mcs/gmcs/convert.cs

   1 //
   2 // conversion.cs: various routines for implementing conversions.
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Ravi Pratap (ravi@ximian.com)
   7 //
   8 // (C) 2001, 2002, 2003 Ximian, Inc.
   9 //
  10
  11 namespace Mono.CSharp {
  12         using System;
  13         using System.Collections;
  14         using System.Diagnostics;
  15         using System.Reflection;
  16         using System.Reflection.Emit;
  17
  18         //
  19         // A container class for all the conversion operations
  20         //
  21         public class Convert {
  22                 //
  23                 // This is used to prettify the code: a null argument is allowed
  24                 // for ImplicitStandardConversion as long as it is known that
  25                 // no anonymous method will play a role.
  26                 //
  27                 // FIXME: renamed from `const' to `static' to allow bootstraping from older
  28                 // versions of the compiler that could not cope with this construct.
  29                 //
  30                 public static EmitContext ConstantEC = null;
  31
  32                 static void Error_CannotConvertType (Location loc, Type source, Type target)
  33                 {
  34                         Report.Error (30, loc, "Cannot convert type '" +
  35                                       TypeManager.CSharpName (source) + "' to '" +
  36                                       TypeManager.CSharpName (target) + "'");
  37                 }
  38
  39                 static Expression TypeParameter_to_Null (Expression expr, Type target_type,
  40                                                          Location loc)
  41                 {
  42                         if (!TypeParameter_to_Null (target_type)) {
  43                                 Report.Error (403, loc, "Cannot convert null to the type " +
  44                                               "parameter `{0}' becaues it could be a value " +
  45                                               "type.  Consider using `default ({0})' instead.",
  46                                               target_type);
  47                                 return null;
  48                         }
  49
  50                         return new NullCast (expr, target_type);
  51                 }
  52
  53                 static bool TypeParameter_to_Null (Type target_type)
  54                 {
  55                         if ((target_type.BaseType == null) ||
  56                             (target_type.BaseType == TypeManager.value_type) ||
  57                             target_type.BaseType.IsValueType)
  58                                 return false;
  59
  60                         return true;
  61                 }
  62
  63                 static Type TypeParam_EffectiveBaseType (EmitContext ec, Type t)
  64                 {
  65                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (t);
  66                         if (gc == null)
  67                                 return TypeManager.object_type;
  68
  69                         return TypeParam_EffectiveBaseType (ec, gc);
  70                 }
  71
  72                 static Type TypeParam_EffectiveBaseType (EmitContext ec, GenericConstraints gc)
  73                 {
  74                         ArrayList list = new ArrayList ();
  75                         list.Add (gc.EffectiveBaseClass);
  76                         foreach (Type t in gc.InterfaceConstraints) {
  77                                 if (!t.IsGenericParameter)
  78                                         continue;
  79
  80                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  81                                 if (new_gc != null)
  82                                         list.Add (TypeParam_EffectiveBaseType (ec, new_gc));
  83                         }
  84                         return FindMostEncompassedType (ec, list);
  85                 }
  86
  87                 static Expression TypeParameterConversion (Expression expr, bool is_reference, Type target_type)
  88                 {
  89                         if (is_reference)
  90                                 return new EmptyCast (expr, target_type);
  91                         else
  92                                 return new BoxedCast (expr, target_type);
  93                 }
  94
  95                 static Expression ImplicitTypeParameterConversion (EmitContext ec, Expression expr,
  96                                                                    Type target_type)
  97                 {
  98                         Type expr_type = expr.Type;
  99
 100                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
 101
 102                         if (gc == null) {
 103                                 if (target_type == TypeManager.object_type)
 104                                         return new BoxedCast (expr);
 105
 106                                 return null;
 107                         }
 108
 109                         // We're converting from a type parameter which is known to be a reference type.
 110                         bool is_reference = gc.IsReferenceType;
 111                         Type base_type = TypeParam_EffectiveBaseType (ec, gc);
 112
 113                         if (TypeManager.IsSubclassOf (base_type, target_type))
 114                                 return TypeParameterConversion (expr, is_reference, target_type);
 115
 116                         if (target_type.IsInterface) {
 117                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 118                                         return TypeParameterConversion (expr, is_reference, target_type);
 119
 120                                 foreach (Type t in gc.InterfaceConstraints) {
 121                                         if (TypeManager.IsSubclassOf (t, target_type))
 122                                                 return TypeParameterConversion (expr, is_reference, target_type);
 123                                 }
 124                         }
 125
 126                         foreach (Type t in gc.InterfaceConstraints) {
 127                                 if (!t.IsGenericParameter)
 128                                         continue;
 129                                 if (TypeManager.IsSubclassOf (t, target_type))
 130                                         return TypeParameterConversion (expr, is_reference, target_type);
 131                         }
 132
 133                         return null;
 134                 }
 135
 136                 static EmptyExpression MyEmptyExpr;
 137                 static public Expression ImplicitReferenceConversion (EmitContext ec, Expression expr, Type target_type)
 138                 {
 139                         Type expr_type = expr.Type;
 140
 141                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 142                                 // if we are a method group, emit a warning
 143
 144                                 expr.Emit (null);
 145                         }
 146
 147                         if (expr_type == TypeManager.void_type)
 148                                 return null;
 149
 150                         if (expr_type.IsGenericParameter)
 151                                 return ImplicitTypeParameterConversion (ec, expr, target_type);
 152
 153                         //
 154                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 155                         // is an abstract class, and not really a value type, so we apply the same rules.
 156                         //
 157                         if (target_type == TypeManager.object_type) {
 158                                 //
 159                                 // A pointer type cannot be converted to object
 160                                 //
 161                                 if (expr_type.IsPointer)
 162                                         return null;
 163
 164                                 if (TypeManager.IsValueType (expr_type))
 165                                         return new BoxedCast (expr);
 166                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 167                                         if (target_type == TypeManager.anonymous_method_type)
 168                                                 return null;
 169                                         return new EmptyCast (expr, target_type);
 170                                 }
 171
 172                                 return null;
 173                         } else if (target_type == TypeManager.value_type) {
 174                                 if (TypeManager.IsValueType (expr_type))
 175                                         return new BoxedCast (expr);
 176                                 if (expr_type == TypeManager.null_type)
 177                                         return new NullCast (expr, target_type);
 178
 179                                 return null;
 180                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 181                                 //
 182                                 // Special case: enumeration to System.Enum.
 183                                 // System.Enum is not a value type, it is a class, so we need
 184                                 // a boxing conversion
 185                                 //
 186                                 if (expr_type.IsEnum || expr_type.IsGenericParameter)
 187                                         return new BoxedCast (expr);
 188
 189                                 return new EmptyCast (expr, target_type);
 190                         }
 191
 192                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 193                         // with the small distinction that we only probe there
 194                         //
 195                         // Always ensure that the code here and there is in sync
 196
 197                         // from the null type to any reference-type.
 198                         if (expr_type == TypeManager.null_type){
 199                                 if (target_type.IsPointer)
 200                                         return new EmptyCast (expr, target_type);
 201
 202                                 if (!target_type.IsValueType)
 203                                         return new NullCast (expr, target_type);
 204                         }
 205
 206                         // from any class-type S to any interface-type T.
 207                         if (target_type.IsInterface) {
 208                                 if (target_type != TypeManager.iconvertible_type &&
 209                                     expr_type.IsValueType && (expr is Constant) &&
 210                                     !(expr is IntLiteral || expr is BoolLiteral ||
 211                                       expr is FloatLiteral || expr is DoubleLiteral ||
 212                                       expr is LongLiteral || expr is CharLiteral ||
 213                                       expr is StringLiteral || expr is DecimalLiteral ||
 214                                       expr is UIntLiteral || expr is ULongLiteral)) {
 215                                         return null;
 216                                 }
 217
 218                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 219                                         if (expr_type.IsGenericParameter || TypeManager.IsValueType (expr_type))
 220                                                 return new BoxedCast (expr, target_type);
 221                                         else
 222                                                 return new EmptyCast (expr, target_type);
 223                                 }
 224                         }
 225
 226                         // from any interface type S to interface-type T.
