mcs/bmcs/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                 //
  23                 // This is used to prettify the code: a null argument is allowed
  24                 // for ImplicitStandardConversion as long as it is known that
  25                 // no anonymous method will play a role.
  26                 //
  27                 // FIXME: renamed from `const' to `static' to allow bootstraping from older
  28                 // versions of the compiler that could not cope with this construct.
  29                 //
  30                 public static EmitContext ConstantEC = null;
  31
  32                 static public void Error_CannotConvertType (Location loc, Type source, Type target)
  33                 {
  34                         Report.Error (30, loc, "Cannot convert type '" +
  35                                       TypeManager.CSharpName (source) + "' to '" +
  36                                       TypeManager.CSharpName (target) + "'");
  37                 }
  38
  39                 static Expression TypeParameter_to_Null (Expression expr, Type target_type,
  40                                                          Location loc)
  41                 {
  42                         if (!TypeParameter_to_Null (target_type)) {
  43                                 Report.Error (403, loc, "Cannot convert null to the type " +
  44                                               "parameter `{0}' becaues it could be a value " +
  45                                               "type.  Consider using `default ({0})' instead.",
  46                                               target_type);
  47                                 return null;
  48                         }
  49
  50                         return new NullCast (expr, target_type);
  51                 }
  52
  53                 static bool TypeParameter_to_Null (Type target_type)
  54                 {
  55                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
  56                         if (gc == null)
  57                                 return false;
  58
  59                         if (gc.HasReferenceTypeConstraint)
  60                                 return true;
  61                         if (gc.HasClassConstraint && !TypeManager.IsValueType (gc.ClassConstraint))
  62                                 return true;
  63
  64                         return false;
  65                 }
  66
  67                 static Type TypeParam_EffectiveBaseType (EmitContext ec, Type t)
  68                 {
  69                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (t);
  70                         if (gc == null)
  71                                 return TypeManager.object_type;
  72
  73                         return TypeParam_EffectiveBaseType (ec, gc);
  74                 }
  75
  76                 static Type TypeParam_EffectiveBaseType (EmitContext ec, GenericConstraints gc)
  77                 {
  78                         ArrayList list = new ArrayList ();
  79                         list.Add (gc.EffectiveBaseClass);
  80                         foreach (Type t in gc.InterfaceConstraints) {
  81                                 if (!t.IsGenericParameter)
  82                                         continue;
  83
  84                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  85                                 if (new_gc != null)
  86                                         list.Add (TypeParam_EffectiveBaseType (ec, new_gc));
  87                         }
  88                         return FindMostEncompassedType (ec, list);
  89                 }
  90
  91                 static Expression TypeParameterConversion (Expression expr, bool is_reference, Type target_type)
  92                 {
  93                         if (is_reference)
  94                                 return new EmptyCast (expr, target_type);
  95                         else
  96                                 return new BoxedCast (expr, target_type);
  97                 }
  98
  99                 static Expression ImplicitTypeParameterConversion (EmitContext ec, Expression expr,
 100                                                                    Type target_type)
 101                 {
 102                         Type expr_type = expr.Type;
 103
 104                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
 105
 106                         if (gc == null) {
 107                                 if (target_type == TypeManager.object_type)
 108                                         return new BoxedCast (expr);
 109
 110                                 return null;
 111                         }
 112
 113                         // We're converting from a type parameter which is known to be a reference type.
 114                         bool is_reference = gc.IsReferenceType;
 115                         Type base_type = TypeParam_EffectiveBaseType (ec, gc);
 116
 117                         if (TypeManager.IsSubclassOf (base_type, target_type))
 118                                 return TypeParameterConversion (expr, is_reference, target_type);
 119
 120                         if (target_type.IsInterface) {
 121                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 122                                         return TypeParameterConversion (expr, is_reference, target_type);
 123
 124                                 foreach (Type t in gc.InterfaceConstraints) {
 125                                         if (TypeManager.IsSubclassOf (t, target_type))
 126                                                 return TypeParameterConversion (expr, is_reference, target_type);
 127                                 }
 128                         }
 129
 130                         foreach (Type t in gc.InterfaceConstraints) {
 131                                 if (!t.IsGenericParameter)
 132                                         continue;
 133                                 if (TypeManager.IsSubclassOf (t, target_type))
 134                                         return TypeParameterConversion (expr, is_reference, target_type);
 135                         }
 136
 137                         return null;
 138                 }
 139
 140                 static EmptyExpression MyEmptyExpr;
 141                 static public Expression WideningReferenceConversion (EmitContext ec, Expression expr, Type target_type)
 142                 {
 143                         Type expr_type = expr.Type;
 144
 145                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 146                                 // if we are a method group, emit a warning
 147
 148                                 expr.Emit (null);
 149                         }
 150
 151                         if (expr_type == TypeManager.void_type)
 152                                 return null;
 153
 154                         if (expr_type.IsGenericParameter)
 155                                 return ImplicitTypeParameterConversion (ec, expr, target_type);
 156
 157                         //
 158                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 159                         // is an abstract class, and not really a value type, so we apply the same rules.
 160                         //
 161                         if (target_type == TypeManager.object_type) {
 162                                 //
 163                                 // A pointer type cannot be converted to object
 164                                 //
 165                                 if (expr_type.IsPointer)
 166                                         return null;
 167
 168                                 if (TypeManager.IsValueType (expr_type))
 169                                         return new BoxedCast (expr);
 170                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 171                                         if (expr_type == TypeManager.anonymous_method_type)
 172                                                 return null;
 173                                         return new EmptyCast (expr, target_type);
 174                                 }
 175
 176                                 return null;
 177                         } else if (target_type == TypeManager.value_type) {
 178                                 if (TypeManager.IsValueType (expr_type))
 179                                         return new BoxedCast (expr);
 180                                 if (expr_type == TypeManager.null_type)
 181                                         return new NullCast (expr, target_type);
 182
 183                                 return null;
 184                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 185                                 //
 186                                 // Special case: enumeration to System.Enum.
 187                                 // System.Enum is not a value type, it is a class, so we need
 188                                 // a boxing conversion
 189                                 //
 190                                 if (expr_type.IsEnum || expr_type.IsGenericParameter)
 191                                         return new BoxedCast (expr);
 192
 193                                 return new EmptyCast (expr, target_type);
 194                         }
 195
 196                         // This code is kind of mirrored inside WideningStandardConversionExists
 197                         // with the small distinction that we only probe there
 198                         //
 199                         // Always ensure that the code here and there is in sync
 200
 201                         // from the null type to any reference-type.
 202                         if (expr_type == TypeManager.null_type){
 203                                 if (target_type.IsPointer)
 204                                         return new EmptyCast (expr, target_type);
 205
 206                                 if (!target_type.IsValueType)
 207                                         return new NullCast (expr, target_type);
 208                         }
 209
 210                         // from any class-type S to any interface-type T.
 211                         if (target_type.IsInterface) {
 212                                 if (target_type != TypeManager.iconvertible_type &&
 213                                     expr_type.IsValueType && (expr is Constant) &&
 214                                     !(expr is IntLiteral || expr is BoolLiteral ||
 215                                       expr is FloatLiteral || expr is DoubleLiteral ||
 216                                       expr is LongLiteral || expr is CharLiteral ||
 217                                       expr is StringLiteral || expr is DecimalLiteral ||
 218                                       expr is UIntLiteral || expr is ULongLiteral)) {
 219                                         return null;
 220                                 }
 221
 222                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 223                                         if (expr_type.IsGenericParameter || TypeManager.IsValueType (expr_type))
 224                                                 return new BoxedCast (expr, target_type);
 225                                         else
 226                                                 return new EmptyCast (expr, target_type);
 227                                 }
 228                         }
 229
 230                         // from any interface type S to interface-type T.
 231                         if (expr_type.IsInterface && target_type.IsInterface) {
 232                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 233                                         return new EmptyCast (expr, target_type);
 234                                 else
 235                                         return null;
 236                         }
 237
 238                         // from an array-type S to an array-type of type T
 239                         if (expr_type.IsArray && target_type.IsArray) {
 240                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 241
 242                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 243
 244                                         if (MyEmptyExpr == null)
 245                                                 MyEmptyExpr = new EmptyExpression ();
 246
 247                                         MyEmptyExpr.SetType (expr_element_type);
 248                                         Type target_element_type = TypeManager.GetElementType (target_type);
 249
 250                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 251                                                 if (WideningStandardConversionExists (ConstantEC, MyEmptyExpr,
 252                                                                                       target_element_type))
 253                                                         return new EmptyCast (expr, target_type);
 254                                 }
 255                         }
 256
 257                         // from an array-type to System.Array
 258                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 259                                 return new EmptyCast (expr, target_type);
 260
 261                         // from any delegate type to System.Delegate
 262                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 263                             target_type == TypeManager.delegate_type)
 264                                 return new EmptyCast (expr, target_type);
 265
 266                         // from any array-type or delegate type into System.ICloneable.
 267                         if (expr_type.IsArray ||
 268                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 269                                 if (target_type == TypeManager.icloneable_type)
 270                                         return new EmptyCast (expr, target_type);
 271
 272                         // from a generic type definition to a generic instance.
