mcs/mcs/convert.cs

   1 //
   2 // conversion.cs: various routines for implementing conversions.
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Ravi Pratap (ravi@ximian.com)
   7 //
   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 #if GMCS_SOURCE
  23                 static bool TypeParameter_to_Null (Type target_type)
  24                 {
  25                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
  26                         if (gc == null)
  27                                 return false;
  28
  29                         if (gc.HasReferenceTypeConstraint)
  30                                 return true;
  31                         if (gc.HasClassConstraint && !TypeManager.IsValueType (gc.ClassConstraint))
  32                                 return true;
  33
  34                         return false;
  35                 }
  36
  37                 static Type TypeParam_EffectiveBaseType (GenericConstraints gc)
  38                 {
  39                         ArrayList list = new ArrayList ();
  40                         list.Add (gc.EffectiveBaseClass);
  41                         foreach (Type t in gc.InterfaceConstraints) {
  42                                 if (!TypeManager.IsGenericParameter (t))
  43                                         continue;
  44
  45                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  46                                 if (new_gc != null)
  47                                         list.Add (TypeParam_EffectiveBaseType (new_gc));
  48                         }
  49                         return FindMostEncompassedType (list);
  50                 }
  51 #endif
  52
  53                 //
  54                 // From a one-dimensional array-type S[] to System.Collections.IList<S> and base
  55                 // interfaces of this interface.
  56                 //
  57                 // From a one-dimensional array-type S[] to System.Collections.IList<T> and base
  58                 // interfaces of this interface, provided there is an implicit reference conversion
  59                 // from S to T.
  60                 //
  61                 static bool Array_To_IList (Type array, Type list)
  62                 {
  63 #if GMCS_SOURCE
  64                         if (!array.IsArray || (array.GetArrayRank () != 1) || !list.IsGenericType)
  65                                 return false;
  66
  67                         Type gt = list.GetGenericTypeDefinition ();
  68                         if ((gt != TypeManager.generic_ilist_type) &&
  69                             (gt != TypeManager.generic_icollection_type) &&
  70                             (gt != TypeManager.generic_ienumerable_type))
  71                                 return false;
  72
  73                         Type element_type = TypeManager.GetElementType (array);
  74                         Type arg_type = TypeManager.GetTypeArguments (list) [0];
  75
  76                         if (element_type == arg_type)
  77                                 return true;
  78
  79                         if (MyEmptyExpr == null)
  80                                 MyEmptyExpr = new EmptyExpression ();
  81                         MyEmptyExpr.SetType (TypeManager.GetElementType (array));
  82
  83                         return ImplicitReferenceConversionExists (MyEmptyExpr, arg_type);
  84 #else
  85                         return false;
  86 #endif
  87                 }
  88
  89                 static Expression ImplicitTypeParameterConversion (Expression expr,
  90                                                                    Type target_type)
  91                 {
  92 #if GMCS_SOURCE
  93                         Type expr_type = expr.Type;
  94
  95                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
  96
  97                         if (gc == null) {
  98                                 if (target_type == TypeManager.object_type)
  99                                         return new BoxedCast (expr, target_type);
 100
 101                                 return null;
 102                         }
 103
 104                         // We're converting from a type parameter which is known to be a reference type.
 105                         Type base_type = TypeParam_EffectiveBaseType (gc);
 106
 107                         if (TypeManager.IsSubclassOf (base_type, target_type))
 108                                 return new ClassCast (expr, target_type);
 109
 110                         if (target_type.IsInterface) {
 111                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 112                                         return new ClassCast (expr, target_type);
 113
 114                                 foreach (Type t in gc.InterfaceConstraints) {
 115                                         if (TypeManager.IsSubclassOf (t, target_type))
 116                                                 return new ClassCast (expr, target_type);
 117                                         if (TypeManager.ImplementsInterface (t, target_type))
 118                                                 return new ClassCast (expr, target_type);
 119                                 }
 120                         }
 121
 122                         foreach (Type t in gc.InterfaceConstraints) {
 123                                 if (!TypeManager.IsGenericParameter (t))
 124                                         continue;
 125                                 if (TypeManager.IsSubclassOf (t, target_type))
 126                                         return new ClassCast (expr, target_type);
 127                                 if (TypeManager.ImplementsInterface (t, target_type))
 128                                         return new ClassCast (expr, target_type);
 129                         }
 130 #endif
 131                         return null;
 132                 }
 133
 134                 static bool ExplicitTypeParameterConversionExists (Type source_type, Type target_type)
 135                 {
 136 #if GMCS_SOURCE
 137                         if (target_type.IsInterface)
 138                                 return true;
 139
 140                         if (TypeManager.IsGenericParameter (target_type)) {
 141                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 142                                 if (gc == null)
 143                                         return false;
 144
 145                                 foreach (Type iface in gc.InterfaceConstraints) {
 146                                         if (!TypeManager.IsGenericParameter (iface))
 147                                                 continue;
 148
 149                                         if (TypeManager.IsSubclassOf (source_type, iface))
 150                                                 return true;
 151                                 }
 152                         }
 153 #endif
 154                         return false;
 155                 }
 156
 157                 static Expression ExplicitTypeParameterConversion (Expression source, Type target_type)
 158                 {
 159 #if GMCS_SOURCE
 160                         Type source_type = source.Type;
 161
 162                         if (target_type.IsInterface)
 163                                 return new ClassCast (source, target_type);
 164
 165                         if (TypeManager.IsGenericParameter (target_type)) {
 166                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 167                                 if (gc == null)
 168                                         return null;
 169
 170                                 foreach (Type iface in gc.InterfaceConstraints) {
 171                                         if (!TypeManager.IsGenericParameter (iface))
 172                                                 continue;
 173
 174                                         if (TypeManager.IsSubclassOf (source_type, iface))
 175                                                 return new ClassCast (source, target_type);
 176                                 }
 177                         }
 178 #endif
 179                         return null;
 180                 }
 181
 182                 static EmptyExpression MyEmptyExpr;
 183                 static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
 184                 {
 185                         Type expr_type = expr.Type;
 186
 187                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 188                                 // if we are a method group, emit a warning
 189
 190                                 expr.Emit (null);
 191                         }
 192
 193                         if (expr_type == TypeManager.void_type)
 194                                 return null;
 195
 196                         if (TypeManager.IsGenericParameter (expr_type))
 197                                 return ImplicitTypeParameterConversion (expr, target_type);
 198
 199                         //
 200                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 201                         // is an abstract class, and not really a value type, so we apply the same rules.
 202                         //
 203                         if (target_type == TypeManager.object_type) {
 204                                 //
 205                                 // A pointer type cannot be converted to object
 206                                 //
 207                                 if (expr_type.IsPointer)
 208                                         return null;
 209
 210                                 if (TypeManager.IsValueType (expr_type))
 211                                         return new BoxedCast (expr, target_type);
 212                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 213                                         if (expr_type == TypeManager.anonymous_method_type)
 214                                                 return null;
 215                                         return new EmptyCast (expr, target_type);
 216                                 }
 217
 218                                 return null;
 219                         } else if (target_type == TypeManager.value_type) {
 220                                 if (TypeManager.IsValueType (expr_type))
 221                                         return new BoxedCast (expr, target_type);
 222                                 if (expr_type == TypeManager.null_type)
 223                                         return new EmptyConstantCast ((Constant)expr, target_type);
 224
 225                                 return null;
 226                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 227                                 //
 228                                 // Special case: enumeration to System.Enum.
 229                                 // System.Enum is not a value type, it is a class, so we need
 230                                 // a boxing conversion
 231                                 //
 232                                 if (expr_type.IsEnum || TypeManager.IsGenericParameter (expr_type))
 233                                         return new BoxedCast (expr, target_type);
 234
 235                                 return new EmptyCast (expr, target_type);
 236                         }
 237
 238                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 239                         // with the small distinction that we only probe there
 240                         //
 241                         // Always ensure that the code here and there is in sync
 242
 243                         // from the null type to any reference-type.
 244                         if (expr_type == TypeManager.null_type) {
 245                                 NullConstant nc = (NullConstant)expr;
 246                                 return nc.ToType(target_type);
 247                         }
 248
 249                         // from any class-type S to any interface-type T.
 250                         if (target_type.IsInterface) {
 251                                 if (target_type != TypeManager.iconvertible_type &&
 252                                     expr_type.IsValueType && (expr is Constant) &&
 253                                     !(expr is IntLiteral || expr is BoolLiteral ||
 254                                       expr is FloatLiteral || expr is DoubleLiteral ||
 255                                       expr is LongLiteral || expr is CharLiteral ||
 256                                       expr is StringLiteral || expr is DecimalLiteral ||
 257                                       expr is UIntLiteral || expr is ULongLiteral)) {
 258                                         return null;
 259                                 }
 260
 261                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 262                                         if (TypeManager.IsGenericParameter (expr_type) || TypeManager.IsValueType (expr_type))
 263                                                 return new BoxedCast (expr, target_type);
 264                                         else
 265                                                 return new EmptyCast (expr, target_type);
 266                                 }
 267                         }
 268
 269                         // from any interface type S to interface-type T.
