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 Type TypeParam_EffectiveBaseType (Type t)
  54                 {
  55                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (t);
  56                         if (gc == null)
  57                                 return TypeManager.object_type;
  58
  59                         return TypeParam_EffectiveBaseType (gc);
  60                 }
  61
  62                 static Type TypeParam_EffectiveBaseType (GenericConstraints gc)
  63                 {
  64                         ArrayList list = new ArrayList ();
  65                         list.Add (gc.EffectiveBaseClass);
  66                         foreach (Type t in gc.InterfaceConstraints) {
  67                                 if (!t.IsGenericParameter)
  68                                         continue;
  69
  70                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  71                                 if (new_gc != null)
  72                                         list.Add (TypeParam_EffectiveBaseType (new_gc));
  73                         }
  74                         return FindMostEncompassedType (list);
  75                 }
  76
  77                 static Expression TypeParameterConversion (Expression expr, bool is_reference, Type target_type)
  78                 {
  79                         if (is_reference)
  80                                 return new EmptyCast (expr, target_type);
  81                         else
  82                                 return new BoxedCast (expr, target_type);
  83                 }
  84
  85                 static Expression ImplicitTypeParameterConversion (Expression expr, Type target_type)
  86                 {
  87                         Type expr_type = expr.Type;
  88
  89                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
  90
  91                         if (gc == null) {
  92                                 if (target_type == TypeManager.object_type)
  93                                         return new BoxedCast (expr);
  94
  95                                 return null;
  96                         }
  97
  98                         // We're converting from a type parameter which is known to be a reference type.
  99                         bool is_reference = gc.IsReferenceType;
 100                         Type base_type = TypeParam_EffectiveBaseType (gc);
 101
 102                         if (TypeManager.IsSubclassOf (base_type, target_type))
 103                                 return TypeParameterConversion (expr, is_reference, target_type);
 104
 105                         if (target_type.IsInterface) {
 106                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 107                                         return TypeParameterConversion (expr, is_reference, target_type);
 108
 109                                 foreach (Type t in gc.InterfaceConstraints) {
 110                                         if (TypeManager.IsSubclassOf (t, target_type))
 111                                                 return TypeParameterConversion (expr, is_reference, target_type);
 112                                 }
 113                         }
 114
 115                         foreach (Type t in gc.InterfaceConstraints) {
 116                                 if (!t.IsGenericParameter)
 117                                         continue;
 118                                 if (TypeManager.IsSubclassOf (t, target_type))
 119                                         return TypeParameterConversion (expr, is_reference, target_type);
 120                         }
 121
 122                         return null;
 123                 }
 124
 125                 static EmptyExpression MyEmptyExpr;
 126                 static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
 127                 {
 128                         Type expr_type = expr.Type;
 129
 130                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 131                                 // if we are a method group, emit a warning
 132
 133                                 expr.Emit (null);
 134                         }
 135
 136                         if (expr_type == TypeManager.void_type)
 137                                 return null;
 138
 139                         if (expr_type.IsGenericParameter)
 140                                 return ImplicitTypeParameterConversion (expr, target_type);
 141
 142                         //
 143                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 144                         // is an abstract class, and not really a value type, so we apply the same rules.
 145                         //
 146                         if (target_type == TypeManager.object_type) {
 147                                 //
 148                                 // A pointer type cannot be converted to object
 149                                 //
 150                                 if (expr_type.IsPointer)
 151                                         return null;
 152
 153                                 if (TypeManager.IsValueType (expr_type))
 154                                         return new BoxedCast (expr);
 155                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type)
 156                                         return new EmptyCast (expr, target_type);
 157
 158                                 return null;
 159                         } else if (target_type == TypeManager.value_type) {
 160                                 if (TypeManager.IsValueType (expr_type))
 161                                         return new BoxedCast (expr);
 162                                 if (expr is NullLiteral)
 163                                         return new NullCast (expr, target_type);
 164
 165                                 return null;
 166                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 167                                 //
 168                                 // Special case: enumeration to System.Enum.
 169                                 // System.Enum is not a value type, it is a class, so we need
 170                                 // a boxing conversion
 171                                 //
 172                                 if (expr_type.IsEnum || expr_type.IsGenericParameter)
 173                                         return new BoxedCast (expr);
 174
 175                                 return new EmptyCast (expr, target_type);
 176                         }
 177
 178                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 179                         // with the small distinction that we only probe there
 180                         //
 181                         // Always ensure that the code here and there is in sync
 182
 183                         // from the null type to any reference-type.
 184                         if (expr is NullLiteral){
 185                                 if (target_type.IsPointer)
 186                                         return NullPointer.Null;
 187
 188                                 if (!target_type.IsValueType)
 189                                         return new NullCast (expr, target_type);
 190                         }
 191
 192                         // from any class-type S to any interface-type T.
 193                         if (target_type.IsInterface) {
 194                                 if (target_type != TypeManager.iconvertible_type &&
 195                                     expr_type.IsValueType && (expr is Constant) &&
 196                                     !(expr is IntLiteral || expr is BoolLiteral ||
 197                                       expr is FloatLiteral || expr is DoubleLiteral ||
 198                                       expr is LongLiteral || expr is CharLiteral ||
 199                                       expr is StringLiteral || expr is DecimalLiteral ||
 200                                       expr is UIntLiteral || expr is ULongLiteral)) {
 201                                         return null;
 202                                 }
 203
 204                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 205                                         if (expr_type.IsGenericParameter || TypeManager.IsValueType (expr_type))
 206                                                 return new BoxedCast (expr, target_type);
 207                                         else
 208                                                 return new EmptyCast (expr, target_type);
 209                                 }
 210                         }
 211
 212                         // from any interface type S to interface-type T.
 213                         if (expr_type.IsInterface && target_type.IsInterface) {
 214                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 215                                         return new EmptyCast (expr, target_type);
 216                                 else
 217                                         return null;
 218                         }
 219
 220                         // from an array-type S to an array-type of type T
 221                         if (expr_type.IsArray && target_type.IsArray) {
 222                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 223
 224                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 225
 226                                         if (MyEmptyExpr == null)
 227                                                 MyEmptyExpr = new EmptyExpression ();
 228
 229                                         MyEmptyExpr.SetType (expr_element_type);
 230                                         Type target_element_type = TypeManager.GetElementType (target_type);
 231
 232                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 233                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 234                                                                                       target_element_type))
 235                                                         return new EmptyCast (expr, target_type);
 236                                 }
 237                         }
 238
 239                         // from an array-type to System.Array
 240                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 241                                 return new EmptyCast (expr, target_type);
 242
 243                         // from any delegate type to System.Delegate
 244                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 245                             target_type == TypeManager.delegate_type)
 246                                 return new EmptyCast (expr, target_type);
 247
 248                         // from any array-type or delegate type into System.ICloneable.
 249                         if (expr_type.IsArray ||
 250                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 251                                 if (target_type == TypeManager.icloneable_type)
 252                                         return new EmptyCast (expr, target_type);
 253
 254                         // from a generic type definition to a generic instance.
 255                         if (TypeManager.IsEqual (expr_type, target_type))
 256                                 return new EmptyCast (expr, target_type);
 257
 258                         return null;
 259                 }
 260
 261                 //
 262                 // Tests whether an implicit reference conversion exists between expr_type
 263                 // and target_type
 264                 //
 265                 public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
 266                 {
 267                         Type expr_type = expr.Type;
 268
 269                         if (expr_type.IsGenericParameter)
 270                                 return ImplicitTypeParameterConversion (expr, target_type) != null;
 271
 272                         //
 273                         // This is the boxed case.
 274                         //
 275                         if (target_type == TypeManager.object_type) {
 276                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 277                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 278                                         return true;
 279
 280                                 return false;
 281                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 282                                 return true;
 283
 284                         // Please remember that all code below actually comes
 285                         // from ImplicitReferenceConversion so make sure code remains in sync
 286
 287                         // from any class-type S to any interface-type T.
 288                         if (target_type.IsInterface) {
 289                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 290                                         return true;
 291                         }
 292
 293                         // from any interface type S to interface-type T.
