mcs/gmcs/convert.cs

   1 //
   2 // conversion.cs: various routines for implementing conversions.
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Ravi Pratap (ravi@ximian.com)
   7 //
   8 // (C) 2001, 2002, 2003 Ximian, Inc.
   9 //
  10
  11 namespace Mono.CSharp {
  12         using System;
  13         using System.Collections;
  14         using System.Diagnostics;
  15         using System.Reflection;
  16         using System.Reflection.Emit;
  17
  18         //
  19         // A container class for all the conversion operations
  20         //
  21         public class Convert {
  22                 //
  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, GenericConstraints gc)
  68                 {
  69                         ArrayList list = new ArrayList ();
  70                         list.Add (gc.EffectiveBaseClass);
  71                         foreach (Type t in gc.InterfaceConstraints) {
  72                                 if (!t.IsGenericParameter)
  73                                         continue;
  74
  75                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  76                                 if (new_gc != null)
  77                                         list.Add (TypeParam_EffectiveBaseType (ec, new_gc));
  78                         }
  79                         return FindMostEncompassedType (ec, list);
  80                 }
  81
  82                 static Expression ImplicitTypeParameterConversion (EmitContext ec, Expression expr,
  83                                                                    Type target_type)
  84                 {
  85                         Type expr_type = expr.Type;
  86
  87                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
  88
  89                         if (gc == null) {
  90                                 if (target_type == TypeManager.object_type)
  91                                         return new BoxedCast (expr, target_type);
  92
  93                                 return null;
  94                         }
  95
  96                         // We're converting from a type parameter which is known to be a reference type.
  97                         Type base_type = TypeParam_EffectiveBaseType (ec, gc);
  98
  99                         if (TypeManager.IsSubclassOf (base_type, target_type))
 100                                 return new BoxedCast (expr, target_type);
 101
 102                         if (target_type.IsInterface) {
 103                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 104                                         return new BoxedCast (expr, target_type);
 105
 106                                 foreach (Type t in gc.InterfaceConstraints) {
 107                                         if (TypeManager.IsSubclassOf (t, target_type))
 108                                                 return new BoxedCast (expr, target_type);
 109                                 }
 110                         }
 111
 112                         foreach (Type t in gc.InterfaceConstraints) {
 113                                 if (!t.IsGenericParameter)
 114                                         continue;
 115                                 if (TypeManager.IsSubclassOf (t, target_type))
 116                                         return new BoxedCast (expr, target_type);
 117                         }
 118
 119                         return null;
 120                 }
 121
 122                 static EmptyExpression MyEmptyExpr;
 123                 static public Expression ImplicitReferenceConversion (EmitContext ec, Expression expr, Type target_type)
 124                 {
 125                         Type expr_type = expr.Type;
 126
 127                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 128                                 // if we are a method group, emit a warning
 129
 130                                 expr.Emit (null);
 131                         }
 132
 133                         if (expr_type == TypeManager.void_type)
 134                                 return null;
 135
 136                         if (expr_type.IsGenericParameter)
 137                                 return ImplicitTypeParameterConversion (ec, expr, target_type);
 138
 139                         //
 140                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 141                         // is an abstract class, and not really a value type, so we apply the same rules.
 142                         //
 143                         if (target_type == TypeManager.object_type) {
 144                                 //
 145                                 // A pointer type cannot be converted to object
 146                                 //
 147                                 if (expr_type.IsPointer)
 148                                         return null;
 149
 150                                 if (TypeManager.IsValueType (expr_type))
 151                                         return new BoxedCast (expr, target_type);
 152                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 153                                         if (expr_type == TypeManager.anonymous_method_type)
 154                                                 return null;
 155                                         return new EmptyCast (expr, target_type);
 156                                 }
 157
 158                                 return null;
 159                         } else if (target_type == TypeManager.value_type) {
 160                                 if (TypeManager.IsValueType (expr_type))
 161                                         return new BoxedCast (expr, target_type);
 162                                 if (expr_type == TypeManager.null_type)
 163                                         return new NullCast (expr, target_type);
 164
 165                                 return null;
 166                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 167                                 //
 168                                 // Special case: enumeration to System.Enum.
 169                                 // System.Enum is not a value type, it is a class, so we need
 170                                 // a boxing conversion
 171                                 //
 172                                 if (expr_type.IsEnum || expr_type.IsGenericParameter)
 173                                         return new BoxedCast (expr, target_type);
 174
 175                                 return new EmptyCast (expr, target_type);
 176                         }
 177
 178                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 179                         // with the small distinction that we only probe there
 180                         //
 181                         // Always ensure that the code here and there is in sync
 182
 183                         // from the null type to any reference-type.
 184                         if (expr_type == TypeManager.null_type){
 185                                 if (target_type.IsPointer)
 186                                         return new EmptyCast (NullPointer.Null, target_type);
 187
 188                                 if (!target_type.IsValueType)
 189                                         return new NullCast (expr, target_type);
 190                         }
 191
 192                         // from any class-type S to any interface-type T.