 270                         if (expr_type.IsInterface && target_type.IsInterface) {
 271                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 272                                         return new EmptyCast (expr, target_type);
 273                                 else
 274                                         return null;
 275                         }
 276
 277                         // from an array-type S to an array-type of type T
 278                         if (expr_type.IsArray && target_type.IsArray) {
 279                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 280
 281                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 282
 283                                         if (MyEmptyExpr == null)
 284                                                 MyEmptyExpr = new EmptyExpression ();
 285
 286                                         MyEmptyExpr.SetType (expr_element_type);
 287                                         Type target_element_type = TypeManager.GetElementType (target_type);
 288
 289                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 290                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 291                                                                                       target_element_type))
 292                                                         return new EmptyCast (expr, target_type);
 293                                 }
 294                         }
 295
 296                         // from an array-type to System.Array
 297                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 298                                 return new EmptyCast (expr, target_type);
 299
 300                         // from an array-type of type T to IList<T>
 301                         if (expr_type.IsArray && Array_To_IList (expr_type, target_type))
 302                                 return new EmptyCast (expr, target_type);
 303
 304                         // from any delegate type to System.Delegate
 305                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 306                             target_type == TypeManager.delegate_type)
 307                                 return new EmptyCast (expr, target_type);
 308
 309                         // from any array-type or delegate type into System.ICloneable.
 310                         if (expr_type.IsArray ||
 311                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 312                                 if (target_type == TypeManager.icloneable_type)
 313                                         return new EmptyCast (expr, target_type);
 314
 315                         // from a generic type definition to a generic instance.
 316                         if (TypeManager.IsEqual (expr_type, target_type))
 317                                 return new EmptyCast (expr, target_type);
 318
 319                         return null;
 320                 }
 321
 322                 //
 323                 // Tests whether an implicit reference conversion exists between expr_type
 324                 // and target_type
 325                 //
 326                 public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
 327                 {
 328                         if (target_type.IsValueType)
 329                                 return false;
 330
 331                         Type expr_type = expr.Type;
 332
 333                         if (TypeManager.IsGenericParameter (expr_type))
 334                                 return ImplicitTypeParameterConversion (expr, target_type) != null;
 335
 336                         //
 337                         // This is the boxed case.
 338                         //
 339                         if (target_type == TypeManager.object_type) {
 340                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 341                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 342                                         if (target_type != TypeManager.anonymous_method_type)
 343                                         return true;
 344
 345                                 return false;
 346                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 347                                 return true;
 348
 349                         // Please remember that all code below actually comes
 350                         // from ImplicitReferenceConversion so make sure code remains in sync
 351
 352                         // from any class-type S to any interface-type T.
 353                         if (target_type.IsInterface) {
 354                                 if (target_type != TypeManager.iconvertible_type &&
 355                                     expr_type.IsValueType && (expr is Constant) &&
 356                                     !(expr is IntLiteral || expr is BoolLiteral ||
 357                                       expr is FloatLiteral || expr is DoubleLiteral ||
 358                                       expr is LongLiteral || expr is CharLiteral ||
 359                                       expr is StringLiteral || expr is DecimalLiteral ||
 360                                       expr is UIntLiteral || expr is ULongLiteral)) {
 361                                         return false;
 362                                 }
 363
 364                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 365                                         return true;
 366                         }
 367
 368                         // from any interface type S to interface-type T.
 369                         if (expr_type.IsInterface && target_type.IsInterface)
 370                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 371                                         return true;
 372
 373                         // from an array-type S to an array-type of type T
 374                         if (expr_type.IsArray && target_type.IsArray) {
 375                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 376
 377                                         Type expr_element_type = expr_type.GetElementType ();
 378
 379                                         if (MyEmptyExpr == null)
 380                                                 MyEmptyExpr = new EmptyExpression ();
 381
 382                                         MyEmptyExpr.SetType (expr_element_type);
 383                                         Type target_element_type = TypeManager.GetElementType (target_type);
 384
 385                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 386                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 387                                                                                       target_element_type))
 388                                                         return true;
 389                                 }
 390                         }
 391
 392                         // from an array-type to System.Array
 393                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 394                                 return true;
 395
 396                         // from an array-type of type T to IList<T>
 397                         if (expr_type.IsArray && Array_To_IList (expr_type, target_type))
 398                                 return true;
 399
 400                         // from any delegate type to System.Delegate
 401                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 402                             target_type == TypeManager.delegate_type)
 403                                 if (target_type.IsAssignableFrom (expr_type))
 404                                         return true;
 405
 406                         // from any array-type or delegate type into System.ICloneable.
 407                         if (expr_type.IsArray ||
 408                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 409                                 if (target_type == TypeManager.icloneable_type)
 410                                         return true;
 411
 412                         // from the null type to any reference-type.
 413                         if (expr_type == TypeManager.null_type){
 414                                 if (target_type.IsPointer)
 415                                         return true;
 416
 417                                 if (!target_type.IsValueType)
 418                                         return true;
 419                         }
 420
 421                         // from a generic type definition to a generic instance.
 422                         if (TypeManager.IsEqual (expr_type, target_type))
 423                                 return true;
 424
 425                         return false;
 426                 }
 427
 428                 /// <summary>
 429                 ///   Implicit Numeric Conversions.
 430                 ///
 431                 ///   expr is the expression to convert, returns a new expression of type
 432                 ///   target_type or null if an implicit conversion is not possible.
 433                 /// </summary>
 434                 static public Expression ImplicitNumericConversion (Expression expr,
 435                                                                     Type target_type)
 436                 {
 437                         Type expr_type = expr.Type;
 438
 439                         //
 440                         // Attempt to do the implicit constant expression conversions
 441
 442                         if (expr is Constant){
 443                                 if (expr is IntConstant){
 444                                         Expression e;
 445
 446                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 447
 448                                         if (e != null)
 449                                                 return e;
 450                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 451                                         //
 452                                         // Try the implicit constant expression conversion
 453                                         // from long to ulong, instead of a nice routine,
 454                                         // we just inline it
 455                                         //
 456                                         long v = ((LongConstant) expr).Value;
 457                                         if (v >= 0)
 458                                                 return new ULongConstant ((ulong) v, expr.Location);
 459                                 }
 460                         }
 461
 462                         Type real_target_type = target_type;
 463
 464                         if (expr_type == TypeManager.sbyte_type){
 465                                 //
 466                                 // From sbyte to short, int, long, float, double, decimal
 467                                 //
 468                                 if (real_target_type == TypeManager.int32_type)
 469                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 470                                 if (real_target_type == TypeManager.int64_type)
 471                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 472                                 if (real_target_type == TypeManager.double_type)
 473                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 474                                 if (real_target_type == TypeManager.float_type)
 475                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 476                                 if (real_target_type == TypeManager.short_type)
 477                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 478                                 if (real_target_type == TypeManager.decimal_type)
 479                                         return new CastToDecimal (expr);
 480                         } else if (expr_type == TypeManager.byte_type){
 481                                 //
 482                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 483                                 //
 484                                 if ((real_target_type == TypeManager.short_type) ||
 485                                     (real_target_type == TypeManager.ushort_type) ||
 486                                     (real_target_type == TypeManager.int32_type) ||
 487                                     (real_target_type == TypeManager.uint32_type))
 488                                         return new EmptyCast (expr, target_type);
 489
 490                                 if (real_target_type == TypeManager.uint64_type)
 491                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 492                                 if (real_target_type == TypeManager.int64_type)
 493                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 494                                 if (real_target_type == TypeManager.float_type)
 495                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 496                                 if (real_target_type == TypeManager.double_type)
 497                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 498                                 if (real_target_type == TypeManager.decimal_type)
 499                                         return new CastToDecimal (expr);
 500
 501                         } else if (expr_type == TypeManager.short_type){
 502                                 //
 503                                 // From short to int, long, float, double, decimal
 504                                 //
 505                                 if (real_target_type == TypeManager.int32_type)
 506                                         return new EmptyCast (expr, target_type);
 507                                 if (real_target_type == TypeManager.int64_type)
 508                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 509                                 if (real_target_type == TypeManager.double_type)
 510                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 511                                 if (real_target_type == TypeManager.float_type)
 512                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 513                                 if (real_target_type == TypeManager.decimal_type)
 514                                         return new CastToDecimal (expr);
 515
 516                         } else if (expr_type == TypeManager.ushort_type){
 517                                 //
 518                                 // From ushort to int, uint, long, ulong, float, double, decimal
 519                                 //
 520                                 if (real_target_type == TypeManager.uint32_type)
 521                                         return new EmptyCast (expr, target_type);
 522
 523                                 if (real_target_type == TypeManager.uint64_type)
 524                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 525                                 if (real_target_type == TypeManager.int32_type)
 526                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 527                                 if (real_target_type == TypeManager.int64_type)
 528                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 529                                 if (real_target_type == TypeManager.double_type)
 530                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 531                                 if (real_target_type == TypeManager.float_type)
 532                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 533                                 if (real_target_type == TypeManager.decimal_type)
 534                                         return new CastToDecimal (expr);
 535                         } else if (expr_type == TypeManager.int32_type){
 536                                 //
 537                                 // From int to long, float, double, decimal
 538                                 //
 539                                 if (real_target_type == TypeManager.int64_type)
 540                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 541                                 if (real_target_type == TypeManager.double_type)
 542                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 543                                 if (real_target_type == TypeManager.float_type)
 544                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 545                                 if (real_target_type == TypeManager.decimal_type)
 546                                         return new CastToDecimal (expr);
 547                         } else if (expr_type == TypeManager.uint32_type){
 548                                 //
 549                                 // From uint to long, ulong, float, double, decimal
 550                                 //