 294                         if (expr_type.IsInterface && target_type.IsInterface)
 295                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 296                                         return true;
 297
 298                         // from an array-type S to an array-type of type T
 299                         if (expr_type.IsArray && target_type.IsArray) {
 300                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 301
 302                                         Type expr_element_type = expr_type.GetElementType ();
 303
 304                                         if (MyEmptyExpr == null)
 305                                                 MyEmptyExpr = new EmptyExpression ();
 306
 307                                         MyEmptyExpr.SetType (expr_element_type);
 308                                         Type target_element_type = TypeManager.GetElementType (target_type);
 309
 310                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 311                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 312                                                                                       target_element_type))
 313                                                         return true;
 314                                 }
 315                         }
 316
 317                         // from an array-type to System.Array
 318                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 319                                 return true;
 320
 321                         // from any delegate type to System.Delegate
 322                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 323                             target_type == TypeManager.delegate_type)
 324                                 if (target_type.IsAssignableFrom (expr_type))
 325                                         return true;
 326
 327                         // from any array-type or delegate type into System.ICloneable.
 328                         if (expr_type.IsArray ||
 329                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 330                                 if (target_type == TypeManager.icloneable_type)
 331                                         return true;
 332
 333                         // from the null type to any reference-type.
 334                         if (expr is NullLiteral && !target_type.IsValueType && !TypeManager.IsEnumType (target_type))
 335                                 return true;
 336
 337                         // from a generic type definition to a generic instance.
 338                         if (TypeManager.IsEqual (expr_type, target_type))
 339                                 return true;
 340
 341                         return false;
 342                 }
 343
 344                 /// <summary>
 345                 ///   Implicit Numeric Conversions.
 346                 ///
 347                 ///   expr is the expression to convert, returns a new expression of type
 348                 ///   target_type or null if an implicit conversion is not possible.
 349                 /// </summary>
 350                 static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
 351                                                                     Type target_type, Location loc)
 352                 {
 353                         Type expr_type = expr.Type;
 354
 355                         //
 356                         // Attempt to do the implicit constant expression conversions
 357
 358                         if (expr is Constant){
 359                                 if (expr is IntConstant){
 360                                         Expression e;
 361
 362                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 363
 364                                         if (e != null)
 365                                                 return e;
 366                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 367                                         //
 368                                         // Try the implicit constant expression conversion
 369                                         // from long to ulong, instead of a nice routine,
 370                                         // we just inline it
 371                                         //
 372                                         long v = ((LongConstant) expr).Value;
 373                                         if (v >= 0)
 374                                                 return new ULongConstant ((ulong) v);
 375                                 }
 376                         }
 377
 378                         Type real_target_type = target_type;
 379
 380                         if (expr_type == TypeManager.sbyte_type){
 381                                 //
 382                                 // From sbyte to short, int, long, float, double.
 383                                 //
 384                                 if (real_target_type == TypeManager.int32_type)
 385                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 386                                 if (real_target_type == TypeManager.int64_type)
 387                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 388                                 if (real_target_type == TypeManager.double_type)
 389                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 390                                 if (real_target_type == TypeManager.float_type)
 391                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 392                                 if (real_target_type == TypeManager.short_type)
 393                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 394                         } else if (expr_type == TypeManager.byte_type){
 395                                 //
 396                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 397                                 //
 398                                 if ((real_target_type == TypeManager.short_type) ||
 399                                     (real_target_type == TypeManager.ushort_type) ||
 400                                     (real_target_type == TypeManager.int32_type) ||
 401                                     (real_target_type == TypeManager.uint32_type))
 402                                         return new EmptyCast (expr, target_type);
 403
 404                                 if (real_target_type == TypeManager.uint64_type)
 405                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 406                                 if (real_target_type == TypeManager.int64_type)
 407                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 408                                 if (real_target_type == TypeManager.float_type)
 409                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 410                                 if (real_target_type == TypeManager.double_type)
 411                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 412                         } else if (expr_type == TypeManager.short_type){
 413                                 //
 414                                 // From short to int, long, float, double
 415                                 //
 416                                 if (real_target_type == TypeManager.int32_type)
 417                                         return new EmptyCast (expr, target_type);
 418                                 if (real_target_type == TypeManager.int64_type)
 419                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 420                                 if (real_target_type == TypeManager.double_type)
 421                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 422                                 if (real_target_type == TypeManager.float_type)
 423                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 424                         } else if (expr_type == TypeManager.ushort_type){
 425                                 //
 426                                 // From ushort to int, uint, long, ulong, float, double
 427                                 //
 428                                 if (real_target_type == TypeManager.uint32_type)
 429                                         return new EmptyCast (expr, target_type);
 430
 431                                 if (real_target_type == TypeManager.uint64_type)
 432                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 433                                 if (real_target_type == TypeManager.int32_type)
 434                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 435                                 if (real_target_type == TypeManager.int64_type)
 436                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 437                                 if (real_target_type == TypeManager.double_type)
 438                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 439                                 if (real_target_type == TypeManager.float_type)
 440                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 441                         } else if (expr_type == TypeManager.int32_type){
 442                                 //
 443                                 // From int to long, float, double
 444                                 //
 445                                 if (real_target_type == TypeManager.int64_type)
 446                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 447                                 if (real_target_type == TypeManager.double_type)
 448                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 449                                 if (real_target_type == TypeManager.float_type)
 450                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 451                         } else if (expr_type == TypeManager.uint32_type){
 452                                 //
 453                                 // From uint to long, ulong, float, double
 454                                 //
 455                                 if (real_target_type == TypeManager.int64_type)
 456                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 457                                 if (real_target_type == TypeManager.uint64_type)
 458                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 459                                 if (real_target_type == TypeManager.double_type)
 460                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 461                                                                OpCodes.Conv_R8);
 462                                 if (real_target_type == TypeManager.float_type)
 463                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 464                                                                OpCodes.Conv_R4);
 465                         } else if (expr_type == TypeManager.int64_type){
 466                                 //
 467                                 // From long/ulong to float, double
 468                                 //
 469                                 if (real_target_type == TypeManager.double_type)
 470                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 471                                 if (real_target_type == TypeManager.float_type)
 472                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 473                         } else if (expr_type == TypeManager.uint64_type){
 474                                 //
 475                                 // From ulong to float, double
 476                                 //
 477                                 if (real_target_type == TypeManager.double_type)
 478                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 479                                                                OpCodes.Conv_R8);
 480                                 if (real_target_type == TypeManager.float_type)
 481                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 482                                                                OpCodes.Conv_R4);
 483                         } else if (expr_type == TypeManager.char_type){
 484                                 //
 485                                 // From char to ushort, int, uint, long, ulong, float, double
 486                                 //
 487                                 if ((real_target_type == TypeManager.ushort_type) ||
 488                                     (real_target_type == TypeManager.int32_type) ||
 489                                     (real_target_type == TypeManager.uint32_type))
 490                                         return new EmptyCast (expr, target_type);
 491                                 if (real_target_type == TypeManager.uint64_type)
 492                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 493                                 if (real_target_type == TypeManager.int64_type)
 494                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 495                                 if (real_target_type == TypeManager.float_type)
 496                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 497                                 if (real_target_type == TypeManager.double_type)
 498                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 499                         } else if (expr_type == TypeManager.float_type){
 500                                 //
 501                                 // float to double
 502                                 //
 503                                 if (real_target_type == TypeManager.double_type)
 504                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 505                         }
 506
 507                         return null;
 508                 }
 509
 510
 511                 /// <summary>
 512                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 513                 ///  implicit user defined conversions - needed for overload resolution
 514                 /// </summary>
 515                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 516                 {
 517                         if ((expr is NullLiteral) && target_type.IsGenericParameter)
 518                                 return TypeParameter_to_Null (target_type);
 519
 520                         if (ImplicitStandardConversionExists (expr, target_type))
 521                                 return true;
 522
 523                         Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);
 524
 525                         if (dummy != null)
 526                                 return true;
 527
 528                         return false;
 529                 }
 530
 531                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 532                 {
 533                         Expression dummy = ImplicitUserConversion (
 534                                 ec, new EmptyExpression (source), target, Location.Null);
 535                         return dummy != null;
 536                 }
 537
 538                 /// <summary>
 539                 ///  Determines if a standard implicit conversion exists from
 540                 ///  expr_type to target_type
 541                 /// </summary>
 542                 public static bool ImplicitStandardConversionExists (Expression expr, Type target_type)
 543                 {
 544                         Type expr_type = expr.Type;
 545
 546                         if (expr_type == TypeManager.void_type)
 547                                 return false;
 548
 549                         //Console.WriteLine ("Expr is {0}", expr);
 550                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 551                         if (expr_type.Equals (target_type))
 552                                 return true;
 553
 554                         // First numeric conversions
 555
 556                         if (expr_type == TypeManager.sbyte_type){
 557                                 //
 558                                 // From sbyte to short, int, long, float, double.
