mcs/gmcs/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 //
   8 // (C) 2001, 2002, 2003 Ximian, Inc.
   9 //
  10
  11 namespace Mono.CSharp {
  12         using System;
  13         using System.Collections;
  14         using System.Diagnostics;
  15         using System.Reflection;
  16         using System.Reflection.Emit;
  17
  18         //
  19         // A container class for all the conversion operations
  20         //
  21         public class Convert {
  22
  23                 static Expression TypeParameter_to_Null (Type target_type, Location loc)
  24                 {
  25                         if (!TypeParameter_to_Null (target_type)) {
  26                                 Report.Error (403, loc, "Cannot convert null to the type " +
  27                                               "parameter `{0}' becaues it could be a value " +
  28                                               "type. Consider using `default ({0})' instead.",
  29                                               target_type.ToString ());
  30                                 return null;
  31                         }
  32
  33                         Constant expr = new Nullable.NullableLiteral (target_type, loc);
  34                         return new NullCast (expr, target_type);
  35                 }
  36
  37                 static bool TypeParameter_to_Null (Type target_type)
  38                 {
  39                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
  40                         if (gc == null)
  41                                 return false;
  42
  43                         if (gc.HasReferenceTypeConstraint)
  44                                 return true;
  45                         if (gc.HasClassConstraint && !TypeManager.IsValueType (gc.ClassConstraint))
  46                                 return true;
  47
  48                         return false;
  49                 }
  50
  51                 static Type TypeParam_EffectiveBaseType (GenericConstraints gc)
  52                 {
  53                         ArrayList list = new ArrayList ();
  54                         list.Add (gc.EffectiveBaseClass);
  55                         foreach (Type t in gc.InterfaceConstraints) {
  56                                 if (!t.IsGenericParameter)
  57                                         continue;
  58
  59                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  60                                 if (new_gc != null)
  61                                         list.Add (TypeParam_EffectiveBaseType (new_gc));
  62                         }
  63                         return FindMostEncompassedType (list);
  64                 }
  65
  66                 static Expression ImplicitTypeParameterConversion (Expression expr,
  67                                                                    Type target_type)
  68                 {
  69                         Type expr_type = expr.Type;
  70
  71                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
  72
  73                         if (gc == null) {
  74                                 if (target_type == TypeManager.object_type)
  75                                         return new BoxedCast (expr, target_type);
  76
  77                                 return null;
  78                         }
  79
  80                         // We're converting from a type parameter which is known to be a reference type.
  81                         Type base_type = TypeParam_EffectiveBaseType (gc);
  82
  83                         if (TypeManager.IsSubclassOf (base_type, target_type))
  84                                 return new ClassCast (expr, target_type);
  85
  86                         if (target_type.IsInterface) {
  87                                 if (TypeManager.ImplementsInterface (base_type, target_type))
  88                                         return new ClassCast (expr, target_type);
  89
  90                                 foreach (Type t in gc.InterfaceConstraints) {
  91                                         if (TypeManager.IsSubclassOf (t, target_type))
  92                                                 return new ClassCast (expr, target_type);
  93                                         if (TypeManager.ImplementsInterface (t, target_type))
  94                                                 return new ClassCast (expr, target_type);
  95                                 }
  96                         }
  97
  98                         foreach (Type t in gc.InterfaceConstraints) {
  99                                 if (!t.IsGenericParameter)
 100                                         continue;
 101                                 if (TypeManager.IsSubclassOf (t, target_type))
 102                                         return new ClassCast (expr, target_type);
 103                                 if (TypeManager.ImplementsInterface (t, target_type))
 104                                         return new ClassCast (expr, target_type);
 105                         }
 106
 107                         return null;
 108                 }
 109
 110                 static bool ExplicitTypeParameterConversionExists (Type source_type, Type target_type)
 111                 {
 112                         if (target_type.IsInterface)
 113                                 return true;
 114
 115                         if (target_type.IsGenericParameter) {
 116                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 117                                 if (gc == null)
 118                                         return false;
 119
 120                                 foreach (Type iface in gc.InterfaceConstraints) {
 121                                         if (!iface.IsGenericParameter)
 122                                                 continue;
 123
 124                                         if (TypeManager.IsSubclassOf (source_type, iface))
 125                                                 return true;
 126                                 }
 127                         }
 128
 129                         return false;
 130                 }
 131
 132                 static Expression ExplicitTypeParameterConversion (Expression source, Type target_type)
 133                 {
 134                         Type source_type = source.Type;
 135
 136                         if (target_type.IsInterface)
 137                                 return new ClassCast (source, target_type);
 138
 139                         if (target_type.IsGenericParameter) {
 140                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 141                                 if (gc == null)
 142                                         return null;
 143
 144                                 foreach (Type iface in gc.InterfaceConstraints) {
 145                                         if (!iface.IsGenericParameter)
 146                                                 continue;
 147
 148                                         if (TypeManager.IsSubclassOf (source_type, iface))
 149                                                 return new ClassCast (source, target_type);
 150                                 }
 151                         }
 152
 153                         return null;
 154                 }
 155
 156                 static EmptyExpression MyEmptyExpr;
 157                 static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
 158                 {
 159                         Type expr_type = expr.Type;
 160
 161                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 162                                 // if we are a method group, emit a warning
 163
 164                                 expr.Emit (null);
 165                         }
 166
 167                         if (expr_type == TypeManager.void_type)
 168                                 return null;
 169
 170                         if (expr_type.IsGenericParameter)
 171                                 return ImplicitTypeParameterConversion (expr, target_type);
 172
 173                         //
 174                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 175                         // is an abstract class, and not really a value type, so we apply the same rules.
 176                         //
 177                         if (target_type == TypeManager.object_type) {
 178                                 //
 179                                 // A pointer type cannot be converted to object
 180                                 //
 181                                 if (expr_type.IsPointer)
 182                                         return null;
 183
 184                                 if (TypeManager.IsValueType (expr_type))
 185                                         return new BoxedCast (expr, target_type);
 186                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 187                                         if (expr_type == TypeManager.anonymous_method_type)
 188                                                 return null;
 189                                         return new EmptyCast (expr, target_type);
 190                                 }
 191
 192                                 return null;
 193                         } else if (target_type == TypeManager.value_type) {
 194                                 if (TypeManager.IsValueType (expr_type))
 195                                         return new BoxedCast (expr, target_type);
 196                                 if (expr_type == TypeManager.null_type)
 197                                         return new NullCast ((Constant)expr, target_type);
 198
 199                                 return null;
 200                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 201                                 //
 202                                 // Special case: enumeration to System.Enum.
 203                                 // System.Enum is not a value type, it is a class, so we need
 204                                 // a boxing conversion
 205                                 //
 206                                 if (expr_type.IsEnum || expr_type.IsGenericParameter)
 207                                         return new BoxedCast (expr, target_type);
 208
 209                                 return new EmptyCast (expr, target_type);
 210                         }
 211
 212                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 213                         // with the small distinction that we only probe there
 214                         //
 215                         // Always ensure that the code here and there is in sync
 216
 217                         // from the null type to any reference-type.
 218                         if (expr_type == TypeManager.null_type){
 219                                 if (target_type.IsPointer)
 220                                         return new EmptyCast (NullPointer.Null, target_type);
 221
 222                                 if (!target_type.IsValueType) {
 223                                         if (expr is Constant)
 224                                                 return new NullCast ((Constant)expr, target_type);
 225
 226                                         // I found only one case when it happens -- Foo () ? null : null;
 227                                         Report.Warning (-100, 1, expr.Location, "The result of the expression is always `null'");
 228                                         return new NullCast (new NullLiteral (expr.Location), target_type);
 229                                 }
 230                         }
 231
 232                         // from any class-type S to any interface-type T.
 233                         if (target_type.IsInterface) {
 234                                 if (target_type != TypeManager.iconvertible_type &&
 235                                     expr_type.IsValueType && (expr is Constant) &&
 236                                     !(expr is IntLiteral || expr is BoolLiteral ||
 237                                       expr is FloatLiteral || expr is DoubleLiteral ||
 238                                       expr is LongLiteral || expr is CharLiteral ||
 239                                       expr is StringLiteral || expr is DecimalLiteral ||
 240                                       expr is UIntLiteral || expr is ULongLiteral)) {
 241                                         return null;
 242                                 }
 243
 244                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 245                                         if (expr_type.IsGenericParameter || TypeManager.IsValueType (expr_type))
 246                                                 return new BoxedCast (expr, target_type);
 247                                         else
 248                                                 return new EmptyCast (expr, target_type);
 249                                 }
 250                         }
 251
 252                         // from any interface type S to interface-type T.
