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