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 (TypeManager.IsNullableTypeOf (target_type, expr_type))
 828                                 return true;
 829
 830                         if (expr_type == TypeManager.anonymous_method_type){
 831                                 if (!TypeManager.IsDelegateType (target_type))
 832                                         return false;
 833
 834                                 AnonymousMethod am = (AnonymousMethod) expr;
 835                                 return am.ImplicitStandardConversionExists (target_type);
 836                         }
 837
 838                         return false;
 839                 }
 840
 841                 /// <summary>
 842                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 843                 ///  amongst the methods in the MethodGroupExpr
 844                 /// </summary>
 845                 static Type FindMostEncompassedType (ArrayList types)
 846                 {
 847                         Type best = null;
 848
 849                         if (types.Count == 0)
 850                                 return null;
 851
 852                         if (types.Count == 1)
 853                                 return (Type) types [0];
 854
 855                         EmptyExpression expr = EmptyExpression.Grab ();
 856
 857                         foreach (Type t in types) {
 858                                 if (best == null) {
 859                                         best = t;
 860                                         continue;
 861                                 }
 862
 863                                 expr.SetType (t);
 864                                 if (ImplicitStandardConversionExists (expr, best))
 865                                         best = t;
 866                         }
 867
 868                         expr.SetType (best);
 869                         foreach (Type t in types) {
 870                                 if (best == t)
 871                                         continue;
 872                                 if (!ImplicitStandardConversionExists (expr, t)) {
 873                                         best = null;
 874                                         break;
 875                                 }
 876                         }
 877
 878                         EmptyExpression.Release (expr);
 879
 880                         return best;
 881                 }
 882
 883                 /// <summary>
 884                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 885                 ///  amongst the types in the given set
 886                 /// </summary>
 887                 static Type FindMostEncompassingType (ArrayList types)
 888                 {
 889                         Type best = null;
 890
 891                         if (types.Count == 0)
 892                                 return null;
 893
 894                         if (types.Count == 1)
 895                                 return (Type) types [0];
 896
 897                         EmptyExpression expr = EmptyExpression.Grab ();
 898
 899                         foreach (Type t in types) {
 900                                 if (best == null) {
 901                                         best = t;
 902                                         continue;
 903                                 }
 904
 905                                 expr.SetType (best);
 906                                 if (ImplicitStandardConversionExists (expr, t))
 907                                         best = t;
 908                         }
 909
 910                         foreach (Type t in types) {
 911                                 if (best == t)
 912                                         continue;
 913                                 expr.SetType (t);
 914                                 if (!ImplicitStandardConversionExists (expr, best)) {
 915                                         best = null;
 916                                         break;
 917                                 }
 918                         }
 919
 920                         EmptyExpression.Release (expr);
 921
 922                         return best;
 923                 }
 924
 925                 /// <summary>
 926                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 927                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 928                 ///   for explicit and implicit conversion operators.
 929                 /// </summary>
 930                 static public Type FindMostSpecificSource (IList list,
 931                                                            Expression source, bool apply_explicit_conv_rules)
 932                 {
 933                         ArrayList src_types_set = new ArrayList ();
 934
 935                         //
 936                         // If any operator converts from S then Sx = S
 937                         //
 938                         Type source_type = source.Type;
 939                         foreach (MethodBase mb in list){
 940                                 ParameterData pd = TypeManager.GetParameterData (mb);
 941                                 Type param_type = pd.ParameterType (0);
 942
 943                                 if (param_type == source_type)
 944                                         return param_type;
 945
 946                                 src_types_set.Add (param_type);
 947                         }
 948
 949                         //
 950                         // Explicit Conv rules
 951                         //
 952                         if (apply_explicit_conv_rules) {
 953                                 ArrayList candidate_set = new ArrayList ();
 954
 955                                 foreach (Type param_type in src_types_set){
 956                                         if (ImplicitStandardConversionExists (source, param_type))
 957                                                 candidate_set.Add (param_type);
 958                                 }
 959
 960                                 if (candidate_set.Count != 0)
 961                                         return FindMostEncompassedType (candidate_set);
 962                         }
 963
 964                         //
 965                         // Final case
 966                         //
 967                         if (apply_explicit_conv_rules)
 968                                 return FindMostEncompassingType (src_types_set);
 969                         else
 970                                 return FindMostEncompassedType (src_types_set);
 971                 }
 972
 973                 /// <summary>
 974                 ///  Finds the most specific target Tx according to section 13.4.4
 975                 /// </summary>
 976                 static public Type FindMostSpecificTarget (IList list,
 977                                                            Type target, bool apply_explicit_conv_rules)
 978                 {
 979                         ArrayList tgt_types_set = new ArrayList ();
 980
 981                         //
 982                         // If any operator converts to T then Tx = T
 983                         //
 984                         foreach (MethodInfo mi in list){
 985                                 Type ret_type = mi.ReturnType;
 986                                 if (ret_type == target)
 987                                         return ret_type;
 988
 989                                 tgt_types_set.Add (ret_type);
 990                         }
 991
 992                         //
 993                         // Explicit conv rules
 994                         //
 995                         if (apply_explicit_conv_rules) {
 996                                 ArrayList candidate_set = new ArrayList ();
 997
 998                                 EmptyExpression expr = EmptyExpression.Grab ();
 999
1000                                 foreach (Type ret_type in tgt_types_set){
1001                                         expr.SetType (ret_type);
1002
1003                                         if (ImplicitStandardConversionExists (expr, target))
1004                                                 candidate_set.Add (ret_type);
1005                                 }
1006
1007                                 EmptyExpression.Release (expr);
1008
1009                                 if (candidate_set.Count != 0)
1010                                         return FindMostEncompassingType (candidate_set);
1011                         }
1012
1013                         //
1014                         // Okay, final case !
