mcs/gmcs/convert.cs

   1 //
   2 // conversion.cs: various routines for implementing conversions.
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Ravi Pratap (ravi@ximian.com)
   7 //
   8 // (C) 2001, 2002, 2003 Ximian, Inc.
   9 //
  10
  11 namespace Mono.CSharp {
  12         using System;
  13         using System.Collections;
  14         using System.Diagnostics;
  15         using System.Reflection;
  16         using System.Reflection.Emit;
  17
  18         //
  19         // A container class for all the conversion operations
  20         //
  21         public class Convert {
  22                 static void Error_CannotConvertType (Location loc, Type source, Type target)
  23                 {
  24                         Report.Error (30, loc, "Cannot convert type '" +
  25                                       TypeManager.CSharpName (source) + "' to '" +
  26                                       TypeManager.CSharpName (target) + "'");
  27                 }
  28
  29                 static Expression TypeParameter_to_Null (Expression expr, Type target_type,
  30                                                          Location loc)
  31                 {
  32                         if (!TypeParameter_to_Null (target_type)) {
  33                                 Report.Error (403, loc, "Cannot convert null to the type " +
  34                                               "parameter `{0}' becaues it could be a value " +
  35                                               "type.  Consider using `default ({0})' instead.",
  36                                               target_type);
  37                                 return null;
  38                         }
  39
  40                         return new NullCast (expr, target_type);
  41                 }
  42
  43                 static bool TypeParameter_to_Null (Type target_type)
  44                 {
  45                         if ((target_type.BaseType == null) ||
  46                             (target_type.BaseType == TypeManager.value_type) ||
  47                             target_type.BaseType.IsValueType)
  48                                 return false;
  49
  50                         return true;
  51                 }
  52
  53                 static EmptyExpression MyEmptyExpr;
  54                 static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
  55                 {
  56                         Type expr_type = expr.Type;
  57
  58                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
  59                                 // if we are a method group, emit a warning
  60
  61                                 expr.Emit (null);
  62                         }
  63
  64                         if (expr_type == TypeManager.void_type)
  65                                 return null;
  66
  67                         //
  68                         // notice that it is possible to write "ValueType v = 1", the ValueType here
  69                         // is an abstract class, and not really a value type, so we apply the same rules.
  70                         //
  71                         if (target_type == TypeManager.object_type) {
  72                                 //
  73                                 // A pointer type cannot be converted to object
  74                                 //
  75                                 if (expr_type.IsPointer)
  76                                         return null;
  77
  78                                 if (TypeManager.IsValueType (expr_type))
  79                                         return new BoxedCast (expr);
  80                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type)
  81                                         return new EmptyCast (expr, target_type);
  82
  83                                 return null;
  84                         } else if (target_type == TypeManager.value_type) {
  85                                 if (TypeManager.IsValueType (expr_type))
  86                                         return new BoxedCast (expr);
  87                                 if (expr is NullLiteral)
  88                                         return new NullCast (expr, target_type);
  89
  90                                 return null;
  91                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
  92                                 //
  93                                 // Special case: enumeration to System.Enum.
  94                                 // System.Enum is not a value type, it is a class, so we need
  95                                 // a boxing conversion
  96                                 //
  97                                 if (expr_type.IsEnum || expr_type.IsGenericParameter)
  98                                         return new BoxedCast (expr);
  99
 100                                 return new EmptyCast (expr, target_type);
 101                         }
 102
 103                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 104                         // with the small distinction that we only probe there
 105                         //
 106                         // Always ensure that the code here and there is in sync
 107
 108                         // from the null type to any reference-type.
 109                         if (expr is NullLiteral){
 110                                 if (target_type.IsPointer)
 111                                         return NullPointer.Null;
 112
 113                                 if (!target_type.IsValueType)
 114                                         return new NullCast (expr, target_type);
 115                         }
 116
 117                         // from any class-type S to any interface-type T.
 118                         if (target_type.IsInterface) {
 119                                 if (target_type != TypeManager.iconvertible_type &&
 120                                     expr_type.IsValueType && (expr is Constant) &&
 121                                     !(expr is IntLiteral || expr is BoolLiteral ||
 122                                       expr is FloatLiteral || expr is DoubleLiteral ||
 123                                       expr is LongLiteral || expr is CharLiteral ||
 124                                       expr is StringLiteral || expr is DecimalLiteral ||
 125                                       expr is UIntLiteral || expr is ULongLiteral)) {
 126                                         return null;
 127                                 }
 128
 129                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 130                                         if (expr_type.IsGenericParameter || TypeManager.IsValueType (expr_type))
 131                                                 return new BoxedCast (expr, target_type);
 132                                         else
 133                                                 return new EmptyCast (expr, target_type);
 134                                 }
 135                         }
 136
 137                         // from any interface type S to interface-type T.
 138                         if (expr_type.IsInterface && target_type.IsInterface) {
 139                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 140                                         return new EmptyCast (expr, target_type);
 141                                 else
 142                                         return null;
 143                         }
 144
 145                         // from an array-type S to an array-type of type T
 146                         if (expr_type.IsArray && target_type.IsArray) {
 147                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 148
 149                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 150
 151                                         if (MyEmptyExpr == null)
 152                                                 MyEmptyExpr = new EmptyExpression ();
 153
 154                                         MyEmptyExpr.SetType (expr_element_type);
 155                                         Type target_element_type = TypeManager.GetElementType (target_type);
 156
 157                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 158                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 159                                                                                       target_element_type))
 160                                                         return new EmptyCast (expr, target_type);
 161                                 }
 162                         }
 163
 164                         // from an array-type to System.Array
 165                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 166                                 return new EmptyCast (expr, target_type);
 167
 168                         // from any delegate type to System.Delegate
 169                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 170                             target_type == TypeManager.delegate_type)
 171                                 return new EmptyCast (expr, target_type);
 172
 173                         // from any array-type or delegate type into System.ICloneable.
 174                         if (expr_type.IsArray ||
 175                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 176                                 if (target_type == TypeManager.icloneable_type)
 177                                         return new EmptyCast (expr, target_type);
 178
 179                         // from a generic type definition to a generic instance.
 180                         if (TypeManager.IsEqualGenericType (expr_type, target_type))
 181                                 return new EmptyCast (expr, target_type);
 182
 183                         if (expr_type.IsGenericParameter) {
 184                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
 185
 186                                 // We're converting from a type parameter which is known to be a reference type.
 187                                 if ((gc != null) && gc.IsReferenceType) {
 188                                         if (gc.HasClassConstraint &&
 189                                             TypeManager.IsSubclassOf (gc.ClassConstraint, target_type))
 190                                                 return new EmptyCast (expr, target_type);
 191
 192                                         foreach (Type t in gc.InterfaceConstraints) {
 193                                                 if (TypeManager.IsSubclassOf (t, target_type))
 194                                                         return new EmptyCast (expr, target_type);
 195                                         }
 196                                 }
 197                         }
 198
 199                         return null;
 200                 }
 201
 202                 //
 203                 // Tests whether an implicit reference conversion exists between expr_type
 204                 // and target_type
 205                 //
 206                 public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
 207                 {
 208                         Type expr_type = expr.Type;
 209
 210                         //
 211                         // This is the boxed case.
 212                         //
 213                         if (target_type == TypeManager.object_type) {
 214                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 215                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 216                                         return true;
 217
 218                                 return false;
 219                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 220                                 return true;
 221
 222                         // Please remember that all code below actually comes
 223                         // from ImplicitReferenceConversion so make sure code remains in sync
 224
 225                         // from any class-type S to any interface-type T.
 226                         if (target_type.IsInterface) {
 227                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 228                                         return true;
 229                         }
 230
 231                         // from any interface type S to interface-type T.