 193                         if (target_type.IsInterface) {
 194                                 if (target_type != TypeManager.iconvertible_type &&
 195                                     expr_type.IsValueType && (expr is Constant) &&
 196                                     !(expr is IntLiteral || expr is BoolLiteral ||
 197                                       expr is FloatLiteral || expr is DoubleLiteral ||
 198                                       expr is LongLiteral || expr is CharLiteral ||
 199                                       expr is StringLiteral || expr is DecimalLiteral ||
 200                                       expr is UIntLiteral || expr is ULongLiteral)) {
 201                                         return null;
 202                                 }
 203
 204                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 205                                         if (expr_type.IsGenericParameter || TypeManager.IsValueType (expr_type))
 206                                                 return new BoxedCast (expr, target_type);
 207                                         else
 208                                                 return new EmptyCast (expr, target_type);
 209                                 }
 210                         }
 211
 212                         // from any interface type S to interface-type T.
 213                         if (expr_type.IsInterface && target_type.IsInterface) {
 214                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 215                                         return new EmptyCast (expr, target_type);
 216                                 else
 217                                         return null;
 218                         }
 219
 220                         // from an array-type S to an array-type of type T
 221                         if (expr_type.IsArray && target_type.IsArray) {
 222                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 223
 224                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 225
 226                                         if (MyEmptyExpr == null)
 227                                                 MyEmptyExpr = new EmptyExpression ();
 228
 229                                         MyEmptyExpr.SetType (expr_element_type);
 230                                         Type target_element_type = TypeManager.GetElementType (target_type);
 231
 232                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 233                                                 if (ImplicitStandardConversionExists (ConstantEC, MyEmptyExpr,
 234                                                                                       target_element_type))
 235                                                         return new EmptyCast (expr, target_type);
 236                                 }
 237                         }
 238
 239                         // from an array-type to System.Array
 240                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 241                                 return new EmptyCast (expr, target_type);
 242
 243                         // from an array-type of type T to IEnumerable<T>
 244                         if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
 245                                 return new EmptyCast (expr, target_type);
 246
 247                         // from any delegate type to System.Delegate
 248                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 249                             target_type == TypeManager.delegate_type)
 250                                 return new EmptyCast (expr, target_type);
 251
 252                         // from any array-type or delegate type into System.ICloneable.
 253                         if (expr_type.IsArray ||
 254                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 255                                 if (target_type == TypeManager.icloneable_type)
 256                                         return new EmptyCast (expr, target_type);
 257
 258                         // from a generic type definition to a generic instance.
 259                         if (TypeManager.IsEqual (expr_type, target_type))
 260                                 return new EmptyCast (expr, target_type);
 261
 262                         return null;
 263                 }
 264
 265                 //
 266                 // Tests whether an implicit reference conversion exists between expr_type
 267                 // and target_type
 268                 //
 269                 public static bool ImplicitReferenceConversionExists (EmitContext ec, Expression expr, Type target_type)
 270                 {
 271                         if (target_type.IsValueType)
 272                                 return false;
 273
 274                         Type expr_type = expr.Type;
 275
 276                         if (expr_type.IsGenericParameter)
 277                                 return ImplicitTypeParameterConversion (ec, expr, target_type) != null;
 278
 279                         //
 280                         // This is the boxed case.
 281                         //
 282                         if (target_type == TypeManager.object_type) {
 283                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 284                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 285                                         if (target_type != TypeManager.anonymous_method_type)
 286                                         return true;
 287
 288                                 return false;
 289                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 290                                 return true;
 291
 292                         // Please remember that all code below actually comes
 293                         // from ImplicitReferenceConversion so make sure code remains in sync
 294
 295                         // from any class-type S to any interface-type T.
 296                         if (target_type.IsInterface) {
 297                                 if (target_type != TypeManager.iconvertible_type &&
 298                                     expr_type.IsValueType && (expr is Constant) &&
 299                                     !(expr is IntLiteral || expr is BoolLiteral ||
 300                                       expr is FloatLiteral || expr is DoubleLiteral ||
 301                                       expr is LongLiteral || expr is CharLiteral ||
 302                                       expr is StringLiteral || expr is DecimalLiteral ||
 303                                       expr is UIntLiteral || expr is ULongLiteral)) {
 304                                         return false;
 305                                 }
 306
 307                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 308                                         return true;
 309                         }
 310
 311                         // from any interface type S to interface-type T.