 559                                 //
 560                                 if ((target_type == TypeManager.int32_type) ||
 561                                     (target_type == TypeManager.int64_type) ||
 562                                     (target_type == TypeManager.double_type) ||
 563                                     (target_type == TypeManager.float_type)  ||
 564                                     (target_type == TypeManager.short_type) ||
 565                                     (target_type == TypeManager.decimal_type))
 566                                         return true;
 567
 568                         } else if (expr_type == TypeManager.byte_type){
 569                                 //
 570                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 571                                 //
 572                                 if ((target_type == TypeManager.short_type) ||
 573                                     (target_type == TypeManager.ushort_type) ||
 574                                     (target_type == TypeManager.int32_type) ||
 575                                     (target_type == TypeManager.uint32_type) ||
 576                                     (target_type == TypeManager.uint64_type) ||
 577                                     (target_type == TypeManager.int64_type) ||
 578                                     (target_type == TypeManager.float_type) ||
 579                                     (target_type == TypeManager.double_type) ||
 580                                     (target_type == TypeManager.decimal_type))
 581                                         return true;
 582
 583                         } else if (expr_type == TypeManager.short_type){
 584                                 //
 585                                 // From short to int, long, float, double
 586                                 //
 587                                 if ((target_type == TypeManager.int32_type) ||
 588                                     (target_type == TypeManager.int64_type) ||
 589                                     (target_type == TypeManager.double_type) ||
 590                                     (target_type == TypeManager.float_type) ||
 591                                     (target_type == TypeManager.decimal_type))
 592                                         return true;
 593
 594                         } else if (expr_type == TypeManager.ushort_type){
 595                                 //
 596                                 // From ushort to int, uint, long, ulong, float, double
 597                                 //
 598                                 if ((target_type == TypeManager.uint32_type) ||
 599                                     (target_type == TypeManager.uint64_type) ||
 600                                     (target_type == TypeManager.int32_type) ||
 601                                     (target_type == TypeManager.int64_type) ||
 602                                     (target_type == TypeManager.double_type) ||
 603                                     (target_type == TypeManager.float_type) ||
 604                                     (target_type == TypeManager.decimal_type))
 605                                         return true;
 606
 607                         } else if (expr_type == TypeManager.int32_type){
 608                                 //
 609                                 // From int to long, float, double
 610                                 //
 611                                 if ((target_type == TypeManager.int64_type) ||
 612                                     (target_type == TypeManager.double_type) ||
 613                                     (target_type == TypeManager.float_type) ||
 614                                     (target_type == TypeManager.decimal_type))
 615                                         return true;
 616
 617                         } else if (expr_type == TypeManager.uint32_type){
 618                                 //
 619                                 // From uint to long, ulong, float, double
 620                                 //
 621                                 if ((target_type == TypeManager.int64_type) ||
 622                                     (target_type == TypeManager.uint64_type) ||
 623                                     (target_type == TypeManager.double_type) ||
 624                                     (target_type == TypeManager.float_type) ||
 625                                     (target_type == TypeManager.decimal_type))
 626                                         return true;
 627
 628                         } else if ((expr_type == TypeManager.uint64_type) ||
 629                                    (expr_type == TypeManager.int64_type)) {
 630                                 //
 631                                 // From long/ulong to float, double
 632                                 //
 633                                 if ((target_type == TypeManager.double_type) ||
 634                                     (target_type == TypeManager.float_type) ||
 635                                     (target_type == TypeManager.decimal_type))
 636                                         return true;
 637
 638                         } else if (expr_type == TypeManager.char_type){
 639                                 //
 640                                 // From char to ushort, int, uint, long, ulong, float, double
 641                                 //
 642                                 if ((target_type == TypeManager.ushort_type) ||
 643                                     (target_type == TypeManager.int32_type) ||
 644                                     (target_type == TypeManager.uint32_type) ||
 645                                     (target_type == TypeManager.uint64_type) ||
 646                                     (target_type == TypeManager.int64_type) ||
 647                                     (target_type == TypeManager.float_type) ||
 648                                     (target_type == TypeManager.double_type) ||
 649                                     (target_type == TypeManager.decimal_type))
 650                                         return true;
 651
 652                         } else if (expr_type == TypeManager.float_type){
 653                                 //
 654                                 // float to double
 655                                 //
 656                                 if (target_type == TypeManager.double_type)
 657                                         return true;
 658                         }
 659
 660                         if (ImplicitReferenceConversionExists (expr, target_type))
 661                                 return true;
 662
 663                         //
 664                         // Implicit Constant Expression Conversions
 665                         //
 666                         if (expr is IntConstant){
 667                                 int value = ((IntConstant) expr).Value;
 668
 669                                 if (target_type == TypeManager.sbyte_type){
 670                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 671                                                 return true;
 672                                 } else if (target_type == TypeManager.byte_type){
 673                                         if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
 674                                                 return true;
 675                                 } else if (target_type == TypeManager.short_type){
 676                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 677                                                 return true;
 678                                 } else if (target_type == TypeManager.ushort_type){
 679                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 680                                                 return true;
 681                                 } else if (target_type == TypeManager.uint32_type){
 682                                         if (value >= 0)
 683                                                 return true;
 684                                 } else if (target_type == TypeManager.uint64_type){
 685                                          //
 686                                          // we can optimize this case: a positive int32
 687                                          // always fits on a uint64.  But we need an opcode
 688                                          // to do it.
 689                                          //
 690                                         if (value >= 0)
 691                                                 return true;
 692                                 }
 693
 694                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 695                                         return true;
 696                         }
 697
 698                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 699                                 //
 700                                 // Try the implicit constant expression conversion
 701                                 // from long to ulong, instead of a nice routine,
 702                                 // we just inline it
 703                                 //
 704                                 long v = ((LongConstant) expr).Value;
 705                                 if (v > 0)
 706                                         return true;
 707                         }
 708
 709                         if ((target_type == TypeManager.enum_type ||
 710                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 711                              expr is IntLiteral){
 712                                 IntLiteral i = (IntLiteral) expr;
 713
 714                                 if (i.Value == 0)
 715                                         return true;
 716                         }
 717
 718                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 719                                 return true;
 720
 721                         return false;
 722                 }
 723
 724                 //
 725                 // Used internally by FindMostEncompassedType, this is used
 726                 // to avoid creating lots of objects in the tight loop inside
 727                 // FindMostEncompassedType
 728                 //
 729                 static EmptyExpression priv_fmet_param;
 730
 731                 /// <summary>
 732                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 733                 ///  amongst the methods in the MethodGroupExpr
 734                 /// </summary>
 735                 static Type FindMostEncompassedType (ArrayList types)
 736                 {
 737                         Type best = null;
 738
 739                         if (priv_fmet_param == null)
 740                                 priv_fmet_param = new EmptyExpression ();
 741
 742                         foreach (Type t in types){
 743                                 priv_fmet_param.SetType (t);
 744
 745                                 if (best == null) {
 746                                         best = t;
 747                                         continue;
 748                                 }
 749
 750                                 if (ImplicitStandardConversionExists (priv_fmet_param, best))
 751                                         best = t;
 752                         }
 753
 754                         return best;
 755                 }
 756
 757                 //
 758                 // Used internally by FindMostEncompassingType, this is used
 759                 // to avoid creating lots of objects in the tight loop inside
 760                 // FindMostEncompassingType
 761                 //
 762                 static EmptyExpression priv_fmee_ret;
 763
 764                 /// <summary>
 765                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 766                 ///  amongst the types in the given set
 767                 /// </summary>
 768                 static Type FindMostEncompassingType (ArrayList types)
 769                 {
 770                         Type best = null;
 771
 772                         if (priv_fmee_ret == null)
 773                                 priv_fmee_ret = new EmptyExpression ();
 774
 775                         foreach (Type t in types){
 776                                 priv_fmee_ret.SetType (best);
 777
 778                                 if (best == null) {
 779                                         best = t;
 780                                         continue;
 781                                 }
 782
 783                                 if (ImplicitStandardConversionExists (priv_fmee_ret, t))
 784                                         best = t;
 785                         }
 786
 787                         return best;
 788                 }
 789
 790                 //
 791                 // Used to avoid creating too many objects
 792                 //
 793                 static EmptyExpression priv_fms_expr;
 794
 795                 /// <summary>
 796                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 797                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 798                 ///   for explicit and implicit conversion operators.
