_is_type_param)
1730                                 return true;
1731
1732                         //
1733                         // From object to any reference type
1734                         //
1735                         if (source_type == TypeManager.object_type && !target_is_value_type)
1736                                 return true;
1737
1738                         //
1739                         // From any class S to any class-type T, provided S is a base class of T
1740                         //
1741                         if (TypeManager.IsSubclassOf (target_type, source_type))
1742                                 return true;
1743
1744                         //
1745                         // From any interface type S to any interface T provided S is not derived from T
1746                         //
1747                         if (source_type.IsInterface && target_type.IsInterface){
1748                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1749                                         return true;
1750                         }
1751
1752                         //
1753                         // From any class type S to any interface T, provided S is not sealed
1754                         // and provided S does not implement T.
1755                         //
1756                         if (target_type.IsInterface && !source_type.IsSealed &&
1757                             !TypeManager.ImplementsInterface (source_type, target_type))
1758                                 return true;
1759
1760                         //
1761                         // From any interface-type S to to any class type T, provided T is not
1762                         // sealed, or provided T implements S.
1763                         //
1764                         if (source_type.IsInterface &&
1765                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1766                                 return true;
1767
1768
1769                         // From an array type S with an element type Se to an array type T with an
1770                         // element type Te provided all the following are true:
1771                         //     * S and T differe only in element type, in other words, S and T
1772                         //       have the same number of dimensions.
1773                         //     * Both Se and Te are reference types
1774                         //     * An explicit referenc conversions exist from Se to Te
1775                         //
1776                         if (source_type.IsArray && target_type.IsArray) {
1777                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1778
1779                                         Type source_element_type = TypeManager.GetElementType (source_type);
1780                                         Type target_element_type = TypeManager.GetElementType (target_type);
1781
1782                                         if (TypeManager.IsGenericParameter (source_element_type) ||
1783                                             (!source_element_type.IsValueType && !target_element_type.IsValueType))
1784                                                 if (ExplicitReferenceConversionExists (source_element_type,
1785                                                                                        target_element_type))
1786                                                         return true;
1787                                 }
1788                         }
1789
1790
1791                         // From System.Array to any array-type
1792                         if (source_type == TypeManager.array_type &&
1793                             target_type.IsArray){
1794                                 return true;
1795                         }
1796
1797                         //
1798                         // From System delegate to any delegate-type
1799                         //
1800                         if (source_type == TypeManager.delegate_type &&
1801                             TypeManager.IsDelegateType (target_type))
1802                                 return true;
1803
1804                         //
1805                         // From ICloneable to Array or Delegate types
1806                         //
1807                         if (source_type == TypeManager.icloneable_type &&
1808                             (target_type == TypeManager.array_type ||
1809                              target_type == TypeManager.delegate_type))
1810                                 return true;
1811
1812                         return false;
1813                 }
1814
1815                 /// <summary>
1816                 ///   Implements Explicit Reference conversions
1817                 /// </summary>
1818                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1819                 {
1820                         Type source_type = source.Type;
1821                         bool target_is_type_param = TypeManager.IsGenericParameter (target_type);
1822                         bool target_is_value_type = target_type.IsValueType;
1823
1824                         //
1825                         // From object to a generic parameter
1826                         //
1827                         if (source_type == TypeManager.object_type && target_is_type_param)
1828                                 return new UnboxCast (source, target_type);
1829
1830                         //
1831                         // Explicit type parameter conversion.
1832                         //
1833
1834                         if (TypeManager.IsGenericParameter (source_type))
1835                                 return ExplicitTypeParameterConversion (source, target_type);
1836
1837                         //
1838                         // From object to any reference type
1839                         //
1840                         if (source_type == TypeManager.object_type && !target_is_value_type)
1841                                 return new ClassCast (source, target_type);
1842
1843                         //
1844                         // Unboxing conversion.
1845                         //
1846                         if (((source_type == TypeManager.enum_type &&
1847                                 !(source is EmptyCast)) ||
1848                                 source_type == TypeManager.value_type) && target_is_value_type)
1849                                 return new UnboxCast (source, target_type);
1850
1851                         //
1852                         // From any class S to any class-type T, provided S is a base class of T
1853                         //
1854                         if (TypeManager.IsSubclassOf (target_type, source_type))
1855                                 return new ClassCast (source, target_type);
1856
1857                         //
1858                         // From any interface type S to any interface T provided S is not derived from T
1859                         //
1860                         if (source_type.IsInterface && target_type.IsInterface){
1861                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1862                                         return null;
1863                                 else
1864                                         return new ClassCast (source, target_type);
1865                         }
1866
1867                         //
1868                         // From any class type S to any interface T, provides S is not sealed
1869                         // and provided S does not implement T.