 253                         if (expr_type.IsInterface && target_type.IsInterface) {
 254                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 255                                         return new EmptyCast (expr, target_type);
 256                                 else
 257                                         return null;
 258                         }
 259
 260                         // from an array-type S to an array-type of type T
 261                         if (expr_type.IsArray && target_type.IsArray) {
 262                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 263
 264                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 265
 266                                         if (MyEmptyExpr == null)
 267                                                 MyEmptyExpr = new EmptyExpression ();
 268
 269                                         MyEmptyExpr.SetType (expr_element_type);
 270                                         Type target_element_type = TypeManager.GetElementType (target_type);
 271
 272                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 273                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 274                                                                                       target_element_type))
 275                                                         return new EmptyCast (expr, target_type);
 276                                 }
 277                         }
 278
 279                         // from an array-type to System.Array
 280                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 281                                 return new EmptyCast (expr, target_type);
 282
 283                         // from an array-type of type T to IEnumerable<T>
 284                         if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
 285                                 return new EmptyCast (expr, target_type);
 286
 287                         // from any delegate type to System.Delegate
 288                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 289                             target_type == TypeManager.delegate_type)
 290                                 return new EmptyCast (expr, target_type);
 291
 292                         // from any array-type or delegate type into System.ICloneable.
 293                         if (expr_type.IsArray ||
 294                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 295                                 if (target_type == TypeManager.icloneable_type)
 296                                         return new EmptyCast (expr, target_type);
 297
 298                         // from a generic type definition to a generic instance.
 299                         if (TypeManager.IsEqual (expr_type, target_type))
 300                                 return new EmptyCast (expr, target_type);
 301
 302                         return null;
 303                 }
 304
 305                 //
 306                 // Tests whether an implicit reference conversion exists between expr_type
 307                 // and target_type
 308                 //
 309                 public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
 310                 {
 311                         if (target_type.IsValueType)
 312                                 return false;
 313
 314                         Type expr_type = expr.Type;
 315
 316                         if (expr_type.IsGenericParameter)
 317                                 return ImplicitTypeParameterConversion (expr, target_type) != null;
 318
 319                         //
 320                         // This is the boxed case.
 321                         //
 322                         if (target_type == TypeManager.object_type) {
 323                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 324                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 325                                         if (target_type != TypeManager.anonymous_method_type)
 326                                         return true;
 327
 328                                 return false;
 329                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 330                                 return true;
 331
 332                         // Please remember that all code below actually comes
 333                         // from ImplicitReferenceConversion so make sure code remains in sync
 334
 335                         // from any class-type S to any interface-type T.
 336                         if (target_type.IsInterface) {
 337                                 if (target_type != TypeManager.iconvertible_type &&
 338                                     expr_type.IsValueType && (expr is Constant) &&
 339                                     !(expr is IntLiteral || expr is BoolLiteral ||
 340                                       expr is FloatLiteral || expr is DoubleLiteral ||
 341                                       expr is LongLiteral || expr is CharLiteral ||
 342                                       expr is StringLiteral || expr is DecimalLiteral ||
 343                                       expr is UIntLiteral || expr is ULongLiteral)) {
 344                                         return false;
 345                                 }
 346
 347                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 348                                         return true;
 349                         }
 350
 351                         // from any interface type S to interface-type T.
 352                         if (expr_type.IsInterface && target_type.IsInterface)
 353                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 354                                         return true;
 355
 356                         // from an array-type S to an array-type of type T
 357                         if (expr_type.IsArray && target_type.IsArray) {
 358                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 359
 360                                         Type expr_element_type = expr_type.GetElementType ();
 361
 362                                         if (MyEmptyExpr == null)
 363                                                 MyEmptyExpr = new EmptyExpression ();
 364
 365                                         MyEmptyExpr.SetType (expr_element_type);
 366                                         Type target_element_type = TypeManager.GetElementType (target_type);
 367
 368                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 369                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 370                                                                                       target_element_type))
 371                                                         return true;
 372                                 }
 373                         }
 374
 375                         // from an array-type to System.Array
 376                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 377                                 return true;
 378
 379                         // from an array-type of type T to IEnumerable<T>
 380                         if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
 381                                 return true;
 382
 383                         // from any delegate type to System.Delegate
 384                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 385                             target_type == TypeManager.delegate_type)
 386                                 if (target_type.IsAssignableFrom (expr_type))
 387                                         return true;
 388
 389                         // from any array-type or delegate type into System.ICloneable.
 390                         if (expr_type.IsArray ||
 391                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 392                                 if (target_type == TypeManager.icloneable_type)
 393                                         return true;
 394
 395                         // from the null type to any reference-type.
 396                         if (expr_type == TypeManager.null_type){
 397                                 if (target_type.IsPointer)
 398                                         return true;
 399
 400                                 if (!target_type.IsValueType)
 401                                         return true;
 402                         }
 403
 404                         // from a generic type definition to a generic instance.
 405                         if (TypeManager.IsEqual (expr_type, target_type))
 406                                 return true;
 407
 408                         return false;
 409                 }
 410
 411                 /// <summary>
 412                 ///   Implicit Numeric Conversions.
 413                 ///
 414                 ///   expr is the expression to convert, returns a new expression of type
 415                 ///   target_type or null if an implicit conversion is not possible.
 416                 /// </summary>
 417                 static public Expression ImplicitNumericConversion (Expression expr,
 418                                                                     Type target_type)
 419                 {
 420                         Type expr_type = expr.Type;
 421
 422                         //
 423                         // Attempt to do the implicit constant expression conversions
 424
 425                         if (expr is Constant){
 426                                 if (expr is IntConstant){
 427                                         Expression e;
 428
 429                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 430
 431                                         if (e != null)
 432                                                 return e;
 433                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 434                                         //
 435                                         // Try the implicit constant expression conversion
 436                                         // from long to ulong, instead of a nice routine,
 437                                         // we just inline it
 438                                         //
 439                                         long v = ((LongConstant) expr).Value;
 440                                         if (v >= 0)
 441                                                 return new ULongConstant ((ulong) v, expr.Location);
 442                                 }
 443                         }
 444
 445                         Type real_target_type = target_type;
 446
 447                         if (expr_type == TypeManager.sbyte_type){
 448                                 //
 449                                 // From sbyte to short, int, long, float, double, decimal
 450                                 //
 451                                 if (real_target_type == TypeManager.int32_type)
 452                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 453                                 if (real_target_type == TypeManager.int64_type)
 454                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 455                                 if (real_target_type == TypeManager.double_type)
 456                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 457                                 if (real_target_type == TypeManager.float_type)
 458                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 459                                 if (real_target_type == TypeManager.short_type)
 460                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 461                                 if (real_target_type == TypeManager.decimal_type)
 462                                         return new CastToDecimal (expr);
 463                         } else if (expr_type == TypeManager.byte_type){
 464                                 //
 465                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 466                                 //
 467                                 if ((real_target_type == TypeManager.short_type) ||
 468                                     (real_target_type == TypeManager.ushort_type) ||
 469                                     (real_target_type == TypeManager.int32_type) ||
 470                                     (real_target_type == TypeManager.uint32_type))
 471                                         return new EmptyCast (expr, target_type);
 472
 473                                 if (real_target_type == TypeManager.uint64_type)
 474                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 475                                 if (real_target_type == TypeManager.int64_type)
 476                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 477                                 if (real_target_type == TypeManager.float_type)
 478                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 479                                 if (real_target_type == TypeManager.double_type)
 480                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 481                                 if (real_target_type == TypeManager.decimal_type)
 482                                         return new CastToDecimal (expr);
 483
 484                         } else if (expr_type == TypeManager.short_type){
 485                                 //
 486                                 // From short to int, long, float, double, decimal
 487                                 //
 488                                 if (real_target_type == TypeManager.int32_type)
 489                                         return new EmptyCast (expr, target_type);
 490                                 if (real_target_type == TypeManager.int64_type)
 491                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 492                                 if (real_target_type == TypeManager.double_type)
 493                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 494                                 if (real_target_type == TypeManager.float_type)
 495                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 496                                 if (real_target_type == TypeManager.decimal_type)
 497                                         return new CastToDecimal (expr);
 498
 499                         } else if (expr_type == TypeManager.ushort_type){
 500                                 //
 501                                 // From ushort to int, uint, long, ulong, float, double, decimal
 502                                 //
 503                                 if (real_target_type == TypeManager.uint32_type)
 504                                         return new EmptyCast (expr, target_type);
 505
 506                                 if (real_target_type == TypeManager.uint64_type)
 507                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 508                                 if (real_target_type == TypeManager.int32_type)
 509                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 510                                 if (real_target_type == TypeManager.int64_type)
 511                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 512                                 if (real_target_type == TypeManager.double_type)
 513                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 514                                 if (real_target_type == TypeManager.float_type)
 515                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 516                                 if (real_target_type == TypeManager.decimal_type)
 517                                         return new CastToDecimal (expr);
 518                         } else if (expr_type == TypeManager.int32_type){
 519                                 //
 520                                 // From int to long, float, double, decimal
 521                                 //
 522                                 if (real_target_type == TypeManager.int64_type)
 523                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 524                                 if (real_target_type == TypeManager.double_type)
 525                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 526                                 if (real_target_type == TypeManager.float_type)