 227                         if (expr_type.IsInterface && target_type.IsInterface) {
 228                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 229                                         return new EmptyCast (expr, target_type);
 230                                 else
 231                                         return null;
 232                         }
 233
 234                         // from an array-type S to an array-type of type T
 235                         if (expr_type.IsArray && target_type.IsArray) {
 236                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 237
 238                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 239
 240                                         if (MyEmptyExpr == null)
 241                                                 MyEmptyExpr = new EmptyExpression ();
 242
 243                                         MyEmptyExpr.SetType (expr_element_type);
 244                                         Type target_element_type = TypeManager.GetElementType (target_type);
 245
 246                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 247                                                 if (ImplicitStandardConversionExists (ConstantEC, MyEmptyExpr,
 248                                                                                       target_element_type))
 249                                                         return new EmptyCast (expr, target_type);
 250                                 }
 251                         }
 252
 253                         // from an array-type to System.Array
 254                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 255                                 return new EmptyCast (expr, target_type);
 256
 257                         // from any delegate type to System.Delegate
 258                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 259                             target_type == TypeManager.delegate_type)
 260                                 return new EmptyCast (expr, target_type);
 261
 262                         // from any array-type or delegate type into System.ICloneable.
 263                         if (expr_type.IsArray ||
 264                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 265                                 if (target_type == TypeManager.icloneable_type)
 266                                         return new EmptyCast (expr, target_type);
 267
 268                         // from a generic type definition to a generic instance.
 269                         if (TypeManager.IsEqual (expr_type, target_type))
 270                                 return new EmptyCast (expr, target_type);
 271
 272                         return null;
 273                 }
 274
 275                 //
 276                 // Tests whether an implicit reference conversion exists between expr_type
 277                 // and target_type
 278                 //
 279                 public static bool ImplicitReferenceConversionExists (EmitContext ec, Expression expr, Type target_type)
 280                 {
 281                         Type expr_type = expr.Type;
 282
 283                         if (expr_type.IsGenericParameter)
 284                                 return ImplicitTypeParameterConversion (ec, expr, target_type) != null;
 285
 286                         //
 287                         // This is the boxed case.
 288                         //
 289                         if (target_type == TypeManager.object_type) {
 290                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 291                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 292                                         if (target_type != TypeManager.anonymous_method_type)
 293                                         return true;
 294
 295                                 return false;
 296                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 297                                 return true;
 298
 299                         // Please remember that all code below actually comes
 300                         // from ImplicitReferenceConversion so make sure code remains in sync
 301
 302                         // from any class-type S to any interface-type T.
 303                         if (target_type.IsInterface) {
 304                                 if (target_type != TypeManager.iconvertible_type &&
 305                                     expr_type.IsValueType && (expr is Constant) &&
 306                                     !(expr is IntLiteral || expr is BoolLiteral ||
 307                                       expr is FloatLiteral || expr is DoubleLiteral ||
 308                                       expr is LongLiteral || expr is CharLiteral ||
 309                                       expr is StringLiteral || expr is DecimalLiteral ||
 310                                       expr is UIntLiteral || expr is ULongLiteral)) {
 311                                         return false;
 312                                 }
 313
 314                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 315                                         return true;
 316                         }
 317
 318                         // from any interface type S to interface-type T.
 319                         if (expr_type.IsInterface && target_type.IsInterface)
 320                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 321                                         return true;
 322
 323                         // from an array-type S to an array-type of type T
 324                         if (expr_type.IsArray && target_type.IsArray) {
 325                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 326
 327                                         Type expr_element_type = expr_type.GetElementType ();
 328
 329                                         if (MyEmptyExpr == null)
 330                                                 MyEmptyExpr = new EmptyExpression ();
 331
 332                                         MyEmptyExpr.SetType (expr_element_type);
 333                                         Type target_element_type = TypeManager.GetElementType (target_type);
 334
 335                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 336                                                 if (ImplicitStandardConversionExists (ConstantEC, MyEmptyExpr,
 337                                                                                       target_element_type))
 338                                                         return true;
 339                                 }
 340                         }
 341
 342                         // from an array-type to System.Array
 343                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 344                                 return true;
 345
 346                         // from any delegate type to System.Delegate
 347                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 348                             target_type == TypeManager.delegate_type)
 349                                 if (target_type.IsAssignableFrom (expr_type))
 350                                         return true;
 351
 352                         // from any array-type or delegate type into System.ICloneable.
 353                         if (expr_type.IsArray ||
 354                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 355                                 if (target_type == TypeManager.icloneable_type)
 356                                         return true;
 357
 358                         // from the null type to any reference-type.
 359                         if (expr_type == TypeManager.null_type){
 360                                 if (target_type.IsPointer)
 361                                         return true;
 362
 363                                 if (!target_type.IsValueType)
 364                                         return true;
 365                         }
 366
 367                         // from a generic type definition to a generic instance.
 368                         if (TypeManager.IsEqual (expr_type, target_type))
 369                                 return true;
 370
 371                         return false;
 372                 }
 373
 374                 /// <summary>
 375                 ///   Implicit Numeric Conversions.
 376                 ///
 377                 ///   expr is the expression to convert, returns a new expression of type
 378                 ///   target_type or null if an implicit conversion is not possible.
 379                 /// </summary>
 380                 static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
 381                                                                     Type target_type, Location loc)
 382                 {
 383                         Type expr_type = expr.Type;
 384
 385                         //
 386                         // Attempt to do the implicit constant expression conversions
 387
 388                         if (expr is Constant){
 389                                 if (expr is IntConstant){
 390                                         Expression e;
 391
 392                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 393
 394                                         if (e != null)
 395                                                 return e;
 396                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 397                                         //
 398                                         // Try the implicit constant expression conversion
 399                                         // from long to ulong, instead of a nice routine,
 400                                         // we just inline it
 401                                         //
 402                                         long v = ((LongConstant) expr).Value;
 403                                         if (v >= 0)
 404                                                 return new ULongConstant ((ulong) v);
 405                                 }
 406                         }
 407
 408                         Type real_target_type = target_type;
 409
 410                         if (expr_type == TypeManager.sbyte_type){
 411                                 //
 412                                 // From sbyte to short, int, long, float, double.
 413                                 //
 414                                 if (real_target_type == TypeManager.int32_type)
 415                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 416                                 if (real_target_type == TypeManager.int64_type)
 417                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 418                                 if (real_target_type == TypeManager.double_type)
 419                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 420                                 if (real_target_type == TypeManager.float_type)
 421                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 422                                 if (real_target_type == TypeManager.short_type)
 423                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 424                         } else if (expr_type == TypeManager.byte_type){
 425                                 //
 426                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 427                                 //
 428                                 if ((real_target_type == TypeManager.short_type) ||
 429                                     (real_target_type == TypeManager.ushort_type) ||
 430                                     (real_target_type == TypeManager.int32_type) ||
 431                                     (real_target_type == TypeManager.uint32_type))
 432                                         return new EmptyCast (expr, target_type);
 433
 434                                 if (real_target_type == TypeManager.uint64_type)
 435                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 436                                 if (real_target_type == TypeManager.int64_type)
 437                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 438                                 if (real_target_type == TypeManager.float_type)
 439                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 440                                 if (real_target_type == TypeManager.double_type)
 441                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 442                         } else if (expr_type == TypeManager.short_type){
 443                                 //
 444                                 // From short to int, long, float, double
 445                                 //
 446                                 if (real_target_type == TypeManager.int32_type)
 447                                         return new EmptyCast (expr, target_type);
 448                                 if (real_target_type == TypeManager.int64_type)
 449                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 450                                 if (real_target_type == TypeManager.double_type)
 451                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 452                                 if (real_target_type == TypeManager.float_type)
 453                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 454                         } else if (expr_type == TypeManager.ushort_type){
 455                                 //
 456                                 // From ushort to int, uint, long, ulong, float, double
 457                                 //
 458                                 if (real_target_type == TypeManager.uint32_type)
 459                                         return new EmptyCast (expr, target_type);
 460
 461                                 if (real_target_type == TypeManager.uint64_type)
 462                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 463                                 if (real_target_type == TypeManager.int32_type)
 464                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 465                                 if (real_target_type == TypeManager.int64_type)
 466                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 467                                 if (real_target_type == TypeManager.double_type)
 468                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 469                                 if (real_target_type == TypeManager.float_type)
 470                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 471                         } else if (expr_type == TypeManager.int32_type){
 472                                 //
 473                                 // From int to long, float, double
 474                                 //
 475                                 if (real_target_type == TypeManager.int64_type)
 476                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 477                                 if (real_target_type == TypeManager.double_type)