 312                         if (expr_type.IsInterface && target_type.IsInterface)
 313                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 314                                         return true;
 315
 316                         // from an array-type S to an array-type of type T
 317                         if (expr_type.IsArray && target_type.IsArray) {
 318                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 319
 320                                         Type expr_element_type = expr_type.GetElementType ();
 321
 322                                         if (MyEmptyExpr == null)
 323                                                 MyEmptyExpr = new EmptyExpression ();
 324
 325                                         MyEmptyExpr.SetType (expr_element_type);
 326                                         Type target_element_type = TypeManager.GetElementType (target_type);
 327
 328                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 329                                                 if (ImplicitStandardConversionExists (ConstantEC, MyEmptyExpr,
 330                                                                                       target_element_type))
 331                                                         return true;
 332                                 }
 333                         }
 334
 335                         // from an array-type to System.Array
 336                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 337                                 return true;
 338
 339                         // from an array-type of type T to IEnumerable<T>
 340                         if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
 341                                 return true;
 342
 343                         // from any delegate type to System.Delegate
 344                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 345                             target_type == TypeManager.delegate_type)
 346                                 if (target_type.IsAssignableFrom (expr_type))
 347                                         return true;
 348
 349                         // from any array-type or delegate type into System.ICloneable.
 350                         if (expr_type.IsArray ||
 351                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 352                                 if (target_type == TypeManager.icloneable_type)
 353                                         return true;
 354
 355                         // from the null type to any reference-type.
 356                         if (expr_type == TypeManager.null_type){
 357                                 if (target_type.IsPointer)
 358                                         return true;
 359
 360                                 if (!target_type.IsValueType)
 361                                         return true;
 362                         }
 363
 364                         // from a generic type definition to a generic instance.
 365                         if (TypeManager.IsEqual (expr_type, target_type))
 366                                 return true;
 367
 368                         return false;
 369                 }
 370
 371                 /// <summary>
 372                 ///   Implicit Numeric Conversions.
 373                 ///
 374                 ///   expr is the expression to convert, returns a new expression of type
 375                 ///   target_type or null if an implicit conversion is not possible.
 376                 /// </summary>
 377                 static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
 378                                                                     Type target_type, Location loc)
 379                 {
 380                         Type expr_type = expr.Type;
 381
 382                         //
 383                         // Attempt to do the implicit constant expression conversions
 384
 385                         if (expr is Constant){
 386                                 if (expr is IntConstant){
 387                                         Expression e;
 388
 389                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 390
 391                                         if (e != null)
 392                                                 return e;
 393                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 394                                         //
 395                                         // Try the implicit constant expression conversion
 396                                         // from long to ulong, instead of a nice routine,
 397                                         // we just inline it
 398                                         //
 399                                         long v = ((LongConstant) expr).Value;
 400                                         if (v >= 0)
 401                                                 return new ULongConstant ((ulong) v);
 402                                 }
 403                         }
 404
 405                         Type real_target_type = target_type;
 406
 407                         if (expr_type == TypeManager.sbyte_type){
 408                                 //
 409                                 // From sbyte to short, int, long, float, double, decimal
 410                                 //
 411                                 if (real_target_type == TypeManager.int32_type)
 412                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 413                                 if (real_target_type == TypeManager.int64_type)
 414                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 415                                 if (real_target_type == TypeManager.double_type)
 416                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 417                                 if (real_target_type == TypeManager.float_type)
 418                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 419                                 if (real_target_type == TypeManager.short_type)
 420                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 421                                 if (real_target_type == TypeManager.decimal_type)
 422                                         return new CastToDecimal (ec, expr);
 423                         } else if (expr_type == TypeManager.byte_type){
 424                                 //
 425                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 426                                 //
 427                                 if ((real_target_type == TypeManager.short_type) ||
 428                                     (real_target_type == TypeManager.ushort_type) ||
 429                                     (real_target_type == TypeManager.int32_type) ||
 430                                     (real_target_type == TypeManager.uint32_type))
 431                                         return new EmptyCast (expr, target_type);
 432
 433                                 if (real_target_type == TypeManager.uint64_type)
 434                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 435                                 if (real_target_type == TypeManager.int64_type)
 436                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 437                                 if (real_target_type == TypeManager.float_type)
 438                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 439                                 if (real_target_type == TypeManager.double_type)
 440                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 441                                 if (real_target_type == TypeManager.decimal_type)
 442                                         return new CastToDecimal (ec, expr);
 443
 444                         } else if (expr_type == TypeManager.short_type){
 445                                 //
 446                                 // From short to int, long, float, double, decimal
 447                                 //
 448                                 if (real_target_type == TypeManager.int32_type)
 449                                         return new EmptyCast (expr, target_type);
 450                                 if (real_target_type == TypeManager.int64_type)
 451                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 452                                 if (real_target_type == TypeManager.double_type)
 453                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 454                                 if (real_target_type == TypeManager.float_type)
 455                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 456                                 if (real_target_type == TypeManager.decimal_type)
 457                                         return new CastToDecimal (ec, expr);
 458
 459                         } else if (expr_type == TypeManager.ushort_type){
 460                                 //
 461                                 // From ushort to int, uint, long, ulong, float, double, decimal
 462                                 //
 463                                 if (real_target_type == TypeManager.uint32_type)
 464                                         return new EmptyCast (expr, target_type);
 465