 527                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 528                                 if (real_target_type == TypeManager.decimal_type)
 529                                         return new CastToDecimal (expr);
 530                         } else if (expr_type == TypeManager.uint32_type){
 531                                 //
 532                                 // From uint to long, ulong, float, double, decimal
 533                                 //
 534                                 if (real_target_type == TypeManager.int64_type)
 535                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 536                                 if (real_target_type == TypeManager.uint64_type)
 537                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 538                                 if (real_target_type == TypeManager.double_type)
 539                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 540                                                                OpCodes.Conv_R8);
 541                                 if (real_target_type == TypeManager.float_type)
 542                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 543                                                                OpCodes.Conv_R4);
 544                                 if (real_target_type == TypeManager.decimal_type)
 545                                         return new CastToDecimal (expr);
 546                         } else if (expr_type == TypeManager.int64_type){
 547                                 //
 548                                 // From long/ulong to float, double
 549                                 //
 550                                 if (real_target_type == TypeManager.double_type)
 551                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 552                                 if (real_target_type == TypeManager.float_type)
 553                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 554                                 if (real_target_type == TypeManager.decimal_type)
 555                                         return new CastToDecimal (expr);
 556                         } else if (expr_type == TypeManager.uint64_type){
 557                                 //
 558                                 // From ulong to float, double
 559                                 //
 560                                 if (real_target_type == TypeManager.double_type)
 561                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 562                                                                OpCodes.Conv_R8);
 563                                 if (real_target_type == TypeManager.float_type)
 564                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 565                                                                OpCodes.Conv_R4);
 566                                 if (real_target_type == TypeManager.decimal_type)
 567                                         return new CastToDecimal (expr);
 568                         } else if (expr_type == TypeManager.char_type){
 569                                 //
 570                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 571                                 //
 572                                 if ((real_target_type == TypeManager.ushort_type) ||
 573                                     (real_target_type == TypeManager.int32_type) ||
 574                                     (real_target_type == TypeManager.uint32_type))
 575                                         return new EmptyCast (expr, target_type);
 576                                 if (real_target_type == TypeManager.uint64_type)
 577                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 578                                 if (real_target_type == TypeManager.int64_type)
 579                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 580                                 if (real_target_type == TypeManager.float_type)
 581                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 582                                 if (real_target_type == TypeManager.double_type)
 583                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 584                                 if (real_target_type == TypeManager.decimal_type)
 585                                         return new CastToDecimal (expr);
 586                         } else if (expr_type == TypeManager.float_type){
 587                                 //
 588                                 // float to double
 589                                 //
 590                                 if (real_target_type == TypeManager.double_type)
 591                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 592                         }
 593
 594                         return null;
 595                 }
 596
 597                 /// <summary>
 598                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 599                 ///  implicit user defined conversions - needed for overload resolution
 600                 /// </summary>
 601                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 602                 {
 603                         if (expr is NullLiteral) {
 604                                 if (target_type.IsGenericParameter)
 605                                         return TypeParameter_to_Null (target_type);
 606
 607                                 if (TypeManager.IsNullableType (target_type))
 608                                         return true;
 609                         }
 610
 611                         if (ImplicitStandardConversionExists (expr, target_type))
 612                                 return true;
 613
 614                         return ImplicitUserConversion (ec, expr, target_type, Location.Null) != null;
 615                 }
 616
 617                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 618                 {
 619                         return ImplicitUserConversion (ec, new EmptyExpression (source), target, Location.Null) != null;
 620                 }
 621
 622                 /// <summary>
 623                 ///  Determines if a standard implicit conversion exists from
 624                 ///  expr_type to target_type
 625                 ///
 626                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 627                 /// </summary>
 628                 public static bool ImplicitStandardConversionExists (Expression expr, Type target_type)
 629                 {
 630                         Type expr_type = expr.Type;
 631
 632                         if (expr_type == TypeManager.void_type)
 633                                 return false;
 634
 635                         //Console.WriteLine ("Expr is {0}", expr);
 636                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 637                         if (expr_type.Equals (target_type))
 638                                 return true;
 639
 640
 641                         // First numeric conversions
 642
 643                         if (expr_type == TypeManager.sbyte_type){
 644                                 //
 645                                 // From sbyte to short, int, long, float, double, decimal
 646                                 //
 647                                 if ((target_type == TypeManager.int32_type) ||
 648                                     (target_type == TypeManager.int64_type) ||
 649                                     (target_type == TypeManager.double_type) ||
 650                                     (target_type == TypeManager.float_type)  ||
 651                                     (target_type == TypeManager.short_type) ||
 652                                     (target_type == TypeManager.decimal_type))
 653                                         return true;
 654
 655                         } else if (expr_type == TypeManager.byte_type){
 656                                 //
 657                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 658                                 //
 659                                 if ((target_type == TypeManager.short_type) ||
 660                                     (target_type == TypeManager.ushort_type) ||
 661                                     (target_type == TypeManager.int32_type) ||
 662                                     (target_type == TypeManager.uint32_type) ||
 663                                     (target_type == TypeManager.uint64_type) ||
 664                                     (target_type == TypeManager.int64_type) ||
 665                                     (target_type == TypeManager.float_type) ||
 666                                     (target_type == TypeManager.double_type) ||
 667                                     (target_type == TypeManager.decimal_type))
 668                                         return true;
 669
 670                         } else if (expr_type == TypeManager.short_type){
 671                                 //
 672                                 // From short to int, long, double, float, decimal
 673                                 //
 674                                 if ((target_type == TypeManager.int32_type) ||
 675                                     (target_type == TypeManager.int64_type) ||
 676                                     (target_type == TypeManager.double_type) ||
 677                                     (target_type == TypeManager.float_type) ||
 678                                     (target_type == TypeManager.decimal_type))
 679                                         return true;
 680
 681                         } else if (expr_type == TypeManager.ushort_type){
 682                                 //
 683                                 // From ushort to int, uint, long, ulong, double, float, decimal
 684                                 //
 685                                 if ((target_type == TypeManager.uint32_type) ||
 686                                     (target_type == TypeManager.uint64_type) ||
 687                                     (target_type == TypeManager.int32_type) ||
 688                                     (target_type == TypeManager.int64_type) ||
 689                                     (target_type == TypeManager.double_type) ||
 690                                     (target_type == TypeManager.float_type) ||
 691                                     (target_type == TypeManager.decimal_type))
 692                                         return true;
 693
 694                         } else if (expr_type == TypeManager.int32_type){
 695                                 //
 696                                 // From int to long, double, float, decimal
 697                                 //
 698                                 if ((target_type == TypeManager.int64_type) ||
 699                                     (target_type == TypeManager.double_type) ||
 700                                     (target_type == TypeManager.float_type) ||
 701                                     (target_type == TypeManager.decimal_type))
 702                                         return true;
 703
 704                         } else if (expr_type == TypeManager.uint32_type){
 705                                 //
 706                                 // From uint to long, ulong, double, float, decimal
 707                                 //
 708                                 if ((target_type == TypeManager.int64_type) ||
 709                                     (target_type == TypeManager.uint64_type) ||
 710                                     (target_type == TypeManager.double_type) ||
 711                                     (target_type == TypeManager.float_type) ||
 712                                     (target_type == TypeManager.decimal_type))
 713                                         return true;
 714
 715                         } else if ((expr_type == TypeManager.uint64_type) ||
 716                                    (expr_type == TypeManager.int64_type)) {
 717                                 //
 718                                 // From long/ulong to double, float, decimal
 719                                 //
 720                                 if ((target_type == TypeManager.double_type) ||
 721                                     (target_type == TypeManager.float_type) ||
 722                                     (target_type == TypeManager.decimal_type))
 723                                         return true;
 724
 725                         } else if (expr_type == TypeManager.char_type){
 726                                 //
 727                                 // From char to ushort, int, uint, ulong, long, float, double, decimal
 728                                 //
 729                                 if ((target_type == TypeManager.ushort_type) ||
 730                                     (target_type == TypeManager.int32_type) ||
 731                                     (target_type == TypeManager.uint32_type) ||
 732                                     (target_type == TypeManager.uint64_type) ||
 733                                     (target_type == TypeManager.int64_type) ||
 734                                     (target_type == TypeManager.float_type) ||
 735                                     (target_type == TypeManager.double_type) ||
 736                                     (target_type == TypeManager.decimal_type))
 737                                         return true;
 738
 739                         } else if (expr_type == TypeManager.float_type){
 740                                 //
 741                                 // float to double
 742                                 //
 743                                 if (target_type == TypeManager.double_type)
 744                                         return true;
 745                         }
 746
 747                         if (expr.eclass == ExprClass.MethodGroup){
 748                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
 749                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 750                                         if (mg != null){
 751                                                 return DelegateCreation.ImplicitStandardConversionExists (mg, target_type) != null;
 752                                         }
 753                                 }
 754                         }
 755
 756                         if (ImplicitReferenceConversionExists (expr, target_type))
 757                                 return true;
 758
 759                         //
 760                         // Implicit Constant Expression Conversions
 761                         //
 762                         if (expr is IntConstant){
 763                                 int value = ((IntConstant) expr).Value;
 764
 765                                 if (target_type == TypeManager.sbyte_type){
 766                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 767                                                 return true;
 768                                 } else if (target_type == TypeManager.byte_type){
 769                                         if (value >= 0 && value <= Byte.MaxValue)
 770                                                 return true;
 771                                 } else if (target_type == TypeManager.short_type){
 772                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 773                                                 return true;
 774                                 } else if (target_type == TypeManager.ushort_type){
 775                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 776                                                 return true;
 777                                 } else if (target_type == TypeManager.uint32_type){
 778                                         if (value >= 0)
 779                                                 return true;
 780                                 } else if (target_type == TypeManager.uint64_type){
 781                                          //
 782                                          // we can optimize this case: a positive int32
 783                                          // always fits on a uint64.  But we need an opcode
 784                                          // to do it.