 273                         if (TypeManager.IsEqual (expr_type, target_type))
 274                                 return new EmptyCast (expr, target_type);
 275
 276                         return null;
 277                 }
 278
 279                 //
 280                 // Tests whether an implicit reference conversion exists between expr_type
 281                 // and target_type
 282                 //
 283                 public static bool WideningReferenceConversionExists (EmitContext ec, Expression expr, Type target_type)
 284                 {
 285                         Type expr_type = expr.Type;
 286
 287                         if (expr_type.IsGenericParameter)
 288                                 return ImplicitTypeParameterConversion (ec, expr, target_type) != null;
 289
 290                         //
 291                         // This is the boxed case.
 292                         //
 293                         if (target_type == TypeManager.object_type) {
 294                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 295                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 296                                         if (target_type != TypeManager.anonymous_method_type)
 297                                         return true;
 298
 299                                 return false;
 300                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 301                                 return true;
 302
 303                         // Please remember that all code below actually comes
 304                         // from WideningReferenceConversion so make sure code remains in sync
 305
 306                         // from any class-type S to any interface-type T.
 307                         if (target_type.IsInterface) {
 308                                 if (target_type != TypeManager.iconvertible_type &&
 309                                     expr_type.IsValueType && (expr is Constant) &&
 310                                     !(expr is IntLiteral || expr is BoolLiteral ||
 311                                       expr is FloatLiteral || expr is DoubleLiteral ||
 312                                       expr is LongLiteral || expr is CharLiteral ||
 313                                       expr is StringLiteral || expr is DecimalLiteral ||
 314                                       expr is UIntLiteral || expr is ULongLiteral)) {
 315                                         return false;
 316                                 }
 317
 318                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 319                                         return true;
 320                         }
 321
 322                         // from any interface type S to interface-type T.
 323                         if (expr_type.IsInterface && target_type.IsInterface)
 324                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 325                                         return true;
 326
 327                         // from an array-type S to an array-type of type T
 328                         if (expr_type.IsArray && target_type.IsArray) {
 329                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 330
 331                                         Type expr_element_type = expr_type.GetElementType ();
 332
 333                                         if (MyEmptyExpr == null)
 334                                                 MyEmptyExpr = new EmptyExpression ();
 335
 336                                         MyEmptyExpr.SetType (expr_element_type);
 337                                         Type target_element_type = TypeManager.GetElementType (target_type);
 338
 339                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 340                                                 if (WideningStandardConversionExists (ConstantEC, MyEmptyExpr,
 341                                                                                       target_element_type))
 342                                                         return true;
 343                                 }
 344                         }
 345
 346                         // from an array-type to System.Array
 347                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 348                                 return true;
 349
 350                         // from any delegate type to System.Delegate
 351                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 352                             target_type == TypeManager.delegate_type)
 353                                 if (target_type.IsAssignableFrom (expr_type))
 354                                         return true;
 355
 356                         // from any array-type or delegate type into System.ICloneable.
 357                         if (expr_type.IsArray ||
 358                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 359                                 if (target_type == TypeManager.icloneable_type)
 360                                         return true;
 361
 362                         // from the null type to any reference-type.
 363                         if (expr_type == TypeManager.null_type){
 364                                 if (target_type.IsPointer)
 365                                         return true;
 366
 367                                 if (!target_type.IsValueType)
 368                                         return true;
 369                         }
 370
 371                         // from a generic type definition to a generic instance.
 372                         if (TypeManager.IsEqual (expr_type, target_type))
 373                                 return true;
 374
 375                         return false;
 376                 }
 377
 378                 /// <summary>
 379                 ///   Implicit Numeric Conversions.
 380                 ///
 381                 ///   expr is the expression to convert, returns a new expression of type
 382                 ///   target_type or null if an implicit conversion is not possible.
 383                 /// </summary>
 384
 385                 static public Expression WideningNumericConversion (EmitContext ec, Expression expr,
 386                                                                     Type target_type, Location loc)
 387                 {
 388                         Type expr_type = expr.Type;
 389
 390                         //
 391                         // Attempt to do the implicit constant expression conversions
 392
 393                         if (expr is Constant){
 394                                 if (expr is IntConstant){
 395                                         Expression e;
 396
 397                                         e = TryWideningIntConversion (target_type, (IntConstant) expr);
 398
 399                                         if (e != null)
 400                                                 return e;
 401                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 402                                         //
 403                                         // Try the implicit constant expression conversion
 404                                         // from long to ulong, instead of a nice routine,
 405                                         // we just inline it
 406                                         //
 407                                         long v = ((LongConstant) expr).Value;
 408                                         if (v >= 0)
 409                                                 return new ULongConstant ((ulong) v);
 410                                 }
 411                         }
 412
 413                         Type real_target_type = target_type;
 414
 415                          if (expr_type == TypeManager.byte_type){
 416                                 //
 417                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 418                                 //
 419                                 if ((real_target_type == TypeManager.short_type) ||
 420                                     (real_target_type == TypeManager.int32_type))
 421                                         return new EmptyCast (expr, target_type);
 422
 423                                 if (real_target_type == TypeManager.int64_type)
 424                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 425                                 if (real_target_type == TypeManager.float_type)
 426                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 427                                 if (real_target_type == TypeManager.double_type)
 428                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 429                                 if (real_target_type == TypeManager.decimal_type)
 430                                         return new ImplicitNew (ec, "System", "Decimal", loc, expr);
 431                         } else if (expr_type == TypeManager.short_type){
 432                                 //
 433                                 // From short to int, long, float, double
 434                                 //
 435                                 if (real_target_type == TypeManager.int32_type)
 436                                         return new EmptyCast (expr, target_type);
 437                                 if (real_target_type == TypeManager.int64_type)
 438                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 439                                 if (real_target_type == TypeManager.double_type)
 440                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 441                                 if (real_target_type == TypeManager.float_type)
 442                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 443                                 if (real_target_type == TypeManager.decimal_type)
 444                                         return new ImplicitNew (ec, "System", "Decimal", loc, expr);
 445                         } else if (expr_type == TypeManager.int32_type){
 446                                 //
 447                                 // From int to long, float, double
 448                                 //
 449                                 if (real_target_type == TypeManager.int64_type)
 450                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 451                                 if (real_target_type == TypeManager.double_type)
 452                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 453                                 if (real_target_type == TypeManager.float_type)
 454                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 455                                 if (real_target_type == TypeManager.decimal_type)
 456                                         return new ImplicitNew (ec, "System", "Decimal", loc, expr);
 457                         } else if (expr_type == TypeManager.int64_type){
 458                                 //
 459                                 // From long/ulong to float, double
 460                                 //
 461                                 if (real_target_type == TypeManager.double_type)
 462                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 463                                 if (real_target_type == TypeManager.float_type)
 464                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 465                                 if (real_target_type == TypeManager.decimal_type)
 466                                         return new ImplicitNew (ec, "System", "Decimal", loc, expr);
 467                         } else if (expr_type == TypeManager.decimal_type){
 468                                 //
 469                                 // From decimal to float, double
 470                                 //
 471                                 if (real_target_type == TypeManager.double_type)
 472                                         return new ImplicitInvocation (ec, "System", "Convert", "ToDouble", loc, expr);
 473                                 if (real_target_type == TypeManager.float_type)
 474                                         return new ImplicitInvocation (ec, "System", "Convert" ,"ToSingle", loc, expr);
 475                         } else if (expr_type == TypeManager.float_type){
 476                                 //
 477                                 // float to double
 478                                 //
 479                                 if (real_target_type == TypeManager.double_type)
 480                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 481                         }
 482
 483                         return null;
 484                 }
 485
 486
 487                 /// <summary>
 488                 ///  Same as WideningStandardConversionExists except that it also looks at
 489                 ///  implicit user defined conversions - needed for overload resolution
 490                 /// </summary>
 491                 public static bool WideningConversionExists (EmitContext ec, Expression expr, Type target_type)
 492                 {
 493                         if (expr is NullLiteral) {
 494                                 if (target_type.IsGenericParameter)
 495                                         return TypeParameter_to_Null (target_type);
 496
 497                                 if (TypeManager.IsNullableType (target_type))
 498                                         return true;
 499                         }
 500
 501                         if (WideningStandardConversionExists (ec, expr, target_type))
 502                                 return true;
 503
 504                         //
 505                         // VB.NET has no notion of User defined conversions
 506                         //
 507
 508 //                      Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);
 509
 510 //                      if (dummy != null)
 511 //                              return true;
 512
 513                         return false;
 514                 }
 515
 516                 //
 517                 // VB.NET has no notion of User defined conversions
 518                 //
 519
 520 //              public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 521 //              {
 522 //                      Expression dummy = ImplicitUserConversion (
 523 //                              ec, new EmptyExpression (source), target, Location.Null);
 524 //                      return dummy != null;
 525 //              }
 526
 527                 /// <summary>
 528                 ///  Determines if a standard implicit conversion exists from
 529                 ///  expr_type to target_type
 530                 ///
 531                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 532                 /// </summary>
 533                 public static bool WideningStandardConversionExists (EmitContext ec, Expression expr, Type target_type)
 534                 {
 535                         Type expr_type = expr.Type;
 536
 537                         if (expr_type == TypeManager.void_type)
 538                                 return false;
 539
 540                         //Console.WriteLine ("Expr is {0}", expr);
 541                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 542                         if (expr_type.Equals (target_type))
 543                                 return true;
 544
 545
 546                         // First numeric conversions
 547
 548                         if (expr_type == TypeManager.sbyte_type){
 549                                 //
 550                                 // From sbyte to short, int, long, float, double.
