mcs/gmcs/convert.cs

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