 799                 /// </summary>
 800                 static public Type FindMostSpecificSource (MethodGroupExpr me, Expression source,
 801                                                            bool apply_explicit_conv_rules,
 802                                                            Location loc)
 803                 {
 804                         ArrayList src_types_set = new ArrayList ();
 805
 806                         if (priv_fms_expr == null)
 807                                 priv_fms_expr = new EmptyExpression ();
 808
 809                         //
 810                         // If any operator converts from S then Sx = S
 811                         //
 812                         Type source_type = source.Type;
 813                         foreach (MethodBase mb in me.Methods){
 814                                 ParameterData pd = Invocation.GetParameterData (mb);
 815                                 Type param_type = pd.ParameterType (0);
 816
 817                                 if (param_type == source_type)
 818                                         return param_type;
 819
 820                                 if (apply_explicit_conv_rules) {
 821                                         //
 822                                         // From the spec :
 823                                         // Find the set of applicable user-defined conversion operators, U.  This set
 824                                         // consists of the
 825                                         // user-defined implicit or explicit conversion operators declared by
 826                                         // the classes or structs in D that convert from a type encompassing
 827                                         // or encompassed by S to a type encompassing or encompassed by T
 828                                         //
 829                                         priv_fms_expr.SetType (param_type);
 830                                         if (ImplicitStandardConversionExists (priv_fms_expr, source_type))
 831                                                 src_types_set.Add (param_type);
 832                                         else {
 833                                                 if (ImplicitStandardConversionExists (source, param_type))
 834                                                         src_types_set.Add (param_type);
 835                                         }
 836                                 } else {
 837                                         //
 838                                         // Only if S is encompassed by param_type
 839                                         //
 840                                         if (ImplicitStandardConversionExists (source, param_type))
 841                                                 src_types_set.Add (param_type);
 842                                 }
 843                         }
 844
 845                         //
 846                         // Explicit Conv rules
 847                         //
 848                         if (apply_explicit_conv_rules) {
 849                                 ArrayList candidate_set = new ArrayList ();
 850
 851                                 foreach (Type param_type in src_types_set){
 852                                         if (ImplicitStandardConversionExists (source, param_type))
 853                                                 candidate_set.Add (param_type);
 854                                 }
 855
 856                                 if (candidate_set.Count != 0)
 857                                         return FindMostEncompassedType (candidate_set);
 858                         }
 859
 860                         //
 861                         // Final case
 862                         //
 863                         if (apply_explicit_conv_rules)
 864                                 return FindMostEncompassingType (src_types_set);
 865                         else
 866                                 return FindMostEncompassedType (src_types_set);
 867                 }
 868
 869                 //
 870                 // Useful in avoiding proliferation of objects
 871                 //
 872                 static EmptyExpression priv_fmt_expr;
 873
 874                 /// <summary>
 875                 ///  Finds the most specific target Tx according to section 13.4.4
 876                 /// </summary>
 877                 static public Type FindMostSpecificTarget (MethodGroupExpr me, Type target,
 878                                                            bool apply_explicit_conv_rules,
 879                                                            Location loc)
 880                 {
 881                         ArrayList tgt_types_set = new ArrayList ();
 882
 883                         if (priv_fmt_expr == null)
 884                                 priv_fmt_expr = new EmptyExpression ();
 885
 886                         //
 887                         // If any operator converts to T then Tx = T
 888                         //
 889                         foreach (MethodInfo mi in me.Methods){
 890                                 Type ret_type = mi.ReturnType;
 891
 892                                 if (ret_type == target)
 893                                         return ret_type;
 894
 895                                 if (apply_explicit_conv_rules) {
 896                                         //
 897                                         // From the spec :
 898                                         // Find the set of applicable user-defined conversion operators, U.
 899                                         //
 900                                         // This set consists of the
 901                                         // user-defined implicit or explicit conversion operators declared by
 902                                         // the classes or structs in D that convert from a type encompassing
 903                                         // or encompassed by S to a type encompassing or encompassed by T
 904                                         //
 905                                         priv_fms_expr.SetType (ret_type);
 906                                         if (ImplicitStandardConversionExists (priv_fms_expr, target))
 907                                                 tgt_types_set.Add (ret_type);
 908                                         else {
 909                                                 priv_fms_expr.SetType (target);
 910                                                 if (ImplicitStandardConversionExists (priv_fms_expr, ret_type))
 911                                                         tgt_types_set.Add (ret_type);
 912                                         }
 913                                 } else {
 914                                         //
 915                                         // Only if T is encompassed by param_type
 916                                         //
 917                                         priv_fms_expr.SetType (ret_type);
 918                                         if (ImplicitStandardConversionExists (priv_fms_expr, target))
 919                                                 tgt_types_set.Add (ret_type);
 920                                 }
 921                         }
 922
 923                         //
 924                         // Explicit conv rules
 925                         //
 926                         if (apply_explicit_conv_rules) {
 927                                 ArrayList candidate_set = new ArrayList ();
 928
 929                                 foreach (Type ret_type in tgt_types_set){
 930                                         priv_fmt_expr.SetType (ret_type);
 931
 932                                         if (ImplicitStandardConversionExists (priv_fmt_expr, target))
 933                                                 candidate_set.Add (ret_type);
 934                                 }
 935
 936                                 if (candidate_set.Count != 0)
 937                                         return FindMostEncompassingType (candidate_set);
 938                         }
 939
 940                         //
 941                         // Okay, final case !
