mcs/gmcs/convert.cs

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