 551                                 if (real_target_type == TypeManager.int64_type)
 552                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 553                                 if (real_target_type == TypeManager.uint64_type)
 554                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 555                                 if (real_target_type == TypeManager.double_type)
 556                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 557                                                                OpCodes.Conv_R8);
 558                                 if (real_target_type == TypeManager.float_type)
 559                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 560                                                                OpCodes.Conv_R4);
 561                                 if (real_target_type == TypeManager.decimal_type)
 562                                         return new CastToDecimal (expr);
 563                         } else if (expr_type == TypeManager.int64_type){
 564                                 //
 565                                 // From long/ulong to float, double
 566                                 //
 567                                 if (real_target_type == TypeManager.double_type)
 568                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 569                                 if (real_target_type == TypeManager.float_type)
 570                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 571                                 if (real_target_type == TypeManager.decimal_type)
 572                                         return new CastToDecimal (expr);
 573                         } else if (expr_type == TypeManager.uint64_type){
 574                                 //
 575                                 // From ulong to float, double
 576                                 //
 577                                 if (real_target_type == TypeManager.double_type)
 578                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 579                                                                OpCodes.Conv_R8);
 580                                 if (real_target_type == TypeManager.float_type)
 581                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 582                                                                OpCodes.Conv_R4);
 583                                 if (real_target_type == TypeManager.decimal_type)
 584                                         return new CastToDecimal (expr);
 585                         } else if (expr_type == TypeManager.char_type){
 586                                 //
 587                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 588                                 //
 589                                 if ((real_target_type == TypeManager.ushort_type) ||
 590                                     (real_target_type == TypeManager.int32_type) ||
 591                                     (real_target_type == TypeManager.uint32_type))
 592                                         return new EmptyCast (expr, target_type);
 593                                 if (real_target_type == TypeManager.uint64_type)
 594                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 595                                 if (real_target_type == TypeManager.int64_type)
 596                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 597                                 if (real_target_type == TypeManager.float_type)
 598                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 599                                 if (real_target_type == TypeManager.double_type)
 600                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 601                                 if (real_target_type == TypeManager.decimal_type)
 602                                         return new CastToDecimal (expr);
 603                         } else if (expr_type == TypeManager.float_type){
 604                                 //
 605                                 // float to double
 606                                 //
 607                                 if (real_target_type == TypeManager.double_type)
 608                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 609                         }
 610
 611                         return null;
 612                 }
 613
 614                 /// <summary>
 615                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 616                 ///  implicit user defined conversions - needed for overload resolution
 617                 /// </summary>
 618                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 619                 {
 620 #if GMCS_SOURCE
 621                         if (expr is NullLiteral) {
 622                                 if (TypeManager.IsGenericParameter (target_type))
 623                                         return TypeParameter_to_Null (target_type);
 624
 625                                 if (TypeManager.IsNullableType (target_type))
 626                                         return true;
 627                         }
 628 #endif
 629                         if (ImplicitStandardConversionExists (expr, target_type))
 630                                 return true;
 631
 632                         return ImplicitUserConversion (ec, expr, target_type, Location.Null) != null;
 633                 }
 634
 635                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 636                 {
 637                         return ImplicitUserConversion (ec, new EmptyExpression (source), target, Location.Null) != null;
 638                 }
 639
 640                 /// <summary>
 641                 ///  Determines if a standard implicit conversion exists from
 642                 ///  expr_type to target_type
 643                 ///
 644                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 645                 /// </summary>
 646                 public static bool ImplicitStandardConversionExists (Expression expr, Type target_type)
 647                 {
 648                         Type expr_type = expr.Type;
 649 #if GMCS_SOURCE
 650                         if (TypeManager.IsNullableType (target_type)) {
 651                                 // if implicit standard conversion S -> T exists, S -> T? and S? -> T? also exists
 652                                 target_type = TypeManager.GetTypeArguments (target_type) [0];
 653
 654                                 // S? -> T?
 655                                 if (TypeManager.IsNullableType (expr_type)) {
 656                                         EmptyExpression new_expr = EmptyExpression.Grab ();
 657                                         new_expr.SetType (TypeManager.GetTypeArguments (expr_type) [0]);
 658                                         bool retval = ImplicitStandardConversionExists (new_expr, target_type);
 659                                         EmptyExpression.Release (new_expr);
 660                                         return retval;
 661                                 }
 662                         }
 663 #endif
 664                         if (expr_type == TypeManager.void_type)
 665                                 return false;
 666
 667                         //Console.WriteLine ("Expr is {0}", expr);
 668                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 669                         if (expr_type.Equals (target_type))
 670                                 return true;
 671
 672
 673                         // First numeric conversions
 674
 675                         if (expr_type == TypeManager.sbyte_type){
 676                                 //
 677                                 // From sbyte to short, int, long, float, double, decimal
 678                                 //
 679                                 if ((target_type == TypeManager.int32_type) ||
 680                                     (target_type == TypeManager.int64_type) ||
 681                                     (target_type == TypeManager.double_type) ||
 682                                     (target_type == TypeManager.float_type)  ||
 683                                     (target_type == TypeManager.short_type) ||
 684                                     (target_type == TypeManager.decimal_type))
 685                                         return true;
 686
 687                         } else if (expr_type == TypeManager.byte_type){
 688                                 //
 689                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 690                                 //
 691                                 if ((target_type == TypeManager.short_type) ||
 692                                     (target_type == TypeManager.ushort_type) ||
 693                                     (target_type == TypeManager.int32_type) ||
 694                                     (target_type == TypeManager.uint32_type) ||
 695                                     (target_type == TypeManager.uint64_type) ||
 696                                     (target_type == TypeManager.int64_type) ||
 697                                     (target_type == TypeManager.float_type) ||
 698                                     (target_type == TypeManager.double_type) ||
 699                                     (target_type == TypeManager.decimal_type))
 700                                         return true;
 701
 702                         } else if (expr_type == TypeManager.short_type){
 703                                 //
 704                                 // From short to int, long, double, float, decimal
 705                                 //
 706                                 if ((target_type == TypeManager.int32_type) ||
 707                                     (target_type == TypeManager.int64_type) ||
 708                                     (target_type == TypeManager.double_type) ||
 709                                     (target_type == TypeManager.float_type) ||
 710                                     (target_type == TypeManager.decimal_type))
 711                                         return true;
 712
 713                         } else if (expr_type == TypeManager.ushort_type){
 714                                 //
 715                                 // From ushort to int, uint, long, ulong, double, float, decimal
 716                                 //
 717                                 if ((target_type == TypeManager.uint32_type) ||
 718                                     (target_type == TypeManager.uint64_type) ||
 719                                     (target_type == TypeManager.int32_type) ||
 720                                     (target_type == TypeManager.int64_type) ||
 721                                     (target_type == TypeManager.double_type) ||
 722                                     (target_type == TypeManager.float_type) ||
 723                                     (target_type == TypeManager.decimal_type))
 724                                         return true;
 725
 726                         } else if (expr_type == TypeManager.int32_type){
 727                                 //
 728                                 // From int to long, double, float, decimal
 729                                 //
 730                                 if ((target_type == TypeManager.int64_type) ||
 731                                     (target_type == TypeManager.double_type) ||
 732                                     (target_type == TypeManager.float_type) ||
 733                                     (target_type == TypeManager.decimal_type))
 734                                         return true;
 735
 736                         } else if (expr_type == TypeManager.uint32_type){
 737                                 //
 738                                 // From uint to long, ulong, double, float, decimal
 739                                 //
 740                                 if ((target_type == TypeManager.int64_type) ||
 741                                     (target_type == TypeManager.uint64_type) ||
 742                                     (target_type == TypeManager.double_type) ||
 743                                     (target_type == TypeManager.float_type) ||
 744                                     (target_type == TypeManager.decimal_type))
 745                                         return true;
 746
 747                         } else if ((expr_type == TypeManager.uint64_type) ||
 748                                    (expr_type == TypeManager.int64_type)) {
 749                                 //
 750                                 // From long/ulong to double, float, decimal
 751                                 //
 752                                 if ((target_type == TypeManager.double_type) ||
 753                                     (target_type == TypeManager.float_type) ||
 754                                     (target_type == TypeManager.decimal_type))
 755                                         return true;
 756
 757                         } else if (expr_type == TypeManager.char_type){
 758                                 //
 759                                 // From char to ushort, int, uint, ulong, long, float, double, decimal
 760                                 //
 761                                 if ((target_type == TypeManager.ushort_type) ||
 762                                     (target_type == TypeManager.int32_type) ||
 763                                     (target_type == TypeManager.uint32_type) ||
 764                                     (target_type == TypeManager.uint64_type) ||
 765                                     (target_type == TypeManager.int64_type) ||
 766                                     (target_type == TypeManager.float_type) ||
 767                                     (target_type == TypeManager.double_type) ||
 768                                     (target_type == TypeManager.decimal_type))
 769                                         return true;
 770
 771                         } else if (expr_type == TypeManager.float_type){
 772                                 //
 773                                 // float to double
 774                                 //
 775                                 if (target_type == TypeManager.double_type)
 776                                         return true;
 777                         }
 778
 779                         if (expr.eclass == ExprClass.MethodGroup){
 780                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
 781                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 782                                         if (mg != null){
 783                                                 return DelegateCreation.ImplicitStandardConversionExists (mg, target_type) != null;
 784                                         }
 785                                 }
 786                         }
 787
 788                         if (ImplicitReferenceConversionExists (expr, target_type))
 789                                 return true;
 790
 791                         //
 792                         // Implicit Constant Expression Conversions
 793                         //
 794                         if (expr is IntConstant){
 795                                 int value = ((IntConstant) expr).Value;
 796
 797                                 if (target_type == TypeManager.sbyte_type){
 798                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 799                                                 return true;
 800                                 } else if (target_type == TypeManager.byte_type){
 801                                         if (value >= 0 && value <= Byte.MaxValue)
 802                                                 return true;
 803                                 } else if (target_type == TypeManager.short_type){
 804                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 805                                                 return true;
 806                                 } else if (target_type == TypeManager.ushort_type){
 807                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 808                                                 return true;
 809                                 } else if (target_type == TypeManager.uint32_type){
 810                                         if (value >= 0)
 811                                                 return true;
 812                                 } else if (target_type == TypeManager.uint64_type){
 813                                          //
 814                                          // we can optimize this case: a positive int32
 815                                          // always fits on a uint64.  But we need an opcode
 816                                          // to do it.