 942                         //
 943                         if (apply_explicit_conv_rules)
 944                                 return FindMostEncompassedType (tgt_types_set);
 945                         else
 946                                 return FindMostEncompassingType (tgt_types_set);
 947                 }
 948
 949                 /// <summary>
 950                 ///  User-defined Implicit conversions
 951                 /// </summary>
 952                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
 953                                                                  Type target, Location loc)
 954                 {
 955                         return UserDefinedConversion (ec, source, target, loc, false);
 956                 }
 957
 958                 /// <summary>
 959                 ///  User-defined Explicit conversions
 960                 /// </summary>
 961                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
 962                                                                  Type target, Location loc)
 963                 {
 964                         return UserDefinedConversion (ec, source, target, loc, true);
 965                 }
 966
 967                 static DoubleHash explicit_conv = new DoubleHash (100);
 968                 static DoubleHash implicit_conv = new DoubleHash (100);
 969                 /// <summary>
 970                 ///   Computes the MethodGroup for the user-defined conversion
 971                 ///   operators from source_type to target_type.  `look_for_explicit'
 972                 ///   controls whether we should also include the list of explicit
 973                 ///   operators
 974                 /// </summary>
 975                 static MethodGroupExpr GetConversionOperators (EmitContext ec,
 976                                                                Type source_type, Type target_type,
 977                                                                Location loc, bool look_for_explicit)
 978                 {
 979                         Expression mg1 = null, mg2 = null;
 980                         Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
 981                         string op_name;
 982
 983                         op_name = "op_Implicit";
 984
 985                         MethodGroupExpr union3;
 986                         object r;
 987                         if ((look_for_explicit ? explicit_conv : implicit_conv).Lookup (source_type, target_type, out r))
 988                                 return (MethodGroupExpr) r;
 989
 990                         mg1 = Expression.MethodLookup (ec, source_type, op_name, loc);
 991                         if (source_type.BaseType != null)
 992                                 mg2 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
 993
 994                         if (mg1 == null)
 995                                 union3 = (MethodGroupExpr) mg2;
 996                         else if (mg2 == null)
 997                                 union3 = (MethodGroupExpr) mg1;
 998                         else
 999                                 union3 = Invocation.MakeUnionSet (mg1, mg2, loc);
1000
1001                         mg1 = Expression.MethodLookup (ec, target_type, op_name, loc);
1002                         if (mg1 != null){
1003                                 if (union3 != null)
1004                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1005                                 else
1006                                         union3 = (MethodGroupExpr) mg1;
1007                         }
1008
1009                         if (target_type.BaseType != null)
1010                                 mg1 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1011
1012                         if (mg1 != null){
1013                                 if (union3 != null)
1014                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1015                                 else
1016                                         union3 = (MethodGroupExpr) mg1;
1017                         }
1018
1019                         MethodGroupExpr union4 = null;
1020
1021                         if (look_for_explicit) {
1022                                 op_name = "op_Explicit";
1023
1024                                 mg5 = Expression.MemberLookup (ec, source_type, op_name, loc);
1025                                 if (source_type.BaseType != null)
1026                                         mg6 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1027
1028                                 mg7 = Expression.MemberLookup (ec, target_type, op_name, loc);
1029                                 if (target_type.BaseType != null)
1030                                         mg8 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1031
1032                                 MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
1033                                 MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);
1034
1035                                 union4 = Invocation.MakeUnionSet (union5, union6, loc);
1036                         }
1037
1038                         MethodGroupExpr ret = Invocation.MakeUnionSet (union3, union4, loc);
1039                         (look_for_explicit ? explicit_conv : implicit_conv).Insert (source_type, target_type, ret);
1040                         return ret;
1041                 }
1042
1043                 /// <summary>
1044                 ///   User-defined conversions
1045                 /// </summary>
1046                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1047                                                                 Type target, Location loc,
1048                                                                 bool look_for_explicit)
1049                 {
1050                         MethodGroupExpr union;
1051                         Type source_type = source.Type;
1052                         MethodBase method = null;
1053
1054                         union = GetConversionOperators (ec, source_type, target, loc, look_for_explicit);
1055                         if (union == null)
1056                                 return null;
1057
1058                         Type most_specific_source, most_specific_target;
1059
1060                         most_specific_source = FindMostSpecificSource (union, source, look_for_explicit, loc);
1061                         if (most_specific_source == null)
1062                                 return null;
1063
1064                         most_specific_target = FindMostSpecificTarget (union, target, look_for_explicit, loc);
1065                         if (most_specific_target == null)
1066                                 return null;
1067
1068                         int count = 0;
1069
1070
1071                         foreach (MethodBase mb in union.Methods){
1072                                 ParameterData pd = Invocation.GetParameterData (mb);
1073                                 MethodInfo mi = (MethodInfo) mb;
1074
1075                                 if (pd.ParameterType (0) == most_specific_source &&
1076                                     mi.ReturnType == most_specific_target) {
1077                                         method = mb;
1078                                         count++;
1079                                 }
1080                         }
1081
1082                         if (method == null || count > 1)
1083                                 return null;
1084
1085
1086                         //
1087                         // This will do the conversion to the best match that we
1088                         // found.  Now we need to perform an implict standard conversion
1089                         // if the best match was not the type that we were requested
1090                         // by target.
1091                         //
1092                         if (look_for_explicit)
1093                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1094                         else
1095                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1096
1097                         if (source == null)
1098                                 return null;
1099
1100                         Expression e;
1101                         e =  new UserCast ((MethodInfo) method, source, loc);
1102                         if (e.Type != target){
1103                                 if (!look_for_explicit)
1104                                         e = ImplicitConversionStandard (ec, e, target, loc);
1105                                 else
1106                                         e = ExplicitConversionStandard (ec, e, target, loc);
1107                         }
1108
1109                         return e;
1110                 }
1111
1112                 /// <summary>
1113                 ///   Converts implicitly the resolved expression `expr' into the
1114                 ///   `target_type'.  It returns a new expression that can be used
1115                 ///   in a context that expects a `target_type'.
1116                 /// </summary>
1117                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1118                                                              Type target_type, Location loc)
1119                 {
1120                         Expression e;
1121
1122                         if (target_type == null)
1123                                 throw new Exception ("Target type is null");
1124
1125                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1126                         if (e != null)
1127                                 return e;
1128
1129                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1130                         if (e != null)
1131                                 return e;
1132
1133                         return null;
1134                 }
1135
1136
1137                 /// <summary>
1138                 ///   Attempts to apply the `Standard Implicit
1139                 ///   Conversion' rules to the expression `expr' into
1140                 ///   the `target_type'.  It returns a new expression
1141                 ///   that can be used in a context that expects a
1142                 ///   `target_type'.
1143                 ///
1144                 ///   This is different from `ImplicitConversion' in that the
1145                 ///   user defined implicit conversions are excluded.
1146                 /// </summary>
1147                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1148                                                                      Type target_type, Location loc)
1149                 {
1150                         Type expr_type = expr.Type;
1151                         Expression e;
1152
1153                         if ((expr is NullLiteral) && target_type.IsGenericParameter)
1154                                 return TypeParameter_to_Null (expr, target_type, loc);
1155
1156                         if (expr.eclass == ExprClass.MethodGroup){
1157                                 if (!TypeManager.IsDelegateType (target_type)){
1158                                         Report.Error (428, loc,
1159                                                       String.Format (
1160                                                            "Cannot convert method group to `{0}', since it is not a delegate",
1161                                                            TypeManager.CSharpName (target_type)));
1162                                         return null;
1163                                 }
1164
1165                                 return ImplicitDelegateCreation.Create (ec, (MethodGroupExpr) expr, target_type, loc);
1166                         }
1167
1168                         if (expr_type.Equals (target_type) && !(expr is NullLiteral))
1169                                 return expr;
1170
1171                         e = ImplicitNumericConversion (ec, expr, target_type, loc);
1172                         if (e != null)
1173                                 return e;
1174
1175                         e = ImplicitReferenceConversion (expr, target_type);
1176                         if (e != null)
1177                                 return e;
1178
1179                         if ((target_type == TypeManager.enum_type ||
1180                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1181                             expr is IntLiteral){
1182                                 IntLiteral i = (IntLiteral) expr;
1183
1184                                 if (i.Value == 0)
1185                                         return new EnumConstant ((Constant) expr, target_type);
1186                         }
1187
1188                         if (ec.InUnsafe) {
1189                                 if (expr_type.IsPointer){
1190                                         if (target_type == TypeManager.void_ptr_type)
1191                                                 return new EmptyCast (expr, target_type);
1192
1193                                         //
1194                                         // yep, comparing pointer types cant be done with
1195                                         // t1 == t2, we have to compare their element types.