 232                         if (expr_type.IsInterface && target_type.IsInterface)
 233                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 234                                         return true;
 235
 236                         // from an array-type S to an array-type of type T
 237                         if (expr_type.IsArray && target_type.IsArray) {
 238                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 239
 240                                         Type expr_element_type = expr_type.GetElementType ();
 241
 242                                         if (MyEmptyExpr == null)
 243                                                 MyEmptyExpr = new EmptyExpression ();
 244
 245                                         MyEmptyExpr.SetType (expr_element_type);
 246                                         Type target_element_type = TypeManager.GetElementType (target_type);
 247
 248                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 249                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 250                                                                                       target_element_type))
 251                                                         return true;
 252                                 }
 253                         }
 254
 255                         // from an array-type to System.Array
 256                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 257                                 return true;
 258
 259                         // from any delegate type to System.Delegate
 260                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 261                             target_type == TypeManager.delegate_type)
 262                                 if (target_type.IsAssignableFrom (expr_type))
 263                                         return true;
 264
 265                         // from any array-type or delegate type into System.ICloneable.
 266                         if (expr_type.IsArray ||
 267                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 268                                 if (target_type == TypeManager.icloneable_type)
 269                                         return true;
 270
 271                         // from the null type to any reference-type.
 272                         if (expr is NullLiteral && !target_type.IsValueType && !TypeManager.IsEnumType (target_type))
 273                                 return true;
 274
 275                         // from a generic type definition to a generic instance.
 276                         if (TypeManager.IsEqualGenericType (expr_type, target_type))
 277                                 return true;
 278
 279                         if (expr_type.IsGenericParameter) {
 280                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
 281
 282                                 // We're converting from a type parameter which is known to be a reference type.
 283                                 if ((gc != null) && gc.IsReferenceType) {
 284                                         if (gc.HasClassConstraint &&
 285                                             TypeManager.IsSubclassOf (gc.ClassConstraint, target_type))
 286                                                 return true;
 287
 288                                         foreach (Type t in gc.InterfaceConstraints) {
 289                                                 if (TypeManager.IsSubclassOf (t, target_type))
 290                                                         return true;
 291                                         }
 292                                 }
 293                         }
 294
 295                         return false;
 296                 }
 297
 298                 /// <summary>
 299                 ///   Implicit Numeric Conversions.
 300                 ///
 301                 ///   expr is the expression to convert, returns a new expression of type
 302                 ///   target_type or null if an implicit conversion is not possible.
 303                 /// </summary>
 304                 static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
 305                                                                     Type target_type, Location loc)
 306                 {
 307                         Type expr_type = expr.Type;
 308
 309                         //
 310                         // Attempt to do the implicit constant expression conversions
 311
 312                         if (expr is Constant){
 313                                 if (expr is IntConstant){
 314                                         Expression e;
 315
 316                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 317
 318                                         if (e != null)
 319                                                 return e;
 320                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 321                                         //
 322                                         // Try the implicit constant expression conversion
 323                                         // from long to ulong, instead of a nice routine,
 324                                         // we just inline it
 325                                         //
 326                                         long v = ((LongConstant) expr).Value;
 327                                         if (v >= 0)
 328                                                 return new ULongConstant ((ulong) v);
 329                                 }
 330                         }
 331
 332                         Type real_target_type = target_type;
 333
 334                         if (expr_type == TypeManager.sbyte_type){
 335                                 //
 336                                 // From sbyte to short, int, long, float, double.
 337                                 //
 338                                 if (real_target_type == TypeManager.int32_type)
 339                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 340                                 if (real_target_type == TypeManager.int64_type)
 341                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 342                                 if (real_target_type == TypeManager.double_type)
 343                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 344                                 if (real_target_type == TypeManager.float_type)
 345                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 346                                 if (real_target_type == TypeManager.short_type)
 347                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 348                         } else if (expr_type == TypeManager.byte_type){
 349                                 //
 350                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 351                                 //
 352                                 if ((real_target_type == TypeManager.short_type) ||
 353                                     (real_target_type == TypeManager.ushort_type) ||
 354                                     (real_target_type == TypeManager.int32_type) ||
 355                                     (real_target_type == TypeManager.uint32_type))
 356                                         return new EmptyCast (expr, target_type);
 357
 358                                 if (real_target_type == TypeManager.uint64_type)
 359                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 360                                 if (real_target_type == TypeManager.int64_type)
 361                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 362                                 if (real_target_type == TypeManager.float_type)
 363                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 364                                 if (real_target_type == TypeManager.double_type)
 365                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 366                         } else if (expr_type == TypeManager.short_type){
 367                                 //
 368                                 // From short to int, long, float, double
 369                                 //
 370                                 if (real_target_type == TypeManager.int32_type)
 371                                         return new EmptyCast (expr, target_type);
 372                                 if (real_target_type == TypeManager.int64_type)
 373                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 374                                 if (real_target_type == TypeManager.double_type)
 375                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 376                                 if (real_target_type == TypeManager.float_type)
 377                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 378                         } else if (expr_type == TypeManager.ushort_type){
 379                                 //
 380                                 // From ushort to int, uint, long, ulong, float, double
 381                                 //
 382                                 if (real_target_type == TypeManager.uint32_type)
 383                                         return new EmptyCast (expr, target_type);
 384
 385                                 if (real_target_type == TypeManager.uint64_type)
 386                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 387                                 if (real_target_type == TypeManager.int32_type)
 388                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 389                                 if (real_target_type == TypeManager.int64_type)
 390                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 391                                 if (real_target_type == TypeManager.double_type)
 392                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 393                                 if (real_target_type == TypeManager.float_type)
 394                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 395                         } else if (expr_type == TypeManager.int32_type){
 396                                 //
 397                                 // From int to long, float, double
 398                                 //
 399                                 if (real_target_type == TypeManager.int64_type)
 400                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 401                                 if (real_target_type == TypeManager.double_type)
 402                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 403                                 if (real_target_type == TypeManager.float_type)
 404                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 405                         } else if (expr_type == TypeManager.uint32_type){
 406                                 //
 407                                 // From uint to long, ulong, float, double
 408                                 //
 409                                 if (real_target_type == TypeManager.int64_type)
 410                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 411                                 if (real_target_type == TypeManager.uint64_type)
 412                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 413                                 if (real_target_type == TypeManager.double_type)
 414                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 415                                                                OpCodes.Conv_R8);
 416                                 if (real_target_type == TypeManager.float_type)
 417                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 418                                                                OpCodes.Conv_R4);
 419                         } else if (expr_type == TypeManager.int64_type){
 420                                 //
 421                                 // From long/ulong to float, double
 422                                 //
 423                                 if (real_target_type == TypeManager.double_type)
 424                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 425                                 if (real_target_type == TypeManager.float_type)
 426                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 427                         } else if (expr_type == TypeManager.uint64_type){
 428                                 //
 429                                 // From ulong to float, double
 430                                 //
 431                                 if (real_target_type == TypeManager.double_type)
 432                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 433                                                                OpCodes.Conv_R8);
 434                                 if (real_target_type == TypeManager.float_type)
 435                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 436                                                                OpCodes.Conv_R4);
 437                         } else if (expr_type == TypeManager.char_type){
 438                                 //
 439                                 // From char to ushort, int, uint, long, ulong, float, double
 440                                 //
 441                                 if ((real_target_type == TypeManager.ushort_type) ||
 442                                     (real_target_type == TypeManager.int32_type) ||
 443                                     (real_target_type == TypeManager.uint32_type))
 444                                         return new EmptyCast (expr, target_type);
 445                                 if (real_target_type == TypeManager.uint64_type)
 446                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 447                                 if (real_target_type == TypeManager.int64_type)
 448                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 449                                 if (real_target_type == TypeManager.float_type)
 450                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 451                                 if (real_target_type == TypeManager.double_type)
 452                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 453                         } else if (expr_type == TypeManager.float_type){
 454                                 //
 455                                 // float to double
 456                                 //
 457                                 if (real_target_type == TypeManager.double_type)
 458                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 459                         }
 460
 461                         return null;
 462                 }
 463
 464
 465                 /// <summary>
 466                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 467                 ///  implicit user defined conversions - needed for overload resolution
 468                 /// </summary>
 469                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 470                 {
 471                         if ((expr is NullLiteral) && target_type.IsGenericParameter)
 472                                 return TypeParameter_to_Null (target_type);
 473
 474                         if (ImplicitStandardConversionExists (expr, target_type))
 475                                 return true;
 476
 477                         Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);
 478
 479                         if (dummy != null)
 480                                 return true;
 481
 482                         return false;
 483                 }
 484
 485                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 486                 {
 487                         Expression dummy = ImplicitUserConversion (
 488                                 ec, new EmptyExpression (source), target, Location.Null);
 489                         return dummy != null;
 490                 }
 491
 492                 /// <summary>
 493                 ///  Determines if a standard implicit conversion exists from
 494                 ///  expr_type to target_type
 495                 /// </summary>
 496                 public static bool ImplicitStandardConversionExists (Expression expr, Type target_type)
 497                 {
 498                         Type expr_type = expr.Type;
 499
 500                         if (expr_type == TypeManager.void_type)
 501                                 return false;
 502
 503                         //Console.WriteLine ("Expr is {0}", expr);
 504                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 505                         if (expr_type.Equals (target_type))
 506                                 return true;
 507
 508                         // First numeric conversions
 509
 510                         if (expr_type == TypeManager.sbyte_type){
 511                                 //
 512                                 // From sbyte to short, int, long, float, double.
