mcs/mcs/convert.cs

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