1196                                         //
1197                                         if (target_type.IsPointer){
1198                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1199                                                         return expr;
1200                                         }
1201                                 }
1202
1203                                 if (target_type.IsPointer) {
1204                                         if (expr is NullLiteral)
1205                                                 return new EmptyCast (expr, target_type);
1206
1207                                         if (expr_type == TypeManager.void_ptr_type)
1208                                                 return new EmptyCast (expr, target_type);
1209                                 }
1210                         }
1211
1212                         return null;
1213                 }
1214
1215                 /// <summary>
1216                 ///   Attemps to perform an implict constant conversion of the IntConstant
1217                 ///   into a different data type using casts (See Implicit Constant
1218                 ///   Expression Conversions)
1219                 /// </summary>
1220                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1221                 {
1222                         int value = ic.Value;
1223
1224                         if (target_type == TypeManager.sbyte_type){
1225                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1226                                         return new SByteConstant ((sbyte) value);
1227                         } else if (target_type == TypeManager.byte_type){
1228                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1229                                         return new ByteConstant ((byte) value);
1230                         } else if (target_type == TypeManager.short_type){
1231                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1232                                         return new ShortConstant ((short) value);
1233                         } else if (target_type == TypeManager.ushort_type){
1234                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1235                                         return new UShortConstant ((ushort) value);
1236                         } else if (target_type == TypeManager.uint32_type){
1237                                 if (value >= 0)
1238                                         return new UIntConstant ((uint) value);
1239                         } else if (target_type == TypeManager.uint64_type){
1240                                 //
1241                                 // we can optimize this case: a positive int32
1242                                 // always fits on a uint64.  But we need an opcode
1243                                 // to do it.
1244                                 //
1245                                 if (value >= 0)
1246                                         return new ULongConstant ((ulong) value);
1247                         } else if (target_type == TypeManager.double_type)
1248                                 return new DoubleConstant ((double) value);
1249                         else if (target_type == TypeManager.float_type)
1250                                 return new FloatConstant ((float) value);
1251
1252                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1253                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1254                                 Constant e = (Constant) ic;
1255
1256                                 //
1257                                 // Possibly, we need to create a different 0 literal before passing
1258                                 // to EnumConstant
1259                                 //n
1260                                 if (underlying == TypeManager.int64_type)
1261                                         e = new LongLiteral (0);
1262                                 else if (underlying == TypeManager.uint64_type)
1263                                         e = new ULongLiteral (0);
1264
1265                                 return new EnumConstant (e, target_type);
1266                         }
1267                         return null;
1268                 }
1269
1270                 static public void Error_CannotImplicitConversion (Location loc, Type source, Type target)
1271                 {
1272                         string msg = "Cannot convert implicitly from `"+
1273                                 TypeManager.CSharpName (source) + "' to `" +
1274                                 TypeManager.CSharpName (target) + "'";
1275
1276                         Report.Error (29, loc, msg);
1277                 }
1278
1279                 /// <summary>
1280                 ///   Attemptes to implicityly convert `target' into `type', using
1281                 ///   ImplicitConversion.  If there is no implicit conversion, then
1282                 ///   an error is signaled
1283                 /// </summary>
1284                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1285                                                                      Type target_type, Location loc)
1286                 {
1287                         Expression e;
1288
1289                         int errors = Report.Errors;
1290                         e = ImplicitConversion (ec, source, target_type, loc);
1291                         if (Report.Errors > errors)
1292                                 return null;
1293                         if (e != null)
1294                                 return e;
1295
1296                         if (source is DoubleLiteral && target_type == TypeManager.float_type){
1297                                 Report.Error (664, loc,
1298                                               "Double literal cannot be implicitly converted to " +
1299                                               "float type, use F suffix to create a float literal");
1300                         }
1301
1302                         if (source is Constant){
1303                                 Constant c = (Constant) source;
1304
1305                                 Expression.Error_ConstantValueCannotBeConverted (loc, c.AsString (), target_type);
1306                                 return null;
1307                         }
1308
1309                         Error_CannotImplicitConversion (loc, source.Type, target_type);
1310
1311                         return null;
1312                 }
1313
1314                 /// <summary>
1315                 ///   Performs the explicit numeric conversions
1316                 /// </summary>
1317                 static Expression ExplicitNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
1318                 {
1319                         Type expr_type = expr.Type;
1320
1321                         //
1322                         // If we have an enumeration, extract the underlying type,
1323                         // use this during the comparison, but wrap around the original
1324                         // target_type
1325                         //
1326                         Type real_target_type = target_type;
1327
1328                         if (TypeManager.IsEnumType (real_target_type))
1329                                 real_target_type = TypeManager.EnumToUnderlying (real_target_type);
1330
1331                         if (ImplicitStandardConversionExists (expr, real_target_type)){
1332                                 Expression ce = ImplicitConversionStandard (ec, expr, real_target_type, loc);
1333
1334                                 if (real_target_type != target_type)
1335                                         return new EmptyCast (ce, target_type);
1336                                 return ce;
1337                         }
1338
1339                         if (expr_type == TypeManager.sbyte_type){
1340                                 //
1341                                 // From sbyte to byte, ushort, uint, ulong, char
1342                                 //
1343                                 if (real_target_type == TypeManager.byte_type)
1344                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U1);
1345                                 if (real_target_type == TypeManager.ushort_type)
1346                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U2);
1347                                 if (real_target_type == TypeManager.uint32_type)
1348                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U4);
1349                                 if (real_target_type == TypeManager.uint64_type)
1350                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U8);
1351                                 if (real_target_type == TypeManager.char_type)
1352                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_CH);
1353                         } else if (expr_type == TypeManager.byte_type){
1354                                 //
1355                                 // From byte to sbyte and char
1356                                 //
1357                                 if (real_target_type == TypeManager.sbyte_type)
1358                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_I1);
1359                                 if (real_target_type == TypeManager.char_type)
1360                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_CH);
1361                         } else if (expr_type == TypeManager.short_type){
1362                                 //
1363                                 // From short to sbyte, byte, ushort, uint, ulong, char
1364                                 //
1365                                 if (real_target_type == TypeManager.sbyte_type)
1366                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_I1);
1367                                 if (real_target_type == TypeManager.byte_type)
1368                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
1369                                 if (real_target_type == TypeManager.ushort_type)
1370                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U2);
1371                                 if (real_target_type == TypeManager.uint32_type)
1372                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U4);
1373                                 if (real_target_type == TypeManager.uint64_type)
1374                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U8);
1375                                 if (real_target_type == TypeManager.char_type)
1376                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_CH);
1377                         } else if (expr_type == TypeManager.ushort_type){
1378                                 //
1379                                 // From ushort to sbyte, byte, short, char
1380                                 //
1381                                 if (real_target_type == TypeManager.sbyte_type)
1382                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I1);
1383                                 if (real_target_type == TypeManager.byte_type)
1384                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_U1);
1385                                 if (real_target_type == TypeManager.short_type)
1386                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I2);
1387                                 if (real_target_type == TypeManager.char_type)
1388                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_CH);
1389                         } else if (expr_type == TypeManager.int32_type){
1390                                 //
1391                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1392                                 //
1393                                 if (real_target_type == TypeManager.sbyte_type)
1394                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I1);
1395                                 if (real_target_type == TypeManager.byte_type)
1396                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
1397                                 if (real_target_type == TypeManager.short_type)
1398                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
1399                                 if (real_target_type == TypeManager.ushort_type)
1400                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U2);
1401                                 if (real_target_type == TypeManager.uint32_type)
1402                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U4);
1403                                 if (real_target_type == TypeManager.uint64_type)
1404                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U8);
1405                                 if (real_target_type == TypeManager.char_type)
1406                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_CH);
1407                         } else if (expr_type == TypeManager.uint32_type){
1408                                 //
1409                                 // From uint to sbyte, byte, short, ushort, int, char
1410                                 //
1411                                 if (real_target_type == TypeManager.sbyte_type)
1412                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I1);
1413                                 if (real_target_type == TypeManager.byte_type)
1414                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U1);
1415                                 if (real_target_type == TypeManager.short_type)
1416                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I2);
1417                                 if (real_target_type == TypeManager.ushort_type)
1418                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U2);
1419                                 if (real_target_type == TypeManager.int32_type)
1420                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I4);
1421                                 if (real_target_type == TypeManager.char_type)
1422                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_CH);
1423                         } else if (expr_type == TypeManager.int64_type){
1424                                 //
1425                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1426                                 //
1427                                 if (real_target_type == TypeManager.sbyte_type)
1428                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I1);
1429                                 if (real_target_type == TypeManager.byte_type)
1430                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
1431                                 if (real_target_type == TypeManager.short_type)
1432                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