 513                                 //
 514                                 if ((target_type == TypeManager.int32_type) ||
 515                                     (target_type == TypeManager.int64_type) ||
 516                                     (target_type == TypeManager.double_type) ||
 517                                     (target_type == TypeManager.float_type)  ||
 518                                     (target_type == TypeManager.short_type) ||
 519                                     (target_type == TypeManager.decimal_type))
 520                                         return true;
 521
 522                         } else if (expr_type == TypeManager.byte_type){
 523                                 //
 524                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 525                                 //
 526                                 if ((target_type == TypeManager.short_type) ||
 527                                     (target_type == TypeManager.ushort_type) ||
 528                                     (target_type == TypeManager.int32_type) ||
 529                                     (target_type == TypeManager.uint32_type) ||
 530                                     (target_type == TypeManager.uint64_type) ||
 531                                     (target_type == TypeManager.int64_type) ||
 532                                     (target_type == TypeManager.float_type) ||
 533                                     (target_type == TypeManager.double_type) ||
 534                                     (target_type == TypeManager.decimal_type))
 535                                         return true;
 536
 537                         } else if (expr_type == TypeManager.short_type){
 538                                 //
 539                                 // From short to int, long, float, double
 540                                 //
 541                                 if ((target_type == TypeManager.int32_type) ||
 542                                     (target_type == TypeManager.int64_type) ||
 543                                     (target_type == TypeManager.double_type) ||
 544                                     (target_type == TypeManager.float_type) ||
 545                                     (target_type == TypeManager.decimal_type))
 546                                         return true;
 547
 548                         } else if (expr_type == TypeManager.ushort_type){
 549                                 //
 550                                 // From ushort to int, uint, long, ulong, float, double
 551                                 //
 552                                 if ((target_type == TypeManager.uint32_type) ||
 553                                     (target_type == TypeManager.uint64_type) ||
 554                                     (target_type == TypeManager.int32_type) ||
 555                                     (target_type == TypeManager.int64_type) ||
 556                                     (target_type == TypeManager.double_type) ||
 557                                     (target_type == TypeManager.float_type) ||
 558                                     (target_type == TypeManager.decimal_type))
 559                                         return true;
 560
 561                         } else if (expr_type == TypeManager.int32_type){
 562                                 //
 563                                 // From int to long, float, double
 564                                 //
 565                                 if ((target_type == TypeManager.int64_type) ||
 566                                     (target_type == TypeManager.double_type) ||
 567                                     (target_type == TypeManager.float_type) ||
 568                                     (target_type == TypeManager.decimal_type))
 569                                         return true;
 570
 571                         } else if (expr_type == TypeManager.uint32_type){
 572                                 //
 573                                 // From uint to long, ulong, float, double
 574                                 //
 575                                 if ((target_type == TypeManager.int64_type) ||
 576                                     (target_type == TypeManager.uint64_type) ||
 577                                     (target_type == TypeManager.double_type) ||
 578                                     (target_type == TypeManager.float_type) ||
 579                                     (target_type == TypeManager.decimal_type))
 580                                         return true;
 581
 582                         } else if ((expr_type == TypeManager.uint64_type) ||
 583                                    (expr_type == TypeManager.int64_type)) {
 584                                 //
 585                                 // From long/ulong to float, double
 586                                 //
 587                                 if ((target_type == TypeManager.double_type) ||
 588                                     (target_type == TypeManager.float_type) ||
 589                                     (target_type == TypeManager.decimal_type))
 590                                         return true;
 591
 592                         } else if (expr_type == TypeManager.char_type){
 593                                 //
 594                                 // From char to ushort, int, uint, long, ulong, float, double
 595                                 //
 596                                 if ((target_type == TypeManager.ushort_type) ||
 597                                     (target_type == TypeManager.int32_type) ||
 598                                     (target_type == TypeManager.uint32_type) ||
 599                                     (target_type == TypeManager.uint64_type) ||
 600                                     (target_type == TypeManager.int64_type) ||
 601                                     (target_type == TypeManager.float_type) ||
 602                                     (target_type == TypeManager.double_type) ||
 603                                     (target_type == TypeManager.decimal_type))
 604                                         return true;
 605
 606                         } else if (expr_type == TypeManager.float_type){
 607                                 //
 608                                 // float to double
 609                                 //
 610                                 if (target_type == TypeManager.double_type)
 611                                         return true;
 612                         }
 613
 614                         if (ImplicitReferenceConversionExists (expr, target_type))
 615                                 return true;
 616
 617                         //
 618                         // Implicit Constant Expression Conversions
 619                         //
 620                         if (expr is IntConstant){
 621                                 int value = ((IntConstant) expr).Value;
 622
 623                                 if (target_type == TypeManager.sbyte_type){
 624                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 625                                                 return true;
 626                                 } else if (target_type == TypeManager.byte_type){
 627                                         if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
 628                                                 return true;
 629                                 } else if (target_type == TypeManager.short_type){
 630                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 631                                                 return true;
 632                                 } else if (target_type == TypeManager.ushort_type){
 633                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 634                                                 return true;
 635                                 } else if (target_type == TypeManager.uint32_type){
 636                                         if (value >= 0)
 637                                                 return true;
 638                                 } else if (target_type == TypeManager.uint64_type){
 639                                          //
 640                                          // we can optimize this case: a positive int32
 641                                          // always fits on a uint64.  But we need an opcode
 642                                          // to do it.
 643                                          //
 644                                         if (value >= 0)
 645                                                 return true;
 646                                 }
 647
 648                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 649                                         return true;
 650                         }
 651
 652                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 653                                 //
 654                                 // Try the implicit constant expression conversion
 655                                 // from long to ulong, instead of a nice routine,
 656                                 // we just inline it
 657                                 //
 658                                 long v = ((LongConstant) expr).Value;
 659                                 if (v > 0)
 660                                         return true;
 661                         }
 662
 663                         if ((target_type == TypeManager.enum_type ||
 664                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 665                              expr is IntLiteral){
 666                                 IntLiteral i = (IntLiteral) expr;
 667
 668                                 if (i.Value == 0)
 669                                         return true;
 670                         }
 671
 672                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 673                                 return true;
 674
 675                         return false;
 676                 }
 677
 678                 //
 679                 // Used internally by FindMostEncompassedType, this is used
 680                 // to avoid creating lots of objects in the tight loop inside
 681                 // FindMostEncompassedType
 682                 //
 683                 static EmptyExpression priv_fmet_param;
 684
 685                 /// <summary>
 686                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 687                 ///  amongst the methods in the MethodGroupExpr
 688                 /// </summary>
 689                 static Type FindMostEncompassedType (ArrayList types)
 690                 {
 691                         Type best = null;
 692
 693                         if (priv_fmet_param == null)
 694                                 priv_fmet_param = new EmptyExpression ();
 695
 696                         foreach (Type t in types){
 697                                 priv_fmet_param.SetType (t);
 698
 699                                 if (best == null) {
 700                                         best = t;
 701                                         continue;
 702                                 }
 703
 704                                 if (ImplicitStandardConversionExists (priv_fmet_param, best))
 705                                         best = t;
 706                         }
 707
 708                         return best;
 709                 }
 710
 711                 //
 712                 // Used internally by FindMostEncompassingType, this is used
 713                 // to avoid creating lots of objects in the tight loop inside
 714                 // FindMostEncompassingType
 715                 //
 716                 static EmptyExpression priv_fmee_ret;
 717
 718                 /// <summary>
 719                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 720                 ///  amongst the types in the given set
 721                 /// </summary>
 722                 static Type FindMostEncompassingType (ArrayList types)
 723                 {
 724                         Type best = null;
 725
 726                         if (priv_fmee_ret == null)
 727                                 priv_fmee_ret = new EmptyExpression ();
 728
 729                         foreach (Type t in types){
 730                                 priv_fmee_ret.SetType (best);
 731
 732                                 if (best == null) {
 733                                         best = t;
 734                                         continue;
 735                                 }
 736
 737                                 if (ImplicitStandardConversionExists (priv_fmee_ret, t))
 738                                         best = t;
 739                         }
 740
 741                         return best;
 742                 }
 743
 744                 //
 745                 // Used to avoid creating too many objects
 746                 //
 747                 static EmptyExpression priv_fms_expr;
 748
 749                 /// <summary>
 750                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 751                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 752                 ///   for explicit and implicit conversion operators.