1870                         //
1871                         if (target_type.IsInterface && !source_type.IsSealed) {
1872                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1873                                         return null;
1874                                 else
1875                                         return new ClassCast (source, target_type);
1876
1877                         }
1878
1879                         //
1880                         // From any interface-type S to to any class type T, provided T is not
1881                         // sealed, or provided T implements S.
1882                         //
1883                         if (source_type.IsInterface) {
1884                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1885                                         if (target_type.IsClass)
1886                                                 return new ClassCast (source, target_type);
1887                                         else
1888                                                 return new UnboxCast (source, target_type);
1889                                 }
1890
1891                                 return null;
1892                         }
1893
1894                         // From an array type S with an element type Se to an array type T with an
1895                         // element type Te provided all the following are true:
1896                         //     * S and T differe only in element type, in other words, S and T
1897                         //       have the same number of dimensions.
1898                         //     * Both Se and Te are reference types
1899                         //     * An explicit referenc conversions exist from Se to Te
1900                         //
1901                         if (source_type.IsArray && target_type.IsArray) {
1902                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1903
1904                                         Type source_element_type = TypeManager.GetElementType (source_type);
1905                                         Type target_element_type = TypeManager.GetElementType (target_type);
1906
1907                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1908                                                 if (ExplicitReferenceConversionExists (source_element_type,
1909                                                                                        target_element_type))
1910                                                         return new ClassCast (source, target_type);
1911                                 }
1912                         }
1913
1914
1915                         // From System.Array to any array-type
1916                         if (source_type == TypeManager.array_type &&
1917                             target_type.IsArray) {
1918                                 return new ClassCast (source, target_type);
1919                         }
1920
1921                         //
1922                         // From System delegate to any delegate-type
1923                         //
1924                         if (source_type == TypeManager.delegate_type &&
1925                             TypeManager.IsDelegateType (target_type))
1926                                 return new ClassCast (source, target_type);
1927
1928                         //
1929                         // From ICloneable to Array or Delegate types
1930                         //
1931                         if (source_type == TypeManager.icloneable_type &&
1932                             (target_type == TypeManager.array_type ||
1933                              target_type == TypeManager.delegate_type))
1934                                 return new ClassCast (source, target_type);
1935
1936                         return null;
1937                 }
1938
1939                 /// <summary>
1940                 ///   Performs an explicit conversion of the expression `expr' whose
1941                 ///   type is expr.Type to `target_type'.
1942                 /// </summary>
1943                 static public Expression ExplicitConversionCore (EmitContext ec, Expression expr,
1944                                                                  Type target_type, Location loc)
1945                 {
1946                         Type expr_type = expr.Type;
1947
1948                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1949                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1950                         if (ne != null)
1951                                 return ne;
1952
1953                         //
1954                         // Unboxing conversions; only object types can be convertible to enum
1955                         //
1956                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1957                                 return new UnboxCast (expr, target_type);
1958
1959                         if (TypeManager.IsEnumType (expr_type)) {
1960                                 if (expr is EnumConstant)
1961                                         return ExplicitConversionCore (ec, ((EnumConstant) expr).Child, target_type, loc);
1962
1963                                 return ExplicitConversionCore (ec, new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type)), target_type, loc);
1964                         }
1965
1966                         if (TypeManager.IsEnumType (target_type)){
1967                                 if (expr_type == TypeManager.enum_type)
1968                                         return new UnboxCast (expr, target_type);
1969
1970                                 Expression ce = ExplicitConversionCore (ec, expr, TypeManager.EnumToUnderlying (target_type), loc);
1971                                 if (ce != null)
1972                                         return new EmptyCast (ce, target_type);
1973                         }
1974
1975                         ne = ExplicitNumericConversion (expr, target_type);
1976                         if (ne != null)
1977                                 return ne;
1978
1979                         //
1980                         // Skip the ExplicitReferenceConversion because we can not convert
1981                         // from Null to a ValueType, and ExplicitReference wont check against
1982                         // null literal explicitly
1983                         //
1984                         if (expr_type != TypeManager.null_type){
1985                                 ne = ExplicitReferenceConversion (expr, target_type);
1986                                 if (ne != null)
1987                                         return ne;
1988                         }
1989
1990                         if (ec.InUnsafe){
1991                                 ne = ExplicitUnsafe (expr, target_type);
1992                                 if (ne != null)