1015                         //
1016                         if (apply_explicit_conv_rules)
1017                                 return FindMostEncompassedType (tgt_types_set);
1018                         else
1019                                 return FindMostEncompassingType (tgt_types_set);
1020                 }
1021
1022                 /// <summary>
1023                 ///  User-defined Implicit conversions
1024                 /// </summary>
1025                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
1026                                                                  Type target, Location loc)
1027                 {
1028                         return UserDefinedConversion (ec, source, target, loc, false);
1029                 }
1030
1031                 /// <summary>
1032                 ///  User-defined Explicit conversions
1033                 /// </summary>
1034                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1035                                                                  Type target, Location loc)
1036                 {
1037                         return UserDefinedConversion (ec, source, target, loc, true);
1038                 }
1039
1040                 static void AddConversionOperators (ArrayList list,
1041                                                     Expression source, Type target_type,
1042                                                     bool look_for_explicit,
1043                                                     MethodGroupExpr mg)
1044                 {
1045                         if (mg == null)
1046                                 return;
1047
1048                         Type source_type = source.Type;
1049                         EmptyExpression expr = EmptyExpression.Grab ();
1050                         foreach (MethodInfo m in mg.Methods) {
1051                                 ParameterData pd = TypeManager.GetParameterData (m);
1052                                 Type return_type = m.ReturnType;
1053                                 Type arg_type = pd.ParameterType (0);
1054
1055                                 if (source_type != arg_type) {
1056                                         if (!ImplicitStandardConversionExists (source, arg_type)) {
1057                                                 if (!look_for_explicit)
1058                                                         continue;
1059                                                 expr.SetType (arg_type);
1060                                                 if (!ImplicitStandardConversionExists (expr, source_type))
1061                                                         continue;
1062                                         }
1063                                 }
1064
1065                                 if (target_type != return_type) {
1066                                         expr.SetType (return_type);
1067                                         if (!ImplicitStandardConversionExists (expr, target_type)) {
1068                                                 if (!look_for_explicit)
1069                                                         continue;
1070                                                 expr.SetType (target_type);
1071                                                 if (!ImplicitStandardConversionExists (expr, return_type))
1072                                                         continue;
1073                                         }
1074                                 }
1075
1076                                 list.Add (m);
1077                         }
1078
1079                         EmptyExpression.Release (expr);
1080                 }
1081
1082                 /// <summary>
1083                 ///   Compute the user-defined conversion operator from source_type to target_type.
1084                 ///   `look_for_explicit' controls whether we should also include the list of explicit operators
1085                 /// </summary>
1086                 static MethodInfo GetConversionOperator (EmitContext ec, Expression source, Type target_type, bool look_for_explicit)
1087                 {
1088                         ArrayList ops = new ArrayList (4);
1089
1090                         Type source_type = source.Type;
1091
1092                         if (source_type != TypeManager.decimal_type) {
1093                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1094                                         Expression.MethodLookup (ec, source_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1095                                 if (look_for_explicit) {
1096                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1097                                                 Expression.MethodLookup (
1098                                                         ec, source_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1099                                 }
1100                         }
1101
1102                         if (target_type != TypeManager.decimal_type) {
1103                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1104                                         Expression.MethodLookup (ec, target_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1105                                 if (look_for_explicit) {
1106                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1107                                                 Expression.MethodLookup (
1108                                                         ec, target_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1109                                 }
1110                         }
1111
1112                         if (ops.Count == 0)
1113                                 return null;
1114
1115                         Type most_specific_source = FindMostSpecificSource (ops, source, look_for_explicit);
1116                         if (most_specific_source == null)
1117                                 return null;
1118
1119                         Type most_specific_target = FindMostSpecificTarget (ops, target_type, look_for_explicit);
1120                         if (most_specific_target == null)
1121                                 return null;
1122
1123                         MethodInfo method = null;
1124
1125                         foreach (MethodInfo m in ops) {
1126                                 if (m.ReturnType != most_specific_target)
1127                                         continue;
1128                                 if (TypeManager.GetParameterData (m).ParameterType (0) != most_specific_source)
1129                                         continue;
1130                                 // Ambiguous: more than one conversion operator satisfies the signature.