 817                                          //
 818                                         if (value >= 0)
 819                                                 return true;
 820                                 }
 821
 822                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 823                                         return true;
 824                         }
 825
 826                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 827                                 //
 828                                 // Try the implicit constant expression conversion
 829                                 // from long to ulong, instead of a nice routine,
 830                                 // we just inline it
 831                                 //
 832                                 long v = ((LongConstant) expr).Value;
 833                                 if (v >= 0)
 834                                         return true;
 835                         }
 836
 837                         if ((target_type == TypeManager.enum_type ||
 838                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 839                              expr is IntLiteral){
 840                                 IntLiteral i = (IntLiteral) expr;
 841
 842                                 if (i.Value == 0)
 843                                         return true;
 844                         }
 845
 846                         //
 847                         // If `expr_type' implements `target_type' (which is an iface)
 848                         // see TryImplicitIntConversion
 849                         //
 850                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 851                                 return true;
 852
 853                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 854                                 return true;
 855
 856                         if (expr_type == TypeManager.anonymous_method_type){
 857                                 if (!TypeManager.IsDelegateType (target_type))
 858                                         return false;
 859
 860                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 861                                 return ame.ImplicitStandardConversionExists (target_type);
 862                         }
 863
 864                         return false;
 865                 }
 866
 867                 /// <summary>
 868                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 869                 ///  amongst the methods in the MethodGroupExpr
 870                 /// </summary>
 871                 static Type FindMostEncompassedType (ArrayList types)
 872                 {
 873                         Type best = null;
 874
 875                         if (types.Count == 0)
 876                                 return null;
 877
 878                         if (types.Count == 1)
 879                                 return (Type) types [0];
 880
 881                         EmptyExpression expr = EmptyExpression.Grab ();
 882
 883                         foreach (Type t in types) {
 884                                 if (best == null) {
 885                                         best = t;
 886                                         continue;
 887                                 }
 888
 889                                 expr.SetType (t);
 890                                 if (ImplicitStandardConversionExists (expr, best))
 891                                         best = t;
 892                         }
 893
 894                         expr.SetType (best);
 895                         foreach (Type t in types) {
 896                                 if (best == t)
 897                                         continue;
 898                                 if (!ImplicitStandardConversionExists (expr, t)) {
 899                                         best = null;
 900                                         break;
 901                                 }
 902                         }
 903
 904                         EmptyExpression.Release (expr);
 905
 906                         return best;
 907                 }
 908
 909                 /// <summary>
 910                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 911                 ///  amongst the types in the given set
 912                 /// </summary>
 913                 static Type FindMostEncompassingType (ArrayList types)
 914                 {
 915                         Type best = null;
 916
 917                         if (types.Count == 0)
 918                                 return null;
 919
 920                         if (types.Count == 1)
 921                                 return (Type) types [0];
 922
 923                         EmptyExpression expr = EmptyExpression.Grab ();
 924
 925                         foreach (Type t in types) {
 926                                 if (best == null) {
 927                                         best = t;
 928                                         continue;
 929                                 }
 930
 931                                 expr.SetType (best);
 932                                 if (ImplicitStandardConversionExists (expr, t))
 933                                         best = t;
 934                         }
 935
 936                         foreach (Type t in types) {
 937                                 if (best == t)
 938                                         continue;
 939                                 expr.SetType (t);
 940                                 if (!ImplicitStandardConversionExists (expr, best)) {
 941                                         best = null;
 942                                         break;
 943                                 }
 944                         }
 945
 946                         EmptyExpression.Release (expr);
 947
 948                         return best;
 949                 }
 950
 951                 /// <summary>
 952                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 953                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 954                 ///   for explicit and implicit conversion operators.
 955                 /// </summary>
 956                 static public Type FindMostSpecificSource (IList list,
 957                                                            Expression source, bool apply_explicit_conv_rules)
 958                 {
 959                         ArrayList src_types_set = new ArrayList ();
 960
 961                         //
 962                         // If any operator converts from S then Sx = S
 963                         //
 964                         Type source_type = source.Type;
 965                         foreach (MethodBase mb in list){
 966                                 ParameterData pd = TypeManager.GetParameterData (mb);
 967                                 Type param_type = pd.ParameterType (0);
 968
 969                                 if (param_type == source_type)
 970                                         return param_type;
 971
 972                                 src_types_set.Add (param_type);
 973                         }
 974
 975                         //
 976                         // Explicit Conv rules
 977                         //
 978                         if (apply_explicit_conv_rules) {
 979                                 ArrayList candidate_set = new ArrayList ();
 980
 981                                 foreach (Type param_type in src_types_set){
 982                                         if (ImplicitStandardConversionExists (source, param_type))
 983                                                 candidate_set.Add (param_type);
 984                                 }
 985
 986                                 if (candidate_set.Count != 0)
 987                                         return FindMostEncompassedType (candidate_set);
 988                         }
 989
 990                         //
 991                         // Final case
 992                         //
 993                         if (apply_explicit_conv_rules)
 994                                 return FindMostEncompassingType (src_types_set);
 995                         else
 996                                 return FindMostEncompassedType (src_types_set);
 997                 }
 998
 999                 /// <summary>
1000                 ///  Finds the most specific target Tx according to section 13.4.4
1001                 /// </summary>
1002                 static public Type FindMostSpecificTarget (IList list,
1003                                                            Type target, bool apply_explicit_conv_rules)
1004                 {
1005                         ArrayList tgt_types_set = new ArrayList ();
1006
1007                         //
1008                         // If any operator converts to T then Tx = T
1009                         //
1010                         foreach (MethodInfo mi in list){
1011                                 Type ret_type = mi.ReturnType;
1012                                 if (ret_type == target)
1013                                         return ret_type;
1014
1015                                 tgt_types_set.Add (ret_type);
1016                         }
1017
1018                         //
1019                         // Explicit conv rules
1020                         //
1021                         if (apply_explicit_conv_rules) {
1022                                 ArrayList candidate_set = new ArrayList ();
1023
1024                                 EmptyExpression expr = EmptyExpression.Grab ();
1025
1026                                 foreach (Type ret_type in tgt_types_set){
1027                                         expr.SetType (ret_type);
1028
1029                                         if (ImplicitStandardConversionExists (expr, target))
1030                                                 candidate_set.Add (ret_type);
1031                                 }
1032
1033                                 EmptyExpression.Release (expr);
1034
1035                                 if (candidate_set.Count != 0)
1036                                         return FindMostEncompassingType (candidate_set);
1037                         }
1038
1039                         //
1040                         // Okay, final case !