 466                                 if (real_target_type == TypeManager.uint64_type)
 467                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 468                                 if (real_target_type == TypeManager.int32_type)
 469                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 470                                 if (real_target_type == TypeManager.int64_type)
 471                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 472                                 if (real_target_type == TypeManager.double_type)
 473                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 474                                 if (real_target_type == TypeManager.float_type)
 475                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 476                                 if (real_target_type == TypeManager.decimal_type)
 477                                         return new CastToDecimal (ec, expr);
 478                         } else if (expr_type == TypeManager.int32_type){
 479                                 //
 480                                 // From int to long, float, double, decimal
 481                                 //
 482                                 if (real_target_type == TypeManager.int64_type)
 483                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 484                                 if (real_target_type == TypeManager.double_type)
 485                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 486                                 if (real_target_type == TypeManager.float_type)
 487                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 488                                 if (real_target_type == TypeManager.decimal_type)
 489                                         return new CastToDecimal (ec, expr);
 490                         } else if (expr_type == TypeManager.uint32_type){
 491                                 //
 492                                 // From uint to long, ulong, float, double, decimal
 493                                 //
 494                                 if (real_target_type == TypeManager.int64_type)
 495                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 496                                 if (real_target_type == TypeManager.uint64_type)
 497                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 498                                 if (real_target_type == TypeManager.double_type)
 499                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 500                                                                OpCodes.Conv_R8);
 501                                 if (real_target_type == TypeManager.float_type)
 502                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 503                                                                OpCodes.Conv_R4);
 504                                 if (real_target_type == TypeManager.decimal_type)
 505                                         return new CastToDecimal (ec, expr);
 506                         } else if (expr_type == TypeManager.int64_type){
 507                                 //
 508                                 // From long/ulong to float, double
 509                                 //
 510                                 if (real_target_type == TypeManager.double_type)
 511                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 512                                 if (real_target_type == TypeManager.float_type)
 513                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 514                                 if (real_target_type == TypeManager.decimal_type)
 515                                         return new CastToDecimal (ec, expr);
 516                         } else if (expr_type == TypeManager.uint64_type){
 517                                 //
 518                                 // From ulong to float, double
 519                                 //
 520                                 if (real_target_type == TypeManager.double_type)
 521                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 522                                                                OpCodes.Conv_R8);
 523                                 if (real_target_type == TypeManager.float_type)
 524                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 525                                                                OpCodes.Conv_R4);
 526                                 if (real_target_type == TypeManager.decimal_type)
 527                                         return new CastToDecimal (ec, expr);
 528                         } else if (expr_type == TypeManager.char_type){
 529                                 //
 530                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 531                                 //
 532                                 if ((real_target_type == TypeManager.ushort_type) ||
 533                                     (real_target_type == TypeManager.int32_type) ||
 534                                     (real_target_type == TypeManager.uint32_type))
 535                                         return new EmptyCast (expr, target_type);
 536                                 if (real_target_type == TypeManager.uint64_type)
 537                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 538                                 if (real_target_type == TypeManager.int64_type)
 539                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 540                                 if (real_target_type == TypeManager.float_type)
 541                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 542                                 if (real_target_type == TypeManager.double_type)
 543                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 544                                 if (real_target_type == TypeManager.decimal_type)
 545                                         return new CastToDecimal (ec, expr);
 546                         } else if (expr_type == TypeManager.float_type){
 547                                 //
 548                                 // float to double
 549                                 //
 550                                 if (real_target_type == TypeManager.double_type)
 551                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 552                         }
 553
 554                         return null;
 555                 }
 556
 557
 558                 /// <summary>
 559                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 560                 ///  implicit user defined conversions - needed for overload resolution
 561                 /// </summary>
 562                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 563                 {
 564                         if (expr is NullLiteral) {
 565                                 if (target_type.IsGenericParameter)
 566                                         return TypeParameter_to_Null (target_type);
 567
 568                                 if (TypeManager.IsNullableType (target_type))
 569                                         return true;
 570                         }
 571
 572                         if (ImplicitStandardConversionExists (ec, expr, target_type))
 573                                 return true;
 574
 575                         Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);
 576
 577                         if (dummy != null)
 578                                 return true;
 579
 580                         return false;
 581                 }
 582
 583                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 584                 {
 585                         Expression dummy = ImplicitUserConversion (
 586                                 ec, new EmptyExpression (source), target, Location.Null);
 587                         return dummy != null;
 588                 }
 589
 590                 /// <summary>
 591                 ///  Determines if a standard implicit conversion exists from
 592                 ///  expr_type to target_type
 593                 ///
 594                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 595                 /// </summary>
 596                 public static bool ImplicitStandardConversionExists (EmitContext ec, Expression expr, Type target_type)
 597                 {
 598                         Type expr_type = expr.Type;
 599
 600                         if (expr_type == TypeManager.void_type)
 601                                 return false;
 602
 603                         //Console.WriteLine ("Expr is {0}", expr);
 604                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 605                         if (expr_type.Equals (target_type))
 606                                 return true;
 607
 608
 609                         // First numeric conversions
 610
 611                         if (expr_type == TypeManager.sbyte_type){
 612                                 //
 613                                 // From sbyte to short, int, long, float, double, decimal
 614                                 //
 615                                 if ((target_type == TypeManager.int32_type) ||
 616                                     (target_type == TypeManager.int64_type) ||