1131                                 if (method != null)
1132                                         return null;
1133                                 method = m;
1134                         }
1135
1136                         return method;
1137                 }
1138
1139                 static DoubleHash explicit_conv = new DoubleHash (100);
1140                 static DoubleHash implicit_conv = new DoubleHash (100);
1141
1142                 /// <summary>
1143                 ///   User-defined conversions
1144                 /// </summary>
1145                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1146                                                                 Type target, Location loc,
1147                                                                 bool look_for_explicit)
1148                 {
1149                         Type source_type = source.Type;
1150                         MethodInfo method = null;
1151
1152                         if (TypeManager.IsNullableType (source_type) && TypeManager.IsNullableType (target))
1153                                 return new Nullable.LiftedConversion (
1154                                         source, target, true, look_for_explicit, loc).Resolve (ec);
1155
1156                         object o;
1157                         DoubleHash hash = look_for_explicit ? explicit_conv : implicit_conv;
1158
1159                         if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
1160                                 method = (MethodInfo) o;
1161                         } else {
1162                                 method = GetConversionOperator (ec, source, target, look_for_explicit);
1163                                 if (!(source is Constant))
1164                                         hash.Insert (source_type, target, method);
1165                         }
1166
1167                         if (method == null)
1168                                 return null;
1169
1170                         Type most_specific_source = TypeManager.GetParameterData (method).ParameterType (0);
1171
1172                         //
1173                         // This will do the conversion to the best match that we
1174                         // found.  Now we need to perform an implict standard conversion
1175                         // if the best match was not the type that we were requested
1176                         // by target.
1177                         //
1178                         if (look_for_explicit)
1179                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1180                         else
1181                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1182
1183                         if (source == null)
1184                                 return null;
1185
1186                         Expression e;
1187                         e =  new UserCast (method, source, loc);
1188                         if (e.Type != target){
1189                                 if (!look_for_explicit)
1190                                         e = ImplicitConversionStandard (ec, e, target, loc);
1191                                 else
1192                                         e = ExplicitConversionStandard (ec, e, target, loc);
1193                         }
1194
1195                         return e;
1196                 }
1197
1198                 /// <summary>
1199                 ///   Converts implicitly the resolved expression `expr' into the
1200                 ///   `target_type'.  It returns a new expression that can be used
1201                 ///   in a context that expects a `target_type'.
1202                 /// </summary>
1203                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1204                                                              Type target_type, Location loc)
1205                 {
1206                         Expression e;
1207
1208                         if (target_type == null)
1209                                 throw new Exception ("Target type is null");
1210
1211                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1212                         if (e != null)
1213                                 return e;
1214
1215                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1216                         if (e != null)
1217                                 return e;
1218
1219                         return null;
1220                 }
1221
1222
1223                 /// <summary>
1224                 ///   Attempts to apply the `Standard Implicit
1225                 ///   Conversion' rules to the expression `expr' into
1226                 ///   the `target_type'.  It returns a new expression
1227                 ///   that can be used in a context that expects a
1228                 ///   `target_type'.
1229                 ///
1230                 ///   This is different from `ImplicitConversion' in that the
1231                 ///   user defined implicit conversions are excluded.
1232                 /// </summary>
1233                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1234                                                                      Type target_type, Location loc)
1235                 {
1236                         Type expr_type = expr.Type;
1237                         Expression e;
1238
1239                         if (expr is NullLiteral) {
1240                                 if (target_type.IsGenericParameter)
1241                                         return TypeParameter_to_Null (target_type, loc);
1242
1243                                 if (TypeManager.IsNullableType (target_type))
1244                                         return new Nullable.NullableLiteral (target_type, loc);
1245                         }
1246
1247                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1248                                 return new Nullable.LiftedConversion (
1249                                         expr, target_type, false, false, loc).Resolve (ec);
1250
1251                         if (expr.eclass == ExprClass.MethodGroup){
1252                                 if (!TypeManager.IsDelegateType (target_type)){
1253                                         return null;
1254                                 }
1255
1256                                 //
1257                                 // Only allow anonymous method conversions on post ISO_1
1258                                 //
1259                                 if (RootContext.Version != LanguageVersion.ISO_1){
1260                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1261                                         if (mg != null)
1262                                                 return ImplicitDelegateCreation.Create (
1263                                                         ec, mg, target_type, loc);
1264                                 }
1265                         }
1266
1267                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1268                                 return expr;
1269
1270                         e = ImplicitNumericConversion (expr, target_type);
1271                         if (e != null)
1272                                 return e;
1273
1274                         e = ImplicitReferenceConversion (expr, target_type);
1275                         if (e != null)
1276                                 return e;
1277
1278                         if (TypeManager.IsEnumType (target_type) && expr is IntLiteral){
1279                                 IntLiteral i = (IntLiteral) expr;
1280
1281                                 if (i.Value == 0)
1282                                         return new EnumConstant ((Constant) expr, target_type);
1283                         }
1284
1285                         if (ec.InUnsafe) {
1286                                 if (expr_type.IsPointer){
1287                                         if (target_type == TypeManager.void_ptr_type)
1288                                                 return new EmptyCast (expr, target_type);
1289
1290                                         //
1291                                         // yep, comparing pointer types cant be done with
1292                                         // t1 == t2, we have to compare their element types.