 785                                          //
 786                                         if (value >= 0)
 787                                                 return true;
 788                                 }
 789
 790                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 791                                         return true;
 792                         }
 793
 794                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 795                                 //
 796                                 // Try the implicit constant expression conversion
 797                                 // from long to ulong, instead of a nice routine,
 798                                 // we just inline it
 799                                 //
 800                                 long v = ((LongConstant) expr).Value;
 801                                 if (v >= 0)
 802                                         return true;
 803                         }
 804
 805                         if ((target_type == TypeManager.enum_type ||
 806                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 807                              expr is IntLiteral){
 808                                 IntLiteral i = (IntLiteral) expr;
 809
 810                                 if (i.Value == 0)
 811                                         return true;
 812                         }
 813
 814                         //
 815                         // If `expr_type' implements `target_type' (which is an iface)
 816                         // see TryImplicitIntConversion
 817                         //
 818                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 819                                 return true;
 820
 821                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 822                                 return true;
 823
 824                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
 825                                 return true;
 826
 827                         if (expr_type == TypeManager.anonymous_method_type){
 828                                 if (!TypeManager.IsDelegateType (target_type))
 829                                         return false;
 830
 831                                 AnonymousMethod am = (AnonymousMethod) expr;
 832                                 return am.ImplicitStandardConversionExists (target_type);
 833                         }
 834
 835                         return false;
 836                 }
 837
 838                 /// <summary>
 839                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 840                 ///  amongst the methods in the MethodGroupExpr
 841                 /// </summary>
 842                 static Type FindMostEncompassedType (ArrayList types)
 843                 {
 844                         Type best = null;
 845
 846                         if (types.Count == 0)
 847                                 return null;
 848
 849                         if (types.Count == 1)
 850                                 return (Type) types [0];
 851
 852                         EmptyExpression expr = EmptyExpression.Grab ();
 853
 854                         foreach (Type t in types) {
 855                                 if (best == null) {
 856                                         best = t;
 857                                         continue;
 858                                 }
 859
 860                                 expr.SetType (t);
 861                                 if (ImplicitStandardConversionExists (expr, best))
 862                                         best = t;
 863                         }
 864
 865                         expr.SetType (best);
 866                         foreach (Type t in types) {
 867                                 if (best == t)
 868                                         continue;
 869                                 if (!ImplicitStandardConversionExists (expr, t)) {
 870                                         best = null;
 871                                         break;
 872                                 }
 873                         }
 874
 875                         EmptyExpression.Release (expr);
 876
 877                         return best;
 878                 }
 879
 880                 /// <summary>
 881                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 882                 ///  amongst the types in the given set
 883                 /// </summary>
 884                 static Type FindMostEncompassingType (ArrayList types)
 885                 {
 886                         Type best = null;
 887
 888                         if (types.Count == 0)
 889                                 return null;
 890
 891                         if (types.Count == 1)
 892                                 return (Type) types [0];
 893
 894                         EmptyExpression expr = EmptyExpression.Grab ();
 895
 896                         foreach (Type t in types) {
 897                                 if (best == null) {
 898                                         best = t;
 899                                         continue;
 900                                 }
 901
 902                                 expr.SetType (best);
 903                                 if (ImplicitStandardConversionExists (expr, t))
 904                                         best = t;
 905                         }
 906
 907                         foreach (Type t in types) {
 908                                 if (best == t)
 909                                         continue;
 910                                 expr.SetType (t);
 911                                 if (!ImplicitStandardConversionExists (expr, best)) {
 912                                         best = null;
 913                                         break;
 914                                 }
 915                         }
 916
 917                         EmptyExpression.Release (expr);
 918
 919                         return best;
 920                 }
 921
 922                 /// <summary>
 923                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 924                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 925                 ///   for explicit and implicit conversion operators.
 926                 /// </summary>
 927                 static public Type FindMostSpecificSource (IList list,
 928                                                            Expression source, bool apply_explicit_conv_rules)
 929                 {
 930                         ArrayList src_types_set = new ArrayList ();
 931
 932                         //
 933                         // If any operator converts from S then Sx = S
 934                         //
 935                         Type source_type = source.Type;
 936                         foreach (MethodBase mb in list){
 937                                 ParameterData pd = TypeManager.GetParameterData (mb);
 938                                 Type param_type = pd.ParameterType (0);
 939
 940                                 if (param_type == source_type)
 941                                         return param_type;
 942
 943                                 src_types_set.Add (param_type);
 944                         }
 945
 946                         //
 947                         // Explicit Conv rules
 948                         //
 949                         if (apply_explicit_conv_rules) {
 950                                 ArrayList candidate_set = new ArrayList ();
 951
 952                                 foreach (Type param_type in src_types_set){
 953                                         if (ImplicitStandardConversionExists (source, param_type))
 954                                                 candidate_set.Add (param_type);
 955                                 }
 956
 957                                 if (candidate_set.Count != 0)
 958                                         return FindMostEncompassedType (candidate_set);
 959                         }
 960
 961                         //
 962                         // Final case
 963                         //
 964                         if (apply_explicit_conv_rules)
 965                                 return FindMostEncompassingType (src_types_set);
 966                         else
 967                                 return FindMostEncompassedType (src_types_set);
 968                 }
 969
 970                 /// <summary>
 971                 ///  Finds the most specific target Tx according to section 13.4.4
 972                 /// </summary>
 973                 static public Type FindMostSpecificTarget (IList list,
 974                                                            Type target, bool apply_explicit_conv_rules)
 975                 {
 976                         ArrayList tgt_types_set = new ArrayList ();
 977
 978                         //
 979                         // If any operator converts to T then Tx = T
 980                         //
 981                         foreach (MethodInfo mi in list){
 982                                 Type ret_type = mi.ReturnType;
 983                                 if (ret_type == target)
 984                                         return ret_type;
 985
 986                                 tgt_types_set.Add (ret_type);
 987                         }
 988
 989                         //
 990                         // Explicit conv rules
 991                         //
 992                         if (apply_explicit_conv_rules) {
 993                                 ArrayList candidate_set = new ArrayList ();
 994
 995                                 EmptyExpression expr = EmptyExpression.Grab ();
 996
 997                                 foreach (Type ret_type in tgt_types_set){
 998                                         expr.SetType (ret_type);
 999
1000                                         if (ImplicitStandardConversionExists (expr, target))
1001                                                 candidate_set.Add (ret_type);
1002                                 }
1003
1004                                 EmptyExpression.Release (expr);
1005
1006                                 if (candidate_set.Count != 0)
1007                                         return FindMostEncompassingType (candidate_set);
1008                         }
1009
1010                         //
1011                         // Okay, final case !