 478                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 479                                 if (real_target_type == TypeManager.float_type)
 480                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 481                         } else if (expr_type == TypeManager.uint32_type){
 482                                 //
 483                                 // From uint to long, ulong, float, double
 484                                 //
 485                                 if (real_target_type == TypeManager.int64_type)
 486                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 487                                 if (real_target_type == TypeManager.uint64_type)
 488                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 489                                 if (real_target_type == TypeManager.double_type)
 490                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 491                                                                OpCodes.Conv_R8);
 492                                 if (real_target_type == TypeManager.float_type)
 493                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 494                                                                OpCodes.Conv_R4);
 495                         } else if (expr_type == TypeManager.int64_type){
 496                                 //
 497                                 // From long/ulong to float, double
 498                                 //
 499                                 if (real_target_type == TypeManager.double_type)
 500                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 501                                 if (real_target_type == TypeManager.float_type)
 502                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 503                         } else if (expr_type == TypeManager.uint64_type){
 504                                 //
 505                                 // From ulong to float, double
 506                                 //
 507                                 if (real_target_type == TypeManager.double_type)
 508                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 509                                                                OpCodes.Conv_R8);
 510                                 if (real_target_type == TypeManager.float_type)
 511                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 512                                                                OpCodes.Conv_R4);
 513                         } else if (expr_type == TypeManager.char_type){
 514                                 //
 515                                 // From char to ushort, int, uint, long, ulong, float, double
 516                                 //
 517                                 if ((real_target_type == TypeManager.ushort_type) ||
 518                                     (real_target_type == TypeManager.int32_type) ||
 519                                     (real_target_type == TypeManager.uint32_type))
 520                                         return new EmptyCast (expr, target_type);
 521                                 if (real_target_type == TypeManager.uint64_type)
 522                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 523                                 if (real_target_type == TypeManager.int64_type)
 524                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 525                                 if (real_target_type == TypeManager.float_type)
 526                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 527                                 if (real_target_type == TypeManager.double_type)
 528                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 529                         } else if (expr_type == TypeManager.float_type){
 530                                 //
 531                                 // float to double
 532                                 //
 533                                 if (real_target_type == TypeManager.double_type)
 534                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 535                         }
 536
 537                         return null;
 538                 }
 539
 540
 541                 /// <summary>
 542                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 543                 ///  implicit user defined conversions - needed for overload resolution
 544                 /// </summary>
 545                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 546                 {
 547                         if ((expr is NullLiteral) && target_type.IsGenericParameter)
 548                                 return TypeParameter_to_Null (target_type);
 549
 550                         if (ImplicitStandardConversionExists (ec, expr, target_type))
 551                                 return true;
 552
 553                         Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);
 554
 555                         if (dummy != null)
 556                                 return true;
 557
 558                         return false;
 559                 }
 560
 561                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 562                 {
 563                         Expression dummy = ImplicitUserConversion (
 564                                 ec, new EmptyExpression (source), target, Location.Null);
 565                         return dummy != null;
 566                 }
 567
 568                 /// <summary>
 569                 ///  Determines if a standard implicit conversion exists from
 570                 ///  expr_type to target_type
 571                 ///
 572                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 573                 /// </summary>
 574                 public static bool ImplicitStandardConversionExists (EmitContext ec, Expression expr, Type target_type)
 575                 {
 576                         Type expr_type = expr.Type;
 577
 578                         if (expr_type == TypeManager.void_type)
 579                                 return false;
 580
 581                         //Console.WriteLine ("Expr is {0}", expr);
 582                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 583                         if (expr_type.Equals (target_type))
 584                                 return true;
 585
 586                         // First numeric conversions
 587
 588                         if (expr_type == TypeManager.sbyte_type){
 589                                 //
 590                                 // From sbyte to short, int, long, float, double.
 591                                 //
 592                                 if ((target_type == TypeManager.int32_type) ||
 593                                     (target_type == TypeManager.int64_type) ||
 594                                     (target_type == TypeManager.double_type) ||
 595                                     (target_type == TypeManager.float_type)  ||
 596                                     (target_type == TypeManager.short_type) ||
 597                                     (target_type == TypeManager.decimal_type))
 598                                         return true;
 599
 600                         } else if (expr_type == TypeManager.byte_type){
 601                                 //
 602                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 603                                 //
 604                                 if ((target_type == TypeManager.short_type) ||
 605                                     (target_type == TypeManager.ushort_type) ||
 606                                     (target_type == TypeManager.int32_type) ||
 607                                     (target_type == TypeManager.uint32_type) ||
 608                                     (target_type == TypeManager.uint64_type) ||
 609                                     (target_type == TypeManager.int64_type) ||
 610                                     (target_type == TypeManager.float_type) ||
 611                                     (target_type == TypeManager.double_type) ||
 612                                     (target_type == TypeManager.decimal_type))
 613                                         return true;
 614
 615                         } else if (expr_type == TypeManager.short_type){
 616                                 //
 617                                 // From short to int, long, float, double
 618                                 //
 619                                 if ((target_type == TypeManager.int32_type) ||
 620                                     (target_type == TypeManager.int64_type) ||
 621                                     (target_type == TypeManager.double_type) ||
 622                                     (target_type == TypeManager.float_type) ||
 623                                     (target_type == TypeManager.decimal_type))
 624                                         return true;
 625
 626                         } else if (expr_type == TypeManager.ushort_type){
 627                                 //
 628                                 // From ushort to int, uint, long, ulong, float, double
 629                                 //
 630                                 if ((target_type == TypeManager.uint32_type) ||
 631                                     (target_type == TypeManager.uint64_type) ||
 632                                     (target_type == TypeManager.int32_type) ||
 633                                     (target_type == TypeManager.int64_type) ||
 634                                     (target_type == TypeManager.double_type) ||
 635                                     (target_type == TypeManager.float_type) ||
 636                                     (target_type == TypeManager.decimal_type))
 637                                         return true;
 638
 639                         } else if (expr_type == TypeManager.int32_type){
 640                                 //
 641                                 // From int to long, float, double
 642                                 //
 643                                 if ((target_type == TypeManager.int64_type) ||
 644                                     (target_type == TypeManager.double_type) ||
 645                                     (target_type == TypeManager.float_type) ||
 646                                     (target_type == TypeManager.decimal_type))
 647                                         return true;
 648
 649                         } else if (expr_type == TypeManager.uint32_type){
 650                                 //
 651                                 // From uint to long, ulong, float, double
 652                                 //
 653                                 if ((target_type == TypeManager.int64_type) ||
 654                                     (target_type == TypeManager.uint64_type) ||
 655                                     (target_type == TypeManager.double_type) ||
 656                                     (target_type == TypeManager.float_type) ||
 657                                     (target_type == TypeManager.decimal_type))
 658                                         return true;
 659
 660                         } else if ((expr_type == TypeManager.uint64_type) ||
 661                                    (expr_type == TypeManager.int64_type)) {
 662                                 //
 663                                 // From long/ulong to float, double
 664                                 //
 665                                 if ((target_type == TypeManager.double_type) ||
 666                                     (target_type == TypeManager.float_type) ||
 667                                     (target_type == TypeManager.decimal_type))
 668                                         return true;
 669
 670                         } else if (expr_type == TypeManager.char_type){
 671                                 //
 672                                 // From char to ushort, int, uint, long, ulong, float, double
 673                                 //
 674                                 if ((target_type == TypeManager.ushort_type) ||
 675                                     (target_type == TypeManager.int32_type) ||
 676                                     (target_type == TypeManager.uint32_type) ||
 677                                     (target_type == TypeManager.uint64_type) ||
 678                                     (target_type == TypeManager.int64_type) ||
 679                                     (target_type == TypeManager.float_type) ||
 680                                     (target_type == TypeManager.double_type) ||
 681                                     (target_type == TypeManager.decimal_type))
 682                                         return true;
 683
 684                         } else if (expr_type == TypeManager.float_type){
 685                                 //
 686                                 // float to double
 687                                 //
 688                                 if (target_type == TypeManager.double_type)
 689                                         return true;
 690                         }
 691
 692                         if (ImplicitReferenceConversionExists (ec, expr, target_type))
 693                                 return true;
 694
 695                         //
 696                         // Implicit Constant Expression Conversions
 697                         //
 698                         if (expr is IntConstant){
 699                                 int value = ((IntConstant) expr).Value;
 700
 701                                 if (target_type == TypeManager.sbyte_type){
 702                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 703                                                 return true;
 704                                 } else if (target_type == TypeManager.byte_type){
 705                                         if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
 706                                                 return true;
 707                                 } else if (target_type == TypeManager.short_type){
 708                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 709                                                 return true;
 710                                 } else if (target_type == TypeManager.ushort_type){
 711                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 712                                                 return true;
 713                                 } else if (target_type == TypeManager.uint32_type){
 714                                         if (value >= 0)
 715                                                 return true;
 716                                 } else if (target_type == TypeManager.uint64_type){
 717                                          //
 718                                          // we can optimize this case: a positive int32
 719                                          // always fits on a uint64.  But we need an opcode
 720                                          // to do it.