 753                 /// </summary>
 754                 static public Type FindMostSpecificSource (MethodGroupExpr me, Expression source,
 755                                                            bool apply_explicit_conv_rules,
 756                                                            Location loc)
 757                 {
 758                         ArrayList src_types_set = new ArrayList ();
 759
 760                         if (priv_fms_expr == null)
 761                                 priv_fms_expr = new EmptyExpression ();
 762
 763                         //
 764                         // If any operator converts from S then Sx = S
 765                         //
 766                         Type source_type = source.Type;
 767                         foreach (MethodBase mb in me.Methods){
 768                                 ParameterData pd = Invocation.GetParameterData (mb);
 769                                 Type param_type = pd.ParameterType (0);
 770
 771                                 if (param_type == source_type)
 772                                         return param_type;
 773
 774                                 if (apply_explicit_conv_rules) {
 775                                         //
 776                                         // From the spec :
 777                                         // Find the set of applicable user-defined conversion operators, U.  This set
 778                                         // consists of the
 779                                         // user-defined implicit or explicit conversion operators declared by
 780                                         // the classes or structs in D that convert from a type encompassing
 781                                         // or encompassed by S to a type encompassing or encompassed by T
 782                                         //
 783                                         priv_fms_expr.SetType (param_type);
 784                                         if (ImplicitStandardConversionExists (priv_fms_expr, source_type))
 785                                                 src_types_set.Add (param_type);
 786                                         else {
 787                                                 if (ImplicitStandardConversionExists (source, param_type))
 788                                                         src_types_set.Add (param_type);
 789                                         }
 790                                 } else {
 791                                         //
 792                                         // Only if S is encompassed by param_type
 793                                         //
 794                                         if (ImplicitStandardConversionExists (source, param_type))
 795                                                 src_types_set.Add (param_type);
 796                                 }
 797                         }
 798
 799                         //
 800                         // Explicit Conv rules
 801                         //
 802                         if (apply_explicit_conv_rules) {
 803                                 ArrayList candidate_set = new ArrayList ();
 804
 805                                 foreach (Type param_type in src_types_set){
 806                                         if (ImplicitStandardConversionExists (source, param_type))
 807                                                 candidate_set.Add (param_type);
 808                                 }
 809
 810                                 if (candidate_set.Count != 0)
 811                                         return FindMostEncompassedType (candidate_set);
 812                         }
 813
 814                         //
 815                         // Final case
 816                         //
 817                         if (apply_explicit_conv_rules)
 818                                 return FindMostEncompassingType (src_types_set);
 819                         else
 820                                 return FindMostEncompassedType (src_types_set);
 821                 }
 822
 823                 //
 824                 // Useful in avoiding proliferation of objects
 825                 //
 826                 static EmptyExpression priv_fmt_expr;
 827
 828                 /// <summary>
 829                 ///  Finds the most specific target Tx according to section 13.4.4
 830                 /// </summary>
 831                 static public Type FindMostSpecificTarget (MethodGroupExpr me, Type target,
 832                                                            bool apply_explicit_conv_rules,
 833                                                            Location loc)
 834                 {
 835                         ArrayList tgt_types_set = new ArrayList ();
 836
 837                         if (priv_fmt_expr == null)
 838                                 priv_fmt_expr = new EmptyExpression ();
 839
 840                         //
 841                         // If any operator converts to T then Tx = T
 842                         //
 843                         foreach (MethodInfo mi in me.Methods){
 844                                 Type ret_type = mi.ReturnType;
 845
 846                                 if (ret_type == target)
 847                                         return ret_type;
 848
 849                                 if (apply_explicit_conv_rules) {
 850                                         //
 851                                         // From the spec :
 852                                         // Find the set of applicable user-defined conversion operators, U.
 853                                         //
 854                                         // This set consists of the
 855                                         // user-defined implicit or explicit conversion operators declared by
 856                                         // the classes or structs in D that convert from a type encompassing
 857                                         // or encompassed by S to a type encompassing or encompassed by T
 858                                         //
 859                                         priv_fms_expr.SetType (ret_type);
 860                                         if (ImplicitStandardConversionExists (priv_fms_expr, target))
 861                                                 tgt_types_set.Add (ret_type);
 862                                         else {
 863                                                 priv_fms_expr.SetType (target);
 864                                                 if (ImplicitStandardConversionExists (priv_fms_expr, ret_type))
 865                                                         tgt_types_set.Add (ret_type);
 866                                         }
 867                                 } else {
 868                                         //
 869                                         // Only if T is encompassed by param_type
 870                                         //
 871                                         priv_fms_expr.SetType (ret_type);
 872                                         if (ImplicitStandardConversionExists (priv_fms_expr, target))
 873                                                 tgt_types_set.Add (ret_type);
 874                                 }
 875                         }
 876
 877                         //
 878                         // Explicit conv rules
 879                         //
 880                         if (apply_explicit_conv_rules) {
 881                                 ArrayList candidate_set = new ArrayList ();
 882
 883                                 foreach (Type ret_type in tgt_types_set){
 884                                         priv_fmt_expr.SetType (ret_type);
 885
 886                                         if (ImplicitStandardConversionExists (priv_fmt_expr, target))
 887                                                 candidate_set.Add (ret_type);
 888                                 }
 889
 890                                 if (candidate_set.Count != 0)
 891                                         return FindMostEncompassingType (candidate_set);
 892                         }
 893
 894                         //
 895                         // Okay, final case !