1012                         //
1013                         if (apply_explicit_conv_rules)
1014                                 return FindMostEncompassedType (tgt_types_set);
1015                         else
1016                                 return FindMostEncompassingType (tgt_types_set);
1017                 }
1018
1019                 /// <summary>
1020                 ///  User-defined Implicit conversions
1021                 /// </summary>
1022                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
1023                                                                  Type target, Location loc)
1024                 {
1025                         return UserDefinedConversion (ec, source, target, loc, false);
1026                 }
1027
1028                 /// <summary>
1029                 ///  User-defined Explicit conversions
1030                 /// </summary>
1031                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1032                                                                  Type target, Location loc)
1033                 {
1034                         return UserDefinedConversion (ec, source, target, loc, true);
1035                 }
1036
1037                 static void AddConversionOperators (ArrayList list,
1038                                                     Expression source, Type target_type,
1039                                                     bool look_for_explicit,
1040                                                     MethodGroupExpr mg)
1041                 {
1042                         if (mg == null)
1043                                 return;
1044
1045                         Type source_type = source.Type;
1046                         EmptyExpression expr = EmptyExpression.Grab ();
1047                         foreach (MethodInfo m in mg.Methods) {
1048                                 ParameterData pd = TypeManager.GetParameterData (m);
1049                                 Type return_type = m.ReturnType;
1050                                 Type arg_type = pd.ParameterType (0);
1051
1052                                 if (source_type != arg_type) {
1053                                         if (!ImplicitStandardConversionExists (source, arg_type)) {
1054                                                 if (!look_for_explicit)
1055                                                         continue;
1056                                                 expr.SetType (arg_type);
1057                                                 if (!ImplicitStandardConversionExists (expr, source_type))
1058                                                         continue;
1059                                         }
1060                                 }
1061
1062                                 if (target_type != return_type) {
1063                                         expr.SetType (return_type);
1064                                         if (!ImplicitStandardConversionExists (expr, target_type)) {
1065                                                 if (!look_for_explicit)
1066                                                         continue;
1067                                                 expr.SetType (target_type);
1068                                                 if (!ImplicitStandardConversionExists (expr, return_type))
1069                                                         continue;
1070                                         }
1071                                 }
1072
1073                                 list.Add (m);
1074                         }
1075
1076                         EmptyExpression.Release (expr);
1077                 }
1078
1079                 /// <summary>
1080                 ///   Compute the user-defined conversion operator from source_type to target_type.
1081                 ///   `look_for_explicit' controls whether we should also include the list of explicit operators
1082                 /// </summary>
1083                 static MethodInfo GetConversionOperator (EmitContext ec, Expression source, Type target_type, bool look_for_explicit)
1084                 {
1085                         ArrayList ops = new ArrayList (4);
1086
1087                         Type source_type = source.Type;
1088
1089                         if (source_type != TypeManager.decimal_type) {
1090                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1091                                         Expression.MethodLookup (ec, source_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1092                                 if (look_for_explicit) {
1093                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1094                                                 Expression.MethodLookup (
1095                                                         ec, source_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1096                                 }
1097                         }
1098
1099                         if (target_type != TypeManager.decimal_type) {
1100                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1101                                         Expression.MethodLookup (ec, target_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1102                                 if (look_for_explicit) {
1103                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1104                                                 Expression.MethodLookup (
1105                                                         ec, target_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1106                                 }
1107                         }
1108
1109                         if (ops.Count == 0)
1110                                 return null;
1111
1112                         Type most_specific_source = FindMostSpecificSource (ops, source, look_for_explicit);
1113                         if (most_specific_source == null)
1114                                 return null;
1115
1116                         Type most_specific_target = FindMostSpecificTarget (ops, target_type, look_for_explicit);
1117                         if (most_specific_target == null)
1118                                 return null;
1119
1120                         MethodInfo method = null;
1121
1122                         foreach (MethodInfo m in ops) {
1123                                 if (m.ReturnType != most_specific_target)
1124                                         continue;
1125                                 if (TypeManager.GetParameterData (m).ParameterType (0) != most_specific_source)
1126                                         continue;
1127                                 // Ambiguous: more than one conversion operator satisfies the signature.
1128                                 if (method != null)
1129                                         return null;
1130                                 method = m;
1131                         }
1132
1133                         return method;
1134                 }
1135
1136                 static DoubleHash explicit_conv = new DoubleHash (100);
1137                 static DoubleHash implicit_conv = new DoubleHash (100);
1138
1139                 /// <summary>
1140                 ///   User-defined conversions
1141                 /// </summary>
1142                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1143                                                                 Type target, Location loc,
1144                                                                 bool look_for_explicit)
1145                 {
1146                         Type source_type = source.Type;
1147                         MethodInfo method = null;
1148
1149                         if (TypeManager.IsNullableType (source_type) && TypeManager.IsNullableType (target))
1150                                 return new Nullable.LiftedConversion (
1151                                         source, target, true, look_for_explicit, loc).Resolve (ec);
1152
1153                         object o;
1154                         DoubleHash hash = look_for_explicit ? explicit_conv : implicit_conv;
1155
1156                         if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
1157                                 method = (MethodInfo) o;
1158                         } else {
1159                                 method = GetConversionOperator (ec, source, target, look_for_explicit);
1160                                 if (!(source is Constant))
1161                                         hash.Insert (source_type, target, method);
1162                         }
1163
1164                         if (method == null)
1165                                 return null;
1166
1167                         Type most_specific_source = TypeManager.GetParameterData (method).ParameterType (0);
1168
1169                         //
1170                         // This will do the conversion to the best match that we
1171                         // found.  Now we need to perform an implict standard conversion
1172                         // if the best match was not the type that we were requested
1173                         // by target.
1174                         //
1175                         if (look_for_explicit)
1176                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1177                         else
1178                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1179
1180                         if (source == null)
1181                                 return null;
1182
1183                         Expression e;
1184                         e =  new UserCast (method, source, loc);
1185                         if (e.Type != target){
1186                                 if (!look_for_explicit)
1187                                         e = ImplicitConversionStandard (ec, e, target, loc);
1188                                 else
1189                                         e = ExplicitConversionStandard (ec, e, target, loc);
1190                         }
1191
1192                         return e;
1193                 }
1194
1195                 /// <summary>
1196                 ///   Converts implicitly the resolved expression `expr' into the
1197                 ///   `target_type'.  It returns a new expression that can be used
1198                 ///   in a context that expects a `target_type'.
1199                 /// </summary>
1200                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1201                                                              Type target_type, Location loc)
1202                 {
1203                         Expression e;
1204
1205                         if (target_type == null)
1206                                 throw new Exception ("Target type is null");
1207
1208                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1209                         if (e != null)
1210                                 return e;
1211
1212                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1213                         if (e != null)
1214                                 return e;
1215
1216                         return null;
1217                 }
1218
1219
1220                 /// <summary>
1221                 ///   Attempts to apply the `Standard Implicit
1222                 ///   Conversion' rules to the expression `expr' into
1223                 ///   the `target_type'.  It returns a new expression
1224                 ///   that can be used in a context that expects a
1225                 ///   `target_type'.
1226                 ///
1227                 ///   This is different from `ImplicitConversion' in that the
1228                 ///   user defined implicit conversions are excluded.