1041                         //
1042                         if (apply_explicit_conv_rules)
1043                                 return FindMostEncompassedType (tgt_types_set);
1044                         else
1045                                 return FindMostEncompassingType (tgt_types_set);
1046                 }
1047
1048                 /// <summary>
1049                 ///  User-defined Implicit conversions
1050                 /// </summary>
1051                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
1052                                                                  Type target, Location loc)
1053                 {
1054                         return UserDefinedConversion (ec, source, target, loc, false);
1055                 }
1056
1057                 /// <summary>
1058                 ///  User-defined Explicit conversions
1059                 /// </summary>
1060                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1061                                                                  Type target, Location loc)
1062                 {
1063                         return UserDefinedConversion (ec, source, target, loc, true);
1064                 }
1065
1066                 static void AddConversionOperators (ArrayList list,
1067                                                     Expression source, Type target_type,
1068                                                     bool look_for_explicit,
1069                                                     MethodGroupExpr mg)
1070                 {
1071                         if (mg == null)
1072                                 return;
1073
1074                         Type source_type = source.Type;
1075                         EmptyExpression expr = EmptyExpression.Grab ();
1076                         foreach (MethodInfo m in mg.Methods) {
1077                                 ParameterData pd = TypeManager.GetParameterData (m);
1078                                 Type return_type = m.ReturnType;
1079                                 Type arg_type = pd.ParameterType (0);
1080
1081                                 if (source_type != arg_type) {
1082                                         if (!ImplicitStandardConversionExists (source, arg_type)) {
1083                                                 if (!look_for_explicit)
1084                                                         continue;
1085                                                 expr.SetType (arg_type);
1086                                                 if (!ImplicitStandardConversionExists (expr, source_type))
1087                                                         continue;
1088                                         }
1089                                 }
1090
1091                                 if (target_type != return_type) {
1092                                         expr.SetType (return_type);
1093                                         if (!ImplicitStandardConversionExists (expr, target_type)) {
1094                                                 if (!look_for_explicit)
1095                                                         continue;
1096                                                 expr.SetType (target_type);
1097                                                 if (!ImplicitStandardConversionExists (expr, return_type))
1098                                                         continue;
1099                                         }
1100                                 }
1101
1102                                 list.Add (m);
1103                         }
1104
1105                         EmptyExpression.Release (expr);
1106                 }
1107
1108                 /// <summary>
1109                 ///   Compute the user-defined conversion operator from source_type to target_type.
1110                 ///   `look_for_explicit' controls whether we should also include the list of explicit operators
1111                 /// </summary>
1112                 static MethodInfo GetConversionOperator (Type container_type, Expression source, Type target_type, bool look_for_explicit)
1113                 {
1114                         ArrayList ops = new ArrayList (4);
1115
1116                         Type source_type = source.Type;
1117
1118                         if (source_type != TypeManager.decimal_type) {
1119                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1120                                         Expression.MethodLookup (container_type, source_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1121                                 if (look_for_explicit) {
1122                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1123                                                 Expression.MethodLookup (
1124                                                         container_type, source_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1125                                 }
1126                         }
1127
1128                         if (target_type != TypeManager.decimal_type) {
1129                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1130                                         Expression.MethodLookup (container_type, target_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1131                                 if (look_for_explicit) {
1132                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1133                                                 Expression.MethodLookup (
1134                                                         container_type, target_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1135                                 }
1136                         }
1137
1138                         if (ops.Count == 0)
1139                                 return null;
1140
1141                         Type most_specific_source = FindMostSpecificSource (ops, source, look_for_explicit);
1142                         if (most_specific_source == null)
1143                                 return null;
1144
1145                         Type most_specific_target = FindMostSpecificTarget (ops, target_type, look_for_explicit);
1146                         if (most_specific_target == null)
1147                                 return null;
1148
1149                         MethodInfo method = null;
1150
1151                         foreach (MethodInfo m in ops) {
1152                                 if (m.ReturnType != most_specific_target)
1153                                         continue;
1154                                 if (TypeManager.GetParameterData (m).ParameterType (0) != most_specific_source)
1155                                         continue;
1156                                 // Ambiguous: more than one conversion operator satisfies the signature.
1157                                 if (method != null)
1158                                         return null;
1159                                 method = m;
1160                         }
1161
1162                         return method;
1163                 }
1164
1165                 static DoubleHash explicit_conv = new DoubleHash (100);
1166                 static DoubleHash implicit_conv = new DoubleHash (100);
1167
1168                 /// <summary>
1169                 ///   User-defined conversions
1170                 /// </summary>
1171                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1172                                                                 Type target, Location loc,
1173                                                                 bool look_for_explicit)
1174                 {
1175                         Type source_type = source.Type;
1176                         MethodInfo method = null;
1177
1178                         object o;
1179                         DoubleHash hash = look_for_explicit ? explicit_conv : implicit_conv;
1180
1181                         if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
1182                                 method = (MethodInfo) o;
1183                         } else {
1184                                 method = GetConversionOperator (null, source, target, look_for_explicit);
1185                                 if (!(source is Constant))
1186                                         hash.Insert (source_type, target, method);
1187                         }
1188
1189                         if (method == null)
1190                                 return null;
1191
1192                         Type most_specific_source = TypeManager.GetParameterData (method).ParameterType (0);
1193
1194                         //
1195                         // This will do the conversion to the best match that we
1196                         // found.  Now we need to perform an implict standard conversion
1197                         // if the best match was not the type that we were requested
1198                         // by target.
1199                         //
1200                         if (look_for_explicit)
1201                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1202                         else
1203                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1204
1205                         if (source == null)
1206                                 return null;
1207
1208                         Expression e;
1209                         e =  new UserCast (method, source, loc);
1210                         if (e.Type != target){
1211                                 if (!look_for_explicit)
1212                                         e = ImplicitConversionStandard (ec, e, target, loc);
1213                                 else
1214                                         e = ExplicitConversionStandard (ec, e, target, loc);
1215                         }
1216
1217                         return e;
1218                 }
1219
1220                 /// <summary>
1221                 ///   Converts implicitly the resolved expression `expr' into the
1222                 ///   `target_type'.  It returns a new expression that can be used
1223                 ///   in a context that expects a `target_type'.
1224                 /// </summary>
1225                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1226                                                              Type target_type, Location loc)
1227                 {
1228                         Expression e;
1229
1230                         if (target_type == null)
1231                                 throw new Exception ("Target type is null");
1232
1233                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1234                         if (e != null)
1235                                 return e;
1236
1237                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1238                         if (e != null)
1239                                 return e;
1240
1241                         return null;
1242                 }
1243
1244
1245                 /// <summary>
1246                 ///   Attempts to apply the `Standard Implicit
1247                 ///   Conversion' rules to the expression `expr' into
1248                 ///   the `target_type'.  It returns a new expression
1249                 ///   that can be used in a context that expects a
1250                 ///   `target_type'.
1251                 ///
1252                 ///   This is different from `ImplicitConversion' in that the
1253                 ///   user defined implicit conversions are excluded.
1254                 /// </summary>
1255                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1256                                                                      Type target_type, Location loc)
1257                 {
1258                         Type expr_type = expr.Type;
1259                         Expression e;
1260 #if GMCS_SOURCE
1261                         // TODO: refactor to be a part of constant infrastructure
1262                         if (expr is NullLiteral) {
1263                             if (TypeManager.IsNullableType (target_type))
1264                                 return new Nullable.NullableLiteral (target_type, loc);
1265                         }
1266
1267                         if (TypeManager.IsNullableType (target_type)) {
1268                                 Type target = TypeManager.GetTypeArguments (target_type) [0];
1269
1270                                 if (TypeManager.IsNullableType (expr.Type)) {
1271                                         e = new Nullable.LiftedConversion (
1272                                                 expr, target_type, false, false, loc).Resolve (ec);
1273                                         if (e != null)
1274                                                 return e;
1275                                 } else {
1276                                         e = ImplicitConversion (ec, expr, target, loc);
1277                                         if (e != null)
1278                                                 return Nullable.Wrap.Create (e, ec);
1279                                 }
1280                         }
1281 #endif
1282                         if (expr.eclass == ExprClass.MethodGroup){
1283                                 if (!TypeManager.IsDelegateType (target_type)){
1284                                         return null;
1285                                 }
1286
1287                                 //
1288                                 // Only allow anonymous method conversions on post ISO_1
1289                                 //
1290                                 if (RootContext.Version != LanguageVersion.ISO_1){
1291                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1292                                         if (mg != null)
1293                                                 return ImplicitDelegateCreation.Create (
1294                                                         ec, mg, target_type, loc);
1295                                 }
1296                         }
1297
1298                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1299                                 return expr;
1300
1301                         e = ImplicitNumericConversion (expr, target_type);
1302                         if (e != null)
1303                                 return e;
1304
1305                         e = ImplicitReferenceConversion (expr, target_type);
1306                         if (e != null)
1307                                 return e;
1308
1309                         if (TypeManager.IsEnumType (target_type) && expr is IntLiteral){
1310                                 IntLiteral i = (IntLiteral) expr;
1311
1312                                 if (i.Value == 0)
1313                                         return new EnumConstant ((Constant) expr, target_type);
1314                         }
1315
1316                         if (ec.InUnsafe) {
1317                                 if (expr_type.IsPointer){
1318                                         if (target_type == TypeManager.void_ptr_type)
1319                                                 return new EmptyCast (expr, target_type);
1320
1321                                         //
1322                                         // yep, comparing pointer types cant be done with
1323                                         // t1 == t2, we have to compare their element types.