1433                                 if (real_target_type == TypeManager.ushort_type)
1434                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U2);
1435                                 if (real_target_type == TypeManager.int32_type)
1436                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
1437                                 if (real_target_type == TypeManager.uint32_type)
1438                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U4);
1439                                 if (real_target_type == TypeManager.uint64_type)
1440                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U8);
1441                                 if (real_target_type == TypeManager.char_type)
1442                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_CH);
1443                         } else if (expr_type == TypeManager.uint64_type){
1444                                 //
1445                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1446                                 //
1447                                 if (real_target_type == TypeManager.sbyte_type)
1448                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I1);
1449                                 if (real_target_type == TypeManager.byte_type)
1450                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U1);
1451                                 if (real_target_type == TypeManager.short_type)
1452                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I2);
1453                                 if (real_target_type == TypeManager.ushort_type)
1454                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U2);
1455                                 if (real_target_type == TypeManager.int32_type)
1456                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I4);
1457                                 if (real_target_type == TypeManager.uint32_type)
1458                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U4);
1459                                 if (real_target_type == TypeManager.int64_type)
1460                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I8);
1461                                 if (real_target_type == TypeManager.char_type)
1462                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_CH);
1463                         } else if (expr_type == TypeManager.char_type){
1464                                 //
1465                                 // From char to sbyte, byte, short
1466                                 //
1467                                 if (real_target_type == TypeManager.sbyte_type)
1468                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I1);
1469                                 if (real_target_type == TypeManager.byte_type)
1470                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_U1);
1471                                 if (real_target_type == TypeManager.short_type)
1472                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I2);
1473                         } else if (expr_type == TypeManager.float_type){
1474                                 //
1475                                 // From float to sbyte, byte, short,
1476                                 // ushort, int, uint, long, ulong, char
1477                                 // or decimal
1478                                 //
1479                                 if (real_target_type == TypeManager.sbyte_type)
1480                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
1481                                 if (real_target_type == TypeManager.byte_type)
1482                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U1);
1483                                 if (real_target_type == TypeManager.short_type)
1484                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I2);
1485                                 if (real_target_type == TypeManager.ushort_type)
1486                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U2);
1487                                 if (real_target_type == TypeManager.int32_type)
1488                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I4);
1489                                 if (real_target_type == TypeManager.uint32_type)
1490                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U4);
1491                                 if (real_target_type == TypeManager.int64_type)
1492                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I8);
1493                                 if (real_target_type == TypeManager.uint64_type)
1494                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U8);
1495                                 if (real_target_type == TypeManager.char_type)
1496                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_CH);
1497                         } else if (expr_type == TypeManager.double_type){
1498                                 //
1499                                 // From double to byte, byte, short,
1500                                 // ushort, int, uint, long, ulong,
1501                                 // char, float or decimal
1502                                 //
1503                                 if (real_target_type == TypeManager.sbyte_type)
1504                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I1);
1505                                 if (real_target_type == TypeManager.byte_type)
1506                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1507                                 if (real_target_type == TypeManager.short_type)
1508                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1509                                 if (real_target_type == TypeManager.ushort_type)
1510                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U2);
1511                                 if (real_target_type == TypeManager.int32_type)
1512                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1513                                 if (real_target_type == TypeManager.uint32_type)
1514                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U4);
1515                                 if (real_target_type == TypeManager.int64_type)
1516                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1517                                 if (real_target_type == TypeManager.uint64_type)
1518                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U8);
1519                                 if (real_target_type == TypeManager.char_type)
1520                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_CH);
1521                                 if (real_target_type == TypeManager.float_type)
1522                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
1523                         }
1524
1525                         // decimal is taken care of by the op_Explicit methods.
1526
1527                         return null;
1528                 }
1529
1530                 /// <summary>
1531                 ///  Returns whether an explicit reference conversion can be performed
1532                 ///  from source_type to target_type
1533                 /// </summary>
1534                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1535                 {
1536                         bool target_is_type_param = target_type.IsGenericParameter;
1537                         bool target_is_value_type = target_type.IsValueType;
1538
1539                         if (source_type == target_type)
1540                                 return true;
1541
1542                         //
1543                         // From object to a generic parameter
1544                         //
1545                         if (source_type == TypeManager.object_type && target_is_type_param)
1546                                 return true;
1547
1548                         //
1549                         // From object to any reference type
1550                         //
1551                         if (source_type == TypeManager.object_type && !target_is_value_type)
1552                                 return true;
1553
1554                         //
1555                         // From any class S to any class-type T, provided S is a base class of T
1556                         //
1557                         if (TypeManager.IsSubclassOf (target_type, source_type))
1558                                 return true;
1559
1560                         //
1561                         // From any interface type S to any interface T provided S is not derived from T
1562                         //
1563                         if (source_type.IsInterface && target_type.IsInterface){
1564                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1565                                         return true;
1566                         }
1567
1568                         //
1569                         // From any class type S to any interface T, provided S is not sealed
1570                         // and provided S does not implement T.
1571                         //
1572                         if (target_type.IsInterface && !source_type.IsSealed &&
1573                             !TypeManager.ImplementsInterface (source_type, target_type))
1574                                 return true;
1575
1576                         //
1577                         // From any interface-type S to to any class type T, provided T is not
1578                         // sealed, or provided T implements S.
1579                         //
1580                         if (source_type.IsInterface &&
1581                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1582                                 return true;
1583
1584
1585                         // From an array type S with an element type Se to an array type T with an
1586                         // element type Te provided all the following are true:
1587                         //     * S and T differe only in element type, in other words, S and T
1588                         //       have the same number of dimensions.
1589                         //     * Both Se and Te are reference types
1590                         //     * An explicit referenc conversions exist from Se to Te
1591                         //
1592                         if (source_type.IsArray && target_type.IsArray) {
1593                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1594
1595                                         Type source_element_type = TypeManager.GetElementType (source_type);
1596                                         Type target_element_type = TypeManager.GetElementType (target_type);
1597
1598                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1599                                                 if (ExplicitReferenceConversionExists (source_element_type,
1600                                                                                        target_element_type))
1601                                                         return true;
1602                                 }
1603                         }
1604
1605
1606                         // From System.Array to any array-type
1607                         if (source_type == TypeManager.array_type &&
1608                             target_type.IsArray){
1609                                 return true;
1610                         }
1611
1612                         //
1613                         // From System delegate to any delegate-type
1614                         //
1615                         if (source_type == TypeManager.delegate_type &&
1616                             TypeManager.IsDelegateType (target_type))
1617                                 return true;
1618
1619                         //
1620                         // From ICloneable to Array or Delegate types
1621                         //
1622                         if (source_type == TypeManager.icloneable_type &&
1623                             (target_type == TypeManager.array_type ||
1624                              target_type == TypeManager.delegate_type))
1625                                 return true;
1626
1627                         return false;
1628                 }
1629
1630                 /// <summary>
1631                 ///   Implements Explicit Reference conversions
1632                 /// </summary>
1633                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1634                 {
1635                         Type source_type = source.Type;
1636                         bool target_is_type_param = target_type.IsGenericParameter;
1637                         bool target_is_value_type = target_type.IsValueType;
1638
1639                         //
1640                         // From object to a generic parameter
1641                         //
1642                         if (source_type == TypeManager.object_type && target_is_type_param)
1643                                 return new UnboxCast (source, target_type);
1644
1645                         //
1646                         // From object to any reference type
1647                         //
1648                         if (source_type == TypeManager.object_type && !target_is_value_type)
1649                                 return new ClassCast (source, target_type);
1650
1651                         //
1652                         // Unboxing conversion.
1653                         //
1654                         if (((source_type == TypeManager.enum_type &&
1655                                 !(source is EmptyCast)) ||
1656                                 source_type == TypeManager.value_type) && target_is_value_type)
1657                                 return new UnboxCast (source, target_type);
1658
1659                         //
1660                         // From any class S to any class-type T, provided S is a base class of T
1661                         //
1662                         if (TypeManager.IsSubclassOf (target_type, source_type))
1663                                 return new ClassCast (source, target_type);
1664
1665                         //
1666                         // From any interface type S to any interface T provided S is not derived from T
1667                         //
1668                         if (source_type.IsInterface && target_type.IsInterface){
1669                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1670                                         return null;
1671                                 else
1672                                         return new ClassCast (source, target_type);
1673                         }
1674
1675                         //
1676                         // From any class type S to any interface T, provides S is not sealed
1677                         // and provided S does not implement T.