 721                                          //
 722                                         if (value >= 0)
 723                                                 return true;
 724                                 }
 725
 726                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 727                                         return true;
 728                         }
 729
 730                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 731                                 //
 732                                 // Try the implicit constant expression conversion
 733                                 // from long to ulong, instead of a nice routine,
 734                                 // we just inline it
 735                                 //
 736                                 long v = ((LongConstant) expr).Value;
 737                                 if (v > 0)
 738                                         return true;
 739                         }
 740
 741                         if ((target_type == TypeManager.enum_type ||
 742                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 743                              expr is IntLiteral){
 744                                 IntLiteral i = (IntLiteral) expr;
 745
 746                                 if (i.Value == 0)
 747                                         return true;
 748                         }
 749
 750                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 751                                 return true;
 752
 753                         if (expr_type == TypeManager.anonymous_method_type){
 754                                 if (!TypeManager.IsDelegateType (target_type))
 755                                         return false;
 756
 757                                 AnonymousMethod am = (AnonymousMethod) expr;
 758                                 int errors = Report.Errors;
 759
 760                                 Expression conv = am.Compatible (ec, target_type, true);
 761                                 if (conv != null)
 762                                         return true;
 763                         }
 764
 765                         return false;
 766                 }
 767
 768                 //
 769                 // Used internally by FindMostEncompassedType, this is used
 770                 // to avoid creating lots of objects in the tight loop inside
 771                 // FindMostEncompassedType
 772                 //
 773                 static EmptyExpression priv_fmet_param;
 774
 775                 /// <summary>
 776                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 777                 ///  amongst the methods in the MethodGroupExpr
 778                 /// </summary>
 779                 static Type FindMostEncompassedType (EmitContext ec, ArrayList types)
 780                 {
 781                         Type best = null;
 782
 783                         if (priv_fmet_param == null)
 784                                 priv_fmet_param = new EmptyExpression ();
 785
 786                         foreach (Type t in types){
 787                                 priv_fmet_param.SetType (t);
 788
 789                                 if (best == null) {
 790                                         best = t;
 791                                         continue;
 792                                 }
 793
 794                                 if (ImplicitStandardConversionExists (ec, priv_fmet_param, best))
 795                                         best = t;
 796                         }
 797
 798                         return best;
 799                 }
 800
 801                 //
 802                 // Used internally by FindMostEncompassingType, this is used
 803                 // to avoid creating lots of objects in the tight loop inside
 804                 // FindMostEncompassingType
 805                 //
 806                 static EmptyExpression priv_fmee_ret;
 807
 808                 /// <summary>
 809                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 810                 ///  amongst the types in the given set
 811                 /// </summary>
 812                 static Type FindMostEncompassingType (EmitContext ec, ArrayList types)
 813                 {
 814                         Type best = null;
 815
 816                         if (priv_fmee_ret == null)
 817                                 priv_fmee_ret = new EmptyExpression ();
 818
 819                         foreach (Type t in types){
 820                                 priv_fmee_ret.SetType (best);
 821
 822                                 if (best == null) {
 823                                         best = t;
 824                                         continue;
 825                                 }
 826
 827                                 if (ImplicitStandardConversionExists (ec, priv_fmee_ret, t))
 828                                         best = t;
 829                         }
 830
 831                         return best;
 832                 }
 833
 834                 //
 835                 // Used to avoid creating too many objects
 836                 //
 837                 static EmptyExpression priv_fms_expr;
 838
 839                 /// <summary>
 840                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 841                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 842                 ///   for explicit and implicit conversion operators.
 843                 /// </summary>
 844                 static public Type FindMostSpecificSource (EmitContext ec, MethodGroupExpr me,
 845                                                            Expression source, bool apply_explicit_conv_rules,
 846                                                            Location loc)
 847                 {
 848                         ArrayList src_types_set = new ArrayList ();
 849
 850                         if (priv_fms_expr == null)
 851                                 priv_fms_expr = new EmptyExpression ();
 852
 853                         //
 854                         // If any operator converts from S then Sx = S
 855                         //
 856                         Type source_type = source.Type;
 857                         foreach (MethodBase mb in me.Methods){
 858                                 ParameterData pd = Invocation.GetParameterData (mb);
 859                                 Type param_type = pd.ParameterType (0);
 860
 861                                 if (param_type == source_type)
 862                                         return param_type;
 863
 864                                 if (apply_explicit_conv_rules) {
 865                                         //
 866                                         // From the spec :
 867                                         // Find the set of applicable user-defined conversion operators, U.  This set
 868                                         // consists of the
 869                                         // user-defined implicit or explicit conversion operators declared by
 870                                         // the classes or structs in D that convert from a type encompassing
 871                                         // or encompassed by S to a type encompassing or encompassed by T
 872                                         //
 873                                         priv_fms_expr.SetType (param_type);
 874                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, source_type))
 875                                                 src_types_set.Add (param_type);
 876                                         else {
 877                                                 if (ImplicitStandardConversionExists (ec, source, param_type))
 878                                                         src_types_set.Add (param_type);
 879                                         }
 880                                 } else {
 881                                         //
 882                                         // Only if S is encompassed by param_type
 883                                         //
 884                                         if (ImplicitStandardConversionExists (ec, source, param_type))
 885                                                 src_types_set.Add (param_type);
 886                                 }
 887                         }
 888
 889                         //
 890                         // Explicit Conv rules
 891                         //
 892                         if (apply_explicit_conv_rules) {
 893                                 ArrayList candidate_set = new ArrayList ();
 894
 895                                 foreach (Type param_type in src_types_set){
 896                                         if (ImplicitStandardConversionExists (ec, source, param_type))
 897                                                 candidate_set.Add (param_type);
 898                                 }
 899
 900                                 if (candidate_set.Count != 0)
 901                                         return FindMostEncompassedType (ec, candidate_set);
 902                         }
 903
 904                         //
 905                         // Final case
 906                         //
 907                         if (apply_explicit_conv_rules)
 908                                 return FindMostEncompassingType (ec, src_types_set);
 909                         else
 910                                 return FindMostEncompassedType (ec, src_types_set);
 911                 }
 912
 913                 //
 914                 // Useful in avoiding proliferation of objects
 915                 //
 916                 static EmptyExpression priv_fmt_expr;
 917
 918                 /// <summary>
 919                 ///  Finds the most specific target Tx according to section 13.4.4
 920                 /// </summary>
 921                 static public Type FindMostSpecificTarget (EmitContext ec, MethodGroupExpr me,
 922                                                            Type target, bool apply_explicit_conv_rules,
 923                                                            Location loc)
 924                 {
 925                         ArrayList tgt_types_set = new ArrayList ();
 926
 927                         if (priv_fmt_expr == null)
 928                                 priv_fmt_expr = new EmptyExpression ();
 929
 930                         //
 931                         // If any operator converts to T then Tx = T
 932                         //
 933                         foreach (MethodInfo mi in me.Methods){
 934                                 Type ret_type = mi.ReturnType;
 935
 936                                 if (ret_type == target)
 937                                         return ret_type;
 938
 939                                 if (apply_explicit_conv_rules) {
 940                                         //
 941                                         // From the spec :
 942                                         // Find the set of applicable user-defined conversion operators, U.
 943                                         //
 944                                         // This set consists of the
 945                                         // user-defined implicit or explicit conversion operators declared by
 946                                         // the classes or structs in D that convert from a type encompassing
 947                                         // or encompassed by S to a type encompassing or encompassed by T
 948                                         //
 949                                         priv_fms_expr.SetType (ret_type);
 950                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, target))
 951                                                 tgt_types_set.Add (ret_type);
 952                                         else {
 953                                                 priv_fms_expr.SetType (target);
 954                                                 if (ImplicitStandardConversionExists (ec, priv_fms_expr, ret_type))
 955                                                         tgt_types_set.Add (ret_type);
 956                                         }
 957                                 } else {
 958                                         //
 959                                         // Only if T is encompassed by param_type
 960                                         //
 961                                         priv_fms_expr.SetType (ret_type);
 962                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, target))
 963                                                 tgt_types_set.Add (ret_type);
 964                                 }
 965                         }
 966
 967                         //
 968                         // Explicit conv rules
 969                         //
 970                         if (apply_explicit_conv_rules) {
 971                                 ArrayList candidate_set = new ArrayList ();
 972
 973                                 foreach (Type ret_type in tgt_types_set){
 974                                         priv_fmt_expr.SetType (ret_type);
 975
 976                                         if (ImplicitStandardConversionExists (ec, priv_fmt_expr, target))
 977                                                 candidate_set.Add (ret_type);
 978                                 }
 979
 980                                 if (candidate_set.Count != 0)
 981                                         return FindMostEncompassingType (ec, candidate_set);
 982                         }
 983
 984                         //
 985                         // Okay, final case !