 617                                     (target_type == TypeManager.double_type) ||
 618                                     (target_type == TypeManager.float_type)  ||
 619                                     (target_type == TypeManager.short_type) ||
 620                                     (target_type == TypeManager.decimal_type))
 621                                         return true;
 622
 623                         } else if (expr_type == TypeManager.byte_type){
 624                                 //
 625                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 626                                 //
 627                                 if ((target_type == TypeManager.short_type) ||
 628                                     (target_type == TypeManager.ushort_type) ||
 629                                     (target_type == TypeManager.int32_type) ||
 630                                     (target_type == TypeManager.uint32_type) ||
 631                                     (target_type == TypeManager.uint64_type) ||
 632                                     (target_type == TypeManager.int64_type) ||
 633                                     (target_type == TypeManager.float_type) ||
 634                                     (target_type == TypeManager.double_type) ||
 635                                     (target_type == TypeManager.decimal_type))
 636                                         return true;
 637
 638                         } else if (expr_type == TypeManager.short_type){
 639                                 //
 640                                 // From short to int, long, double, float, decimal
 641                                 //
 642                                 if ((target_type == TypeManager.int32_type) ||
 643                                     (target_type == TypeManager.int64_type) ||
 644                                     (target_type == TypeManager.double_type) ||
 645                                     (target_type == TypeManager.float_type) ||
 646                                     (target_type == TypeManager.decimal_type))
 647                                         return true;
 648
 649                         } else if (expr_type == TypeManager.ushort_type){
 650                                 //
 651                                 // From ushort to int, uint, long, ulong, double, float, decimal
 652                                 //
 653                                 if ((target_type == TypeManager.uint32_type) ||
 654                                     (target_type == TypeManager.uint64_type) ||
 655                                     (target_type == TypeManager.int32_type) ||
 656                                     (target_type == TypeManager.int64_type) ||
 657                                     (target_type == TypeManager.double_type) ||
 658                                     (target_type == TypeManager.float_type) ||
 659                                     (target_type == TypeManager.decimal_type))
 660                                         return true;
 661
 662                         } else if (expr_type == TypeManager.int32_type){
 663                                 //
 664                                 // From int to long, double, float, decimal
 665                                 //
 666                                 if ((target_type == TypeManager.int64_type) ||
 667                                     (target_type == TypeManager.double_type) ||
 668                                     (target_type == TypeManager.float_type) ||
 669                                     (target_type == TypeManager.decimal_type))
 670                                         return true;
 671
 672                         } else if (expr_type == TypeManager.uint32_type){
 673                                 //
 674                                 // From uint to long, ulong, double, float, decimal
 675                                 //
 676                                 if ((target_type == TypeManager.int64_type) ||
 677                                     (target_type == TypeManager.uint64_type) ||
 678                                     (target_type == TypeManager.double_type) ||
 679                                     (target_type == TypeManager.float_type) ||
 680                                     (target_type == TypeManager.decimal_type))
 681                                         return true;
 682
 683                         } else if ((expr_type == TypeManager.uint64_type) ||
 684                                    (expr_type == TypeManager.int64_type)) {
 685                                 //
 686                                 // From long/ulong to double, float, decimal
 687                                 //
 688                                 if ((target_type == TypeManager.double_type) ||
 689                                     (target_type == TypeManager.float_type) ||
 690                                     (target_type == TypeManager.decimal_type))
 691                                         return true;
 692
 693                         } else if (expr_type == TypeManager.char_type){
 694                                 //
 695                                 // From char to ushort, int, uint, ulong, long, float, double, decimal
 696                                 //
 697                                 if ((target_type == TypeManager.ushort_type) ||
 698                                     (target_type == TypeManager.int32_type) ||
 699                                     (target_type == TypeManager.uint32_type) ||
 700                                     (target_type == TypeManager.uint64_type) ||
 701                                     (target_type == TypeManager.int64_type) ||
 702                                     (target_type == TypeManager.float_type) ||
 703                                     (target_type == TypeManager.double_type) ||
 704                                     (target_type == TypeManager.decimal_type))
 705                                         return true;
 706
 707                         } else if (expr_type == TypeManager.float_type){
 708                                 //
 709                                 // float to double
 710                                 //
 711                                 if (target_type == TypeManager.double_type)
 712                                         return true;
 713                         }
 714
 715                         if (expr.eclass == ExprClass.MethodGroup){
 716                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
 717                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 718                                         if (mg != null){
 719                                                 //
 720                                                 // This should not happen frequently, so we can create an object
 721                                                 // to test compatibility
 722                                                 //
 723                                                 Expression c = ImplicitDelegateCreation.Create (
 724                                                         ec, mg, target_type, true, Location.Null);
 725                                                 return c != null;
 726                                         }
 727                                 }
 728                         }
 729
 730                         if (ImplicitReferenceConversionExists (ec, expr, target_type))
 731                                 return true;
 732
 733                         //
 734                         // Implicit Constant Expression Conversions
 735                         //
 736                         if (expr is IntConstant){
 737                                 int value = ((IntConstant) expr).Value;
 738
 739                                 if (target_type == TypeManager.sbyte_type){
 740                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 741                                                 return true;
 742                                 } else if (target_type == TypeManager.byte_type){
 743                                         if (value >= 0 && value <= Byte.MaxValue)
 744                                                 return true;
 745                                 } else if (target_type == TypeManager.short_type){
 746                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 747                                                 return true;
 748                                 } else if (target_type == TypeManager.ushort_type){
 749                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 750                                                 return true;
 751                                 } else if (target_type == TypeManager.uint32_type){
 752                                         if (value >= 0)
 753                                                 return true;
 754                                 } else if (target_type == TypeManager.uint64_type){
 755                                          //
 756                                          // we can optimize this case: a positive int32
 757                                          // always fits on a uint64.  But we need an opcode
 758                                          // to do it.