1293                                         //
1294                                         if (target_type.IsPointer){
1295                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1296                                                         return expr;
1297
1298                                                 //return null;
1299                                         }
1300                                 }
1301
1302                                 if (expr_type == TypeManager.null_type && target_type.IsPointer)
1303                                         return new EmptyCast (NullPointer.Null, target_type);
1304                         }
1305
1306                         if (TypeManager.IsNullableTypeOf (target_type, expr_type))
1307                                 return new Nullable.Wrap (expr, loc).Resolve (ec);
1308
1309                         if (expr_type == TypeManager.anonymous_method_type){
1310                                 if (!TypeManager.IsDelegateType (target_type)){
1311                                         Report.Error (1660, loc,
1312                                                 "Cannot convert anonymous method block to type `{0}' because it is not a delegate type",
1313                                                 TypeManager.CSharpName (target_type));
1314                                         return null;
1315                                 }
1316
1317                                 AnonymousMethod am = (AnonymousMethod) expr;
1318                                 int errors = Report.Errors;
1319
1320                                 Expression conv = am.Compatible (ec, target_type);
1321                                 if (conv != null)
1322                                         return conv;
1323
1324                                 //
1325                                 // We return something instead of null, to avoid
1326                                 // the duplicate error, since am.Compatible would have
1327                                 // reported that already
1328                                 //
1329                                 if (errors != Report.Errors)
1330                                         return new EmptyCast (expr, target_type);
1331                         }
1332
1333                         return null;
1334                 }
1335
1336                 /// <summary>
1337                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1338                 ///   into a different data type using casts (See Implicit Constant
1339                 ///   Expression Conversions)
1340                 /// </summary>
1341                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1342                 {
1343                         int value = ic.Value;
1344
1345                         if (target_type == TypeManager.sbyte_type){
1346                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1347                                         return new SByteConstant ((sbyte) value, ic.Location);
1348                         } else if (target_type == TypeManager.byte_type){
1349                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1350                                         return new ByteConstant ((byte) value, ic.Location);
1351                         } else if (target_type == TypeManager.short_type){
1352                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1353                                         return new ShortConstant ((short) value, ic.Location);
1354                         } else if (target_type == TypeManager.ushort_type){
1355                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1356                                         return new UShortConstant ((ushort) value, ic.Location);
1357                         } else if (target_type == TypeManager.uint32_type){
1358                                 if (value >= 0)
1359                                         return new UIntConstant ((uint) value, ic.Location);
1360                         } else if (target_type == TypeManager.uint64_type){
1361                                 //
1362                                 // we can optimize this case: a positive int32
1363                                 // always fits on a uint64.  But we need an opcode
1364                                 // to do it.
1365                                 //
1366                                 if (value >= 0)
1367                                         return new ULongConstant ((ulong) value, ic.Location);
1368                         } else if (target_type == TypeManager.double_type)
1369                                 return new DoubleConstant ((double) value, ic.Location);
1370                         else if (target_type == TypeManager.float_type)
1371                                 return new FloatConstant ((float) value, ic.Location);
1372
1373                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1374                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1375                                 Constant e = (Constant) ic;
1376
1377                                 //
1378                                 // Possibly, we need to create a different 0 literal before passing
1379                                 // to EnumConstant
1380                                 //
1381                                 if (underlying == TypeManager.int64_type)
1382                                         e = new LongLiteral (0, ic.Location);
1383                                 else if (underlying == TypeManager.uint64_type)
1384                                         e = new ULongLiteral (0, ic.Location);
1385
1386                                 return new EnumConstant (e, target_type);
1387                         }
1388
1389                         //
1390                         // If `target_type' is an interface and the type of `ic' implements the interface
1391                         // e.g. target_type is IComparable, IConvertible, IFormattable
1392                         //
1393                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1394                                 return new BoxedCast (ic, target_type);
1395
1396                         return null;
1397                 }
1398
1399                 /// <summary>
1400                 ///   Attempts to implicitly convert `source' into `target_type', using
1401                 ///   ImplicitConversion.  If there is no implicit conversion, then
1402                 ///   an error is signaled
1403                 /// </summary>
1404                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1405                                                                      Type target_type, Location loc)
1406                 {
1407                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1408                         if (e != null)
1409                                 return e;
1410
1411                         source.Error_ValueCannotBeConverted (loc, target_type, false);
1412                         return null;
1413                 }
1414
1415                 /// <summary>
1416                 ///   Performs the explicit numeric conversions
1417                 /// </summary>
1418                 public static Expression ExplicitNumericConversion (Expression expr, Type target_type)
1419                 {
1420                         Type expr_type = expr.Type;
1421                         Type real_target_type = target_type;
1422
1423                         if (expr_type == TypeManager.sbyte_type){
1424                                 //
1425                                 // From sbyte to byte, ushort, uint, ulong, char
1426                                 //
1427                                 if (real_target_type == TypeManager.byte_type)
1428                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1429                                 if (real_target_type == TypeManager.ushort_type)
1430                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1431                                 if (real_target_type == TypeManager.uint32_type)
1432                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1433                                 if (real_target_type == TypeManager.uint64_type)