 986                         //
 987                         if (apply_explicit_conv_rules)
 988                                 return FindMostEncompassedType (ec, tgt_types_set);
 989                         else
 990                                 return FindMostEncompassingType (ec, tgt_types_set);
 991                 }
 992
 993                 /// <summary>
 994                 ///  User-defined Implicit conversions
 995                 /// </summary>
 996                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
 997                                                                  Type target, Location loc)
 998                 {
 999                         return UserDefinedConversion (ec, source, target, loc, false);
1000                 }
1001
1002                 /// <summary>
1003                 ///  User-defined Explicit conversions
1004                 /// </summary>
1005                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1006                                                                  Type target, Location loc)
1007                 {
1008                         return UserDefinedConversion (ec, source, target, loc, true);
1009                 }
1010
1011                 static DoubleHash explicit_conv = new DoubleHash (100);
1012                 static DoubleHash implicit_conv = new DoubleHash (100);
1013                 /// <summary>
1014                 ///   Computes the MethodGroup for the user-defined conversion
1015                 ///   operators from source_type to target_type.  `look_for_explicit'
1016                 ///   controls whether we should also include the list of explicit
1017                 ///   operators
1018                 /// </summary>
1019                 static MethodGroupExpr GetConversionOperators (EmitContext ec,
1020                                                                Type source_type, Type target_type,
1021                                                                Location loc, bool look_for_explicit)
1022                 {
1023                         Expression mg1 = null, mg2 = null;
1024                         Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
1025                         string op_name;
1026
1027                         op_name = "op_Implicit";
1028
1029                         MethodGroupExpr union3;
1030                         object r;
1031                         if ((look_for_explicit ? explicit_conv : implicit_conv).Lookup (source_type, target_type, out r))
1032                                 return (MethodGroupExpr) r;
1033
1034                         mg1 = Expression.MethodLookup (ec, source_type, op_name, loc);
1035                         if (source_type.BaseType != null)
1036                                 mg2 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1037
1038                         if (mg1 == null)
1039                                 union3 = (MethodGroupExpr) mg2;
1040                         else if (mg2 == null)
1041                                 union3 = (MethodGroupExpr) mg1;
1042                         else
1043                                 union3 = Invocation.MakeUnionSet (mg1, mg2, loc);
1044
1045                         mg1 = Expression.MethodLookup (ec, target_type, op_name, loc);
1046                         if (mg1 != null){
1047                                 if (union3 != null)
1048                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1049                                 else
1050                                         union3 = (MethodGroupExpr) mg1;
1051                         }
1052
1053                         if (target_type.BaseType != null)
1054                                 mg1 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1055
1056                         if (mg1 != null){
1057                                 if (union3 != null)
1058                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1059                                 else
1060                                         union3 = (MethodGroupExpr) mg1;
1061                         }
1062
1063                         MethodGroupExpr union4 = null;
1064
1065                         if (look_for_explicit) {
1066                                 op_name = "op_Explicit";
1067
1068                                 mg5 = Expression.MemberLookup (ec, source_type, op_name, loc);
1069                                 if (source_type.BaseType != null)
1070                                         mg6 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1071
1072                                 mg7 = Expression.MemberLookup (ec, target_type, op_name, loc);
1073                                 if (target_type.BaseType != null)
1074                                         mg8 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1075
1076                                 MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
1077                                 MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);
1078
1079                                 union4 = Invocation.MakeUnionSet (union5, union6, loc);
1080                         }
1081
1082                         MethodGroupExpr ret = Invocation.MakeUnionSet (union3, union4, loc);
1083                         (look_for_explicit ? explicit_conv : implicit_conv).Insert (source_type, target_type, ret);
1084                         return ret;
1085                 }
1086
1087                 /// <summary>
1088                 ///   User-defined conversions
1089                 /// </summary>
1090                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1091                                                                 Type target, Location loc,
1092                                                                 bool look_for_explicit)
1093                 {
1094                         MethodGroupExpr union;
1095                         Type source_type = source.Type;
1096                         MethodBase method = null;
1097
1098                         union = GetConversionOperators (ec, source_type, target, loc, look_for_explicit);
1099                         if (union == null)
1100                                 return null;
1101
1102                         Type most_specific_source, most_specific_target;
1103
1104                         most_specific_source = FindMostSpecificSource (ec, union, source, look_for_explicit, loc);
1105                         if (most_specific_source == null)
1106                                 return null;
1107
1108                         most_specific_target = FindMostSpecificTarget (ec, union, target, look_for_explicit, loc);
1109                         if (most_specific_target == null)
1110                                 return null;
1111
1112                         int count = 0;
1113
1114
1115                         foreach (MethodBase mb in union.Methods){
1116                                 ParameterData pd = Invocation.GetParameterData (mb);
1117                                 MethodInfo mi = (MethodInfo) mb;
1118
1119                                 if (pd.ParameterType (0) == most_specific_source &&
1120                                     mi.ReturnType == most_specific_target) {
1121                                         method = mb;
1122                                         count++;
1123                                 }
1124                         }
1125
1126                         if (method == null || count > 1)
1127                                 return null;
1128
1129
1130                         //
1131                         // This will do the conversion to the best match that we
1132                         // found.  Now we need to perform an implict standard conversion
1133                         // if the best match was not the type that we were requested
1134                         // by target.
1135                         //
1136                         if (look_for_explicit)
1137                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1138                         else
1139                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1140
1141                         if (source == null)
1142                                 return null;
1143
1144                         Expression e;
1145                         e =  new UserCast ((MethodInfo) method, source, loc);
1146                         if (e.Type != target){
1147                                 if (!look_for_explicit)
1148                                         e = ImplicitConversionStandard (ec, e, target, loc);
1149                                 else
1150                                         e = ExplicitConversionStandard (ec, e, target, loc);
1151                         }
1152
1153                         return e;
1154                 }
1155
1156                 /// <summary>
1157                 ///   Converts implicitly the resolved expression `expr' into the
1158                 ///   `target_type'.  It returns a new expression that can be used
1159                 ///   in a context that expects a `target_type'.
1160                 /// </summary>
1161                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1162                                                              Type target_type, Location loc)
1163                 {
1164                         Expression e;
1165
1166                         if (target_type == null)
1167                                 throw new Exception ("Target type is null");
1168
1169                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1170                         if (e != null)
1171                                 return e;
1172
1173                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1174                         if (e != null)
1175                                 return e;
1176
1177                         return null;
1178                 }
1179
1180
1181                 /// <summary>
1182                 ///   Attempts to apply the `Standard Implicit
1183                 ///   Conversion' rules to the expression `expr' into
1184                 ///   the `target_type'.  It returns a new expression
1185                 ///   that can be used in a context that expects a
1186                 ///   `target_type'.
1187                 ///
1188                 ///   This is different from `ImplicitConversion' in that the
1189                 ///   user defined implicit conversions are excluded.
1190                 /// </summary>
1191                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1192                                                                      Type target_type, Location loc)
1193                 {
1194                         Type expr_type = expr.Type;
1195                         Expression e;
1196
1197                         if ((expr is NullLiteral) && target_type.IsGenericParameter)
1198                                 return TypeParameter_to_Null (expr, target_type, loc);
1199
1200                         if (expr.eclass == ExprClass.MethodGroup){
1201                                 if (!TypeManager.IsDelegateType (target_type)){
1202                                         return null;
1203                                 }
1204
1205                                 //
1206                                 // Only allow anonymous method conversions on post ISO_1
1207                                 //
1208                                 if (RootContext.Version != LanguageVersion.ISO_1){
1209                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1210                                         if (mg != null)
1211                                                 return ImplicitDelegateCreation.Create (ec, mg, target_type, loc);
1212                                 }
1213                         }
1214
1215                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1216                                 return expr;
1217
1218                         e = ImplicitNumericConversion (ec, expr, target_type, loc);
1219                         if (e != null)
1220                                 return e;
1221
1222                         e = ImplicitReferenceConversion (ec, expr, target_type);
1223                         if (e != null)
1224                                 return e;
1225
1226                         if ((target_type == TypeManager.enum_type ||
1227                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1228                             expr is IntLiteral){
1229                                 IntLiteral i = (IntLiteral) expr;
1230
1231                                 if (i.Value == 0)
1232                                         return new EnumConstant ((Constant) expr, target_type);
1233                         }
1234
1235                         if (ec.InUnsafe) {
1236                                 if (expr_type.IsPointer){
1237                                         if (target_type == TypeManager.void_ptr_type)
1238                                                 return new EmptyCast (expr, target_type);
1239
1240                                         //
1241                                         // yep, comparing pointer types cant be done with
1242                                         // t1 == t2, we have to compare their element types.