 551                                 //
 552                                 if ((target_type == TypeManager.int32_type) ||
 553                                     (target_type == TypeManager.int64_type) ||
 554                                     (target_type == TypeManager.double_type) ||
 555                                     (target_type == TypeManager.float_type)  ||
 556                                     (target_type == TypeManager.short_type) ||
 557                                     (target_type == TypeManager.decimal_type))
 558                                         return true;
 559
 560                         } else if (expr_type == TypeManager.byte_type){
 561                                 //
 562                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 563                                 //
 564                                 if ((target_type == TypeManager.short_type) ||
 565                                     (target_type == TypeManager.ushort_type) ||
 566                                     (target_type == TypeManager.int32_type) ||
 567                                     (target_type == TypeManager.uint32_type) ||
 568                                     (target_type == TypeManager.uint64_type) ||
 569                                     (target_type == TypeManager.int64_type) ||
 570                                     (target_type == TypeManager.float_type) ||
 571                                     (target_type == TypeManager.double_type) ||
 572                                     (target_type == TypeManager.decimal_type))
 573                                         return true;
 574
 575                         } else if (expr_type == TypeManager.short_type){
 576                                 //
 577                                 // From short to int, long, float, double
 578                                 //
 579                                 if ((target_type == TypeManager.int32_type) ||
 580                                     (target_type == TypeManager.int64_type) ||
 581                                     (target_type == TypeManager.double_type) ||
 582                                     (target_type == TypeManager.float_type) ||
 583                                     (target_type == TypeManager.decimal_type))
 584                                         return true;
 585
 586                         } else if (expr_type == TypeManager.ushort_type){
 587                                 //
 588                                 // From ushort to int, uint, long, ulong, float, double
 589                                 //
 590                                 if ((target_type == TypeManager.uint32_type) ||
 591                                     (target_type == TypeManager.uint64_type) ||
 592                                     (target_type == TypeManager.int32_type) ||
 593                                     (target_type == TypeManager.int64_type) ||
 594                                     (target_type == TypeManager.double_type) ||
 595                                     (target_type == TypeManager.float_type) ||
 596                                     (target_type == TypeManager.decimal_type))
 597                                         return true;
 598
 599                         } else if (expr_type == TypeManager.int32_type){
 600                                 //
 601                                 // From int to long, float, double
 602                                 //
 603                                 if ((target_type == TypeManager.int64_type) ||
 604                                     (target_type == TypeManager.double_type) ||
 605                                     (target_type == TypeManager.float_type) ||
 606                                     (target_type == TypeManager.decimal_type))
 607                                         return true;
 608
 609                         } else if (expr_type == TypeManager.uint32_type){
 610                                 //
 611                                 // From uint to long, ulong, float, double
 612                                 //
 613                                 if ((target_type == TypeManager.int64_type) ||
 614                                     (target_type == TypeManager.uint64_type) ||
 615                                     (target_type == TypeManager.double_type) ||
 616                                     (target_type == TypeManager.float_type) ||
 617                                     (target_type == TypeManager.decimal_type))
 618                                         return true;
 619
 620                         } else if ((expr_type == TypeManager.uint64_type) ||
 621                                    (expr_type == TypeManager.int64_type)) {
 622                                 //
 623                                 // From long/ulong to float, double
 624                                 //
 625                                 if ((target_type == TypeManager.double_type) ||
 626                                     (target_type == TypeManager.float_type) ||
 627                                     (target_type == TypeManager.decimal_type))
 628                                         return true;
 629
 630                         } else if (expr_type == TypeManager.char_type){
 631                                 //
 632                                 // From char to ushort, int, uint, long, ulong, float, double
 633                                 //
 634                                 if ((target_type == TypeManager.ushort_type) ||
 635                                     (target_type == TypeManager.int32_type) ||
 636                                     (target_type == TypeManager.uint32_type) ||
 637                                     (target_type == TypeManager.uint64_type) ||
 638                                     (target_type == TypeManager.int64_type) ||
 639                                     (target_type == TypeManager.float_type) ||
 640                                     (target_type == TypeManager.double_type) ||
 641                                     (target_type == TypeManager.decimal_type))
 642                                         return true;
 643
 644                         } else if (expr_type == TypeManager.float_type){
 645                                 //
 646                                 // float to double
 647                                 //
 648                                 if (target_type == TypeManager.double_type)
 649                                         return true;
 650                         }
 651
 652                         if (expr.eclass == ExprClass.MethodGroup){
 653                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
 654                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 655                                         if (mg != null){
 656                                                 //
 657                                                 // This should not happen frequently, so we can create an object
 658                                                 // to test compatibility
 659                                                 //
 660                                                 Expression c = ImplicitDelegateCreation.Create (ec, mg, target_type, Location.Null);
 661                                                 return c != null;
 662                                         }
 663                                 }
 664                         }
 665
 666                         if (WideningReferenceConversionExists (ec, expr, target_type))
 667                                 return true;
 668
 669                         //
 670                         // Implicit Constant Expression Conversions
 671                         //
 672                         if (expr is IntConstant){
 673                                 int value = ((IntConstant) expr).Value;
 674
 675                                 if (target_type == TypeManager.sbyte_type){
 676                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 677                                                 return true;
 678                                 } else if (target_type == TypeManager.byte_type){
 679                                         if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
 680                                                 return true;
 681                                 } else if (target_type == TypeManager.short_type){
 682                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 683                                                 return true;
 684                                 } else if (target_type == TypeManager.ushort_type){
 685                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 686                                                 return true;
 687                                 } else if (target_type == TypeManager.uint32_type){
 688                                         if (value >= 0)
 689                                                 return true;
 690                                 } else if (target_type == TypeManager.uint64_type){
 691                                          //
 692                                          // we can optimize this case: a positive int32
 693                                          // always fits on a uint64.  But we need an opcode
 694                                          // to do it.
 695                                          //
 696                                         if (value >= 0)
 697                                                 return true;
 698                                 }
 699
 700                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 701                                         return true;
 702                         }
 703
 704                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 705                                 //
 706                                 // Try the implicit constant expression conversion
 707                                 // from long to ulong, instead of a nice routine,
 708                                 // we just inline it
 709                                 //
 710                                 long v = ((LongConstant) expr).Value;
 711                                 if (v > 0)
 712                                         return true;
 713                         }
 714
 715                         if ((target_type == TypeManager.enum_type ||
 716                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 717                              expr is IntLiteral){
 718                                 IntLiteral i = (IntLiteral) expr;
 719
 720                                 if (i.Value == 0)
 721                                         return true;
 722                         }
 723
 724                         //
 725                         // If `expr_type' implements `target_type' (which is an iface)
 726                         // see TryWideningIntConversion
 727                         //
 728                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 729                                 return true;
 730
 731                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 732                                 return true;
 733
 734                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
 735                                 return true;
 736
 737                         if (expr_type == TypeManager.anonymous_method_type){
 738                                 if (!TypeManager.IsDelegateType (target_type))
 739                                         return false;
 740
 741                                 AnonymousMethod am = (AnonymousMethod) expr;
 742
 743                                 Expression conv = am.Compatible (ec, target_type, true);
 744                                 if (conv != null)
 745                                         return true;
 746                         }
 747
 748                         return false;
 749                 }
 750
 751                 //
 752                 // Used internally by FindMostEncompassedType, this is used
 753                 // to avoid creating lots of objects in the tight loop inside
 754                 // FindMostEncompassedType
 755                 //
 756                 static EmptyExpression priv_fmet_param;
 757
 758                 /// <summary>
 759                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 760                 ///  amongst the methods in the MethodGroupExpr
 761                 /// </summary>
 762                 static Type FindMostEncompassedType (EmitContext ec, ArrayList types)
 763                 {
 764                         Type best = null;
 765
 766                         if (priv_fmet_param == null)
 767                                 priv_fmet_param = new EmptyExpression ();
 768
 769                         foreach (Type t in types){
 770                                 priv_fmet_param.SetType (t);
 771
 772                                 if (best == null) {
 773                                         best = t;
 774                                         continue;
 775                                 }
 776
 777                                 if (WideningStandardConversionExists (ec, priv_fmet_param, best))
 778                                         best = t;
 779                         }
 780
 781                         return best;
 782                 }
 783
 784                 //
 785                 // Used internally by FindMostEncompassingType, this is used
 786                 // to avoid creating lots of objects in the tight loop inside
 787                 // FindMostEncompassingType
 788                 //
 789                 static EmptyExpression priv_fmee_ret;
 790
 791                 /// <summary>
 792                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 793                 ///  amongst the types in the given set
 794                 /// </summary>
 795                 static Type FindMostEncompassingType (EmitContext ec, ArrayList types)
 796                 {
 797                         Type best = null;
 798
 799                         if (priv_fmee_ret == null)
 800                                 priv_fmee_ret = new EmptyExpression ();
 801
 802                         foreach (Type t in types){
 803                                 priv_fmee_ret.SetType (best);
 804
 805                                 if (best == null) {
 806                                         best = t;
 807                                         continue;
 808                                 }
 809
 810                                 if (WideningStandardConversionExists (ec, priv_fmee_ret, t))
 811                                         best = t;
 812                         }
 813
 814                         return best;
 815                 }
 816
 817                 //
 818                 // Used to avoid creating too many objects
 819                 //
 820                 static EmptyExpression priv_fms_expr;
 821
 822                 /// <summary>
 823                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 824                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 825                 ///   for explicit and implicit conversion operators.