1229                 /// </summary>
1230                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1231                                                                      Type target_type, Location loc)
1232                 {
1233                         Type expr_type = expr.Type;
1234                         Expression e;
1235
1236                         if (expr is NullLiteral) {
1237                                 if (target_type.IsGenericParameter)
1238                                         return TypeParameter_to_Null (target_type, loc);
1239
1240                                 if (TypeManager.IsNullableType (target_type))
1241                                         return new Nullable.NullableLiteral (target_type, loc);
1242                         }
1243
1244                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1245                                 return new Nullable.LiftedConversion (
1246                                         expr, target_type, false, false, loc).Resolve (ec);
1247
1248                         if (expr.eclass == ExprClass.MethodGroup){
1249                                 if (!TypeManager.IsDelegateType (target_type)){
1250                                         return null;
1251                                 }
1252
1253                                 //
1254                                 // Only allow anonymous method conversions on post ISO_1
1255                                 //
1256                                 if (RootContext.Version != LanguageVersion.ISO_1){
1257                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1258                                         if (mg != null)
1259                                                 return ImplicitDelegateCreation.Create (
1260                                                         ec, mg, target_type, loc);
1261                                 }
1262                         }
1263
1264                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1265                                 return expr;
1266
1267                         e = ImplicitNumericConversion (expr, target_type);
1268                         if (e != null)
1269                                 return e;
1270
1271                         e = ImplicitReferenceConversion (expr, target_type);
1272                         if (e != null)
1273                                 return e;
1274
1275                         if (TypeManager.IsEnumType (target_type) && expr is IntLiteral){
1276                                 IntLiteral i = (IntLiteral) expr;
1277
1278                                 if (i.Value == 0)
1279                                         return new EnumConstant ((Constant) expr, target_type);
1280                         }
1281
1282                         if (ec.InUnsafe) {
1283                                 if (expr_type.IsPointer){
1284                                         if (target_type == TypeManager.void_ptr_type)
1285                                                 return new EmptyCast (expr, target_type);
1286
1287                                         //
1288                                         // yep, comparing pointer types cant be done with
1289                                         // t1 == t2, we have to compare their element types.
1290                                         //
1291                                         if (target_type.IsPointer){
1292                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1293                                                         return expr;
1294
1295                                                 //return null;
1296                                         }
1297                                 }
1298
1299                                 if (expr_type == TypeManager.null_type && target_type.IsPointer)
1300                                         return new EmptyCast (NullPointer.Null, target_type);
1301                         }
1302
1303                         if (expr_type == TypeManager.anonymous_method_type){
1304                                 if (!TypeManager.IsDelegateType (target_type)){
1305                                         Report.Error (1660, loc,
1306                                                 "Cannot convert anonymous method block to type `{0}' because it is not a delegate type",
1307                                                 TypeManager.CSharpName (target_type));
1308                                         return null;
1309                                 }
1310
1311                                 AnonymousMethod am = (AnonymousMethod) expr;
1312                                 int errors = Report.Errors;
1313
1314                                 Expression conv = am.Compatible (ec, target_type);
1315                                 if (conv != null)
1316                                         return conv;
1317
1318                                 //
1319                                 // We return something instead of null, to avoid
1320                                 // the duplicate error, since am.Compatible would have
1321                                 // reported that already
1322                                 //
1323                                 if (errors != Report.Errors)
1324                                         return new EmptyCast (expr, target_type);
1325                         }
1326
1327                         return null;
1328                 }
1329
1330                 /// <summary>
1331                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1332                 ///   into a different data type using casts (See Implicit Constant
1333                 ///   Expression Conversions)
1334                 /// </summary>
1335                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1336                 {
1337                         int value = ic.Value;
1338
1339                         if (target_type == TypeManager.sbyte_type){
1340                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1341                                         return new SByteConstant ((sbyte) value, ic.Location);
1342                         } else if (target_type == TypeManager.byte_type){
1343                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1344                                         return new ByteConstant ((byte) value, ic.Location);
1345                         } else if (target_type == TypeManager.short_type){
1346                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1347                                         return new ShortConstant ((short) value, ic.Location);
1348                         } else if (target_type == TypeManager.ushort_type){
1349                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1350                                         return new UShortConstant ((ushort) value, ic.Location);
1351                         } else if (target_type == TypeManager.uint32_type){
1352                                 if (value >= 0)
1353                                         return new UIntConstant ((uint) value, ic.Location);
1354                         } else if (target_type == TypeManager.uint64_type){
1355                                 //
1356                                 // we can optimize this case: a positive int32
1357                                 // always fits on a uint64.  But we need an opcode
1358                                 // to do it.
1359                                 //
1360                                 if (value >= 0)
1361                                         return new ULongConstant ((ulong) value, ic.Location);
1362                         } else if (target_type == TypeManager.double_type)
1363                                 return new DoubleConstant ((double) value, ic.Location);
1364                         else if (target_type == TypeManager.float_type)
1365                                 return new FloatConstant ((float) value, ic.Location);
1366
1367                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1368                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1369                                 Constant e = (Constant) ic;
1370
1371                                 //
1372                                 // Possibly, we need to create a different 0 literal before passing
1373                                 // to EnumConstant
1374                                 //
1375                                 if (underlying == TypeManager.int64_type)
1376                                         e = new LongLiteral (0, ic.Location);
1377                                 else if (underlying == TypeManager.uint64_type)
1378                                         e = new ULongLiteral (0, ic.Location);
1379
1380                                 return new EnumConstant (e, target_type);
1381                         }
1382
1383                         //
1384                         // If `target_type' is an interface and the type of `ic' implements the interface
1385                         // e.g. target_type is IComparable, IConvertible, IFormattable
1386                         //
1387                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1388                                 return new BoxedCast (ic, target_type);
1389
1390                         return null;
1391                 }
1392
1393                 /// <summary>
1394                 ///   Attempts to implicitly convert `source' into `target_type', using
1395                 ///   ImplicitConversion.  If there is no implicit conversion, then
1396                 ///   an error is signaled
1397                 /// </summary>
1398                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1399                                                                      Type target_type, Location loc)
1400                 {
1401                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1402                         if (e != null)
1403                                 return e;
1404
1405                         source.Error_ValueCannotBeConverted (loc, target_type, false);
1406                         return null;
1407                 }
1408
1409                 /// <summary>
1410                 ///   Performs the explicit numeric conversions
1411                 /// </summary>
1412                 public static Expression ExplicitNumericConversion (Expression expr, Type target_type)
1413                 {
1414                         Type expr_type = expr.Type;
1415                         Type real_target_type = target_type;
1416
1417                         if (expr_type == TypeManager.sbyte_type){
1418                                 //
1419                                 // From sbyte to byte, ushort, uint, ulong, char
1420                                 //
1421                                 if (real_target_type == TypeManager.byte_type)
1422                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1423                                 if (real_target_type == TypeManager.ushort_type)
1424                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1425                                 if (real_target_type == TypeManager.uint32_type)
1426                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1427                                 if (real_target_type == TypeManager.uint64_type)
1428                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1429                                 if (real_target_type == TypeManager.char_type)
1430                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1431                         } else if (expr_type == TypeManager.byte_type){
1432                                 //
1433                                 // From byte to sbyte and char
1434                                 //
1435                                 if (real_target_type == TypeManager.sbyte_type)
1436                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1437                                 if (real_target_type == TypeManager.char_type)
1438                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1439                         } else if (expr_type == TypeManager.short_type){
1440                                 //
1441                                 // From short to sbyte, byte, ushort, uint, ulong, char
1442                                 //
1443                                 if (real_target_type == TypeManager.sbyte_type)
1444                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1445                                 if (real_target_type == TypeManager.byte_type)
1446                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1447                                 if (real_target_type == TypeManager.ushort_type)
1448                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1449                                 if (real_target_type == TypeManager.uint32_type)
1450                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1451                                 if (real_target_type == TypeManager.uint64_type)
1452                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1453                                 if (real_target_type == TypeManager.char_type)
1454                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1455                         } else if (expr_type == TypeManager.ushort_type){
1456                                 //
1457                                 // From ushort to sbyte, byte, short, char
1458                                 //
1459                                 if (real_target_type == TypeManager.sbyte_type)
1460                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1461                                 if (real_target_type == TypeManager.byte_type)
1462                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1463                                 if (real_target_type == TypeManager.short_type)
1464                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1465                                 if (real_target_type == TypeManager.char_type)
1466                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1467                         } else if (expr_type == TypeManager.int32_type){
1468                                 //
1469                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1470                                 //
1471                                 if (real_target_type == TypeManager.sbyte_type)
1472                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1473                                 if (real_target_type == TypeManager.byte_type)
1474                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1475                                 if (real_target_type == TypeManager.short_type)
1476                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1477                                 if (real_target_type == TypeManager.ushort_type)
1478                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1479                                 if (real_target_type == TypeManager.uint32_type)
1480                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1481                                 if (real_target_type == TypeManager.uint64_type)
1482                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1483                                 if (real_target_type == TypeManager.char_type)
1484                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1485                         } else if (expr_type == TypeManager.uint32_type){
1486                                 //
1487                                 // From uint to sbyte, byte, short, ushort, int, char
1488                                 //
1489                                 if (real_target_type == TypeManager.sbyte_type)
1490                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1491                                 if (real_target_type == TypeManager.byte_type)