1243                                         //
1244                                         if (target_type.IsPointer){
1245                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1246                                                         return expr;
1247                                         }
1248                                 }
1249
1250                                 if (target_type.IsPointer) {
1251                                         if (expr_type == TypeManager.null_type)
1252                                                 return new EmptyCast (expr, target_type);
1253
1254                                         if (expr_type == TypeManager.void_ptr_type)
1255                                                 return new EmptyCast (expr, target_type);
1256                                 }
1257                         }
1258
1259                         if (expr_type == TypeManager.anonymous_method_type){
1260                                 if (!TypeManager.IsDelegateType (target_type)){
1261                                         Report.Error (1660, loc,
1262                                                               "Cannot convert anonymous method to `{0}', since it is not a delegate",
1263                                                               TypeManager.CSharpName (target_type));
1264                                         return null;
1265                                 }
1266
1267                                 AnonymousMethod am = (AnonymousMethod) expr;
1268                                 int errors = Report.Errors;
1269
1270                                 Expression conv = am.Compatible (ec, target_type, false);
1271                                 if (conv != null)
1272                                         return conv;
1273
1274                                 //
1275                                 // We return something instead of null, to avoid
1276                                 // the duplicate error, since am.Compatible would have
1277                                 // reported that already
1278                                 //
1279                                 if (errors != Report.Errors)
1280                                         return new EmptyCast (expr, target_type);
1281                         }
1282
1283                         return null;
1284                 }
1285
1286                 /// <summary>
1287                 ///   Attemps to perform an implict constant conversion of the IntConstant
1288                 ///   into a different data type using casts (See Implicit Constant
1289                 ///   Expression Conversions)
1290                 /// </summary>
1291                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1292                 {
1293                         int value = ic.Value;
1294
1295                         if (target_type == TypeManager.sbyte_type){
1296                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1297                                         return new SByteConstant ((sbyte) value);
1298                         } else if (target_type == TypeManager.byte_type){
1299                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1300                                         return new ByteConstant ((byte) value);
1301                         } else if (target_type == TypeManager.short_type){
1302                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1303                                         return new ShortConstant ((short) value);
1304                         } else if (target_type == TypeManager.ushort_type){
1305                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1306                                         return new UShortConstant ((ushort) value);
1307                         } else if (target_type == TypeManager.uint32_type){
1308                                 if (value >= 0)
1309                                         return new UIntConstant ((uint) value);
1310                         } else if (target_type == TypeManager.uint64_type){
1311                                 //
1312                                 // we can optimize this case: a positive int32
1313                                 // always fits on a uint64.  But we need an opcode
1314                                 // to do it.
1315                                 //
1316                                 if (value >= 0)
1317                                         return new ULongConstant ((ulong) value);
1318                         } else if (target_type == TypeManager.double_type)
1319                                 return new DoubleConstant ((double) value);
1320                         else if (target_type == TypeManager.float_type)
1321                                 return new FloatConstant ((float) value);
1322
1323                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1324                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1325                                 Constant e = (Constant) ic;
1326
1327                                 //
1328                                 // Possibly, we need to create a different 0 literal before passing
1329                                 // to EnumConstant
1330                                 //n
1331                                 if (underlying == TypeManager.int64_type)
1332                                         e = new LongLiteral (0);
1333                                 else if (underlying == TypeManager.uint64_type)
1334                                         e = new ULongLiteral (0);
1335
1336                                 return new EnumConstant (e, target_type);
1337                         }
1338                         return null;
1339                 }
1340
1341                 static public void Error_CannotImplicitConversion (Location loc, Type source, Type target)
1342                 {
1343                         Report.Error (29, loc, "Cannot convert implicitly from {0} to `{1}'",
1344                                       source == TypeManager.anonymous_method_type ?
1345                                       "anonymous method" : "`" + TypeManager.CSharpName (source) + "'",
1346                                       TypeManager.CSharpName (target));
1347                 }
1348
1349                 /// <summary>
1350                 ///   Attemptes to implicityly convert `target' into `type', using
1351                 ///   ImplicitConversion.  If there is no implicit conversion, then
1352                 ///   an error is signaled
1353                 /// </summary>
1354                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1355                                                                      Type target_type, Location loc)
1356                 {
1357                         Expression e;
1358
1359                         int errors = Report.Errors;
1360                         e = ImplicitConversion (ec, source, target_type, loc);
1361                         if (Report.Errors > errors)
1362                                 return null;
1363                         if (e != null)
1364                                 return e;
1365
1366                         if (source is DoubleLiteral && target_type == TypeManager.float_type){
1367                                 Report.Error (664, loc,
1368                                               "Double literal cannot be implicitly converted to " +
1369                                               "float type, use F suffix to create a float literal");
1370                         }
1371
1372                         if (source is Constant){
1373                                 Constant c = (Constant) source;
1374
1375                                 Expression.Error_ConstantValueCannotBeConverted (loc, c.AsString (), target_type);
1376                                 return null;
1377                         }
1378
1379                         Error_CannotImplicitConversion (loc, source.Type, target_type);
1380
1381                         return null;
1382                 }
1383
1384                 /// <summary>
1385                 ///   Performs the explicit numeric conversions
1386                 /// </summary>
1387                 static Expression ExplicitNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
1388                 {
1389                         Type expr_type = expr.Type;
1390
1391                         //
1392                         // If we have an enumeration, extract the underlying type,
1393                         // use this during the comparison, but wrap around the original
1394                         // target_type
1395                         //
1396                         Type real_target_type = target_type;
1397
1398                         if (TypeManager.IsEnumType (real_target_type))
1399                                 real_target_type = TypeManager.EnumToUnderlying (real_target_type);
1400
1401                         if (ImplicitStandardConversionExists (ec, expr, real_target_type)){
1402                                 Expression ce = ImplicitConversionStandard (ec, expr, real_target_type, loc);
1403
1404                                 if (real_target_type != target_type)
1405                                         return new EmptyCast (ce, target_type);
1406                                 return ce;
1407                         }
1408
1409                         if (expr_type == TypeManager.sbyte_type){
1410                                 //
1411                                 // From sbyte to byte, ushort, uint, ulong, char
1412                                 //
1413                                 if (real_target_type == TypeManager.byte_type)
1414                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U1);
1415                                 if (real_target_type == TypeManager.ushort_type)
1416                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U2);
1417                                 if (real_target_type == TypeManager.uint32_type)
1418                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U4);
1419                                 if (real_target_type == TypeManager.uint64_type)
1420                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U8);
1421                                 if (real_target_type == TypeManager.char_type)
1422                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_CH);
1423                         } else if (expr_type == TypeManager.byte_type){
1424                                 //
1425                                 // From byte to sbyte and char
1426                                 //
1427                                 if (real_target_type == TypeManager.sbyte_type)
1428                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_I1);
1429                                 if (real_target_type == TypeManager.char_type)
1430                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_CH);
1431                         } else if (expr_type == TypeManager.short_type){
1432                                 //
1433                                 // From short to sbyte, byte, ushort, uint, ulong, char
1434                                 //
1435                                 if (real_target_type == TypeManager.sbyte_type)
1436                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_I1);
1437                                 if (real_target_type == TypeManager.byte_type)
1438                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
1439                                 if (real_target_type == TypeManager.ushort_type)
1440                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U2);
1441                                 if (real_target_type == TypeManager.uint32_type)
1442                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U4);
1443                                 if (real_target_type == TypeManager.uint64_type)
1444                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U8);
1445                                 if (real_target_type == TypeManager.char_type)
1446                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_CH);
1447                         } else if (expr_type == TypeManager.ushort_type){
1448                                 //
1449                                 // From ushort to sbyte, byte, short, char
1450                                 //
1451                                 if (real_target_type == TypeManager.sbyte_type)
1452                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I1);
1453                                 if (real_target_type == TypeManager.byte_type)
1454                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_U1);
1455                                 if (real_target_type == TypeManager.short_type)
1456                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I2);
1457                                 if (real_target_type == TypeManager.char_type)
1458                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_CH);
1459                         } else if (expr_type == TypeManager.int32_type){
1460                                 //
1461                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1462                                 //
1463                                 if (real_target_type == TypeManager.sbyte_type)
1464                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I1);
1465                                 if (real_target_type == TypeManager.byte_type)
1466                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
1467                                 if (real_target_type == TypeManager.short_type)
1468                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
1469                                 if (real_target_type == TypeManager.ushort_type)
1470                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U2);
1471                                 if (real_target_type == TypeManager.uint32_type)
1472                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U4);
1473                                 if (real_target_type == TypeManager.uint64_type)
1474                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U8);
1475                                 if (real_target_type == TypeManager.char_type)
1476                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_CH);
1477                         } else if (expr_type == TypeManager.uint32_type){
1478                                 //
1479                                 // From uint to sbyte, byte, short, ushort, int, char
1480                                 //
1481                                 if (real_target_type == TypeManager.sbyte_type)
1482                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I1);
1483                                 if (real_target_type == TypeManager.byte_type)