 826                 /// </summary>
 827                 static public Type FindMostSpecificSource (EmitContext ec, MethodGroupExpr me,
 828                                                            Expression source, bool apply_explicit_conv_rules,
 829                                                            Location loc)
 830                 {
 831                         ArrayList src_types_set = new ArrayList ();
 832
 833                         if (priv_fms_expr == null)
 834                                 priv_fms_expr = new EmptyExpression ();
 835
 836                         //
 837                         // If any operator converts from S then Sx = S
 838                         //
 839                         Type source_type = source.Type;
 840                         foreach (MethodBase mb in me.Methods){
 841                                 ParameterData pd = Invocation.GetParameterData (mb);
 842                                 Type param_type = pd.ParameterType (0);
 843
 844                                 if (param_type == source_type)
 845                                         return param_type;
 846
 847                                 if (apply_explicit_conv_rules) {
 848                                         //
 849                                         // From the spec :
 850                                         // Find the set of applicable user-defined conversion operators, U.  This set
 851                                         // consists of the
 852                                         // user-defined implicit or explicit conversion operators declared by
 853                                         // the classes or structs in D that convert from a type encompassing
 854                                         // or encompassed by S to a type encompassing or encompassed by T
 855                                         //
 856                                         priv_fms_expr.SetType (param_type);
 857                                         if (WideningStandardConversionExists (ec, priv_fms_expr, source_type))
 858                                                 src_types_set.Add (param_type);
 859                                         else {
 860                                                 if (WideningStandardConversionExists (ec, source, param_type))
 861                                                         src_types_set.Add (param_type);
 862                                         }
 863                                 } else {
 864                                         //
 865                                         // Only if S is encompassed by param_type
 866                                         //
 867                                         if (WideningStandardConversionExists (ec, source, param_type))
 868                                                 src_types_set.Add (param_type);
 869                                 }
 870                         }
 871
 872                         //
 873                         // Explicit Conv rules
 874                         //
 875                         if (apply_explicit_conv_rules) {
 876                                 ArrayList candidate_set = new ArrayList ();
 877
 878                                 foreach (Type param_type in src_types_set){
 879                                         if (WideningStandardConversionExists (ec, source, param_type))
 880                                                 candidate_set.Add (param_type);
 881                                 }
 882
 883                                 if (candidate_set.Count != 0)
 884                                         return FindMostEncompassedType (ec, candidate_set);
 885                         }
 886
 887                         //
 888                         // Final case
 889                         //
 890                         if (apply_explicit_conv_rules)
 891                                 return FindMostEncompassingType (ec, src_types_set);
 892                         else
 893                                 return FindMostEncompassedType (ec, src_types_set);
 894                 }
 895
 896                 //
 897                 // Useful in avoiding proliferation of objects
 898                 //
 899                 static EmptyExpression priv_fmt_expr;
 900
 901                 /// <summary>
 902                 ///  Finds the most specific target Tx according to section 13.4.4
 903                 /// </summary>
 904                 static public Type FindMostSpecificTarget (EmitContext ec, MethodGroupExpr me,
 905                                                            Type target, bool apply_explicit_conv_rules,
 906                                                            Location loc)
 907                 {
 908                         ArrayList tgt_types_set = new ArrayList ();
 909
 910                         if (priv_fmt_expr == null)
 911                                 priv_fmt_expr = new EmptyExpression ();
 912
 913                         //
 914                         // If any operator converts to T then Tx = T
 915                         //
 916                         foreach (MethodInfo mi in me.Methods){
 917                                 Type ret_type = mi.ReturnType;
 918
 919                                 if (ret_type == target)
 920                                         return ret_type;
 921
 922                                 if (apply_explicit_conv_rules) {
 923                                         //
 924                                         // From the spec :
 925                                         // Find the set of applicable user-defined conversion operators, U.
 926                                         //
 927                                         // This set consists of the
 928                                         // user-defined implicit or explicit conversion operators declared by
 929                                         // the classes or structs in D that convert from a type encompassing
 930                                         // or encompassed by S to a type encompassing or encompassed by T
 931                                         //
 932                                         priv_fms_expr.SetType (ret_type);
 933                                         if (WideningStandardConversionExists (ec, priv_fms_expr, target))
 934                                                 tgt_types_set.Add (ret_type);
 935                                         else {
 936                                                 priv_fms_expr.SetType (target);
 937                                                 if (WideningStandardConversionExists (ec, priv_fms_expr, ret_type))
 938                                                         tgt_types_set.Add (ret_type);
 939                                         }
 940                                 } else {
 941                                         //
 942                                         // Only if T is encompassed by param_type
 943                                         //
 944                                         priv_fms_expr.SetType (ret_type);
 945                                         if (WideningStandardConversionExists (ec, priv_fms_expr, target))
 946                                                 tgt_types_set.Add (ret_type);
 947                                 }
 948                         }
 949
 950                         //
 951                         // Explicit conv rules
 952                         //
 953                         if (apply_explicit_conv_rules) {
 954                                 ArrayList candidate_set = new ArrayList ();
 955
 956                                 foreach (Type ret_type in tgt_types_set){
 957                                         priv_fmt_expr.SetType (ret_type);
 958
 959                                         if (WideningStandardConversionExists (ec, priv_fmt_expr, target))
 960                                                 candidate_set.Add (ret_type);
 961                                 }
 962
 963                                 if (candidate_set.Count != 0)
 964                                         return FindMostEncompassingType (ec, candidate_set);
 965                         }
 966
 967                         //
 968                         // Okay, final case !
 969                         //
 970                         if (apply_explicit_conv_rules)
 971                                 return FindMostEncompassedType (ec, tgt_types_set);
 972                         else
 973                                 return FindMostEncompassingType (ec, tgt_types_set);
 974                 }
 975
 976                 /// <summary>
 977                 ///  User-defined Implicit conversions
 978                 /// </summary>
 979
 980                 //
 981                 // VB.NET has no notion of User defined conversions
 982                 //
 983
 984 //              static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
 985 //                                                               Type target, Location loc)
 986 //              {
 987 //                      return UserDefinedConversion (ec, source, target, loc, false);
 988 //              }
 989
 990                 /// <summary>
 991                 ///  User-defined Explicit conversions
 992                 /// </summary>
 993
 994                 //
 995                 // VB.NET has no notion of User defined conversions
 996                 //
 997
 998 //              static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
 999 //                                                               Type target, Location loc)
1000 //              {
1001 //                      return UserDefinedConversion (ec, source, target, loc, true);
1002 //              }
1003
1004                 static DoubleHash explicit_conv = new DoubleHash (100);
1005                 static DoubleHash implicit_conv = new DoubleHash (100);
1006                 /// <summary>
1007                 ///   Computes the MethodGroup for the user-defined conversion
1008                 ///   operators from source_type to target_type.  `look_for_explicit'
1009                 ///   controls whether we should also include the list of explicit
1010                 ///   operators
1011                 /// </summary>
1012                 static MethodGroupExpr GetConversionOperators (EmitContext ec,
1013                                                                Type source_type, Type target_type,
1014                                                                Location loc, bool look_for_explicit)
1015                 {
1016                         Expression mg1 = null, mg2 = null;
1017                         Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
1018                         string op_name;
1019
1020                         op_name = "op_Implicit";
1021
1022                         MethodGroupExpr union3;
1023                         object r;
1024                         if ((look_for_explicit ? explicit_conv : implicit_conv).Lookup (source_type, target_type, out r))
1025                                 return (MethodGroupExpr) r;
1026
1027                         mg1 = Expression.MethodLookup (ec, source_type, op_name, loc);
1028                         if (source_type.BaseType != null)
1029                                 mg2 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1030
1031                         if (mg1 == null)
1032                                 union3 = (MethodGroupExpr) mg2;
1033                         else if (mg2 == null)
1034                                 union3 = (MethodGroupExpr) mg1;
1035                         else
1036                                 union3 = Invocation.MakeUnionSet (mg1, mg2, loc);
1037
1038                         mg1 = Expression.MethodLookup (ec, target_type, op_name, loc);
1039                         if (mg1 != null){
1040                                 if (union3 != null)
1041                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1042                                 else
1043                                         union3 = (MethodGroupExpr) mg1;
1044                         }
1045
1046                         if (target_type.BaseType != null)
1047                                 mg1 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1048
1049                         if (mg1 != null){
1050                                 if (union3 != null)
1051                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1052                                 else
1053                                         union3 = (MethodGroupExpr) mg1;
1054                         }
1055
1056                         MethodGroupExpr union4 = null;
1057
1058                         if (look_for_explicit) {
1059                                 op_name = "op_Explicit";
1060
1061                                 mg5 = Expression.MemberLookup (ec, source_type, op_name, loc);
1062                                 if (source_type.BaseType != null)
1063                                         mg6 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1064
1065                                 mg7 = Expression.MemberLookup (ec, target_type, op_name, loc);
1066                                 if (target_type.BaseType != null)
1067                                         mg8 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1068
1069                                 MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
1070                                 MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);
1071
1072                                 union4 = Invocation.MakeUnionSet (union5, union6, loc);
1073                         }
1074
1075                         MethodGroupExpr ret = Invocation.MakeUnionSet (union3, union4, loc);
1076                         (look_for_explicit ? explicit_conv : implicit_conv).Insert (source_type, target_type, ret);
1077                         return ret;
1078                 }
1079
1080                 /// <summary>
1081                 ///   User-defined conversions
1082                 /// </summary>
1083
1084                 //
1085                 // VB.NET has no notion of User defined conversions. This method is not used.