 896                         //
 897                         if (apply_explicit_conv_rules)
 898                                 return FindMostEncompassedType (tgt_types_set);
 899                         else
 900                                 return FindMostEncompassingType (tgt_types_set);
 901                 }
 902
 903                 /// <summary>
 904                 ///  User-defined Implicit conversions
 905                 /// </summary>
 906                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
 907                                                                  Type target, Location loc)
 908                 {
 909                         return UserDefinedConversion (ec, source, target, loc, false);
 910                 }
 911
 912                 /// <summary>
 913                 ///  User-defined Explicit conversions
 914                 /// </summary>
 915                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
 916                                                                  Type target, Location loc)
 917                 {
 918                         return UserDefinedConversion (ec, source, target, loc, true);
 919                 }
 920
 921                 static DoubleHash explicit_conv = new DoubleHash (100);
 922                 static DoubleHash implicit_conv = new DoubleHash (100);
 923                 /// <summary>
 924                 ///   Computes the MethodGroup for the user-defined conversion
 925                 ///   operators from source_type to target_type.  `look_for_explicit'
 926                 ///   controls whether we should also include the list of explicit
 927                 ///   operators
 928                 /// </summary>
 929                 static MethodGroupExpr GetConversionOperators (EmitContext ec,
 930                                                                Type source_type, Type target_type,
 931                                                                Location loc, bool look_for_explicit)
 932                 {
 933                         Expression mg1 = null, mg2 = null;
 934                         Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
 935                         string op_name;
 936
 937                         op_name = "op_Implicit";
 938
 939                         MethodGroupExpr union3;
 940                         object r;
 941                         if ((look_for_explicit ? explicit_conv : implicit_conv).Lookup (source_type, target_type, out r))
 942                                 return (MethodGroupExpr) r;
 943
 944                         mg1 = Expression.MethodLookup (ec, source_type, op_name, loc);
 945                         if (source_type.BaseType != null)
 946                                 mg2 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
 947
 948                         if (mg1 == null)
 949                                 union3 = (MethodGroupExpr) mg2;
 950                         else if (mg2 == null)
 951                                 union3 = (MethodGroupExpr) mg1;
 952                         else
 953                                 union3 = Invocation.MakeUnionSet (mg1, mg2, loc);
 954
 955                         mg1 = Expression.MethodLookup (ec, target_type, op_name, loc);
 956                         if (mg1 != null){
 957                                 if (union3 != null)
 958                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
 959                                 else
 960                                         union3 = (MethodGroupExpr) mg1;
 961                         }
 962
 963                         if (target_type.BaseType != null)
 964                                 mg1 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
 965
 966                         if (mg1 != null){
 967                                 if (union3 != null)
 968                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
 969                                 else
 970                                         union3 = (MethodGroupExpr) mg1;
 971                         }
 972
 973                         MethodGroupExpr union4 = null;
 974
 975                         if (look_for_explicit) {
 976                                 op_name = "op_Explicit";
 977
 978                                 mg5 = Expression.MemberLookup (ec, source_type, op_name, loc);
 979                                 if (source_type.BaseType != null)
 980                                         mg6 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
 981
 982                                 mg7 = Expression.MemberLookup (ec, target_type, op_name, loc);
 983                                 if (target_type.BaseType != null)
 984                                         mg8 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
 985
 986                                 MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
 987                                 MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);
 988
 989                                 union4 = Invocation.MakeUnionSet (union5, union6, loc);
 990                         }
 991
 992                         MethodGroupExpr ret = Invocation.MakeUnionSet (union3, union4, loc);
 993                         (look_for_explicit ? explicit_conv : implicit_conv).Insert (source_type, target_type, ret);
 994                         return ret;
 995                 }
 996
 997                 /// <summary>
 998                 ///   User-defined conversions
 999                 /// </summary>
1000                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1001                                                                 Type target, Location loc,
1002                                                                 bool look_for_explicit)
1003                 {
1004                         MethodGroupExpr union;
1005                         Type source_type = source.Type;
1006                         MethodBase method = null;
1007
1008                         union = GetConversionOperators (ec, source_type, target, loc, look_for_explicit);
1009                         if (union == null)
1010                                 return null;
1011
1012                         Type most_specific_source, most_specific_target;
1013
1014                         most_specific_source = FindMostSpecificSource (union, source, look_for_explicit, loc);
1015                         if (most_specific_source == null)
1016                                 return null;
1017
1018                         most_specific_target = FindMostSpecificTarget (union, target, look_for_explicit, loc);
1019                         if (most_specific_target == null)
1020                                 return null;
1021
1022                         int count = 0;
1023
1024
1025                         foreach (MethodBase mb in union.Methods){
1026                                 ParameterData pd = Invocation.GetParameterData (mb);
1027                                 MethodInfo mi = (MethodInfo) mb;
1028
1029                                 if (pd.ParameterType (0) == most_specific_source &&
1030                                     mi.ReturnType == most_specific_target) {
1031                                         method = mb;
1032                                         count++;
1033                                 }
1034                         }
1035
1036                         if (method == null || count > 1)
1037                                 return null;
1038
1039
1040                         //
1041                         // This will do the conversion to the best match that we
1042                         // found.  Now we need to perform an implict standard conversion
1043                         // if the best match was not the type that we were requested
1044                         // by target.
1045                         //
1046                         if (look_for_explicit)
1047                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1048                         else
1049                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1050
1051                         if (source == null)
1052                                 return null;
1053
1054                         Expression e;
1055                         e =  new UserCast ((MethodInfo) method, source, loc);
1056                         if (e.Type != target){
1057                                 if (!look_for_explicit)
1058                                         e = ImplicitConversionStandard (ec, e, target, loc);
1059                                 else
1060                                         e = ExplicitConversionStandard (ec, e, target, loc);
1061                         }
1062
1063                         return e;
1064                 }
1065
1066                 /// <summary>
1067                 ///   Converts implicitly the resolved expression `expr' into the
1068                 ///   `target_type'.  It returns a new expression that can be used
1069                 ///   in a context that expects a `target_type'.
1070                 /// </summary>
1071                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1072                                                              Type target_type, Location loc)
1073                 {
1074                         Expression e;
1075
1076                         if (target_type == null)
1077                                 throw new Exception ("Target type is null");
1078
1079                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1080                         if (e != null)
1081                                 return e;
1082
1083                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1084                         if (e != null)
1085                                 return e;
1086
1087                         return null;
1088                 }
1089
1090
1091                 /// <summary>
1092                 ///   Attempts to apply the `Standard Implicit
1093                 ///   Conversion' rules to the expression `expr' into
1094                 ///   the `target_type'.  It returns a new expression
1095                 ///   that can be used in a context that expects a
1096                 ///   `target_type'.
1097                 ///
1098                 ///   This is different from `ImplicitConversion' in that the
1099                 ///   user defined implicit conversions are excluded.
1100                 /// </summary>
1101                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1102                                                                      Type target_type, Location loc)
1103                 {
1104                         Type expr_type = expr.Type;
1105                         Expression e;
1106
1107                         if ((expr is NullLiteral) && target_type.IsGenericParameter)
1108                                 return TypeParameter_to_Null (expr, target_type, loc);
1109
1110                         if (expr.eclass == ExprClass.MethodGroup){
1111                                 if (!TypeManager.IsDelegateType (target_type)){
1112                                         Report.Error (428, loc,
1113                                                       String.Format (
1114                                                            "Cannot convert method group to `{0}', since it is not a delegate",
1115                                                            TypeManager.CSharpName (target_type)));
1116                                         return null;
1117                                 }
1118
1119                                 return ImplicitDelegateCreation.Create (ec, (MethodGroupExpr) expr, target_type, loc);
1120                         }
1121
1122                         if (expr_type.Equals (target_type) && !(expr is NullLiteral))
1123                                 return expr;
1124
1125                         e = ImplicitNumericConversion (ec, expr, target_type, loc);
1126                         if (e != null)
1127                                 return e;
1128
1129                         e = ImplicitReferenceConversion (expr, target_type);
1130                         if (e != null)
1131                                 return e;
1132
1133                         if ((target_type == TypeManager.enum_type ||
1134                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1135                             expr is IntLiteral){
1136                                 IntLiteral i = (IntLiteral) expr;
1137
1138                                 if (i.Value == 0)
1139                                         return new EnumConstant ((Constant) expr, target_type);
1140                         }
1141
1142                         if (ec.InUnsafe) {
1143                                 if (expr_type.IsPointer){
1144                                         if (target_type == TypeManager.void_ptr_type)
1145                                                 return new EmptyCast (expr, target_type);
1146
1147                                         //
1148                                         // yep, comparing pointer types cant be done with
1149                                         // t1 == t2, we have to compare their element types.
