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