1086                 //
1087                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1088                                                                 Type target, Location loc,
1089                                                                 bool look_for_explicit)
1090                 {
1091                         MethodGroupExpr union;
1092                         Type source_type = source.Type;
1093                         MethodBase method = null;
1094
1095                         union = GetConversionOperators (ec, source_type, target, loc, look_for_explicit);
1096                         if (union == null)
1097                                 return null;
1098
1099                         Type most_specific_source, most_specific_target;
1100
1101                         most_specific_source = FindMostSpecificSource (ec, union, source, look_for_explicit, loc);
1102                         if (most_specific_source == null)
1103                                 return null;
1104
1105                         most_specific_target = FindMostSpecificTarget (ec, union, target, look_for_explicit, loc);
1106                         if (most_specific_target == null)
1107                                 return null;
1108
1109                         int count = 0;
1110
1111
1112                         foreach (MethodBase mb in union.Methods){
1113                                 ParameterData pd = Invocation.GetParameterData (mb);
1114                                 MethodInfo mi = (MethodInfo) mb;
1115
1116                                 if (pd.ParameterType (0) == most_specific_source &&
1117                                     mi.ReturnType == most_specific_target) {
1118                                         method = mb;
1119                                         count++;
1120                                 }
1121                         }
1122
1123                         if (method == null || count > 1)
1124                                 return null;
1125
1126
1127                         //
1128                         // This will do the conversion to the best match that we
1129                         // found.  Now we need to perform an implict standard conversion
1130                         // if the best match was not the type that we were requested
1131                         // by target.
1132                         //
1133                         if (look_for_explicit)
1134                                 source = WideningAndNarrowingConversionStandard (ec, source, most_specific_source, loc);
1135                         else
1136                                 source = WideningConversionStandard (ec, source, most_specific_source, loc);
1137
1138                         if (source == null)
1139                                 return null;
1140
1141                         Expression e;
1142                         e =  new UserCast ((MethodInfo) method, source, loc);
1143                         if (e.Type != target){
1144                                 if (!look_for_explicit)
1145                                         e = WideningConversionStandard (ec, e, target, loc);
1146                                 else
1147                                         e = WideningAndNarrowingConversionStandard (ec, e, target, loc);
1148                         }
1149
1150                         return e;
1151                 }
1152
1153                 /// <summary>
1154                 ///   Converts implicitly the resolved expression `expr' into the
1155                 ///   `target_type'.  It returns a new expression that can be used
1156                 ///   in a context that expects a `target_type'.
1157                 /// </summary>
1158                 static public Expression WideningConversion (EmitContext ec, Expression expr,
1159                                                              Type target_type, Location loc)
1160                 {
1161                         Expression e;
1162
1163                         if (target_type == null)
1164                                 throw new Exception ("Target type is null");
1165
1166                         e = WideningConversionStandard (ec, expr, target_type, loc);
1167                         if (e != null)
1168                                 return e;
1169
1170                         //
1171                         // VB.NET has no notion of User defined conversions
1172                         //
1173
1174 //                      e = ImplicitUserConversion (ec, expr, target_type, loc);
1175 //                      if (e != null)
1176 //                              return e;
1177
1178                         return null;
1179                 }
1180
1181
1182                 /// <summary>
1183                 ///   Attempts to apply the `Standard Implicit
1184                 ///   Conversion' rules to the expression `expr' into
1185                 ///   the `target_type'.  It returns a new expression
1186                 ///   that can be used in a context that expects a
1187                 ///   `target_type'.
1188                 ///
1189                 ///   This is different from `WideningConversion' in that the
1190                 ///   user defined implicit conversions are excluded.
1191                 /// </summary>
1192                 static public Expression WideningConversionStandard (EmitContext ec, Expression expr,
1193                                                                      Type target_type, Location loc)
1194                 {
1195                         Type expr_type = expr.Type;
1196                         Expression e;
1197
1198                         if (expr is NullLiteral) {
1199                                 if (target_type.IsGenericParameter)
1200                                         return TypeParameter_to_Null (expr, target_type, loc);
1201
1202                                 if (TypeManager.IsNullableType (target_type))
1203                                         return new Nullable.NullLiteral (target_type, loc);
1204                         }
1205
1206                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1207                                 return Nullable.LiftedConversion.Create (ec, expr, target_type, false, loc);
1208
1209                         if (expr.eclass == ExprClass.MethodGroup){
1210                                 if (!TypeManager.IsDelegateType (target_type)){
1211                                         return null;
1212                                 }
1213
1214                                 //
1215                                 // Only allow anonymous method conversions on post ISO_1
1216                                 //
1217                                 if (RootContext.Version != LanguageVersion.ISO_1){
1218                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1219                                         if (mg != null)
1220                                                 return ImplicitDelegateCreation.Create (ec, mg, target_type, loc);
1221                                 }
1222                         }
1223
1224                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1225                                 return expr;
1226
1227                         e = WideningNumericConversion (ec, expr, target_type, loc);
1228                         if (e != null)
1229                                 return e;
1230
1231                         e = WideningReferenceConversion (ec, expr, target_type);
1232                         if (e != null)
1233                                 return e;
1234
1235                         if ((target_type == TypeManager.enum_type ||
1236                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1237                             expr is IntLiteral){
1238                                 IntLiteral i = (IntLiteral) expr;
1239
1240                                 if (i.Value == 0)
1241                                         return new EnumConstant ((Constant) expr, target_type);
1242                         }
1243
1244                         if (ec.InUnsafe) {
1245                                 if (expr_type.IsPointer){
1246                                         if (target_type == TypeManager.void_ptr_type)
1247                                                 return new EmptyCast (expr, target_type);
1248
1249                                         //
1250                                         // yep, comparing pointer types cant be done with
1251                                         // t1 == t2, we have to compare their element types.
1252                                         //
1253                                         if (target_type.IsPointer){
1254                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1255                                                         return expr;
1256                                         }
1257                                 }
1258
1259                                 if (target_type.IsPointer) {
1260                                         if (expr_type == TypeManager.null_type)
1261                                                 return new EmptyCast (expr, target_type);
1262
1263                                         if (expr_type == TypeManager.void_ptr_type)
1264                                                 return new EmptyCast (expr, target_type);
1265                                 }
1266                         }
1267
1268                         if (expr_type == TypeManager.anonymous_method_type){
1269                                 if (!TypeManager.IsDelegateType (target_type)){
1270                                         Report.Error (1660, loc,
1271                                                               "Cannot convert anonymous method to `{0}', since it is not a delegate",
1272                                                               TypeManager.CSharpName (target_type));
1273                                         return null;
1274                                 }
1275
1276                                 AnonymousMethod am = (AnonymousMethod) expr;
1277                                 int errors = Report.Errors;
1278
1279                                 Expression conv = am.Compatible (ec, target_type, false);
1280                                 if (conv != null)
1281                                         return conv;
1282
1283                                 //
1284                                 // We return something instead of null, to avoid
1285                                 // the duplicate error, since am.Compatible would have
1286                                 // reported that already
1287                                 //
1288                                 if (errors != Report.Errors)
1289                                         return new EmptyCast (expr, target_type);
1290                         }
1291
1292                         //
1293                         // VB.NET specific conversions
1294                         //
1295
1296                         e = WideningStringConversions (ec, expr, target_type, loc);
1297                         if (e != null)
1298                                 return e;
1299
1300
1301                         return null;
1302                 }
1303
1304                 /// <summary>
1305                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1306                 ///   into a different data type using casts (See Implicit Constant
1307                 ///   Expression Conversions)
1308                 /// </summary>
1309                 static public Expression TryWideningIntConversion (Type target_type, IntConstant ic)
1310                 {
1311                         int value = ic.Value;
1312
1313                         if (target_type == TypeManager.sbyte_type){
1314                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1315                                         return new SByteConstant ((sbyte) value);
1316                         } else if (target_type == TypeManager.byte_type){
1317                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1318                                         return new ByteConstant ((byte) value);
1319                         } else if (target_type == TypeManager.short_type){
1320                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1321                                         return new ShortConstant ((short) value);
1322                         } else if (target_type == TypeManager.ushort_type){
1323                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1324                                         return new UShortConstant ((ushort) value);
1325                         } else if (target_type == TypeManager.uint32_type){
1326                                 if (value >= 0)
1327                                         return new UIntConstant ((uint) value);
1328                         } else if (target_type == TypeManager.uint64_type){
1329                                 //
1330                                 // we can optimize this case: a positive int32
1331                                 // always fits on a uint64.  But we need an opcode
1332                                 // to do it.