1150                                         //
1151                                         if (target_type.IsPointer){
1152                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1153                                                         return expr;
1154                                         }
1155                                 }
1156
1157                                 if (target_type.IsPointer) {
1158                                         if (expr is NullLiteral)
1159                                                 return new EmptyCast (expr, target_type);
1160
1161                                         if (expr_type == TypeManager.void_ptr_type)
1162                                                 return new EmptyCast (expr, target_type);
1163                                 }
1164                         }
1165
1166                         return null;
1167                 }
1168
1169                 /// <summary>
1170                 ///   Attemps to perform an implict constant conversion of the IntConstant
1171                 ///   into a different data type using casts (See Implicit Constant
1172                 ///   Expression Conversions)
1173                 /// </summary>
1174                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1175                 {
1176                         int value = ic.Value;
1177
1178                         if (target_type == TypeManager.sbyte_type){
1179                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1180                                         return new SByteConstant ((sbyte) value);
1181                         } else if (target_type == TypeManager.byte_type){
1182                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1183                                         return new ByteConstant ((byte) value);
1184                         } else if (target_type == TypeManager.short_type){
1185                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1186                                         return new ShortConstant ((short) value);
1187                         } else if (target_type == TypeManager.ushort_type){
1188                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1189                                         return new UShortConstant ((ushort) value);
1190                         } else if (target_type == TypeManager.uint32_type){
1191                                 if (value >= 0)
1192                                         return new UIntConstant ((uint) value);
1193                         } else if (target_type == TypeManager.uint64_type){
1194                                 //
1195                                 // we can optimize this case: a positive int32
1196                                 // always fits on a uint64.  But we need an opcode
1197                                 // to do it.
1198                                 //
1199                                 if (value >= 0)
1200                                         return new ULongConstant ((ulong) value);
1201                         } else if (target_type == TypeManager.double_type)
1202                                 return new DoubleConstant ((double) value);
1203                         else if (target_type == TypeManager.float_type)
1204                                 return new FloatConstant ((float) value);
1205
1206                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1207                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1208                                 Constant e = (Constant) ic;
1209
1210                                 //
1211                                 // Possibly, we need to create a different 0 literal before passing
1212                                 // to EnumConstant
1213                                 //n
1214                                 if (underlying == TypeManager.int64_type)
1215                                         e = new LongLiteral (0);
1216                                 else if (underlying == TypeManager.uint64_type)
1217                                         e = new ULongLiteral (0);
1218
1219                                 return new EnumConstant (e, target_type);
1220                         }
1221                         return null;
1222                 }
1223
1224                 static public void Error_CannotImplicitConversion (Location loc, Type source, Type target)
1225                 {
1226                         string msg = "Cannot convert implicitly from `"+
1227                                 TypeManager.CSharpName (source) + "' to `" +
1228                                 TypeManager.CSharpName (target) + "'";
1229
1230                         Report.Error (29, loc, msg);
1231                 }
1232
1233                 /// <summary>
1234                 ///   Attemptes to implicityly convert `target' into `type', using
1235                 ///   ImplicitConversion.  If there is no implicit conversion, then
1236                 ///   an error is signaled
1237                 /// </summary>
1238                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1239                                                                      Type target_type, Location loc)
1240                 {
1241                         Expression e;
1242
1243                         int errors = Report.Errors;
1244                         e = ImplicitConversion (ec, source, target_type, loc);
1245                         if (Report.Errors > errors)
1246                                 return null;
1247                         if (e != null)
1248                                 return e;
1249
1250                         if (source is DoubleLiteral && target_type == TypeManager.float_type){
1251                                 Report.Error (664, loc,
1252                                               "Double literal cannot be implicitly converted to " +
1253                                               "float type, use F suffix to create a float literal");
1254                         }
1255
1256                         if (source is Constant){
1257                                 Constant c = (Constant) source;
1258
1259                                 Expression.Error_ConstantValueCannotBeConverted (loc, c.AsString (), target_type);
1260                                 return null;
1261                         }
1262
1263                         Error_CannotImplicitConversion (loc, source.Type, target_type);
1264
1265                         return null;
1266                 }
1267
1268                 /// <summary>
1269                 ///   Performs the explicit numeric conversions
1270                 /// </summary>
1271                 static Expression ExplicitNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
1272                 {
1273                         Type expr_type = expr.Type;
1274
1275                         //
1276                         // If we have an enumeration, extract the underlying type,
1277                         // use this during the comparison, but wrap around the original
1278                         // target_type
1279                         //
1280                         Type real_target_type = target_type;
1281
1282                         if (TypeManager.IsEnumType (real_target_type))
1283                                 real_target_type = TypeManager.EnumToUnderlying (real_target_type);
1284
1285                         if (ImplicitStandardConversionExists (expr, real_target_type)){
1286                                 Expression ce = ImplicitConversionStandard (ec, expr, real_target_type, loc);
1287
1288                                 if (real_target_type != target_type)
1289                                         return new EmptyCast (ce, target_type);
1290                                 return ce;
1291                         }
1292
1293                         if (expr_type == TypeManager.sbyte_type){
1294                                 //
1295                                 // From sbyte to byte, ushort, uint, ulong, char
1296                                 //
1297                                 if (real_target_type == TypeManager.byte_type)
1298                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U1);
1299                                 if (real_target_type == TypeManager.ushort_type)
1300                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U2);
1301                                 if (real_target_type == TypeManager.uint32_type)
1302                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U4);
1303                                 if (real_target_type == TypeManager.uint64_type)
1304                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U8);
1305                                 if (real_target_type == TypeManager.char_type)
1306                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_CH);
1307                         } else if (expr_type == TypeManager.byte_type){
1308                                 //
1309                                 // From byte to sbyte and char
1310                                 //
1311                                 if (real_target_type == TypeManager.sbyte_type)
1312                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_I1);
1313                                 if (real_target_type == TypeManager.char_type)
1314                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_CH);
1315                         } else if (expr_type == TypeManager.short_type){
1316                                 //
1317                                 // From short to sbyte, byte, ushort, uint, ulong, char
1318                                 //
1319                                 if (real_target_type == TypeManager.sbyte_type)
1320                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_I1);
1321                                 if (real_target_type == TypeManager.byte_type)
1322                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
1323                                 if (real_target_type == TypeManager.ushort_type)
1324                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U2);
1325                                 if (real_target_type == TypeManager.uint32_type)
1326                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U4);
1327                                 if (real_target_type == TypeManager.uint64_type)
1328                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U8);
1329                                 if (real_target_type == TypeManager.char_type)
1330                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_CH);
1331                         } else if (expr_type == TypeManager.ushort_type){
1332                                 //
1333                                 // From ushort to sbyte, byte, short, char
1334                                 //
1335                                 if (real_target_type == TypeManager.sbyte_type)
1336                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I1);
1337                                 if (real_target_type == TypeManager.byte_type)
1338                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_U1);
1339                                 if (real_target_type == TypeManager.short_type)
1340                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I2);
1341                                 if (real_target_type == TypeManager.char_type)
1342                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_CH);
1343                         } else if (expr_type == TypeManager.int32_type){
1344                                 //
1345                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1346                                 //
1347                                 if (real_target_type == TypeManager.sbyte_type)
1348                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I1);
1349                                 if (real_target_type == TypeManager.byte_type)
1350                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
1351                                 if (real_target_type == TypeManager.short_type)
1352                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
1353                                 if (real_target_type == TypeManager.ushort_type)
1354                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U2);
1355                                 if (real_target_type == TypeManager.uint32_type)
1356                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U4);
1357                                 if (real_target_type == TypeManager.uint64_type)
1358                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U8);
1359                                 if (real_target_type == TypeManager.char_type)
1360                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_CH);
1361                         } else if (expr_type == TypeManager.uint32_type){
1362                                 //
1363                                 // From uint to sbyte, byte, short, ushort, int, char
1364                                 //
1365                                 if (real_target_type == TypeManager.sbyte_type)
1366                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I1);
1367                                 if (real_target_type == TypeManager.byte_type)
1368                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U1);
1369                                 if (real_target_type == TypeManager.short_type)
1370                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I2);
1371                                 if (real_target_type == TypeManager.ushort_type)
1372                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U2);
1373                                 if (real_target_type == TypeManager.int32_type)
1374                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I4);
1375                                 if (real_target_type == TypeManager.char_type)
1376                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_CH);
1377                         } else if (expr_type == TypeManager.int64_type){
1378                                 //
1379                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1380                                 //
1381                                 if (real_target_type == TypeManager.sbyte_type)
1382                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I1);
1383                                 if (real_target_type == TypeManager.byte_type)
1384                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
1385                                 if (real_target_type == TypeManager.short_type)
1386                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