 759                                          //
 760                                         if (value >= 0)
 761                                                 return true;
 762                                 }
 763
 764                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 765                                         return true;
 766                         }
 767
 768                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 769                                 //
 770                                 // Try the implicit constant expression conversion
 771                                 // from long to ulong, instead of a nice routine,
 772                                 // we just inline it
 773                                 //
 774                                 long v = ((LongConstant) expr).Value;
 775                                 if (v >= 0)
 776                                         return true;
 777                         }
 778
 779                         if ((target_type == TypeManager.enum_type ||
 780                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 781                              expr is IntLiteral){
 782                                 IntLiteral i = (IntLiteral) expr;
 783
 784                                 if (i.Value == 0)
 785                                         return true;
 786                         }
 787
 788                         //
 789                         // If `expr_type' implements `target_type' (which is an iface)
 790                         // see TryImplicitIntConversion
 791                         //
 792                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 793                                 return true;
 794
 795                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 796                                 return true;
 797
 798                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
 799                                 return true;
 800
 801                         if (expr_type == TypeManager.anonymous_method_type){
 802                                 if (!TypeManager.IsDelegateType (target_type))
 803                                         return false;
 804
 805                                 AnonymousMethod am = (AnonymousMethod) expr;
 806
 807                                 Expression conv = am.Compatible (ec, target_type, true);
 808                                 if (conv != null)
 809                                         return true;
 810                         }
 811
 812                         return false;
 813                 }
 814
 815                 /// <summary>
 816                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 817                 ///  amongst the methods in the MethodGroupExpr
 818                 /// </summary>
 819                 static Type FindMostEncompassedType (EmitContext ec, ArrayList types)
 820                 {
 821                         Type best = null;
 822
 823                         if (types.Count == 0)
 824                                 return null;
 825
 826                         if (types.Count == 1)
 827                                 return (Type) types [0];
 828
 829                         EmptyExpression expr = EmptyExpression.Grab ();
 830
 831                         foreach (Type t in types) {
 832                                 if (best == null) {
 833                                         best = t;
 834                                         continue;
 835                                 }
 836
 837                                 expr.SetType (t);
 838                                 if (ImplicitStandardConversionExists (ec, expr, best))
 839                                         best = t;
 840                         }
 841
 842                         expr.SetType (best);
 843                         foreach (Type t in types) {
 844                                 if (best == t)
 845                                         continue;
 846                                 if (!ImplicitStandardConversionExists (ec, expr, t)) {
 847                                         best = null;
 848                                         break;
 849                                 }
 850                         }
 851
 852                         EmptyExpression.Release (expr);
 853
 854                         return best;
 855                 }
 856
 857                 /// <summary>
 858                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 859                 ///  amongst the types in the given set
 860                 /// </summary>
 861                 static Type FindMostEncompassingType (EmitContext ec, ArrayList types)
 862                 {
 863                         Type best = null;
 864
 865                         if (types.Count == 0)
 866                                 return null;
 867
 868                         if (types.Count == 1)
 869                                 return (Type) types [0];
 870
 871                         EmptyExpression expr = EmptyExpression.Grab ();
 872
 873                         foreach (Type t in types) {
 874                                 if (best == null) {
 875                                         best = t;
 876                                         continue;
 877                                 }
 878
 879                                 expr.SetType (best);
 880                                 if (ImplicitStandardConversionExists (ec, expr, t))
 881                                         best = t;
 882                         }
 883
 884                         foreach (Type t in types) {
 885                                 if (best == t)
 886                                         continue;
 887                                 expr.SetType (t);
 888                                 if (!ImplicitStandardConversionExists (ec, expr, best)) {
 889                                         best = null;
 890                                         break;
 891                                 }
 892                         }
 893
 894                         EmptyExpression.Release (expr);
 895
 896                         return best;
 897                 }
 898
 899                 /// <summary>
 900                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 901                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 902                 ///   for explicit and implicit conversion operators.