1434                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1435                                 if (real_target_type == TypeManager.char_type)
1436                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1437                         } else if (expr_type == TypeManager.byte_type){
1438                                 //
1439                                 // From byte to sbyte and char
1440                                 //
1441                                 if (real_target_type == TypeManager.sbyte_type)
1442                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1443                                 if (real_target_type == TypeManager.char_type)
1444                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1445                         } else if (expr_type == TypeManager.short_type){
1446                                 //
1447                                 // From short to sbyte, byte, ushort, uint, ulong, char
1448                                 //
1449                                 if (real_target_type == TypeManager.sbyte_type)
1450                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1451                                 if (real_target_type == TypeManager.byte_type)
1452                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1453                                 if (real_target_type == TypeManager.ushort_type)
1454                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1455                                 if (real_target_type == TypeManager.uint32_type)
1456                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1457                                 if (real_target_type == TypeManager.uint64_type)
1458                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1459                                 if (real_target_type == TypeManager.char_type)
1460                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1461                         } else if (expr_type == TypeManager.ushort_type){
1462                                 //
1463                                 // From ushort to sbyte, byte, short, char
1464                                 //
1465                                 if (real_target_type == TypeManager.sbyte_type)
1466                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1467                                 if (real_target_type == TypeManager.byte_type)
1468                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1469                                 if (real_target_type == TypeManager.short_type)
1470                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1471                                 if (real_target_type == TypeManager.char_type)
1472                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1473                         } else if (expr_type == TypeManager.int32_type){
1474                                 //
1475                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1476                                 //
1477                                 if (real_target_type == TypeManager.sbyte_type)
1478                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1479                                 if (real_target_type == TypeManager.byte_type)
1480                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1481                                 if (real_target_type == TypeManager.short_type)
1482                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1483                                 if (real_target_type == TypeManager.ushort_type)
1484                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1485                                 if (real_target_type == TypeManager.uint32_type)
1486                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1487                                 if (real_target_type == TypeManager.uint64_type)
1488                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1489                                 if (real_target_type == TypeManager.char_type)
1490                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1491                         } else if (expr_type == TypeManager.uint32_type){
1492                                 //
1493                                 // From uint to sbyte, byte, short, ushort, int, char
1494                                 //
1495                                 if (real_target_type == TypeManager.sbyte_type)
1496                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1497                                 if (real_target_type == TypeManager.byte_type)
1498                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1499                                 if (real_target_type == TypeManager.short_type)
1500                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1501                                 if (real_target_type == TypeManager.ushort_type)
1502                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1503                                 if (real_target_type == TypeManager.int32_type)
1504                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1505                                 if (real_target_type == TypeManager.char_type)
1506                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1507                         } else if (expr_type == TypeManager.int64_type){
1508                                 //
1509                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1510                                 //
1511                                 if (real_target_type == TypeManager.sbyte_type)
1512                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1513                                 if (real_target_type == TypeManager.byte_type)
1514                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1515                                 if (real_target_type == TypeManager.short_type)
1516                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1517                                 if (real_target_type == TypeManager.ushort_type)
1518                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1519                                 if (real_target_type == TypeManager.int32_type)
1520                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1521                                 if (real_target_type == TypeManager.uint32_type)
1522                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1523                                 if (real_target_type == TypeManager.uint64_type)
1524                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1525                                 if (real_target_type == TypeManager.char_type)
1526                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1527                         } else if (expr_type == TypeManager.uint64_type){
1528                                 //
1529                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1530                                 //
1531                                 if (real_target_type == TypeManager.sbyte_type)
1532                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1533                                 if (real_target_type == TypeManager.byte_type)
1534                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1535                                 if (real_target_type == TypeManager.short_type)
1536                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1537                                 if (real_target_type == TypeManager.ushort_type)
1538                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1539                                 if (real_target_type == TypeManager.int32_type)
1540                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1541                                 if (real_target_type == TypeManager.uint32_type)
1542                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1543                                 if (real_target_type == TypeManager.int64_type)
1544                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1545                                 if (real_target_type == TypeManager.char_type)
1546                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1547                         } else if (expr_type == TypeManager.char_type){
1548                                 //
