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