mcs/mcs/convert.cs

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