1484                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U1);
1485                                 if (real_target_type == TypeManager.short_type)
1486                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I2);
1487                                 if (real_target_type == TypeManager.ushort_type)
1488                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U2);
1489                                 if (real_target_type == TypeManager.int32_type)
1490                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I4);
1491                                 if (real_target_type == TypeManager.char_type)
1492                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_CH);
1493                         } else if (expr_type == TypeManager.int64_type){
1494                                 //
1495                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1496                                 //
1497                                 if (real_target_type == TypeManager.sbyte_type)
1498                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I1);
1499                                 if (real_target_type == TypeManager.byte_type)
1500                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
1501                                 if (real_target_type == TypeManager.short_type)
1502                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
1503                                 if (real_target_type == TypeManager.ushort_type)
1504                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U2);
1505                                 if (real_target_type == TypeManager.int32_type)
1506                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
1507                                 if (real_target_type == TypeManager.uint32_type)
1508                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U4);
1509                                 if (real_target_type == TypeManager.uint64_type)
1510                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U8);
1511                                 if (real_target_type == TypeManager.char_type)
1512                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_CH);
1513                         } else if (expr_type == TypeManager.uint64_type){
1514                                 //
1515                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1516                                 //
1517                                 if (real_target_type == TypeManager.sbyte_type)
1518                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I1);
1519                                 if (real_target_type == TypeManager.byte_type)
1520                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U1);
1521                                 if (real_target_type == TypeManager.short_type)
1522                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I2);
1523                                 if (real_target_type == TypeManager.ushort_type)
1524                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U2);
1525                                 if (real_target_type == TypeManager.int32_type)
1526                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I4);
1527                                 if (real_target_type == TypeManager.uint32_type)
1528                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U4);
1529                                 if (real_target_type == TypeManager.int64_type)
1530                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I8);
1531                                 if (real_target_type == TypeManager.char_type)
1532                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_CH);
1533                         } else if (expr_type == TypeManager.char_type){
1534                                 //
1535                                 // From char to sbyte, byte, short
1536                                 //
1537                                 if (real_target_type == TypeManager.sbyte_type)
1538                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I1);
1539                                 if (real_target_type == TypeManager.byte_type)
1540                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_U1);
1541                                 if (real_target_type == TypeManager.short_type)
1542                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I2);
1543                         } else if (expr_type == TypeManager.float_type){
1544                                 //
1545                                 // From float to sbyte, byte, short,
1546                                 // ushort, int, uint, long, ulong, char
1547                                 // or decimal
1548                                 //
1549                                 if (real_target_type == TypeManager.sbyte_type)
1550                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
1551                                 if (real_target_type == TypeManager.byte_type)
1552                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U1);
1553                                 if (real_target_type == TypeManager.short_type)
1554                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I2);
1555                                 if (real_target_type == TypeManager.ushort_type)
1556                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U2);
1557                                 if (real_target_type == TypeManager.int32_type)
1558                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I4);
1559                                 if (real_target_type == TypeManager.uint32_type)
1560                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U4);
1561                                 if (real_target_type == TypeManager.int64_type)
1562                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I8);
1563                                 if (real_target_type == TypeManager.uint64_type)
1564                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U8);
1565                                 if (real_target_type == TypeManager.char_type)
1566                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_CH);
1567                         } else if (expr_type == TypeManager.double_type){
1568                                 //
1569                                 // From double to byte, byte, short,
1570                                 // ushort, int, uint, long, ulong,
1571                                 // char, float or decimal
1572                                 //
1573                                 if (real_target_type == TypeManager.sbyte_type)
1574                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I1);
1575                                 if (real_target_type == TypeManager.byte_type)
1576                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1577                                 if (real_target_type == TypeManager.short_type)
1578                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1579                                 if (real_target_type == TypeManager.ushort_type)
1580                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U2);
1581                                 if (real_target_type == TypeManager.int32_type)
1582                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1583                                 if (real_target_type == TypeManager.uint32_type)
1584                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U4);
1585                                 if (real_target_type == TypeManager.int64_type)
1586                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1587                                 if (real_target_type == TypeManager.uint64_type)
1588                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U8);
1589                                 if (real_target_type == TypeManager.char_type)
1590                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_CH);
1591                                 if (real_target_type == TypeManager.float_type)
1592                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
1593                         }
1594
1595                         // decimal is taken care of by the op_Explicit methods.
1596
1597                         return null;
1598                 }
1599
1600                 /// <summary>
1601                 ///  Returns whether an explicit reference conversion can be performed
1602                 ///  from source_type to target_type
1603                 /// </summary>
1604                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1605                 {
1606                         bool target_is_type_param = target_type.IsGenericParameter;
1607                         bool target_is_value_type = target_type.IsValueType;
1608
1609                         if (source_type == target_type)
1610                                 return true;
1611
1612                         //
1613                         // From object to a generic parameter
1614                         //
1615                         if (source_type == TypeManager.object_type && target_is_type_param)
1616                                 return true;
1617
1618                         //
1619                         // From object to any reference type
1620                         //
1621                         if (source_type == TypeManager.object_type && !target_is_value_type)
1622                                 return true;
1623
1624                         //
1625                         // From any class S to any class-type T, provided S is a base class of T
1626                         //
1627                         if (TypeManager.IsSubclassOf (target_type, source_type))
1628                                 return true;
1629
1630                         //
1631                         // From any interface type S to any interface T provided S is not derived from T
1632                         //
1633                         if (source_type.IsInterface && target_type.IsInterface){
1634                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1635                                         return true;
1636                         }
1637
1638                         //
1639                         // From any class type S to any interface T, provided S is not sealed
1640                         // and provided S does not implement T.
1641                         //
1642                         if (target_type.IsInterface && !source_type.IsSealed &&
1643                             !TypeManager.ImplementsInterface (source_type, target_type))
1644                                 return true;
1645
1646                         //
1647                         // From any interface-type S to to any class type T, provided T is not
1648                         // sealed, or provided T implements S.
1649                         //
1650                         if (source_type.IsInterface &&
1651                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1652                                 return true;
1653
1654
1655                         // From an array type S with an element type Se to an array type T with an
1656                         // element type Te provided all the following are true:
1657                         //     * S and T differe only in element type, in other words, S and T
1658                         //       have the same number of dimensions.
1659                         //     * Both Se and Te are reference types
1660                         //     * An explicit referenc conversions exist from Se to Te
1661                         //
1662                         if (source_type.IsArray && target_type.IsArray) {
1663                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1664
1665                                         Type source_element_type = TypeManager.GetElementType (source_type);
1666                                         Type target_element_type = TypeManager.GetElementType (target_type);
1667
1668                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1669                                                 if (ExplicitReferenceConversionExists (source_element_type,
1670                                                                                        target_element_type))
1671                                                         return true;
1672                                 }
1673                         }
1674
1675
1676                         // From System.Array to any array-type
1677                         if (source_type == TypeManager.array_type &&
1678                             target_type.IsArray){
1679                                 return true;
1680                         }
1681
1682                         //
1683                         // From System delegate to any delegate-type
1684                         //
1685                         if (source_type == TypeManager.delegate_type &&
1686                             TypeManager.IsDelegateType (target_type))
1687                                 return true;
1688
1689                         //
1690                         // From ICloneable to Array or Delegate types
1691                         //
1692                         if (source_type == TypeManager.icloneable_type &&
1693                             (target_type == TypeManager.array_type ||
1694                              target_type == TypeManager.delegate_type))
1695                                 return true;
1696
1697                         return false;
1698                 }
1699
1700                 /// <summary>
1701                 ///   Implements Explicit Reference conversions
1702                 /// </summary>
1703                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1704                 {
1705                         Type source_type = source.Type;
1706                         bool target_is_type_param = target_type.IsGenericParameter;
1707                         bool target_is_value_type = target_type.IsValueType;
1708
1709                         //
1710                         // From object to a generic parameter
1711                         //
1712                         if (source_type == TypeManager.object_type && target_is_type_param)
1713                                 return new UnboxCast (source, target_type);
1714
1715                         //
1716                         // From object to any reference type
1717                         //
1718                         if (source_type == TypeManager.object_type && !target_is_value_type)
1719                                 return new ClassCast (source, target_type);
1720
1721                         //
1722                         // Unboxing conversion.