1333                                 //
1334                                 if (value >= 0)
1335                                         return new ULongConstant ((ulong) value);
1336                         } else if (target_type == TypeManager.double_type)
1337                                 return new DoubleConstant ((double) value);
1338                         else if (target_type == TypeManager.float_type)
1339                                 return new FloatConstant ((float) value);
1340
1341                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1342                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1343                                 Constant e = (Constant) ic;
1344
1345                                 //
1346                                 // Possibly, we need to create a different 0 literal before passing
1347                                 // to EnumConstant
1348                                 //
1349                                 if (underlying == TypeManager.int64_type)
1350                                         e = new LongLiteral (0);
1351                                 else if (underlying == TypeManager.uint64_type)
1352                                         e = new ULongLiteral (0);
1353
1354                                 return new EnumConstant (e, target_type);
1355                         }
1356
1357                         //
1358                         // If `target_type' is an interface and the type of `ic' implements the interface
1359                         // e.g. target_type is IComparable, IConvertible, IFormattable
1360                         //
1361                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1362                                 return new BoxedCast (ic);
1363
1364                         return null;
1365                 }
1366
1367                 static public void Error_CannotWideningConversion (Location loc, Type source, Type target)
1368                 {
1369                         if (source.Name == target.Name){
1370                                 Report.ExtraInformation (loc,
1371                                          String.Format (
1372                                                 "The type {0} has two conflicting definitons, one comes from {0} and the other from {1}",
1373                                                 source.Assembly.FullName, target.Assembly.FullName));
1374
1375                         }
1376                         Report.Error (29, loc, "Cannot convert implicitly from {0} to `{1}'",
1377                                       source == TypeManager.anonymous_method_type ?
1378                                       "anonymous method" : "`" + TypeManager.CSharpName (source) + "'",
1379                                       TypeManager.CSharpName (target));
1380                 }
1381
1382                 /// <summary>
1383                 ///   Attempts to implicitly convert `source' into `target_type', using
1384                 ///   WideningConversion.  If there is no implicit conversion, then
1385                 ///   an error is signaled
1386                 /// </summary>
1387                 static public Expression WideningConversionRequired (EmitContext ec, Expression source,
1388                                                                      Type target_type, Location loc)
1389                 {
1390                         Expression e;
1391
1392                         int errors = Report.Errors;
1393                         e = WideningConversion (ec, source, target_type, loc);
1394                         if (Report.Errors > errors)
1395                                 return null;
1396                         if (e != null)
1397                                 return e;
1398
1399                         if (source is DoubleLiteral) {
1400                                 if (target_type == TypeManager.float_type) {
1401                                         Error_664 (loc, "float", "f");
1402                                         return null;
1403                                 }
1404                                 if (target_type == TypeManager.decimal_type) {
1405                                         Error_664 (loc, "decimal", "m");
1406                                         return null;
1407                                 }
1408                         }
1409
1410                         if (source is Constant){
1411                                 Constant c = (Constant) source;
1412
1413                                 Expression.Error_ConstantValueCannotBeConverted (loc, c.AsString (), target_type);
1414                                 return null;
1415                         }
1416
1417                         Error_CannotWideningConversion (loc, source.Type, target_type);
1418
1419                         return null;
1420                 }
1421
1422                 static void Error_664 (Location loc, string type, string suffix) {
1423                         Report.Error (664, loc,
1424                                 "Literal of type double cannot be implicitly converted to type '{0}'. Add suffix '{1}' to create a literal of this type",
1425                                 type, suffix);
1426                 }
1427
1428                 /// <summary>
1429                 ///   Performs the explicit numeric conversions
1430                 /// </summary>
1431
1432                 /// <summary>
1433                 ///   Performs the explicit numeric conversions
1434                 /// </summary>
1435                 static Expression NarrowingNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
1436                 {
1437                         Type expr_type = expr.Type;
1438
1439                         //
1440                         // If we have an enumeration, extract the underlying type,
1441                         // use this during the comparison, but wrap around the original
1442                         // target_type
1443                         //
1444                         Type real_target_type = target_type;
1445
1446                         if (TypeManager.IsEnumType (real_target_type))
1447                                 real_target_type = TypeManager.EnumToUnderlying (real_target_type);
1448
1449                         if (WideningStandardConversionExists (ec, expr, real_target_type)){
1450                                 Expression ce = WideningConversionStandard (ec, expr, real_target_type, loc);
1451
1452                                 if (real_target_type != target_type)
1453                                         return new EmptyCast (ce, target_type);
1454                                 return ce;
1455                         }
1456
1457                         if (expr_type == TypeManager.short_type){
1458                                 //
1459                                 // From short to byte
1460                                 //
1461                                 if (real_target_type == TypeManager.byte_type)
1462                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
1463                         } else if (expr_type == TypeManager.int32_type){
1464                                 //
1465                                 // From int to byte, short
1466                                 //
1467                                 if (real_target_type == TypeManager.byte_type)
1468                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
1469                                 if (real_target_type == TypeManager.short_type)
1470                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
1471                         } else if (expr_type == TypeManager.int64_type){
1472                                 //
1473                                 // From long to byte, short, int
1474                                 //
1475                                 if (real_target_type == TypeManager.byte_type)
1476                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
1477                                 if (real_target_type == TypeManager.short_type)
1478                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
1479                                 if (real_target_type == TypeManager.int32_type)
1480                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
1481                         } else if (expr_type == TypeManager.decimal_type){
1482                                 //
1483                                 // From decimal to byte, short, int, long
1484                                 //
1485                                 if (real_target_type == TypeManager.byte_type)
1486                                         return new ImplicitInvocation (ec, "System", "Convert" , "ToByte", loc, expr);
1487                                 if (real_target_type == TypeManager.short_type)
1488                                         return new ImplicitInvocation (ec, "System", "Convert", "ToInt16", loc, expr);
1489                                 if (real_target_type == TypeManager.int32_type)
1490                                         return new ImplicitInvocation (ec, "System", "Convert", "ToInt32", loc, expr);
1491                                 if (real_target_type == TypeManager.int64_type)
1492                                         return new ImplicitInvocation (ec, "System", "Convert", "ToInt64", loc, expr);
1493                         } else if (expr_type == TypeManager.float_type){
1494                                 //
1495                                 // From float to byte, short, int, long, decimal
1496                                 //
1497                                 if (real_target_type == TypeManager.byte_type)
1498                                         return new FloatingToFixedCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1499                                 if (real_target_type == TypeManager.short_type)
1500                                         return new FloatingToFixedCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1501                                 if (real_target_type == TypeManager.int32_type)
1502                                         return new FloatingToFixedCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1503                                 if (real_target_type == TypeManager.int64_type)
1504                                         return new FloatingToFixedCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1505                                 if (real_target_type == TypeManager.decimal_type)
1506                                         return new ImplicitNew (ec, "System", "Decimal", loc, expr);
1507                         } else if (expr_type == TypeManager.double_type){
1508                                 //
1509                                 // From double to byte, short, int, long, float, decimal
1510                                 //
1511                                 if (real_target_type == TypeManager.byte_type)
1512                                         return new FloatingToFixedCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1513                                 if (real_target_type == TypeManager.short_type)
1514                                         return new FloatingToFixedCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1515                                 if (real_target_type == TypeManager.int32_type)
1516                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1517                                 if (real_target_type == TypeManager.int64_type)
1518                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1519                                 if (real_target_type == TypeManager.float_type)
1520                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
1521                                 if (real_target_type == TypeManager.decimal_type)
1522                                         return new ImplicitNew (ec, "System", "Decimal", loc, expr);
1523                         }
1524
1525                         return null;
1526                 }
1527
1528                 /// <summary>
1529                 /// VB.NET specific: Convert to and from boolean
1530                 /// </summary>
1531
1532                 static public Expression BooleanConversions (EmitContext ec, Expression expr,
1533                                                                     Type target_type, Location loc)
1534                 {
1535                         Type expr_type = expr.Type;
1536                         Type real_target_type = target_type;
1537
1538                         if (expr_type == TypeManager.bool_type) {
1539
1540                                 //
1541                                 // From boolean to byte, short, int,
1542                                 // long, float, double, decimal
1543                                 //
1544
1545                                 if (real_target_type == TypeManager.byte_type)
1546                                         return new BooleanToNumericCast (expr, target_type, OpCodes.Conv_U1);
1547                                 if (real_target_type == TypeManager.short_type)
1548                                         return new BooleanToNumericCast (expr, target_type, OpCodes.Conv_I2);
1549                                 if (real_target_type == TypeManager.int32_type)
1550                                         return new BooleanToNumericCast (expr, target_type, OpCodes.Conv_I4);
1551                                 if (real_target_type == TypeManager.int64_type)
1552                                         return new BooleanToNumericCast (expr, target_type, OpCodes.Conv_I8);
1553                                 if (real_target_type == TypeManager.float_type)
1554                                         return new BooleanToNumericCast (expr, target_type, OpCodes.Conv_R4);
1555                                 if (real_target_type == TypeManager.double_type)
1556                                         return new BooleanToNumericCast (expr, target_type, OpCodes.Conv_R8);
1557                                 if (real_target_type == TypeManager.decimal_type) {
1558                                         return new ImplicitInvocation (ec, "DecimalType", "FromBoolean", loc, expr);
1559                                 }
1560                         } if (real_target_type == TypeManager.bool_type) {
1561
1562                                 //
1563                                 // From byte, short, int, long, float,