1492                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1493                                 if (real_target_type == TypeManager.short_type)
1494                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1495                                 if (real_target_type == TypeManager.ushort_type)
1496                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1497                                 if (real_target_type == TypeManager.int32_type)
1498                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1499                                 if (real_target_type == TypeManager.char_type)
1500                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1501                         } else if (expr_type == TypeManager.int64_type){
1502                                 //
1503                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1504                                 //
1505                                 if (real_target_type == TypeManager.sbyte_type)
1506                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1507                                 if (real_target_type == TypeManager.byte_type)
1508                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1509                                 if (real_target_type == TypeManager.short_type)
1510                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1511                                 if (real_target_type == TypeManager.ushort_type)
1512                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1513                                 if (real_target_type == TypeManager.int32_type)
1514                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1515                                 if (real_target_type == TypeManager.uint32_type)
1516                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1517                                 if (real_target_type == TypeManager.uint64_type)
1518                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1519                                 if (real_target_type == TypeManager.char_type)
1520                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1521                         } else if (expr_type == TypeManager.uint64_type){
1522                                 //
1523                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1524                                 //
1525                                 if (real_target_type == TypeManager.sbyte_type)
1526                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1527                                 if (real_target_type == TypeManager.byte_type)
1528                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1529                                 if (real_target_type == TypeManager.short_type)
1530                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1531                                 if (real_target_type == TypeManager.ushort_type)
1532                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1533                                 if (real_target_type == TypeManager.int32_type)
1534                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1535                                 if (real_target_type == TypeManager.uint32_type)
1536                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1537                                 if (real_target_type == TypeManager.int64_type)
1538                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1539                                 if (real_target_type == TypeManager.char_type)
1540                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1541                         } else if (expr_type == TypeManager.char_type){
1542                                 //
1543                                 // From char to sbyte, byte, short
1544                                 //
1545                                 if (real_target_type == TypeManager.sbyte_type)
1546                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1547                                 if (real_target_type == TypeManager.byte_type)
1548                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1549                                 if (real_target_type == TypeManager.short_type)
1550                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1551                         } else if (expr_type == TypeManager.float_type){
1552                                 //
1553                                 // From float to sbyte, byte, short,
1554                                 // ushort, int, uint, long, ulong, char
1555                                 // or decimal
1556                                 //
1557                                 if (real_target_type == TypeManager.sbyte_type)
1558                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1559                                 if (real_target_type == TypeManager.byte_type)
1560                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1561                                 if (real_target_type == TypeManager.short_type)
1562                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1563                                 if (real_target_type == TypeManager.ushort_type)
1564                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1565                                 if (real_target_type == TypeManager.int32_type)
1566                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1567                                 if (real_target_type == TypeManager.uint32_type)
1568                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1569                                 if (real_target_type == TypeManager.int64_type)
1570                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1571                                 if (real_target_type == TypeManager.uint64_type)
1572                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1573                                 if (real_target_type == TypeManager.char_type)
1574                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1575                                 if (real_target_type == TypeManager.decimal_type)
1576                                         return new CastToDecimal (expr, true);
1577                         } else if (expr_type == TypeManager.double_type){
1578                                 //
1579                                 // From double to sbyte, byte, short,
1580                                 // ushort, int, uint, long, ulong,
1581                                 // char, float or decimal
1582                                 //
1583                                 if (real_target_type == TypeManager.sbyte_type)
1584                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1585                                 if (real_target_type == TypeManager.byte_type)
1586                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1587                                 if (real_target_type == TypeManager.short_type)
1588                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1589                                 if (real_target_type == TypeManager.ushort_type)
1590                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1591                                 if (real_target_type == TypeManager.int32_type)
1592                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1593                                 if (real_target_type == TypeManager.uint32_type)
1594                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1595                                 if (real_target_type == TypeManager.int64_type)
1596                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1597                                 if (real_target_type == TypeManager.uint64_type)
1598                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1599                                 if (real_target_type == TypeManager.char_type)
1600                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1601                                 if (real_target_type == TypeManager.float_type)
1602                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1603                                 if (real_target_type == TypeManager.decimal_type)
1604                                         return new CastToDecimal (expr, true);
1605                         } else if (expr_type == TypeManager.decimal_type) {
1606                                 return new CastFromDecimal (expr, target_type).Resolve ();
1607                         }
1608                         return null;
1609                 }
1610
1611                 /// <summary>
1612                 ///  Returns whether an explicit reference conversion can be performed
1613                 ///  from source_type to target_type
1614                 /// </summary>
1615                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1616                 {
1617                         bool target_is_type_param = target_type.IsGenericParameter;
1618                         bool target_is_value_type = target_type.IsValueType;
1619
1620                         if (source_type == target_type)
1621                                 return true;
1622
1623                         //
1624                         // From generic parameter to any type
1625                         //
1626                         if (source_type.IsGenericParameter)
1627                                 return ExplicitTypeParameterConversionExists (source_type, target_type);
1628
1629                         //
1630                         // From object to a generic parameter
1631                         //
1632                         if (source_type == TypeManager.object_type && target_is_type_param)
1633                                 return true;
1634
1635                         //
1636                         // From object to any reference type
1637                         //
1638                         if (source_type == TypeManager.object_type && !target_is_value_type)
1639                                 return true;
1640
1641                         //
1642                         // From any class S to any class-type T, provided S is a base class of T
1643                         //
1644                         if (TypeManager.IsSubclassOf (target_type, source_type))
1645                                 return true;
1646
1647                         //
1648                         // From any interface type S to any interface T provided S is not derived from T
1649                         //
1650                         if (source_type.IsInterface && target_type.IsInterface){
1651                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1652                                         return true;
1653                         }
1654
1655                         //
1656                         // From any class type S to any interface T, provided S is not sealed
1657                         // and provided S does not implement T.
1658                         //
1659                         if (target_type.IsInterface && !source_type.IsSealed &&
1660                             !TypeManager.ImplementsInterface (source_type, target_type))
1661                                 return true;
1662
1663                         //
1664                         // From any interface-type S to to any class type T, provided T is not
1665                         // sealed, or provided T implements S.
1666                         //
1667                         if (source_type.IsInterface &&
1668                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1669                                 return true;
1670
1671
1672                         // From an array type S with an element type Se to an array type T with an
1673                         // element type Te provided all the following are true:
1674                         //     * S and T differe only in element type, in other words, S and T
1675                         //       have the same number of dimensions.
1676                         //     * Both Se and Te are reference types
1677                         //     * An explicit referenc conversions exist from Se to Te
1678                         //
1679                         if (source_type.IsArray && target_type.IsArray) {
1680                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1681
1682                                         Type source_element_type = TypeManager.GetElementType (source_type);
1683                                         Type target_element_type = TypeManager.GetElementType (target_type);
1684
1685                                         if (source_element_type.IsGenericParameter ||
1686                                             (!source_element_type.IsValueType && !target_element_type.IsValueType))
1687                                                 if (ExplicitReferenceConversionExists (source_element_type,
1688                                                                                        target_element_type))
1689                                                         return true;
1690                                 }
1691                         }
1692
1693
1694                         // From System.Array to any array-type
1695                         if (source_type == TypeManager.array_type &&
1696                             target_type.IsArray){
1697                                 return true;
1698                         }
1699
1700                         //
1701                         // From System delegate to any delegate-type
1702                         //
1703                         if (source_type == TypeManager.delegate_type &&
1704                             TypeManager.IsDelegateType (target_type))
1705                                 return true;
1706
1707                         //
1708                         // From ICloneable to Array or Delegate types
1709                         //
1710                         if (source_type == TypeManager.icloneable_type &&
1711                             (target_type == TypeManager.array_type ||
1712                              target_type == TypeManager.delegate_type))
1713                                 return true;
1714
1715                         return false;
1716                 }
1717
1718                 /// <summary>
1719                 ///   Implements Explicit Reference conversions
1720                 /// </summary>
1721                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1722                 {
1723                         Type source_type = source.Type;
1724                         bool target_is_type_param = target_type.IsGenericParameter;
1725                         bool target_is_value_type = target_type.IsValueType;
1726
1727                         //
1728                         // From object to a generic parameter
1729                         //
1730                         if (source_type == TypeManager.object_type && target_is_type_param)
1731                                 return new UnboxCast (source, target_type);
1732
1733                         //
1734                         // Explicit type parameter conversion.
1735                         //
1736
1737                         if (source_type.IsGenericParameter)
1738                                 return ExplicitTypeParameterConversion (source, target_type);
1739
1740                         //
1741                         // From object to any reference type
1742                         //
1743                         if (source_type == TypeManager.object_type && !target_is_value_type)
1744                                 return new ClassCast (source, target_type);
1745
1746                         //
1747                         // Unboxing conversion.