1387                                 if (real_target_type == TypeManager.ushort_type)
1388                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U2);
1389                                 if (real_target_type == TypeManager.int32_type)
1390                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
1391                                 if (real_target_type == TypeManager.uint32_type)
1392                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U4);
1393                                 if (real_target_type == TypeManager.uint64_type)
1394                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U8);
1395                                 if (real_target_type == TypeManager.char_type)
1396                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_CH);
1397                         } else if (expr_type == TypeManager.uint64_type){
1398                                 //
1399                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1400                                 //
1401                                 if (real_target_type == TypeManager.sbyte_type)
1402                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I1);
1403                                 if (real_target_type == TypeManager.byte_type)
1404                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U1);
1405                                 if (real_target_type == TypeManager.short_type)
1406                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I2);
1407                                 if (real_target_type == TypeManager.ushort_type)
1408                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U2);
1409                                 if (real_target_type == TypeManager.int32_type)
1410                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I4);
1411                                 if (real_target_type == TypeManager.uint32_type)
1412                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U4);
1413                                 if (real_target_type == TypeManager.int64_type)
1414                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I8);
1415                                 if (real_target_type == TypeManager.char_type)
1416                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_CH);
1417                         } else if (expr_type == TypeManager.char_type){
1418                                 //
1419                                 // From char to sbyte, byte, short
1420                                 //
1421                                 if (real_target_type == TypeManager.sbyte_type)
1422                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I1);
1423                                 if (real_target_type == TypeManager.byte_type)
1424                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_U1);
1425                                 if (real_target_type == TypeManager.short_type)
1426                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I2);
1427                         } else if (expr_type == TypeManager.float_type){
1428                                 //
1429                                 // From float to sbyte, byte, short,
1430                                 // ushort, int, uint, long, ulong, char
1431                                 // or decimal
1432                                 //
1433                                 if (real_target_type == TypeManager.sbyte_type)
1434                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
1435                                 if (real_target_type == TypeManager.byte_type)
1436                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U1);
1437                                 if (real_target_type == TypeManager.short_type)
1438                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I2);
1439                                 if (real_target_type == TypeManager.ushort_type)
1440                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U2);
1441                                 if (real_target_type == TypeManager.int32_type)
1442                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I4);
1443                                 if (real_target_type == TypeManager.uint32_type)
1444                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U4);
1445                                 if (real_target_type == TypeManager.int64_type)
1446                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I8);
1447                                 if (real_target_type == TypeManager.uint64_type)
1448                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U8);
1449                                 if (real_target_type == TypeManager.char_type)
1450                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_CH);
1451                         } else if (expr_type == TypeManager.double_type){
1452                                 //
1453                                 // From double to byte, byte, short,
1454                                 // ushort, int, uint, long, ulong,
1455                                 // char, float or decimal
1456                                 //
1457                                 if (real_target_type == TypeManager.sbyte_type)
1458                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I1);
1459                                 if (real_target_type == TypeManager.byte_type)
1460                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1461                                 if (real_target_type == TypeManager.short_type)
1462                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1463                                 if (real_target_type == TypeManager.ushort_type)
1464                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U2);
1465                                 if (real_target_type == TypeManager.int32_type)
1466                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1467                                 if (real_target_type == TypeManager.uint32_type)
1468                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U4);
1469                                 if (real_target_type == TypeManager.int64_type)
1470                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1471                                 if (real_target_type == TypeManager.uint64_type)
1472                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U8);
1473                                 if (real_target_type == TypeManager.char_type)
1474                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_CH);
1475                                 if (real_target_type == TypeManager.float_type)
1476                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
1477                         }
1478
1479                         // decimal is taken care of by the op_Explicit methods.
1480
1481                         return null;
1482                 }
1483
1484                 /// <summary>
1485                 ///  Returns whether an explicit reference conversion can be performed
1486                 ///  from source_type to target_type
1487                 /// </summary>
1488                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1489                 {
1490                         bool target_is_type_param = target_type.IsGenericParameter;
1491                         bool target_is_value_type = target_type.IsValueType;
1492
1493                         if (source_type == target_type)
1494                                 return true;
1495
1496                         //
1497                         // From object to a generic parameter
1498                         //
1499                         if (source_type == TypeManager.object_type && target_is_type_param)
1500                                 return true;
1501
1502                         //
1503                         // From object to any reference type
1504                         //
1505                         if (source_type == TypeManager.object_type && !target_is_value_type)
1506                                 return true;
1507
1508                         //
1509                         // From any class S to any class-type T, provided S is a base class of T
1510                         //
1511                         if (TypeManager.IsSubclassOf (target_type, source_type))
1512                                 return true;
1513
1514                         //
1515                         // From any interface type S to any interface T provided S is not derived from T
1516                         //
1517                         if (source_type.IsInterface && target_type.IsInterface){
1518                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1519                                         return true;
1520                         }
1521
1522                         //
1523                         // From any class type S to any interface T, provided S is not sealed
1524                         // and provided S does not implement T.
1525                         //
1526                         if (target_type.IsInterface && !source_type.IsSealed &&
1527                             !TypeManager.ImplementsInterface (source_type, target_type))
1528                                 return true;
1529
1530                         //
1531                         // From any interface-type S to to any class type T, provided T is not
1532                         // sealed, or provided T implements S.
1533                         //
1534                         if (source_type.IsInterface &&
1535                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1536                                 return true;
1537
1538
1539                         // From an array type S with an element type Se to an array type T with an
1540                         // element type Te provided all the following are true:
1541                         //     * S and T differe only in element type, in other words, S and T
1542                         //       have the same number of dimensions.
1543                         //     * Both Se and Te are reference types
1544                         //     * An explicit referenc conversions exist from Se to Te
1545                         //
1546                         if (source_type.IsArray && target_type.IsArray) {
1547                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1548
1549                                         Type source_element_type = TypeManager.GetElementType (source_type);
1550                                         Type target_element_type = TypeManager.GetElementType (target_type);
1551
1552                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1553                                                 if (ExplicitReferenceConversionExists (source_element_type,
1554                                                                                        target_element_type))
1555                                                         return true;
1556                                 }
1557                         }
1558
1559
1560                         // From System.Array to any array-type
1561                         if (source_type == TypeManager.array_type &&
1562                             target_type.IsArray){
1563                                 return true;
1564                         }
1565
1566                         //
1567                         // From System delegate to any delegate-type
1568                         //
1569                         if (source_type == TypeManager.delegate_type &&
1570                             TypeManager.IsDelegateType (target_type))
1571                                 return true;
1572
1573                         //
1574                         // From ICloneable to Array or Delegate types
1575                         //
1576                         if (source_type == TypeManager.icloneable_type &&
1577                             (target_type == TypeManager.array_type ||
1578                              target_type == TypeManager.delegate_type))
1579                                 return true;
1580
1581                         return false;
1582                 }
1583
1584                 /// <summary>
1585                 ///   Implements Explicit Reference conversions
1586                 /// </summary>
1587                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1588                 {
1589                         Type source_type = source.Type;
1590                         bool target_is_type_param = target_type.IsGenericParameter;
1591                         bool target_is_value_type = target_type.IsValueType;
1592
1593                         //
1594                         // From object to a generic parameter
1595                         //
1596                         if (source_type == TypeManager.object_type && target_is_type_param)
1597                                 return new UnboxCast (source, target_type);
1598
1599                         //
1600                         // From object to any reference type
1601                         //
1602                         if (source_type == TypeManager.object_type && !target_is_value_type)
1603                                 return new ClassCast (source, target_type);
1604
1605                         //
1606                         // Unboxing conversion.
1607                         //
1608                         if (((source_type == TypeManager.enum_type &&
1609                                 !(source is EmptyCast)) ||
1610                                 source_type == TypeManager.value_type) && target_is_value_type)
1611                                 return new UnboxCast (source, target_type);
1612
1613                         //
1614                         // From any class S to any class-type T, provided S is a base class of T
1615                         //
1616                         if (TypeManager.IsSubclassOf (target_type, source_type))
1617                                 return new ClassCast (source, target_type);
1618
1619                         //
1620                         // From any interface type S to any interface T provided S is not derived from T
1621                         //
1622                         if (source_type.IsInterface && target_type.IsInterface){
1623                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1624                                         return null;
1625                                 else
1626                                         return new ClassCast (source, target_type);
1627                         }
1628
1629                         //
1630                         // From any class type S to any interface T, provides S is not sealed
1631                         // and provided S does not implement T.