1564                                 // double, decimal to boolean
1565                                 //
1566
1567                                 if (expr_type == TypeManager.byte_type ||
1568                                         expr_type == TypeManager.short_type ||
1569                                         expr_type == TypeManager.int32_type ||
1570                                         expr_type == TypeManager.int64_type ||
1571                                         expr_type == TypeManager.float_type ||
1572                                         expr_type == TypeManager.double_type)
1573                                                 return new NumericToBooleanCast (expr, expr_type);
1574                                 if (expr_type == TypeManager.decimal_type) {
1575                                         return new ImplicitInvocation (ec, "System", "Convert", "ToBoolean", loc, expr);
1576                                 }
1577                         }
1578
1579                         return null;
1580                 }
1581
1582                 /// <summary>
1583                 /// VB.NET specific: Widening conversions to string
1584                 /// </summary>
1585
1586                 static public Expression WideningStringConversions (EmitContext ec, Expression expr,
1587                                                                     Type target_type, Location loc)
1588
1589                 {
1590                         Type expr_type = expr.Type;
1591                         Type real_target_type = target_type;
1592
1593                         if (real_target_type == TypeManager.string_type) {
1594                                 //
1595                                 // From char to string
1596                                 //
1597                                 if (expr_type == TypeManager.char_type)
1598                                         return new ImplicitInvocation (ec, "StringType", "FromChar", loc, expr);
1599                         }
1600
1601                         if(expr_type.IsArray && (expr_type.GetElementType() == TypeManager.char_type)) {
1602                                 //
1603                                 // From char array to string
1604                                 //
1605                                 return new ImplicitNew (ec, "System", "String", loc, expr);
1606                         }
1607
1608                         return null;
1609                 }
1610
1611                 /// <summary>
1612                 /// VB.NET specific: Narrowing conversions involving strings
1613                 /// </summary>
1614
1615                 static public Expression NarrowingStringConversions (EmitContext ec, Expression expr,
1616                                                                     Type target_type, Location loc)
1617                 {
1618                         Type expr_type = expr.Type;
1619                         Type real_target_type = target_type;
1620
1621                         // FIXME: Need to take care of Constants
1622
1623                         if (expr_type == TypeManager.string_type) {
1624
1625                                 //
1626                                 // From string to chararray, bool,
1627                                 // byte, short, char, int, long,
1628                                 // float, double, decimal and date
1629                                 //
1630
1631                                 if (real_target_type.IsArray && (real_target_type.GetElementType() == TypeManager.char_type))
1632                                         return new ImplicitInvocation (ec, "CharArrayType", "FromString", loc, expr);
1633                                 if (real_target_type == TypeManager.bool_type)
1634                                         return new ImplicitInvocation (ec, "BooleanType", "FromString", loc, expr);
1635                                 if (real_target_type == TypeManager.byte_type)
1636                                         return new ImplicitInvocation (ec, "ByteType", "FromString", loc, expr);
1637                                 if (real_target_type == TypeManager.short_type)
1638                                         return new ImplicitInvocation (ec, "ShortType", "FromString", loc, expr);
1639                                 if (real_target_type == TypeManager.char_type)
1640                                         return new ImplicitInvocation (ec, "CharType", "FromString", loc, expr);
1641                                 if (real_target_type == TypeManager.int32_type)
1642                                         return new ImplicitInvocation (ec, "IntegerType", "FromString", loc, expr);
1643                                 if (real_target_type == TypeManager.int64_type)
1644                                         return new ImplicitInvocation (ec, "LongType", "FromString", loc, expr);
1645                                 if (real_target_type == TypeManager.float_type)
1646                                         return new ImplicitInvocation (ec, "SingleType", "FromString", loc, expr);
1647                                 if (real_target_type == TypeManager.double_type)
1648                                         return new ImplicitInvocation (ec, "DoubleType", "FromString", loc, expr);
1649                                 if (real_target_type == TypeManager.decimal_type)
1650                                         return new ImplicitInvocation (ec, "DecimalType", "FromString", loc, expr);
1651                                 if (real_target_type == TypeManager.date_type)
1652                                         return new ImplicitInvocation (ec, "DateType", "FromString", loc, expr);
1653                         } if (real_target_type == TypeManager.string_type) {
1654
1655                                 //
1656                                 // From bool, byte, short, char, int,
1657                                 // long, float, double, decimal and
1658                                 // date to string
1659                                 //
1660
1661                                 if (expr_type == TypeManager.bool_type)
1662                                         return new ImplicitInvocation (ec, "StringType", "FromBoolean", loc, expr);
1663                                 if (expr_type == TypeManager.byte_type)
1664                                         return new ImplicitInvocation (ec, "StringType", "FromByte", loc, expr);
1665                                 if (expr_type == TypeManager.short_type)
1666                                         return new ImplicitInvocation (ec, "StringType", "FromShort", loc, expr);
1667                                 if (expr_type == TypeManager.int32_type)
1668                                         return new ImplicitInvocation (ec, "StringType", "FromInteger", loc, expr);
1669                                 if (expr_type == TypeManager.int64_type)
1670                                         return new ImplicitInvocation (ec, "StringType", "FromLong", loc, expr);
1671                                 if (expr_type == TypeManager.float_type)
1672                                         return new ImplicitInvocation (ec, "StringType", "FromSingle", loc, expr);
1673                                 if (expr_type == TypeManager.double_type)
1674                                         return new ImplicitInvocation (ec, "StringType", "FromDouble", loc, expr);
1675                                 if (expr_type == TypeManager.decimal_type)
1676                                         return new ImplicitInvocation (ec, "StringType", "FromDecimal", loc, expr);
1677                                 if (expr_type == TypeManager.date_type)
1678                                         return new ImplicitInvocation (ec, "StringType", "FromDate", loc, expr);
1679                         }
1680
1681                         return null;
1682                 }
1683
1684                 /// <summary>
1685                 ///  Returns whether an explicit reference conversion can be performed
1686                 ///  from source_type to target_type
1687                 /// </summary>
1688                 public static bool NarrowingReferenceConversionExists (Type source_type, Type target_type)
1689                 {
1690                         bool target_is_type_param = target_type.IsGenericParameter;
1691                         bool target_is_value_type = target_type.IsValueType;
1692
1693                         if (source_type == target_type)
1694                                 return true;
1695
1696                         //
1697                         // From object to a generic parameter
1698                         //
1699                         if (source_type == TypeManager.object_type && target_is_type_param)
1700                                 return true;
1701
1702                         //
1703                         // From object to any reference type
1704                         //
1705                         if (source_type == TypeManager.object_type && !target_is_value_type)
1706                                 return true;
1707
1708                         //
1709                         // From any class S to any class-type T, provided S is a base class of T
1710                         //
1711                         if (TypeManager.IsSubclassOf (target_type, source_type))
1712                                 return true;
1713
1714                         //
1715                         // From any interface type S to any interface T provided S is not derived from T
1716                         //
1717                         if (source_type.IsInterface && target_type.IsInterface){
1718                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1719                                         return true;
1720                         }
1721
1722                         //
1723                         // From any class type S to any interface T, provided S is not sealed
1724                         // and provided S does not implement T.
1725                         //
1726                         if (target_type.IsInterface && !source_type.IsSealed &&
1727                             !TypeManager.ImplementsInterface (source_type, target_type))
1728                                 return true;
1729
1730                         //
1731                         // From any interface-type S to to any class type T, provided T is not
1732                         // sealed, or provided T implements S.
1733                         //
1734                         if (source_type.IsInterface &&
1735                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1736                                 return true;
1737
1738
1739                         // From an array type S with an element type Se to an array type T with an
1740                         // element type Te provided all the following are true:
1741                         //     * S and T differe only in element type, in other words, S and T
1742                         //       have the same number of dimensions.
1743                         //     * Both Se and Te are reference types
1744                         //     * An explicit referenc conversions exist from Se to Te
1745                         //
1746                         if (source_type.IsArray && target_type.IsArray) {
1747                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1748
1749                                         Type source_element_type = TypeManager.GetElementType (source_type);
1750                                         Type target_element_type = TypeManager.GetElementType (target_type);
1751
1752                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1753                                                 if (NarrowingReferenceConversionExists (source_element_type,
1754                                                                                        target_element_type))
1755                                                         return true;
1756                                 }
1757                         }
1758
1759
1760                         // From System.Array to any array-type
1761                         if (source_type == TypeManager.array_type &&
1762                             target_type.IsArray){
1763                                 return true;
1764                         }
1765
1766                         //
1767                         // From System delegate to any delegate-type
1768                         //
1769                         if (source_type == TypeManager.delegate_type &&
1770                             TypeManager.IsDelegateType (target_type))
1771                                 return true;
1772
1773                         //
1774                         // From ICloneable to Array or Delegate types
1775                         //
1776                         if (source_type == TypeManager.icloneable_type &&
1777                             (target_type == TypeManager.array_type ||
1778                              target_type == TypeManager.delegate_type))
1779                                 return true;
1780
1781                         return false;
1782                 }
1783
1784                 /// <summary>
1785                 ///   Implements Explicit Reference conversions
1786                 /// </summary>
1787                 static Expression NarrowingReferenceConversion (Expression source, Type target_type)
1788                 {
1789                         Type source_type = source.Type;
1790                         bool target_is_type_param = target_type.IsGenericParameter;
1791                         bool target_is_value_type = target_type.IsValueType;
1792
1793                         //
1794                         // From object to a generic parameter
1795                         //
1796                         if (source_type == TypeManager.object_type && target_is_type_param)
1797                                 return new UnboxCast (source, target_type);
1798
1799                         //
1800                         // From object to any reference type
1801                         //
1802                         if (source_type == TypeManager.object_type && !target_is_value_type)
1803                                 return new ClassCast (source, target_type);
1804
1805                         //
1806                         // Unboxing conversion.