 903                 /// </summary>
 904                 static public Type FindMostSpecificSource (EmitContext ec, IList list,
 905                                                            Expression source, bool apply_explicit_conv_rules,
 906                                                            Location loc)
 907                 {
 908                         ArrayList src_types_set = new ArrayList ();
 909
 910                         //
 911                         // If any operator converts from S then Sx = S
 912                         //
 913                         Type source_type = source.Type;
 914                         foreach (MethodBase mb in list){
 915                                 ParameterData pd = TypeManager.GetParameterData (mb);
 916                                 Type param_type = pd.ParameterType (0);
 917
 918                                 if (param_type == source_type)
 919                                         return param_type;
 920
 921                                 src_types_set.Add (param_type);
 922                         }
 923
 924                         //
 925                         // Explicit Conv rules
 926                         //
 927                         if (apply_explicit_conv_rules) {
 928                                 ArrayList candidate_set = new ArrayList ();
 929
 930                                 foreach (Type param_type in src_types_set){
 931                                         if (ImplicitStandardConversionExists (ec, source, param_type))
 932                                                 candidate_set.Add (param_type);
 933                                 }
 934
 935                                 if (candidate_set.Count != 0)
 936                                         return FindMostEncompassedType (ec, candidate_set);
 937                         }
 938
 939                         //
 940                         // Final case
 941                         //
 942                         if (apply_explicit_conv_rules)
 943                                 return FindMostEncompassingType (ec, src_types_set);
 944                         else
 945                                 return FindMostEncompassedType (ec, src_types_set);
 946                 }
 947
 948                 /// <summary>
 949                 ///  Finds the most specific target Tx according to section 13.4.4
 950                 /// </summary>
 951                 static public Type FindMostSpecificTarget (EmitContext ec, IList list,
 952                                                            Type target, bool apply_explicit_conv_rules,
 953                                                            Location loc)
 954                 {
 955                         ArrayList tgt_types_set = new ArrayList ();
 956
 957                         //
 958                         // If any operator converts to T then Tx = T
 959                         //
 960                         foreach (MethodInfo mi in list){
 961                                 Type ret_type = mi.ReturnType;
 962                                 if (ret_type == target)
 963                                         return ret_type;
 964
 965                                 tgt_types_set.Add (ret_type);
 966                         }
 967
 968                         //
 969                         // Explicit conv rules
 970                         //
 971                         if (apply_explicit_conv_rules) {
 972                                 ArrayList candidate_set = new ArrayList ();
 973
 974                                 EmptyExpression expr = EmptyExpression.Grab ();
 975
 976                                 foreach (Type ret_type in tgt_types_set){
 977                                         expr.SetType (ret_type);
 978
 979                                         if (ImplicitStandardConversionExists (ec, expr, target))
 980                                                 candidate_set.Add (ret_type);
 981                                 }
 982
 983                                 EmptyExpression.Release (expr);
 984
 985                                 if (candidate_set.Count != 0)
 986                                         return FindMostEncompassingType (ec, candidate_set);
 987                         }
 988
 989                         //
 990                         // Okay, final case !
 991                         //
 992                         if (apply_explicit_conv_rules)
 993                                 return FindMostEncompassedType (ec, tgt_types_set);
 994                         else
 995                                 return FindMostEncompassingType (ec, tgt_types_set);
 996                 }
 997
 998                 /// <summary>
 999                 ///  User-defined Implicit conversions
1000                 /// </summary>
1001                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
1002                                                                  Type target, Location loc)
1003                 {
1004                         return UserDefinedConversion (ec, source, target, loc, false);
1005                 }
1006
1007                 /// <summary>
1008                 ///  User-defined Explicit conversions
1009                 /// </summary>
1010                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1011                                                                  Type target, Location loc)
1012                 {
1013                         return UserDefinedConversion (ec, source, target, loc, true);
1014                 }
1015
1016                 static void AddConversionOperators (EmitContext ec, ArrayList list,
1017                                                     Expression source, Type target_type,
1018                                                     bool look_for_explicit,
1019                                                     MethodGroupExpr mg)
1020                 {
1021                         if (mg == null)
1022                                 return;
1023
1024                         Type source_type = source.Type;
1025                         EmptyExpression expr = EmptyExpression.Grab ();
1026                         foreach (MethodInfo m in mg.Methods) {
1027                                 ParameterData pd = TypeManager.GetParameterData (m);
1028                                 Type return_type = m.ReturnType;
1029                                 Type arg_type = pd.ParameterType (0);
1030
1031                                 if (source_type != arg_type) {
1032                                         if (!ImplicitStandardConversionExists (ec, source, arg_type)) {
1033                                                 if (!look_for_explicit)
1034                                                         continue;
1035                                                 expr.SetType (arg_type);
1036                                                 if (!ImplicitStandardConversionExists (ec, expr, source_type))
1037                                                         continue;
1038                                         }
1039                                 }
1040
1041                                 if (target_type != return_type) {
1042                                         expr.SetType (return_type);
1043                                         if (!ImplicitStandardConversionExists (ec, expr, target_type)) {
1044                                                 if (!look_for_explicit)
1045                                                         continue;
1046                                                 expr.SetType (target_type);