1549                                 // From char to sbyte, byte, short
1550                                 //
1551                                 if (real_target_type == TypeManager.sbyte_type)
1552                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1553                                 if (real_target_type == TypeManager.byte_type)
1554                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1555                                 if (real_target_type == TypeManager.short_type)
1556                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1557                         } else if (expr_type == TypeManager.float_type){
1558                                 //
1559                                 // From float to sbyte, byte, short,
1560                                 // ushort, int, uint, long, ulong, char
1561                                 // or decimal
1562                                 //
1563                                 if (real_target_type == TypeManager.sbyte_type)
1564                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1565                                 if (real_target_type == TypeManager.byte_type)
1566                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1567                                 if (real_target_type == TypeManager.short_type)
1568                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1569                                 if (real_target_type == TypeManager.ushort_type)
1570                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1571                                 if (real_target_type == TypeManager.int32_type)
1572                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1573                                 if (real_target_type == TypeManager.uint32_type)
1574                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1575                                 if (real_target_type == TypeManager.int64_type)
1576                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1577                                 if (real_target_type == TypeManager.uint64_type)
1578                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1579                                 if (real_target_type == TypeManager.char_type)
1580                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1581                                 if (real_target_type == TypeManager.decimal_type)
1582                                         return new CastToDecimal (expr, true);
1583                         } else if (expr_type == TypeManager.double_type){
1584                                 //
1585                                 // From double to sbyte, byte, short,
1586                                 // ushort, int, uint, long, ulong,
1587                                 // char, float or decimal
1588                                 //
1589                                 if (real_target_type == TypeManager.sbyte_type)
1590                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1591                                 if (real_target_type == TypeManager.byte_type)
1592                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1593                                 if (real_target_type == TypeManager.short_type)
1594                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1595                                 if (real_target_type == TypeManager.ushort_type)
1596                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1597                                 if (real_target_type == TypeManager.int32_type)
1598                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1599                                 if (real_target_type == TypeManager.uint32_type)
1600                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1601                                 if (real_target_type == TypeManager.int64_type)
1602                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1603                                 if (real_target_type == TypeManager.uint64_type)
1604                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1605                                 if (real_target_type == TypeManager.char_type)
1606                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1607                                 if (real_target_type == TypeManager.float_type)
1608                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1609                                 if (real_target_type == TypeManager.decimal_type)
1610                                         return new CastToDecimal (expr, true);
1611                         } else if (expr_type == TypeManager.decimal_type) {
1612                                 return new CastFromDecimal (expr, target_type).Resolve ();
1613                         }
1614                         return null;
1615                 }
1616
1617                 /// <summary>
1618                 ///  Returns whether an explicit reference conversion can be performed
1619                 ///  from source_type to target_type
1620                 /// </summary>
1621                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1622                 {
1623                         bool target_is_type_param = target_type.IsGenericParameter;
1624                         bool target_is_value_type = target_type.IsValueType;
1625
1626                         if (source_type == target_type)
1627                                 return true;
1628
1629                         //
1630                         // From generic parameter to any type
1631                         //
1632                         if (source_type.IsGenericParameter)
1633                                 return ExplicitTypeParameterConversionExists (source_type, target_type);
1634
1635                         //
1636                         // From object to a generic parameter
1637                         //
1638                         if (source_type == TypeManager.object_type && target_is_type_param)
1639                                 return true;
1640
1641                         //
1642                         // From object to any reference type
1643                         //
1644                         if (source_type == TypeManager.object_type && !target_is_value_type)
1645                                 return true;
1646
1647                         //
1648                         // From any class S to any class-type T, provided S is a base class of T
1649                         //
1650                         if (TypeManager.IsSubclassOf (target_type, source_type))
1651                                 return true;
1652
1653                         //
1654                         // From any interface type S to any interface T provided S is not derived from T
1655                         //
1656                         if (source_type.IsInterface && target_type.IsInterface){
1657                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1658                                         return true;
1659                         }
1660
1661                         //
1662                         // From any class type S to any interface T, provided S is not sealed
1663                         // and provided S does not implement T.
1664                         //
1665                         if (target_type.IsInterface && !source_type.IsSealed &&
1666                             !TypeManager.ImplementsInterface (source_type, target_type))
1667                                 return true;
1668
1669                         //
1670                         // From any interface-type S to to any class type T, provided T is not
1671                         // sealed, or provided T implements S.
1672                         //
1673                         if (source_type.IsInterface &&
1674                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1675                                 return true;
1676
1677
1678                         // From an array type S with an element type Se to an array type T with an
1679                         // element type Te provided all the following are true:
1680                         //     * S and T differe only in element type, in other words, S and T
1681                         //       have the same number of dimensions.