1807                         //
1808                         if (((source_type == TypeManager.enum_type &&
1809                                 !(source is EmptyCast)) ||
1810                                 source_type == TypeManager.value_type) && target_is_value_type)
1811                                 return new UnboxCast (source, target_type);
1812
1813                         //
1814                         // From any class S to any class-type T, provided S is a base class of T
1815                         //
1816                         if (TypeManager.IsSubclassOf (target_type, source_type))
1817                                 return new ClassCast (source, target_type);
1818
1819                         //
1820                         // From any interface type S to any interface T provided S is not derived from T
1821                         //
1822                         if (source_type.IsInterface && target_type.IsInterface){
1823                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1824                                         return null;
1825                                 else
1826                                         return new ClassCast (source, target_type);
1827                         }
1828
1829                         //
1830                         // From any class type S to any interface T, provides S is not sealed
1831                         // and provided S does not implement T.
1832                         //
1833                         if (target_type.IsInterface && !source_type.IsSealed) {
1834                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1835                                         return null;
1836                                 else
1837                                         return new ClassCast (source, target_type);
1838
1839                         }
1840
1841                         //
1842                         // From any interface-type S to to any class type T, provided T is not
1843                         // sealed, or provided T implements S.
1844                         //
1845                         if (source_type.IsInterface) {
1846                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1847                                         if (target_type.IsClass)
1848                                                 return new ClassCast (source, target_type);
1849                                         else
1850                                                 return new UnboxCast (source, target_type);
1851                                 }
1852
1853                                 return null;
1854                         }
1855
1856                         // From an array type S with an element type Se to an array type T with an
1857                         // element type Te provided all the following are true:
1858                         //     * S and T differe only in element type, in other words, S and T
1859                         //       have the same number of dimensions.
1860                         //     * Both Se and Te are reference types
1861                         //     * An explicit referenc conversions exist from Se to Te
1862                         //
1863                         if (source_type.IsArray && target_type.IsArray) {
1864                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1865
1866                                         Type source_element_type = TypeManager.GetElementType (source_type);
1867                                         Type target_element_type = TypeManager.GetElementType (target_type);
1868
1869                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1870                                                 if (NarrowingReferenceConversionExists (source_element_type,
1871                                                                                        target_element_type))
1872                                                         return new ClassCast (source, target_type);
1873                                 }
1874                         }
1875
1876
1877                         // From System.Array to any array-type
1878                         if (source_type == TypeManager.array_type &&
1879                             target_type.IsArray) {
1880                                 return new ClassCast (source, target_type);
1881                         }
1882
1883                         //
1884                         // From System delegate to any delegate-type
1885                         //
1886                         if (source_type == TypeManager.delegate_type &&
1887                             TypeManager.IsDelegateType (target_type))
1888                                 return new ClassCast (source, target_type);
1889
1890                         //
1891                         // From ICloneable to Array or Delegate types
1892                         //
1893                         if (source_type == TypeManager.icloneable_type &&
1894                             (target_type == TypeManager.array_type ||
1895                              target_type == TypeManager.delegate_type))
1896                                 return new ClassCast (source, target_type);
1897
1898                         return null;
1899                 }
1900
1901                 /// <summary>
1902                 ///   Performs an explicit conversion of the expression `expr' whose
1903                 ///   type is expr.Type to `target_type'.
1904                 /// </summary>
1905                 static public Expression WideningAndNarrowingConversion (EmitContext ec, Expression expr,
1906                                                              Type target_type, Location loc)
1907                 {
1908                         Type expr_type = expr.Type;
1909                         Type original_expr_type = expr_type;
1910
1911                         if (expr_type.IsSubclassOf (TypeManager.enum_type)){
1912                                 if (target_type == TypeManager.enum_type ||
1913                                     target_type == TypeManager.object_type) {
1914                                         if (expr is EnumConstant)
1915                                                 expr = ((EnumConstant) expr).Child;
1916                                         // We really need all these casts here .... :-(
1917                                         expr = new BoxedCast (new EmptyCast (expr, expr_type));
1918                                         return new EmptyCast (expr, target_type);
1919                                 } else if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
1920                                            target_type.IsSubclassOf (TypeManager.enum_type))
1921                                         return new UnboxCast (expr, target_type);
1922
1923                                 //
1924                                 // Notice that we have kept the expr_type unmodified, which is only
1925                                 // used later on to
1926                                 if (expr is EnumConstant)
1927                                         expr = ((EnumConstant) expr).Child;
1928                                 else
1929                                         expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
1930                                 expr_type = expr.Type;
1931                         }
1932
1933                         int errors = Report.Errors;
1934                         Expression ne = WideningConversionStandard (ec, expr, target_type, loc);
1935                         if (Report.Errors > errors)
1936                                 return null;
1937
1938                         if (ne != null)
1939                                 return ne;
1940
1941                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
1942                                 return Nullable.LiftedConversion.Create (ec, expr, target_type, true, loc);
1943
1944                         ne = NarrowingNumericConversion (ec, expr, target_type, loc);
1945                         if (ne != null)
1946                                 return ne;
1947
1948                         //
1949                         // Unboxing conversion.
1950                         //
1951                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1952                                 return new UnboxCast (expr, target_type);
1953
1954                         //
1955                         // Skip the NarrowingReferenceConversion because we can not convert
1956                         // from Null to a ValueType, and ExplicitReference wont check against
1957                         // null literal explicitly
1958                         //
1959                         if (expr_type != TypeManager.null_type){
1960                                 ne = NarrowingReferenceConversion (expr, target_type);
1961                                 if (ne != null)
1962                                         return ne;
1963                         }
1964
1965                 skip_explicit:
1966                         if (ec.InUnsafe){
1967                                 if (target_type.IsPointer){
1968                                         if (expr_type.IsPointer)
1969                                                 return new EmptyCast (expr, target_type);
1970
1971                                         if (expr_type == TypeManager.sbyte_type ||
1972                                             expr_type == TypeManager.byte_type ||
1973                                             expr_type == TypeManager.short_type ||
1974                                             expr_type == TypeManager.ushort_type ||
1975                                             expr_type == TypeManager.int32_type ||
1976                                             expr_type == TypeManager.uint32_type ||
1977                                             expr_type == TypeManager.uint64_type ||
1978                                             expr_type == TypeManager.int64_type)
1979                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1980                                 }
1981                                 if (expr_type.IsPointer){
1982                                         Expression e = null;
1983
1984                                         if (target_type == TypeManager.sbyte_type)
1985                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1986                                         else if (target_type == TypeManager.byte_type)
1987                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1988                                         else if (target_type == TypeManager.short_type)
1989                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1990                                         else if (target_type == TypeManager.ushort_type)
1991                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1992                                         else if (target_type == TypeManager.int32_type)
1993                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1994                                         else if (target_type == TypeManager.uint32_type)
1995                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1996                                         else if (target_type == TypeManager.uint64_type)
1997                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1998                                         else if (target_type == TypeManager.int64_type){
1999                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
2000                                         }
2001
2002                                         if (e != null){
2003                                                 Expression ci, ce;
2004
2005                                                 ci = WideningConversionStandard (ec, e, target_type, loc);
2006
2007                                                 if (ci != null)
2008                                                         return ci;
2009
2010                                                 ce = NarrowingNumericConversion (ec, e, target_type, loc);
2011                                                 if (ce != null)
2012                                                         return ce;
2013                                                 //
2014                                                 // We should always be able to go from an uint32
2015                                                 // implicitly or explicitly to the other integral
2016                                                 // types
2017                                                 //
2018                                                 throw new Exception ("Internal compiler error");
2019                                         }
2020                                 }
2021                         }
2022
2023                         //
2024                         // VB.NET specific conversions
2025                         //
2026
2027                         ne = BooleanConversions (ec, expr, target_type, loc);
2028                         if (ne != null)
2029                                 return ne;
2030
2031                         ne = NarrowingStringConversions (ec, expr, target_type, loc);
2032                         if (ne != null)
2033                                 return ne;
2034
2035
2036                         //
2037                         // VB.NET has no notion of User defined conversions
2038                         //
2039
2040 //                      ne = ExplicitUserConversion (ec, expr, target_type, loc);
2041 //                      if (ne != null)
2042 //                              return ne;
2043
2044                         if (expr is NullLiteral){
2045                                 Report.Error (37, loc, "Cannot convert null to value type `" +
2046                                               TypeManager.CSharpName (target_type) + "'");
2047                                 return null;
2048                         }
2049
2050                         Error_CannotConvertType (loc, original_expr_type, target_type);
2051                         return null;
2052                 }
2053
2054                 /// <summary>
2055                 ///   Same as WideningAndNarrowingConversion, only it doesn't include user defined conversions
2056                 /// </summary>
2057                 static public Expression WideningAndNarrowingConversionStandard (EmitContext ec, Expression expr,
2058                                                                      Type target_type, Location l)
2059                 {
2060                         int errors = Report.Errors;
2061                         Expression ne = WideningConversionStandard (ec, expr, target_type, l);
2062                         if (Report.Errors > errors)
2063                                 return null;
2064
2065                         if (ne != null)
2066                                 return ne;
2067
2068                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
2069                                 return Nullable.LiftedConversion.Create (ec, expr, target_type, true, l);
2070
2071                         ne = NarrowingNumericConversion (ec, expr, target_type, l);
2072                         if (ne != null)
2073                                 return ne;
2074
2075                         ne = NarrowingReferenceConversion (expr, target_type);
2076                         if (ne != null)
2077                                 return ne;
2078
2079                         Error_CannotConvertType (l, expr.Type, target_type);
2080                         return null;
2081                 }
2082         }
2083 }