1993                                         return ne;
1994                         }
1995
1996                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1997                         if (ne != null)
1998                                 return ne;
1999
2000                         return null;
2001                 }
2002
2003                 public static Expression ExplicitUnsafe (Expression expr, Type target_type)
2004                 {
2005                         Type expr_type = expr.Type;
2006
2007                         if (target_type.IsPointer){
2008                                 if (expr_type.IsPointer)
2009                                         return new EmptyCast (expr, target_type);
2010
2011                                 if (expr_type == TypeManager.sbyte_type ||
2012                                         expr_type == TypeManager.short_type ||
2013                                         expr_type == TypeManager.int32_type ||
2014                                         expr_type == TypeManager.int64_type)
2015                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
2016
2017                                 if (expr_type == TypeManager.ushort_type ||
2018                                         expr_type == TypeManager.uint32_type ||
2019                                         expr_type == TypeManager.uint64_type ||
2020                                         expr_type == TypeManager.byte_type)
2021                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
2022                         }
2023
2024                         if (expr_type.IsPointer){
2025                                 if (target_type == TypeManager.sbyte_type)
2026                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
2027                                 else if (target_type == TypeManager.byte_type)
2028                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
2029                                 else if (target_type == TypeManager.short_type)
2030                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
2031                                 else if (target_type == TypeManager.ushort_type)
2032                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
2033                                 else if (target_type == TypeManager.int32_type)
2034                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
2035                                 else if (target_type == TypeManager.uint32_type)
2036                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
2037                                 else if (target_type == TypeManager.uint64_type)
2038                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
2039                                 else if (target_type == TypeManager.int64_type){
2040                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
2041                                 }
2042                         }
2043                         return null;
2044                 }
2045
2046                 /// <summary>
2047                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
2048                 /// </summary>
2049                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
2050                                                                      Type target_type, Location l)
2051                 {
2052                         int errors = Report.Errors;
2053                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
2054                         if (Report.Errors > errors)
2055                                 return null;
2056
2057                         if (ne != null)
2058                                 return ne;
2059
2060                         ne = ExplicitNumericConversion (expr, target_type);
2061                         if (ne != null)
2062                                 return ne;
2063
2064                         ne = ExplicitReferenceConversion (expr, target_type);
2065                         if (ne != null)
2066                                 return ne;
2067
2068                         if (ec.InUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
2069                                 return new EmptyCast (expr, target_type);
2070
2071                         expr.Error_ValueCannotBeConverted (ec, l, target_type, true);
2072                         return null;
2073                 }
2074
2075                 /// <summary>
2076                 ///   Performs an explicit conversion of the expression `expr' whose
2077                 ///   type is expr.Type to `target_type'.
2078                 /// </summary>
2079                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
2080                         Type target_type, Location loc)
2081                 {
2082                         Expression e;
2083 #if GMCS_SOURCE
2084                         Type expr_type = expr.Type;
2085                         if (TypeManager.IsNullableType (target_type)) {
2086                                 if (TypeManager.IsNullableType (expr_type)) {
2087                                         e = new Nullable.LiftedConversion (
2088                                                 expr, target_type, false, true, loc).Resolve (ec);
2089                                         if (e != null)
2090                                                 return e;
2091                                 } else if (expr_type == TypeManager.object_type) {
2092                                         return new UnboxCast (expr, target_type);
2093                                 } else {
2094                                         Type target = TypeManager.GetTypeArguments (target_type) [0];
2095
2096                                         e = ExplicitConversionCore (ec, expr, target, loc);
2097                                         if (e != null)
2098                                                 return Nullable.Wrap.Create (e, ec);
2099                                 }
2100                         } else if (TypeManager.IsNullableType (expr_type)) {
2101                                 Expression source = Nullable.Unwrap.Create (expr, ec);
2102                                 if (source != null) {
2103                                         e = ExplicitConversionCore (ec, source, target_type, loc);
2104                                         if (e != null)
2105                                                 return e;
2106                                 }
2107                         }
2108 #endif
2109                         e = ExplicitConversionCore (ec, expr, target_type, loc);
2110                         if (e != null)
2111                                 return e;
2112
2113                         expr.Error_ValueCannotBeConverted (ec, loc, target_type, true);
2114                         return null;
2115                 }
2116         }
2117 }