1682                         //     * Both Se and Te are reference types
1683                         //     * An explicit referenc conversions exist from Se to Te
1684                         //
1685                         if (source_type.IsArray && target_type.IsArray) {
1686                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1687
1688                                         Type source_element_type = TypeManager.GetElementType (source_type);
1689                                         Type target_element_type = TypeManager.GetElementType (target_type);
1690
1691                                         if (source_element_type.IsGenericParameter ||
1692                                             (!source_element_type.IsValueType && !target_element_type.IsValueType))
1693                                                 if (ExplicitReferenceConversionExists (source_element_type,
1694                                                                                        target_element_type))
1695                                                         return true;
1696                                 }
1697                         }
1698
1699
1700                         // From System.Array to any array-type
1701                         if (source_type == TypeManager.array_type &&
1702                             target_type.IsArray){
1703                                 return true;
1704                         }
1705
1706                         //
1707                         // From System delegate to any delegate-type
1708                         //
1709                         if (source_type == TypeManager.delegate_type &&
1710                             TypeManager.IsDelegateType (target_type))
1711                                 return true;
1712
1713                         //
1714                         // From ICloneable to Array or Delegate types
1715                         //
1716                         if (source_type == TypeManager.icloneable_type &&
1717                             (target_type == TypeManager.array_type ||
1718                              target_type == TypeManager.delegate_type))
1719                                 return true;
1720
1721                         return false;
1722                 }
1723
1724                 /// <summary>
1725                 ///   Implements Explicit Reference conversions
1726                 /// </summary>
1727                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1728                 {
1729                         Type source_type = source.Type;
1730                         bool target_is_type_param = target_type.IsGenericParameter;
1731                         bool target_is_value_type = target_type.IsValueType;
1732
1733                         //
1734                         // From object to a generic parameter
1735                         //
1736                         if (source_type == TypeManager.object_type && target_is_type_param)
1737                                 return new UnboxCast (source, target_type);
1738
1739                         //
1740                         // Explicit type parameter conversion.
1741                         //
1742
1743                         if (source_type.IsGenericParameter)
1744                                 return ExplicitTypeParameterConversion (source, target_type);
1745
1746                         //
1747                         // From object to any reference type
1748                         //
1749                         if (source_type == TypeManager.object_type && !target_is_value_type)
1750                                 return new ClassCast (source, target_type);
1751
1752                         //
1753                         // Unboxing conversion.
1754                         //
1755                         if (((source_type == TypeManager.enum_type &&
1756                                 !(source is EmptyCast)) ||
1757                                 source_type == TypeManager.value_type) && target_is_value_type)
1758                                 return new UnboxCast (source, target_type);
1759
1760                         //
1761                         // From any class S to any class-type T, provided S is a base class of T
1762                         //
1763                         if (TypeManager.IsSubclassOf (target_type, source_type))
1764                                 return new ClassCast (source, target_type);
1765
1766                         //
1767                         // From any interface type S to any interface T provided S is not derived from T
1768                         //
1769                         if (source_type.IsInterface && target_type.IsInterface){
1770                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1771                                         return null;
1772                                 else
1773                                         return new ClassCast (source, target_type);
1774                         }
1775
1776                         //
1777                         // From any class type S to any interface T, provides S is not sealed
1778                         // and provided S does not implement T.
1779                         //
1780                         if (target_type.IsInterface && !source_type.IsSealed) {
1781                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1782                                         return null;
1783                                 else
1784                                         return new ClassCast (source, target_type);
1785
1786                         }
1787
1788                         //
1789                         // From any interface-type S to to any class type T, provided T is not
1790                         // sealed, or provided T implements S.
1791                         //
1792                         if (source_type.IsInterface) {
1793                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1794                                         if (target_type.IsClass)
1795                                                 return new ClassCast (source, target_type);
1796                                         else
1797                                                 return new UnboxCast (source, target_type);
1798                                 }
1799
1800                                 return null;
1801                         }
1802
1803                         // From an array type S with an element type Se to an array type T with an
1804                         // element type Te provided all the following are true:
1805                         //     * S and T differe only in element type, in other words, S and T
1806                         //       have the same number of dimensions.
1807                         //     * Both Se and Te are reference types
1808                         //     * An explicit referenc conversions exist from Se to Te
1809                         //
1810                         if (source_type.IsArray && target_type.IsArray) {
1811                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1812
1813                                         Type source_element_type = TypeManager.GetElementType (source_type);
1814                                         Type target_element_type = TypeManager.GetElementType (target_type);
1815
1816                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1817                                                 if (ExplicitReferenceConversionExists (source_element_type,
1818                                                                                        target_element_type))
1819                                                         return new ClassCast (source, target_type);
1820                                 }
1821                         }
1822
1823
1824                         // From System.Array to any array-type
1825                         if (source_type == TypeManager.array_type &&
1826                             target_type.IsArray) {
1827                                 return new ClassCast (source, target_type);
1828                         }
1829
1830                         //
1831                         // From System delegate to any delegate-type
1832                         //
1833                         if (source_type == TypeManager.delegate_type &&
1834                             TypeManager.IsDelegateType (target_type))
1835                                 return new ClassCast (source, target_type);
1836
1837                         //
1838                         // From ICloneable to Array or Delegate types
1839                         //
1840                         if (source_type == TypeManager.icloneable_type &&
1841                             (target_type == TypeManager.array_type ||
1842                              target_type == TypeManager.delegate_type))
1843                                 return new ClassCast (source, target_type);
1844
1845                         return null;
1846                 }
1847
1848                 /// <summary>
1849                 ///   Performs an explicit conversion of the expression `expr' whose
1850                 ///   type is expr.Type to `target_type'.