1632                         //
1633                         if (target_type.IsInterface && !source_type.IsSealed) {
1634                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1635                                         return null;
1636                                 else
1637                                         return new ClassCast (source, target_type);
1638
1639                         }
1640
1641                         //
1642                         // From any interface-type S to to any class type T, provided T is not
1643                         // sealed, or provided T implements S.
1644                         //
1645                         if (source_type.IsInterface) {
1646                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1647                                         if (target_type.IsClass)
1648                                                 return new ClassCast (source, target_type);
1649                                         else
1650                                                 return new UnboxCast (source, target_type);
1651                                 }
1652
1653                                 return null;
1654                         }
1655
1656                         // From an array type S with an element type Se to an array type T with an
1657                         // element type Te provided all the following are true:
1658                         //     * S and T differe only in element type, in other words, S and T
1659                         //       have the same number of dimensions.
1660                         //     * Both Se and Te are reference types
1661                         //     * An explicit referenc conversions exist from Se to Te
1662                         //
1663                         if (source_type.IsArray && target_type.IsArray) {
1664                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1665
1666                                         Type source_element_type = TypeManager.GetElementType (source_type);
1667                                         Type target_element_type = TypeManager.GetElementType (target_type);
1668
1669                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1670                                                 if (ExplicitReferenceConversionExists (source_element_type,
1671                                                                                        target_element_type))
1672                                                         return new ClassCast (source, target_type);
1673                                 }
1674                         }
1675
1676
1677                         // From System.Array to any array-type
1678                         if (source_type == TypeManager.array_type &&
1679                             target_type.IsArray) {
1680                                 return new ClassCast (source, target_type);
1681                         }
1682
1683                         //
1684                         // From System delegate to any delegate-type
1685                         //
1686                         if (source_type == TypeManager.delegate_type &&
1687                             TypeManager.IsDelegateType (target_type))
1688                                 return new ClassCast (source, target_type);
1689
1690                         //
1691                         // From ICloneable to Array or Delegate types
1692                         //
1693                         if (source_type == TypeManager.icloneable_type &&
1694                             (target_type == TypeManager.array_type ||
1695                              target_type == TypeManager.delegate_type))
1696                                 return new ClassCast (source, target_type);
1697
1698                         return null;
1699                 }
1700
1701                 /// <summary>
1702                 ///   Performs an explicit conversion of the expression `expr' whose
1703                 ///   type is expr.Type to `target_type'.
1704                 /// </summary>
1705                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1706                                                              Type target_type, Location loc)
1707                 {
1708                         Type expr_type = expr.Type;
1709                         Type original_expr_type = expr_type;
1710
1711                         if (expr_type.IsSubclassOf (TypeManager.enum_type)){
1712                                 if (target_type == TypeManager.enum_type ||
1713                                     target_type == TypeManager.object_type) {
1714                                         if (expr is EnumConstant)
1715                                                 expr = ((EnumConstant) expr).Child;
1716                                         // We really need all these casts here .... :-(
1717                                         expr = new BoxedCast (new EmptyCast (expr, expr_type));
1718                                         return new EmptyCast (expr, target_type);
1719                                 } else if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
1720                                            target_type.IsSubclassOf (TypeManager.enum_type))
1721                                         return new UnboxCast (expr, target_type);
1722
1723                                 //
1724                                 // Notice that we have kept the expr_type unmodified, which is only
1725                                 // used later on to
1726                                 if (expr is EnumConstant)
1727                                         expr = ((EnumConstant) expr).Child;
1728                                 else
1729                                         expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
1730                                 expr_type = expr.Type;
1731                         }
1732
1733                         int errors = Report.Errors;
1734                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1735                         if (Report.Errors > errors)
1736                                 return null;
1737
1738                         if (ne != null)
1739                                 return ne;
1740
1741                         ne = ExplicitNumericConversion (ec, expr, target_type, loc);
1742                         if (ne != null)
1743                                 return ne;
1744
1745                         //
1746                         // Unboxing conversion.
1747                         //
1748                         if (expr_type == TypeManager.object_type && target_type.IsValueType){
1749                                 if (expr is NullLiteral){
1750                                         //
1751                                         // Skip the ExplicitReferenceConversion because we can not convert
1752                                         // from Null to a ValueType, and ExplicitReference wont check against
1753                                         // null literal explicitly
1754                                         //
1755                                         goto skip_explicit;
1756                                 }
1757                                 return new UnboxCast (expr, target_type);
1758
1759                         }
1760
1761                         ne = ExplicitReferenceConversion (expr, target_type);
1762                         if (ne != null)
1763                                 return ne;
1764
1765                 skip_explicit:
1766                         if (ec.InUnsafe){
1767                                 if (target_type.IsPointer){
1768                                         if (expr_type.IsPointer)
1769                                                 return new EmptyCast (expr, target_type);
1770
1771                                         if (expr_type == TypeManager.sbyte_type ||
1772                                             expr_type == TypeManager.byte_type ||
1773                                             expr_type == TypeManager.short_type ||
1774                                             expr_type == TypeManager.ushort_type ||
1775                                             expr_type == TypeManager.int32_type ||
1776                                             expr_type == TypeManager.uint32_type ||
1777                                             expr_type == TypeManager.uint64_type ||
1778                                             expr_type == TypeManager.int64_type)
1779                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1780                                 }
1781                                 if (expr_type.IsPointer){
1782                                         Expression e = null;
1783
1784                                         if (target_type == TypeManager.sbyte_type)
1785                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1786                                         else if (target_type == TypeManager.byte_type)
1787                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1788                                         else if (target_type == TypeManager.short_type)
1789                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1790                                         else if (target_type == TypeManager.ushort_type)
1791                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1792                                         else if (target_type == TypeManager.int32_type)
1793                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1794                                         else if (target_type == TypeManager.uint32_type)
1795                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1796                                         else if (target_type == TypeManager.uint64_type)
1797                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1798                                         else if (target_type == TypeManager.int64_type){
1799                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1800                                         }
1801
1802                                         if (e != null){
1803                                                 Expression ci, ce;
1804
1805                                                 ci = ImplicitConversionStandard (ec, e, target_type, loc);
1806
1807                                                 if (ci != null)
1808                                                         return ci;
1809
1810                                                 ce = ExplicitNumericConversion (ec, e, target_type, loc);
1811                                                 if (ce != null)
1812                                                         return ce;
1813                                                 //
1814                                                 // We should always be able to go from an uint32
1815                                                 // implicitly or explicitly to the other integral
1816                                                 // types
1817                                                 //
1818                                                 throw new Exception ("Internal compiler error");
1819                                         }
1820                                 }
1821                         }
1822
1823                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1824                         if (ne != null)
1825                                 return ne;
1826
1827                         if (expr is NullLiteral){
1828                                 Report.Error (37, loc, "Cannot convert null to value type `" +
1829                                               TypeManager.CSharpName (target_type) + "'");
1830                                 return null;
1831                         }
1832
1833                         Error_CannotConvertType (loc, original_expr_type, target_type);
1834                         return null;
1835                 }
1836
1837                 /// <summary>
1838                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1839                 /// </summary>
1840                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1841                                                                      Type target_type, Location l)
1842                 {
1843                         int errors = Report.Errors;
1844                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1845                         if (Report.Errors > errors)
1846                                 return null;
1847
1848                         if (ne != null)
1849                                 return ne;
1850
1851                         ne = ExplicitNumericConversion (ec, expr, target_type, l);
1852                         if (ne != null)
1853                                 return ne;
1854
1855                         ne = ExplicitReferenceConversion (expr, target_type);
1856                         if (ne != null)
1857                                 return ne;
1858
1859                         Error_CannotConvertType (l, expr.Type, target_type);
1860                         return null;
1861                 }
1862         }
1863 }