1324                                         //
1325                                         if (target_type.IsPointer){
1326                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1327                                                         return expr;
1328
1329                                                 //return null;
1330                                         }
1331                                 }
1332
1333                                 if (expr_type == TypeManager.null_type && target_type.IsPointer)
1334                                         return new EmptyCast (NullPointer.Null, target_type);
1335                         }
1336
1337                         if (expr_type == TypeManager.anonymous_method_type){
1338                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1339
1340                                 int errors = Report.Errors;
1341
1342                                 Expression conv = ame.Compatible (ec, target_type);
1343                                 if (conv != null)
1344                                         return conv;
1345
1346                                 //
1347                                 // We return something instead of null, to avoid
1348                                 // the duplicate error, since am.Compatible would have
1349                                 // reported that already
1350                                 //
1351                                 if (errors != Report.Errors)
1352                                         return new EmptyCast (expr, target_type);
1353                         }
1354
1355                         return null;
1356                 }
1357
1358                 /// <summary>
1359                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1360                 ///   into a different data type using casts (See Implicit Constant
1361                 ///   Expression Conversions)
1362                 /// </summary>
1363                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1364                 {
1365                         int value = ic.Value;
1366
1367                         if (target_type == TypeManager.sbyte_type){
1368                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1369                                         return new SByteConstant ((sbyte) value, ic.Location);
1370                         } else if (target_type == TypeManager.byte_type){
1371                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1372                                         return new ByteConstant ((byte) value, ic.Location);
1373                         } else if (target_type == TypeManager.short_type){
1374                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1375                                         return new ShortConstant ((short) value, ic.Location);
1376                         } else if (target_type == TypeManager.ushort_type){
1377                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1378                                         return new UShortConstant ((ushort) value, ic.Location);
1379                         } else if (target_type == TypeManager.uint32_type){
1380                                 if (value >= 0)
1381                                         return new UIntConstant ((uint) value, ic.Location);
1382                         } else if (target_type == TypeManager.uint64_type){
1383                                 //
1384                                 // we can optimize this case: a positive int32
1385                                 // always fits on a uint64.  But we need an opcode
1386                                 // to do it.
1387                                 //
1388                                 if (value >= 0)
1389                                         return new ULongConstant ((ulong) value, ic.Location);
1390                         } else if (target_type == TypeManager.double_type)
1391                                 return new DoubleConstant ((double) value, ic.Location);
1392                         else if (target_type == TypeManager.float_type)
1393                                 return new FloatConstant ((float) value, ic.Location);
1394
1395                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1396                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1397                                 Constant e = (Constant) ic;
1398
1399                                 //
1400                                 // Possibly, we need to create a different 0 literal before passing
1401                                 // to EnumConstant
1402                                 //
1403                                 if (underlying == TypeManager.int64_type)
1404                                         e = new LongLiteral (0, ic.Location);
1405                                 else if (underlying == TypeManager.uint64_type)
1406                                         e = new ULongLiteral (0, ic.Location);
1407
1408                                 return new EnumConstant (e, target_type);
1409                         }
1410
1411                         //
1412                         // If `target_type' is an interface and the type of `ic' implements the interface
1413                         // e.g. target_type is IComparable, IConvertible, IFormattable
1414                         //
1415                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1416                                 return new BoxedCast (ic, target_type);
1417
1418                         return null;
1419                 }
1420
1421                 /// <summary>
1422                 ///   Attempts to implicitly convert `source' into `target_type', using
1423                 ///   ImplicitConversion.  If there is no implicit conversion, then
1424                 ///   an error is signaled
1425                 /// </summary>
1426                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1427                                                                      Type target_type, Location loc)
1428                 {
1429                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1430                         if (e != null)
1431                                 return e;
1432
1433                         source.Error_ValueCannotBeConverted (loc, target_type, false);
1434                         return null;
1435                 }
1436
1437                 /// <summary>
1438                 ///   Performs the explicit numeric conversions
1439                 ///
1440                 /// There are a few conversions that are not part of the C# standard,
1441                 /// they were interim hacks in the C# compiler that were supposed to
1442                 /// become explicit operators in the UIntPtr class and IntPtr class,
1443                 /// but for historical reasons it did not happen, so the C# compiler
1444                 /// ended up with these special hacks.
1445                 ///
1446                 /// See bug 59800 for details.
1447                 ///
1448                 /// The conversion are:
1449                 ///   UIntPtr->SByte
1450                 ///   UIntPtr->Int16
1451                 ///   UIntPtr->Int32
1452                 ///   IntPtr->UInt64
1453                 ///   UInt64->IntPtr
1454                 ///   SByte->UIntPtr
1455                 ///   Int16->UIntPtr
1456                 ///
1457                 /// </summary>
1458                 public static Expression ExplicitNumericConversion (Expression expr, Type target_type)
1459                 {
1460                         Type expr_type = expr.Type;
1461                         Type real_target_type = target_type;
1462
1463                         if (expr_type == TypeManager.sbyte_type){
1464                                 //
1465                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1466                                 //
1467                                 if (real_target_type == TypeManager.byte_type)
1468                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1469                                 if (real_target_type == TypeManager.ushort_type)
1470                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1471                                 if (real_target_type == TypeManager.uint32_type)
1472                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1473                                 if (real_target_type == TypeManager.uint64_type)
1474                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1475                                 if (real_target_type == TypeManager.char_type)
1476                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1477
1478                                 // One of the built-in conversions that belonged in the class library
1479                                 if (real_target_type == TypeManager.uintptr_type){
1480                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
1481
1482                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1483                                 }
1484                         } else if (expr_type == TypeManager.byte_type){
1485                                 //
1486                                 // From byte to sbyte and char
1487                                 //
1488                                 if (real_target_type == TypeManager.sbyte_type)
1489                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1490                                 if (real_target_type == TypeManager.char_type)
1491                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1492                         } else if (expr_type == TypeManager.short_type){
1493                                 //
1494                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1495                                 //
1496                                 if (real_target_type == TypeManager.sbyte_type)
1497                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1498                                 if (real_target_type == TypeManager.byte_type)
1499                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1500                                 if (real_target_type == TypeManager.ushort_type)
1501                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1502                                 if (real_target_type == TypeManager.uint32_type)
1503                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1504                                 if (real_target_type == TypeManager.uint64_type)
1505                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1506                                 if (real_target_type == TypeManager.char_type)
1507                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1508
1509                                 // One of the built-in conversions that belonged in the class library
1510                                 if (real_target_type == TypeManager.uintptr_type){
1511                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1512
1513                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1514                                 }
1515                         } else if (expr_type == TypeManager.ushort_type){
1516                                 //
1517                                 // From ushort to sbyte, byte, short, char
1518                                 //
1519                                 if (real_target_type == TypeManager.sbyte_type)
1520                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1521                                 if (real_target_type == TypeManager.byte_type)
1522                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1523                                 if (real_target_type == TypeManager.short_type)
1524                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1525                                 if (real_target_type == TypeManager.char_type)
1526                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1527                         } else if (expr_type == TypeManager.int32_type){
1528                                 //
1529                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1530                                 //
1531                                 if (real_target_type == TypeManager.sbyte_type)
1532                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1533                                 if (real_target_type == TypeManager.byte_type)
1534                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1535                                 if (real_target_type == TypeManager.short_type)
1536                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1537                                 if (real_target_type == TypeManager.ushort_type)
1538                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1539                                 if (real_target_type == TypeManager.uint32_type)
1540                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1541                                 if (real_target_type == TypeManager.uint64_type)
1542                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1543                                 if (real_target_type == TypeManager.char_type)
1544                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1545
1546                                 // One of the built-in conversions that belonged in the class library
1547                                 if (real_target_type == TypeManager.uintptr_type){
1548                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1549
1550                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1551                                 }
1552                         } else if (expr_type == TypeManager.uint32_type){
1553                                 //
1554                                 // From uint to sbyte, byte, short, ushort, int, char
1555                                 //
1556                                 if (real_target_type == TypeManager.sbyte_type)
1557                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1558                                 if (real_target_type == TypeManager.byte_type)
1559                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1560                                 if (real_target_type == TypeManager.short_type)
1561                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1562                                 if (real_target_type == TypeManager.ushort_type)
1563                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1564                                 if (real_target_type == TypeManager.int32_type)
1565                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1566                                 if (real_target_type == TypeManager.char_type)
1567                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1568                         } else if (expr_type == TypeManager.int64_type){
1569                                 //
1570                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1571                                 //
1572                                 if (real_target_type == TypeManager.sbyte_type)
1573                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1574                                 if (real_target_type == TypeManager.byte_type)
1575                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1576                                 if (real_target_type == TypeManager.short_type)
1577                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1578                                 if (real_target_type == TypeManager.ushort_type)
1579                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1580                                 if (real_target_type == TypeManager.int32_type)
1581                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1582                                 if (real_target_type == TypeManager.uint32_type)
1583                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1584                                 if (real_target_type == TypeManager.uint64_type)