1851                 /// </summary>
1852                 static public Expression ExplicitConversionCore (EmitContext ec, Expression expr,
1853                                                                  Type target_type, Location loc)
1854                 {
1855                         Type expr_type = expr.Type;
1856
1857                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1858                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1859                         if (ne != null)
1860                                 return ne;
1861
1862                         //
1863                         // Unboxing conversions; only object types can be convertible to enum
1864                         //
1865                         if (expr_type == TypeManager.object_type && target_type.IsValueType || expr_type == TypeManager.enum_type)
1866                                 return new UnboxCast (expr, target_type);
1867
1868                         if (TypeManager.IsEnumType (expr_type)) {
1869                                 if (expr is EnumConstant)
1870                                         return ExplicitConversionCore (ec, ((EnumConstant) expr).Child, target_type, loc);
1871
1872                                 return ExplicitConversionCore (ec, new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type)), target_type, loc);
1873                         }
1874
1875                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1876                                 return new Nullable.LiftedConversion (
1877                                         expr, target_type, false, true, loc).Resolve (ec);
1878
1879                         if (TypeManager.IsEnumType (target_type)){
1880                                 Expression ce = ExplicitConversionCore (ec, expr, TypeManager.EnumToUnderlying (target_type), loc);
1881                                 if (ce != null)
1882                                         return new EmptyCast (ce, target_type);
1883                         }
1884
1885                         ne = ExplicitNumericConversion (expr, target_type);
1886                         if (ne != null)
1887                                 return ne;
1888
1889                         //
1890                         // Skip the ExplicitReferenceConversion because we can not convert
1891                         // from Null to a ValueType, and ExplicitReference wont check against
1892                         // null literal explicitly
1893                         //
1894                         if (expr_type != TypeManager.null_type){
1895                                 ne = ExplicitReferenceConversion (expr, target_type);
1896                                 if (ne != null)
1897                                         return ne;
1898                         }
1899
1900                         if (ec.InUnsafe){
1901                                 ne = ExplicitUnsafe (expr, target_type);
1902                                 if (ne != null)
1903                                         return ne;
1904                         }
1905
1906                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1907                         if (ne != null)
1908                                 return ne;
1909
1910                         return null;
1911                 }
1912
1913                 public static Expression ExplicitUnsafe (Expression expr, Type target_type)
1914                 {
1915                         Type expr_type = expr.Type;
1916
1917                         if (target_type.IsPointer){
1918                                 if (expr_type.IsPointer)
1919                                         return new EmptyCast (expr, target_type);
1920
1921                                 if (expr_type == TypeManager.sbyte_type ||
1922                                         expr_type == TypeManager.short_type ||
1923                                         expr_type == TypeManager.int32_type ||
1924                                         expr_type == TypeManager.int64_type)
1925                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1926
1927                                 if (expr_type == TypeManager.ushort_type ||
1928                                         expr_type == TypeManager.uint32_type ||
1929                                         expr_type == TypeManager.uint64_type ||
1930                                         expr_type == TypeManager.byte_type)
1931                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1932                         }
1933
1934                         if (expr_type.IsPointer){
1935                                 if (target_type == TypeManager.sbyte_type)
1936                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1937                                 else if (target_type == TypeManager.byte_type)
1938                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1939                                 else if (target_type == TypeManager.short_type)
1940                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1941                                 else if (target_type == TypeManager.ushort_type)
1942                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1943                                 else if (target_type == TypeManager.int32_type)
1944                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1945                                 else if (target_type == TypeManager.uint32_type)
1946                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1947                                 else if (target_type == TypeManager.uint64_type)
1948                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1949                                 else if (target_type == TypeManager.int64_type){
1950                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1951                                 }
1952                         }
1953                         return null;
1954                 }
1955
1956                 /// <summary>
1957                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1958                 /// </summary>
1959                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1960                                                                      Type target_type, Location l)
1961                 {
1962                         int errors = Report.Errors;
1963                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1964                         if (Report.Errors > errors)
1965                                 return null;
1966
1967                         if (ne != null)
1968                                 return ne;
1969
1970                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
1971                                 return new Nullable.LiftedConversion (
1972                                         expr, target_type, false, true, l).Resolve (ec);
1973
1974                         ne = ExplicitNumericConversion (expr, target_type);
1975                         if (ne != null)
1976                                 return ne;
1977
1978                         ne = ExplicitReferenceConversion (expr, target_type);
1979                         if (ne != null)
1980                                 return ne;
1981
1982                         if (ec.InUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
1983                                 return new EmptyCast (expr, target_type);
1984
1985                         expr.Error_ValueCannotBeConverted (l, target_type, true);
1986                         return null;
1987                 }
1988
1989                 /// <summary>
1990                 ///   Performs an explicit conversion of the expression `expr' whose
1991                 ///   type is expr.Type to `target_type'.
1992                 /// </summary>
1993                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1994                         Type target_type, Location loc)
1995                 {
1996                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
1997                         if (e != null)
1998                                 return e;
1999
2000                         expr.Error_ValueCannotBeConverted (loc, target_type, true);
2001                         return null;
2002                 }
2003         }
2004 }