1723                         //
1724                         if (((source_type == TypeManager.enum_type &&
1725                                 !(source is EmptyCast)) ||
1726                                 source_type == TypeManager.value_type) && target_is_value_type)
1727                                 return new UnboxCast (source, target_type);
1728
1729                         //
1730                         // From any class S to any class-type T, provided S is a base class of T
1731                         //
1732                         if (TypeManager.IsSubclassOf (target_type, source_type))
1733                                 return new ClassCast (source, target_type);
1734
1735                         //
1736                         // From any interface type S to any interface T provided S is not derived from T
1737                         //
1738                         if (source_type.IsInterface && target_type.IsInterface){
1739                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1740                                         return null;
1741                                 else
1742                                         return new ClassCast (source, target_type);
1743                         }
1744
1745                         //
1746                         // From any class type S to any interface T, provides S is not sealed
1747                         // and provided S does not implement T.
1748                         //
1749                         if (target_type.IsInterface && !source_type.IsSealed) {
1750                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1751                                         return null;
1752                                 else
1753                                         return new ClassCast (source, target_type);
1754
1755                         }
1756
1757                         //
1758                         // From any interface-type S to to any class type T, provided T is not
1759                         // sealed, or provided T implements S.
1760                         //
1761                         if (source_type.IsInterface) {
1762                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1763                                         if (target_type.IsClass)
1764                                                 return new ClassCast (source, target_type);
1765                                         else
1766                                                 return new UnboxCast (source, target_type);
1767                                 }
1768
1769                                 return null;
1770                         }
1771
1772                         // From an array type S with an element type Se to an array type T with an
1773                         // element type Te provided all the following are true:
1774                         //     * S and T differe only in element type, in other words, S and T
1775                         //       have the same number of dimensions.
1776                         //     * Both Se and Te are reference types
1777                         //     * An explicit referenc conversions exist from Se to Te
1778                         //
1779                         if (source_type.IsArray && target_type.IsArray) {
1780                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1781
1782                                         Type source_element_type = TypeManager.GetElementType (source_type);
1783                                         Type target_element_type = TypeManager.GetElementType (target_type);
1784
1785                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1786                                                 if (ExplicitReferenceConversionExists (source_element_type,
1787                                                                                        target_element_type))
1788                                                         return new ClassCast (source, target_type);
1789                                 }
1790                         }
1791
1792
1793                         // From System.Array to any array-type
1794                         if (source_type == TypeManager.array_type &&
1795                             target_type.IsArray) {
1796                                 return new ClassCast (source, target_type);
1797                         }
1798
1799                         //
1800                         // From System delegate to any delegate-type
1801                         //
1802                         if (source_type == TypeManager.delegate_type &&
1803                             TypeManager.IsDelegateType (target_type))
1804                                 return new ClassCast (source, target_type);
1805
1806                         //
1807                         // From ICloneable to Array or Delegate types
1808                         //
1809                         if (source_type == TypeManager.icloneable_type &&
1810                             (target_type == TypeManager.array_type ||
1811                              target_type == TypeManager.delegate_type))
1812                                 return new ClassCast (source, target_type);
1813
1814                         return null;
1815                 }
1816
1817                 /// <summary>
1818                 ///   Performs an explicit conversion of the expression `expr' whose
1819                 ///   type is expr.Type to `target_type'.
1820                 /// </summary>
1821                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1822                                                              Type target_type, Location loc)
1823                 {
1824                         Type expr_type = expr.Type;
1825                         Type original_expr_type = expr_type;
1826
1827                         if (expr_type.IsSubclassOf (TypeManager.enum_type)){
1828                                 if (target_type == TypeManager.enum_type ||
1829                                     target_type == TypeManager.object_type) {
1830                                         if (expr is EnumConstant)
1831                                                 expr = ((EnumConstant) expr).Child;
1832                                         // We really need all these casts here .... :-(
1833                                         expr = new BoxedCast (new EmptyCast (expr, expr_type));
1834                                         return new EmptyCast (expr, target_type);
1835                                 } else if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
1836                                            target_type.IsSubclassOf (TypeManager.enum_type))
1837                                         return new UnboxCast (expr, target_type);
1838
1839                                 //
1840                                 // Notice that we have kept the expr_type unmodified, which is only
1841                                 // used later on to
1842                                 if (expr is EnumConstant)
1843                                         expr = ((EnumConstant) expr).Child;
1844                                 else
1845                                         expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
1846                                 expr_type = expr.Type;
1847                         }
1848
1849                         int errors = Report.Errors;
1850                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1851                         if (Report.Errors > errors)
1852                                 return null;
1853
1854                         if (ne != null)
1855                                 return ne;
1856
1857                         ne = ExplicitNumericConversion (ec, expr, target_type, loc);
1858                         if (ne != null)
1859                                 return ne;
1860
1861                         //
1862                         // Unboxing conversion.
1863                         //
1864                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1865                                 return new UnboxCast (expr, target_type);
1866
1867                         //
1868                         // Skip the ExplicitReferenceConversion because we can not convert
1869                         // from Null to a ValueType, and ExplicitReference wont check against
1870                         // null literal explicitly
1871                         //
1872                         if (expr_type != TypeManager.null_type){
1873                                 ne = ExplicitReferenceConversion (expr, target_type);
1874                                 if (ne != null)
1875                                         return ne;
1876                         }
1877
1878                 skip_explicit:
1879                         if (ec.InUnsafe){
1880                                 if (target_type.IsPointer){
1881                                         if (expr_type.IsPointer)
1882                                                 return new EmptyCast (expr, target_type);
1883
1884                                         if (expr_type == TypeManager.sbyte_type ||
1885                                             expr_type == TypeManager.byte_type ||
1886                                             expr_type == TypeManager.short_type ||
1887                                             expr_type == TypeManager.ushort_type ||
1888                                             expr_type == TypeManager.int32_type ||
1889                                             expr_type == TypeManager.uint32_type ||
1890                                             expr_type == TypeManager.uint64_type ||
1891                                             expr_type == TypeManager.int64_type)
1892                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1893                                 }
1894                                 if (expr_type.IsPointer){
1895                                         Expression e = null;
1896
1897                                         if (target_type == TypeManager.sbyte_type)
1898                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1899                                         else if (target_type == TypeManager.byte_type)
1900                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1901                                         else if (target_type == TypeManager.short_type)
1902                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1903                                         else if (target_type == TypeManager.ushort_type)
1904                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1905                                         else if (target_type == TypeManager.int32_type)
1906                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1907                                         else if (target_type == TypeManager.uint32_type)
1908                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1909                                         else if (target_type == TypeManager.uint64_type)
1910                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1911                                         else if (target_type == TypeManager.int64_type){
1912                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1913                                         }
1914
1915                                         if (e != null){
1916                                                 Expression ci, ce;
1917
1918                                                 ci = ImplicitConversionStandard (ec, e, target_type, loc);
1919
1920                                                 if (ci != null)
1921                                                         return ci;
1922
1923                                                 ce = ExplicitNumericConversion (ec, e, target_type, loc);
1924                                                 if (ce != null)
1925                                                         return ce;
1926                                                 //
1927                                                 // We should always be able to go from an uint32
1928                                                 // implicitly or explicitly to the other integral
1929                                                 // types
1930                                                 //
1931                                                 throw new Exception ("Internal compiler error");
1932                                         }
1933                                 }
1934                         }
1935
1936                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1937                         if (ne != null)
1938                                 return ne;
1939
1940                         if (expr is NullLiteral){
1941                                 Report.Error (37, loc, "Cannot convert null to value type `" +
1942                                               TypeManager.CSharpName (target_type) + "'");
1943                                 return null;
1944                         }
1945
1946                         Error_CannotConvertType (loc, original_expr_type, target_type);
1947                         return null;
1948                 }
1949
1950                 /// <summary>
1951                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1952                 /// </summary>
1953                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1954                                                                      Type target_type, Location l)
1955                 {
1956                         int errors = Report.Errors;
1957                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1958                         if (Report.Errors > errors)
1959                                 return null;
1960
1961                         if (ne != null)
1962                                 return ne;
1963
1964                         ne = ExplicitNumericConversion (ec, expr, target_type, l);
1965                         if (ne != null)
1966                                 return ne;
1967
1968                         ne = ExplicitReferenceConversion (expr, target_type);
1969                         if (ne != null)
1970                                 return ne;
1971
1972                         Error_CannotConvertType (l, expr.Type, target_type);
1973                         return null;
1974                 }
1975         }
1976 }