1585                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1586                                 if (real_target_type == TypeManager.char_type)
1587                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1588                         } else if (expr_type == TypeManager.uint64_type){
1589                                 //
1590                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1591                                 //
1592                                 if (real_target_type == TypeManager.sbyte_type)
1593                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1594                                 if (real_target_type == TypeManager.byte_type)
1595                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1596                                 if (real_target_type == TypeManager.short_type)
1597                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1598                                 if (real_target_type == TypeManager.ushort_type)
1599                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1600                                 if (real_target_type == TypeManager.int32_type)
1601                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1602                                 if (real_target_type == TypeManager.uint32_type)
1603                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1604                                 if (real_target_type == TypeManager.int64_type)
1605                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1606                                 if (real_target_type == TypeManager.char_type)
1607                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1608
1609                                 // One of the built-in conversions that belonged in the class library
1610                                 if (real_target_type == TypeManager.intptr_type){
1611                                         return new OperatorCast (new EmptyCast (expr, TypeManager.int64_type),
1612                                                                  TypeManager.intptr_type, true);
1613                                 }
1614                         } else if (expr_type == TypeManager.char_type){
1615                                 //
1616                                 // From char to sbyte, byte, short
1617                                 //
1618                                 if (real_target_type == TypeManager.sbyte_type)
1619                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1620                                 if (real_target_type == TypeManager.byte_type)
1621                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1622                                 if (real_target_type == TypeManager.short_type)
1623                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1624                         } else if (expr_type == TypeManager.float_type){
1625                                 //
1626                                 // From float to sbyte, byte, short,
1627                                 // ushort, int, uint, long, ulong, char
1628                                 // or decimal
1629                                 //
1630                                 if (real_target_type == TypeManager.sbyte_type)
1631                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1632                                 if (real_target_type == TypeManager.byte_type)
1633                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1634                                 if (real_target_type == TypeManager.short_type)
1635                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1636                                 if (real_target_type == TypeManager.ushort_type)
1637                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1638                                 if (real_target_type == TypeManager.int32_type)
1639                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1640                                 if (real_target_type == TypeManager.uint32_type)
1641                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1642                                 if (real_target_type == TypeManager.int64_type)
1643                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1644                                 if (real_target_type == TypeManager.uint64_type)
1645                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1646                                 if (real_target_type == TypeManager.char_type)
1647                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1648                                 if (real_target_type == TypeManager.decimal_type)
1649                                         return new CastToDecimal (expr, true);
1650                         } else if (expr_type == TypeManager.double_type){
1651                                 //
1652                                 // From double to sbyte, byte, short,
1653                                 // ushort, int, uint, long, ulong,
1654                                 // char, float or decimal
1655                                 //
1656                                 if (real_target_type == TypeManager.sbyte_type)
1657                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1658                                 if (real_target_type == TypeManager.byte_type)
1659                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1660                                 if (real_target_type == TypeManager.short_type)
1661                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1662                                 if (real_target_type == TypeManager.ushort_type)
1663                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1664                                 if (real_target_type == TypeManager.int32_type)
1665                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1666                                 if (real_target_type == TypeManager.uint32_type)
1667                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1668                                 if (real_target_type == TypeManager.int64_type)
1669                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1670                                 if (real_target_type == TypeManager.uint64_type)
1671                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1672                                 if (real_target_type == TypeManager.char_type)
1673                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1674                                 if (real_target_type == TypeManager.float_type)
1675                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1676                                 if (real_target_type == TypeManager.decimal_type)
1677                                         return new CastToDecimal (expr, true);
1678                         } else if (expr_type == TypeManager.uintptr_type){
1679                                 //
1680                                 // Various built-in conversions that belonged in the class library
1681                                 //
1682                                 // from uintptr to sbyte, short, int32
1683                                 //
1684                                 if (real_target_type == TypeManager.sbyte_type){
1685                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1686                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
1687                                 }
1688                                 if (real_target_type == TypeManager.short_type){
1689                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1690                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
1691                                 }
1692                                 if (real_target_type == TypeManager.int32_type){
1693                                         return new EmptyCast (new OperatorCast (expr, TypeManager.uint32_type, true),
1694                                                               TypeManager.int32_type);
1695                                 }
1696                         } else if (expr_type == TypeManager.intptr_type){
1697                                 if (real_target_type == TypeManager.uint64_type){
1698                                         return new EmptyCast (new OperatorCast (expr, TypeManager.int64_type, true),
1699                                                               TypeManager.uint64_type);
1700                                 }
1701                         } else if (expr_type == TypeManager.decimal_type) {
1702                                 return new CastFromDecimal (expr, target_type).Resolve ();
1703                         }
1704                         return null;
1705                 }
1706
1707                 /// <summary>
1708                 ///  Returns whether an explicit reference conversion can be performed
1709                 ///  from source_type to target_type
1710                 /// </summary>
1711                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1712                 {
1713                         bool target_is_type_param = TypeManager.IsGenericParameter (target_type);
1714                         bool target_is_value_type = target_type.IsValueType;
1715
1716                         if (source_type == target_type)
1717                                 return true;
1718
1719                         //
1720                         // From generic parameter to any type
1721                         //
1722                         if (TypeManager.IsGenericParameter (source_type))
1723                                 return ExplicitTypeParameterConversionExists (source_type, target_type);
1724
1725                         //
1726                         // From object to a generic parameter
1727                         //
1728                         if (source_type == TypeManager.object_type && target_is_type_param)
1729                                 return true;
1730
1731                         //
1732                         // From object to any reference type
1733                         //
1734                         if (source_type == TypeManager.object_type && !target_is_value_type)
1735                                 return true;
1736
1737                         //
1738                         // From any class S to any class-type T, provided S is a base class of T
1739                         //
1740                         if (TypeManager.IsSubclassOf (target_type, source_type))
1741                                 return true;
1742
1743                         //
1744                         // From any interface type S to any interface T provided S is not derived from T
1745                         //
1746                         if (source_type.IsInterface && target_type.IsInterface){
1747                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1748                                         return true;
1749                         }
1750
1751                         //
1752                         // From any class type S to any interface T, provided S is not sealed
1753                         // and provided S does not implement T.
1754                         //
1755                         if (target_type.IsInterface && !source_type.IsSealed &&
1756                             !TypeManager.ImplementsInterface (source_type, target_type))
1757                                 return true;
1758
1759                         //
1760                         // From any interface-type S to to any class type T, provided T is not
1761                         // sealed, or provided T implements S.
1762                         //
1763                         if (source_type.IsInterface &&
1764                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1765                                 return true;
1766
1767
1768                         // From an array type S with an element type Se to an array type T with an
1769                         // element type Te provided all the following are true:
1770                         //     * S and T differe only in element type, in other words, S and T
1771                         //       have the same number of dimensions.
1772                         //     * Both Se and Te are reference types
1773                         //     * An explicit referenc conversions exist from Se to Te
1774                         //
1775                         if (source_type.IsArray && target_type.IsArray) {
1776                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1777
1778                                         Type source_element_type = TypeManager.GetElementType (source_type);
1779                                         Type target_element_type = TypeManager.GetElementType (target_type);
1780
1781                                         if (TypeManager.IsGenericParameter (source_element_type) ||
1782                                             (!source_element_type.IsValueType && !target_element_type.IsValueType))
1783                                                 if (ExplicitReferenceConversionExists (source_element_type,
1784                                                                                        target_element_type))
1785                                                         return true;
1786                                 }
1787                         }
1788
1789
1790                         // From System.Array to any array-type
1791                         if (source_type == TypeManager.array_type &&
1792                             target_type.IsArray){
1793                                 return true;
1794                         }
1795
1796                         //
1797                         // From System delegate to any delegate-type
1798                         //
1799                         if (source_type == TypeManager.delegate_type &&
1800                             TypeManager.IsDelegateType (target_type))
1801                                 return true;
1802
1803                         //
1804                         // From ICloneable to Array or Delegate types
1805                         //
1806                         if (source_type == TypeManager.icloneable_type &&
1807                             (target_type == TypeManager.array_type ||
1808                              target_type == TypeManager.delegate_type))
1809                                 return true;
1810
1811                         return false;
1812                 }
1813
1814                 /// <summary>
1815                 ///   Implements Explicit Reference conversions
1816                 /// </summary>
1817                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1818                 {
1819                         Type source_type = source.Type;
1820                         bool target_is_type_param = TypeManager.IsGenericParameter (target_type);
1821                         bool target_is_value_type = target_type.IsValueType;
1822
1823                         //
1824                         // From object to a generic parameter
1825                         //
1826                         if (source_type == TypeManager.object_type && target_is_type_param)
1827                                 return new UnboxCast (source, target_type);
1828
1829                         //
1830                         // Explicit type parameter conversion.
1831                         //
1832
1833                         if (TypeManager.IsGenericParameter (source_type))
1834                                 return ExplicitTypeParameterConversion (source, target_type);
1835
1836                         //
1837                         // From object to any reference type
1838                         //
1839                         if (source_type == TypeManager.object_type && !target_is_value_type)
1840                                 return new ClassCast (source, target_type);
1841
1842                         //
1843                         // Unboxing conversion.