1748                         //
1749                         if (((source_type == TypeManager.enum_type &&
1750                                 !(source is EmptyCast)) ||
1751                                 source_type == TypeManager.value_type) && target_is_value_type)
1752                                 return new UnboxCast (source, target_type);
1753
1754                         //
1755                         // From any class S to any class-type T, provided S is a base class of T
1756                         //
1757                         if (TypeManager.IsSubclassOf (target_type, source_type))
1758                                 return new ClassCast (source, target_type);
1759
1760                         //
1761                         // From any interface type S to any interface T provided S is not derived from T
1762                         //
1763                         if (source_type.IsInterface && target_type.IsInterface){
1764                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1765                                         return null;
1766                                 else
1767                                         return new ClassCast (source, target_type);
1768                         }
1769
1770                         //
1771                         // From any class type S to any interface T, provides S is not sealed
1772                         // and provided S does not implement T.
1773                         //
1774                         if (target_type.IsInterface && !source_type.IsSealed) {
1775                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1776                                         return null;
1777                                 else
1778                                         return new ClassCast (source, target_type);
1779
1780                         }
1781
1782                         //
1783                         // From any interface-type S to to any class type T, provided T is not
1784                         // sealed, or provided T implements S.
1785                         //
1786                         if (source_type.IsInterface) {
1787                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1788                                         if (target_type.IsClass)
1789                                                 return new ClassCast (source, target_type);
1790                                         else
1791                                                 return new UnboxCast (source, target_type);
1792                                 }
1793
1794                                 return null;
1795                         }
1796
1797                         // From an array type S with an element type Se to an array type T with an
1798                         // element type Te provided all the following are true:
1799                         //     * S and T differe only in element type, in other words, S and T
1800                         //       have the same number of dimensions.
1801                         //     * Both Se and Te are reference types
1802                         //     * An explicit referenc conversions exist from Se to Te
1803                         //
1804                         if (source_type.IsArray && target_type.IsArray) {
1805                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1806
1807                                         Type source_element_type = TypeManager.GetElementType (source_type);
1808                                         Type target_element_type = TypeManager.GetElementType (target_type);
1809
1810                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1811                                                 if (ExplicitReferenceConversionExists (source_element_type,
1812                                                                                        target_element_type))
1813                                                         return new ClassCast (source, target_type);
1814                                 }
1815                         }
1816
1817
1818                         // From System.Array to any array-type
1819                         if (source_type == TypeManager.array_type &&
1820                             target_type.IsArray) {
1821                                 return new ClassCast (source, target_type);
1822                         }
1823
1824                         //
1825                         // From System delegate to any delegate-type
1826                         //
1827                         if (source_type == TypeManager.delegate_type &&
1828                             TypeManager.IsDelegateType (target_type))
1829                                 return new ClassCast (source, target_type);
1830
1831                         //
1832                         // From ICloneable to Array or Delegate types
1833                         //
1834                         if (source_type == TypeManager.icloneable_type &&
1835                             (target_type == TypeManager.array_type ||
1836                              target_type == TypeManager.delegate_type))
1837                                 return new ClassCast (source, target_type);
1838
1839                         return null;
1840                 }
1841
1842                 /// <summary>
1843                 ///   Performs an explicit conversion of the expression `expr' whose
1844                 ///   type is expr.Type to `target_type'.
1845                 /// </summary>
1846                 static public Expression ExplicitConversionCore (EmitContext ec, Expression expr,
1847                                                                  Type target_type, Location loc)
1848                 {
1849                         Type expr_type = expr.Type;
1850
1851                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1852                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1853                         if (ne != null)
1854                                 return ne;
1855
1856                         //
1857                         // Unboxing conversions; only object types can be convertible to enum
1858                         //
1859                         if (expr_type == TypeManager.object_type && target_type.IsValueType || expr_type == TypeManager.enum_type)
1860                                 return new UnboxCast (expr, target_type);
1861
1862                         if (TypeManager.IsEnumType (expr_type)) {
1863                                 if (expr is EnumConstant)
1864                                         return ExplicitConversionCore (ec, ((EnumConstant) expr).Child, target_type, loc);
1865
1866                                 return ExplicitConversionCore (ec, new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type)), target_type, loc);
1867                         }
1868
1869                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1870                                 return new Nullable.LiftedConversion (
1871                                         expr, target_type, false, true, loc).Resolve (ec);
1872
1873                         if (TypeManager.IsEnumType (target_type)){
1874                                 Expression ce = ExplicitConversionCore (ec, expr, TypeManager.EnumToUnderlying (target_type), loc);
1875                                 if (ce != null)
1876                                         return new EmptyCast (ce, target_type);
1877                         }
1878
1879                         ne = ExplicitNumericConversion (expr, target_type);
1880                         if (ne != null)
1881                                 return ne;
1882
1883                         //
1884                         // Skip the ExplicitReferenceConversion because we can not convert
1885                         // from Null to a ValueType, and ExplicitReference wont check against
1886                         // null literal explicitly
1887                         //
1888                         if (expr_type != TypeManager.null_type){
1889                                 ne = ExplicitReferenceConversion (expr, target_type);
1890                                 if (ne != null)
1891                                         return ne;
1892                         }
1893
1894                         if (ec.InUnsafe){
1895                                 ne = ExplicitUnsafe (expr, target_type);
1896                                 if (ne != null)
1897                                         return ne;
1898                         }
1899
1900                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1901                         if (ne != null)
1902                                 return ne;
1903
1904                         return null;
1905                 }
1906
1907                 public static Expression ExplicitUnsafe (Expression expr, Type target_type)
1908                 {
1909                         Type expr_type = expr.Type;
1910
1911                         if (target_type.IsPointer){
1912                                 if (expr_type.IsPointer)
1913                                         return new EmptyCast (expr, target_type);
1914
1915                                 if (expr_type == TypeManager.sbyte_type ||
1916                                         expr_type == TypeManager.short_type ||
1917                                         expr_type == TypeManager.int32_type ||
1918                                         expr_type == TypeManager.int64_type)
1919                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1920
1921                                 if (expr_type == TypeManager.ushort_type ||
1922                                         expr_type == TypeManager.uint32_type ||
1923                                         expr_type == TypeManager.uint64_type ||
1924                                         expr_type == TypeManager.byte_type)
1925                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1926                         }
1927
1928                         if (expr_type.IsPointer){
1929                                 if (target_type == TypeManager.sbyte_type)
1930                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1931                                 else if (target_type == TypeManager.byte_type)
1932                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1933                                 else if (target_type == TypeManager.short_type)
1934                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1935                                 else if (target_type == TypeManager.ushort_type)
1936                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1937                                 else if (target_type == TypeManager.int32_type)
1938                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1939                                 else if (target_type == TypeManager.uint32_type)
1940                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1941                                 else if (target_type == TypeManager.uint64_type)
1942                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1943                                 else if (target_type == TypeManager.int64_type){
1944                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1945                                 }
1946                         }
1947                         return null;
1948                 }
1949
1950                 /// <summary>
1951                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1952                 /// </summary>
1953                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1954                                                                      Type target_type, Location l)
1955                 {
1956                         int errors = Report.Errors;
1957                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1958                         if (Report.Errors > errors)
1959                                 return null;
1960
1961                         if (ne != null)
1962                                 return ne;
1963
1964                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
1965                                 return new Nullable.LiftedConversion (
1966                                         expr, target_type, false, true, l).Resolve (ec);
1967
1968                         ne = ExplicitNumericConversion (expr, target_type);
1969                         if (ne != null)
1970                                 return ne;
1971
1972                         ne = ExplicitReferenceConversion (expr, target_type);
1973                         if (ne != null)
1974                                 return ne;
1975
1976                         if (ec.InUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
1977                                 return new EmptyCast (expr, target_type);
1978
1979                         expr.Error_ValueCannotBeConverted (l, target_type, true);
1980                         return null;
1981                 }
1982
1983                 /// <summary>
1984                 ///   Performs an explicit conversion of the expression `expr' whose
1985                 ///   type is expr.Type to `target_type'.
1986                 /// </summary>
1987                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1988                         Type target_type, Location loc)
1989                 {
1990                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
1991                         if (e != null)
1992                                 return e;
1993
1994                         expr.Error_ValueCannotBeConverted (loc, target_type, true);
1995                         return null;
1996                 }
1997         }
1998 }