1678                         //
1679                         if (target_type.IsInterface && !source_type.IsSealed) {
1680                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1681                                         return null;
1682                                 else
1683                                         return new ClassCast (source, target_type);
1684
1685                         }
1686
1687                         //
1688                         // From any interface-type S to to any class type T, provided T is not
1689                         // sealed, or provided T implements S.
1690                         //
1691                         if (source_type.IsInterface) {
1692                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1693                                         if (target_type.IsClass)
1694                                                 return new ClassCast (source, target_type);
1695                                         else
1696                                                 return new UnboxCast (source, target_type);
1697                                 }
1698
1699                                 return null;
1700                         }
1701
1702                         // From an array type S with an element type Se to an array type T with an
1703                         // element type Te provided all the following are true:
1704                         //     * S and T differe only in element type, in other words, S and T
1705                         //       have the same number of dimensions.
1706                         //     * Both Se and Te are reference types
1707                         //     * An explicit referenc conversions exist from Se to Te
1708                         //
1709                         if (source_type.IsArray && target_type.IsArray) {
1710                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1711
1712                                         Type source_element_type = TypeManager.GetElementType (source_type);
1713                                         Type target_element_type = TypeManager.GetElementType (target_type);
1714
1715                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1716                                                 if (ExplicitReferenceConversionExists (source_element_type,
1717                                                                                        target_element_type))
1718                                                         return new ClassCast (source, target_type);
1719                                 }
1720                         }
1721
1722
1723                         // From System.Array to any array-type
1724                         if (source_type == TypeManager.array_type &&
1725                             target_type.IsArray) {
1726                                 return new ClassCast (source, target_type);
1727                         }
1728
1729                         //
1730                         // From System delegate to any delegate-type
1731                         //
1732                         if (source_type == TypeManager.delegate_type &&
1733                             TypeManager.IsDelegateType (target_type))
1734                                 return new ClassCast (source, target_type);
1735
1736                         //
1737                         // From ICloneable to Array or Delegate types
1738                         //
1739                         if (source_type == TypeManager.icloneable_type &&
1740                             (target_type == TypeManager.array_type ||
1741                              target_type == TypeManager.delegate_type))
1742                                 return new ClassCast (source, target_type);
1743
1744                         return null;
1745                 }
1746
1747                 /// <summary>
1748                 ///   Performs an explicit conversion of the expression `expr' whose
1749                 ///   type is expr.Type to `target_type'.
1750                 /// </summary>
1751                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1752                                                              Type target_type, Location loc)
1753                 {
1754                         Type expr_type = expr.Type;
1755                         Type original_expr_type = expr_type;
1756
1757                         if (expr_type.IsSubclassOf (TypeManager.enum_type)){
1758                                 if (target_type == TypeManager.enum_type ||
1759                                     target_type == TypeManager.object_type) {
1760                                         if (expr is EnumConstant)
1761                                                 expr = ((EnumConstant) expr).Child;
1762                                         // We really need all these casts here .... :-(
1763                                         expr = new BoxedCast (new EmptyCast (expr, expr_type));
1764                                         return new EmptyCast (expr, target_type);
1765                                 } else if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
1766                                            target_type.IsSubclassOf (TypeManager.enum_type))
1767                                         return new UnboxCast (expr, target_type);
1768
1769                                 //
1770                                 // Notice that we have kept the expr_type unmodified, which is only
1771                                 // used later on to
1772                                 if (expr is EnumConstant)
1773                                         expr = ((EnumConstant) expr).Child;
1774                                 else
1775                                         expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
1776                                 expr_type = expr.Type;
1777                         }
1778
1779                         int errors = Report.Errors;
1780                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1781                         if (Report.Errors > errors)
1782                                 return null;
1783
1784                         if (ne != null)
1785                                 return ne;
1786
1787                         ne = ExplicitNumericConversion (ec, expr, target_type, loc);
1788                         if (ne != null)
1789                                 return ne;
1790
1791                         //
1792                         // Unboxing conversion.
1793                         //
1794                         if (expr_type == TypeManager.object_type && target_type.IsValueType){
1795                                 if (expr is NullLiteral){
1796                                         //
1797                                         // Skip the ExplicitReferenceConversion because we can not convert
1798                                         // from Null to a ValueType, and ExplicitReference wont check against
1799                                         // null literal explicitly
1800                                         //
1801                                         goto skip_explicit;
1802                                 }
1803                                 return new UnboxCast (expr, target_type);
1804
1805                         }
1806
1807                         ne = ExplicitReferenceConversion (expr, target_type);
1808                         if (ne != null)
1809                                 return ne;
1810
1811                 skip_explicit:
1812                         if (ec.InUnsafe){
1813                                 if (target_type.IsPointer){
1814                                         if (expr_type.IsPointer)
1815                                                 return new EmptyCast (expr, target_type);
1816
1817                                         if (expr_type == TypeManager.sbyte_type ||
1818                                             expr_type == TypeManager.byte_type ||
1819                                             expr_type == TypeManager.short_type ||
1820                                             expr_type == TypeManager.ushort_type ||
1821                                             expr_type == TypeManager.int32_type ||
1822                                             expr_type == TypeManager.uint32_type ||
1823                                             expr_type == TypeManager.uint64_type ||
1824                                             expr_type == TypeManager.int64_type)
1825                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1826                                 }
1827                                 if (expr_type.IsPointer){
1828                                         Expression e = null;
1829
1830                                         if (target_type == TypeManager.sbyte_type)
1831                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1832                                         else if (target_type == TypeManager.byte_type)
1833                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1834                                         else if (target_type == TypeManager.short_type)
1835                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1836                                         else if (target_type == TypeManager.ushort_type)
1837                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1838                                         else if (target_type == TypeManager.int32_type)
1839                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1840                                         else if (target_type == TypeManager.uint32_type)
1841                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1842                                         else if (target_type == TypeManager.uint64_type)
1843                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1844                                         else if (target_type == TypeManager.int64_type){
1845                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1846                                         }
1847
1848                                         if (e != null){
1849                                                 Expression ci, ce;
1850
1851                                                 ci = ImplicitConversionStandard (ec, e, target_type, loc);
1852
1853                                                 if (ci != null)
1854                                                         return ci;
1855
1856                                                 ce = ExplicitNumericConversion (ec, e, target_type, loc);
1857                                                 if (ce != null)
1858                                                         return ce;
1859                                                 //
1860                                                 // We should always be able to go from an uint32
1861                                                 // implicitly or explicitly to the other integral
1862                                                 // types
1863                                                 //
1864                                                 throw new Exception ("Internal compiler error");
1865                                         }
1866                                 }
1867                         }
1868
1869                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1870                         if (ne != null)
1871                                 return ne;
1872
1873                         if (expr is NullLiteral){
1874                                 Report.Error (37, loc, "Cannot convert null to value type `" +
1875                                               TypeManager.CSharpName (target_type) + "'");
1876                                 return null;
1877                         }
1878
1879                         Error_CannotConvertType (loc, original_expr_type, target_type);
1880                         return null;
1881                 }
1882
1883                 /// <summary>
1884                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1885                 /// </summary>
1886                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1887                                                                      Type target_type, Location l)
1888                 {
1889                         int errors = Report.Errors;
1890                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1891                         if (Report.Errors > errors)
1892                                 return null;
1893
1894                         if (ne != null)
1895                                 return ne;
1896
1897                         ne = ExplicitNumericConversion (ec, expr, target_type, l);
1898                         if (ne != null)
1899                                 return ne;
1900
1901                         ne = ExplicitReferenceConversion (expr, target_type);
1902                         if (ne != null)
1903                                 return ne;
1904
1905                         Error_CannotConvertType (l, expr.Type, target_type);
1906                         return null;
1907                 }
1908         }
1909 }