1844                         //
1845                         if (((source_type == TypeManager.enum_type &&
1846                                 !(source is EmptyCast)) ||
1847                                 source_type == TypeManager.value_type) && target_is_value_type)
1848                                 return new UnboxCast (source, target_type);
1849
1850                         //
1851                         // From any class S to any class-type T, provided S is a base class of T
1852                         //
1853                         if (TypeManager.IsSubclassOf (target_type, source_type))
1854                                 return new ClassCast (source, target_type);
1855
1856                         //
1857                         // From any interface type S to any interface T provided S is not derived from T
1858                         //
1859                         if (source_type.IsInterface && target_type.IsInterface){
1860                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1861                                         return null;
1862                                 else
1863                                         return new ClassCast (source, target_type);
1864                         }
1865
1866                         //
1867                         // From any class type S to any interface T, provides S is not sealed
1868                         // and provided S does not implement T.
1869                         //
1870                         if (target_type.IsInterface && !source_type.IsSealed) {
1871                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1872                                         return null;
1873                                 else
1874                                         return new ClassCast (source, target_type);
1875
1876                         }
1877
1878                         //
1879                         // From any interface-type S to to any class type T, provided T is not
1880                         // sealed, or provided T implements S.
1881                         //
1882                         if (source_type.IsInterface) {
1883                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1884                                         if (target_type.IsClass)
1885                                                 return new ClassCast (source, target_type);
1886                                         else
1887                                                 return new UnboxCast (source, target_type);
1888                                 }
1889
1890                                 return null;
1891                         }
1892
1893                         // From an array type S with an element type Se to an array type T with an
1894                         // element type Te provided all the following are true:
1895                         //     * S and T differe only in element type, in other words, S and T
1896                         //       have the same number of dimensions.
1897                         //     * Both Se and Te are reference types
1898                         //     * An explicit referenc conversions exist from Se to Te
1899                         //
1900                         if (source_type.IsArray && target_type.IsArray) {
1901                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1902
1903                                         Type source_element_type = TypeManager.GetElementType (source_type);
1904                                         Type target_element_type = TypeManager.GetElementType (target_type);
1905
1906                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1907                                                 if (ExplicitReferenceConversionExists (source_element_type,
1908                                                                                        target_element_type))
1909                                                         return new ClassCast (source, target_type);
1910                                 }
1911                         }
1912
1913
1914                         // From System.Array to any array-type
1915                         if (source_type == TypeManager.array_type &&
1916                             target_type.IsArray) {
1917                                 return new ClassCast (source, target_type);
1918                         }
1919
1920                         //
1921                         // From System delegate to any delegate-type
1922                         //
1923                         if (source_type == TypeManager.delegate_type &&
1924                             TypeManager.IsDelegateType (target_type))
1925                                 return new ClassCast (source, target_type);
1926
1927                         //
1928                         // From ICloneable to Array or Delegate types
1929                         //
1930                         if (source_type == TypeManager.icloneable_type &&
1931                             (target_type == TypeManager.array_type ||
1932                              target_type == TypeManager.delegate_type))
1933                                 return new ClassCast (source, target_type);
1934
1935                         return null;
1936                 }
1937
1938                 /// <summary>
1939                 ///   Performs an explicit conversion of the expression `expr' whose
1940                 ///   type is expr.Type to `target_type'.
1941                 /// </summary>
1942                 static public Expression ExplicitConversionCore (EmitContext ec, Expression expr,
1943                                                                  Type target_type, Location loc)
1944                 {
1945                         Type expr_type = expr.Type;
1946
1947                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1948                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1949                         if (ne != null)
1950                                 return ne;
1951
1952                         //
1953                         // Unboxing conversions; only object types can be convertible to enum
1954                         //
1955                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1956                                 return new UnboxCast (expr, target_type);
1957
1958                         if (TypeManager.IsEnumType (expr_type)) {
1959                                 if (expr is EnumConstant)
1960                                         return ExplicitConversionCore (ec, ((EnumConstant) expr).Child, target_type, loc);
1961
1962                                 return ExplicitConversionCore (ec, new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type)), target_type, loc);
1963                         }
1964
1965                         if (TypeManager.IsEnumType (target_type)){
1966                                 if (expr_type == TypeManager.enum_type)
1967                                         return new UnboxCast (expr, target_type);
1968
1969                                 Expression ce = ExplicitConversionCore (ec, expr, TypeManager.EnumToUnderlying (target_type), loc);
1970                                 if (ce != null)
1971                                         return new EmptyCast (ce, target_type);
1972                         }
1973
1974                         ne = ExplicitNumericConversion (expr, target_type);
1975                         if (ne != null)
1976                                 return ne;
1977
1978                         //
1979                         // Skip the ExplicitReferenceConversion because we can not convert
1980                         // from Null to a ValueType, and ExplicitReference wont check against
1981                         // null literal explicitly
1982                         //
1983                         if (expr_type != TypeManager.null_type){
1984                                 ne = ExplicitReferenceConversion (expr, target_type);
1985                                 if (ne != null)
1986                                         return ne;
1987                         }
1988
1989                         if (ec.InUnsafe){
1990                                 ne = ExplicitUnsafe (expr, target_type);
1991                                 if (ne != null)
1992                                         return ne;
1993                         }
1994
1995                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1996                         if (ne != null)
1997                                 return ne;
1998
1999                         return null;
2000                 }
2001
2002                 public static Expression ExplicitUnsafe (Expression expr, Type target_type)
2003                 {
2004                         Type expr_type = expr.Type;
2005
2006                         if (target_type.IsPointer){
2007                                 if (expr_type.IsPointer)
2008                                         return new EmptyCast (expr, target_type);
2009
2010                                 if (expr_type == TypeManager.sbyte_type ||
2011                                         expr_type == TypeManager.short_type ||
2012                                         expr_type == TypeManager.int32_type ||
2013                                         expr_type == TypeManager.int64_type)
2014                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
2015
2016                                 if (expr_type == TypeManager.ushort_type ||
2017                                         expr_type == TypeManager.uint32_type ||
2018                                         expr_type == TypeManager.uint64_type ||
2019                                         expr_type == TypeManager.byte_type)
2020                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
2021                         }
2022
2023                         if (expr_type.IsPointer){
2024                                 if (target_type == TypeManager.sbyte_type)
2025                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
2026                                 else if (target_type == TypeManager.byte_type)
2027                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
2028                                 else if (target_type == TypeManager.short_type)
2029                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
2030                                 else if (target_type == TypeManager.ushort_type)
2031                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
2032                                 else if (target_type == TypeManager.int32_type)
2033                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
2034                                 else if (target_type == TypeManager.uint32_type)
2035                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
2036                                 else if (target_type == TypeManager.uint64_type)
2037                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
2038                                 else if (target_type == TypeManager.int64_type){
2039                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
2040                                 }
2041                         }
2042                         return null;
2043                 }
2044
2045                 /// <summary>
2046                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
2047                 /// </summary>
2048                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
2049                                                                      Type target_type, Location l)
2050                 {
2051                         int errors = Report.Errors;
2052                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
2053                         if (Report.Errors > errors)
2054                                 return null;
2055
2056                         if (ne != null)
2057                                 return ne;
2058
2059                         ne = ExplicitNumericConversion (expr, target_type);
2060                         if (ne != null)
2061                                 return ne;
2062
2063                         ne = ExplicitReferenceConversion (expr, target_type);
2064                         if (ne != null)
2065                                 return ne;
2066
2067                         if (ec.InUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
2068                                 return new EmptyCast (expr, target_type);
2069
2070                         expr.Error_ValueCannotBeConverted (l, target_type, true);
2071                         return null;
2072                 }
2073
2074                 /// <summary>
2075                 ///   Performs an explicit conversion of the expression `expr' whose
2076                 ///   type is expr.Type to `target_type'.
2077                 /// </summary>
2078                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
2079                         Type target_type, Location loc)
2080                 {
2081                         Expression e;
2082 #if GMCS_SOURCE
2083                         Type expr_type = expr.Type;
2084                         if (TypeManager.IsNullableType (target_type)) {
2085                                 if (TypeManager.IsNullableType (expr_type)) {
2086                                         e = new Nullable.LiftedConversion (
2087                                                 expr, target_type, false, true, loc).Resolve (ec);
2088                                         if (e != null)
2089                                                 return e;
2090                                 } else if (expr_type == TypeManager.object_type) {
2091                                         return new UnboxCast (expr, target_type);
2092                                 } else {
2093                                         Type target = TypeManager.GetTypeArguments (target_type) [0];
2094
2095                                         e = ExplicitConversionCore (ec, expr, target, loc);
2096                                         if (e != null)
2097                                                 return Nullable.Wrap.Create (e, ec);
2098                                 }
2099                         } else if (TypeManager.IsNullableType (expr_type)) {
2100                                 Expression source = Nullable.Unwrap.Create (expr, ec);
2101                                 if (source != null) {
2102                                         e = ExplicitConversionCore (ec, source, target_type, loc);
2103                                         if (e != null)
2104                                                 return e;
2105                                 }
2106                         }
2107 #endif
2108                         e = ExplicitConversionCore (ec, expr, target_type, loc);
2109                         if (e != null)
2110                                 return e;
2111
2112                         expr.Error_ValueCannotBeConverted (loc, target_type, true);
2113                         return null;
2114                 }
2115         }
2116 }