1047                                                 if (!ImplicitStandardConversionExists (ec, expr, return_type))
1048                                                         continue;
1049                                         }
1050                                 }
1051
1052                                 list.Add (m);
1053                         }
1054
1055                         EmptyExpression.Release (expr);
1056                 }
1057
1058                 /// <summary>
1059                 ///   Computes the list of the user-defined conversion
1060                 ///   operators from source_type to target_type.  `look_for_explicit'
1061                 ///   controls whether we should also include the list of explicit
1062                 ///   operators
1063                 /// </summary>
1064                 static IList GetConversionOperators (EmitContext ec,
1065                                                      Expression source, Type target_type,
1066                                                      Location loc, bool look_for_explicit)
1067                 {
1068                         ArrayList ret = new ArrayList (4);
1069
1070                         Type source_type = source.Type;
1071
1072                         if (source_type != TypeManager.decimal_type) {
1073                                 AddConversionOperators (ec, ret, source, target_type, look_for_explicit,
1074                                         Expression.MethodLookup (
1075                                                 ec, source_type, "op_Implicit", loc) as MethodGroupExpr);
1076                                 if (look_for_explicit) {
1077                                         AddConversionOperators (ec, ret, source, target_type, look_for_explicit,
1078                                                 Expression.MethodLookup (
1079                                                         ec, source_type, "op_Explicit", loc) as MethodGroupExpr);
1080                                 }
1081                         }
1082
1083                         if (target_type != TypeManager.decimal_type) {
1084                                 AddConversionOperators (ec, ret, source, target_type, look_for_explicit,
1085                                         Expression.MethodLookup (
1086                                                 ec, target_type, "op_Implicit", loc) as MethodGroupExpr);
1087                                 if (look_for_explicit) {
1088                                         AddConversionOperators (ec, ret, source, target_type, look_for_explicit,
1089                                                 Expression.MethodLookup (
1090                                                         ec, target_type, "op_Explicit", loc) as MethodGroupExpr);
1091                                 }
1092                         }
1093
1094                         return ret;
1095                 }
1096
1097                 static DoubleHash explicit_conv = new DoubleHash (100);
1098                 static DoubleHash implicit_conv = new DoubleHash (100);
1099
1100                 /// <summary>
1101                 ///   User-defined conversions
1102                 /// </summary>
1103                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1104                                                                 Type target, Location loc,
1105                                                                 bool look_for_explicit)
1106                 {
1107                         Type source_type = source.Type;
1108                         MethodInfo method = null;
1109                         Type most_specific_source = null;
1110                         Type most_specific_target = null;
1111
1112                         if (TypeManager.IsNullableType (source_type) && TypeManager.IsNullableType (target))
1113                                 return new Nullable.LiftedConversion (
1114                                         source, target, true, look_for_explicit, loc).Resolve (ec);
1115
1116                         object o;
1117                         DoubleHash hash = look_for_explicit ? explicit_conv : implicit_conv;
1118
1119                         if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
1120                                 method = (MethodInfo) o;
1121                                 if (method != null) {
1122                                         ParameterData pd = TypeManager.GetParameterData (method);
1123                                         most_specific_source = pd.ParameterType (0);
1124                                         most_specific_target = method.ReturnType;
1125                                 }
1126                         } else {
1127                                 IList ops = GetConversionOperators (ec, source, target, loc, look_for_explicit);
1128                                 if (ops == null || ops.Count == 0) {
1129                                         method = null;
1130                                         goto skip;
1131                                 }
1132
1133                                 most_specific_source = FindMostSpecificSource (ec, ops, source, look_for_explicit, loc);
1134                                 if (most_specific_source == null) {
1135                                         method = null;
1136                                         goto skip;
1137                                 }
1138
1139                                 most_specific_target = FindMostSpecificTarget (ec, ops, target, look_for_explicit, loc);
1140                                 if (most_specific_target == null) {
1141                                         method = null;
1142                                         goto skip;
1143                                 }
1144
1145                                 int count = 0;
1146
1147                                 foreach (MethodInfo m in ops) {
1148                                         ParameterData pd = TypeManager.GetParameterData (m);
1149
1150                                         if (pd.ParameterType (0) == most_specific_source &&
1151                                             m.ReturnType == most_specific_target) {
1152                                                 method = m;
1153                                                 count++;
1154                                         }
1155                                 }
1156                                 if (count > 1)
1157                                         method = null;
1158
1159                         skip:
1160                                 if (!(source is Constant))
1161                                         hash.Insert (source_type, target, method);
1162                         }
1163
1164                         if (method == null)
1165                                 return null;
1166
1167                         //
1168                         // This will do the conversion to the best match that we
1169                         // found.  Now we need to perform an implict standard conversion
1170                         // if the best match was not the type that we were requested
1171                         // by target.
1172                         //
1173                         if (look_for_explicit)
1174                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1175                         else
1176                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1177
1178                         if (source == null)
1179                                 return null;
1180
1181                         Expression e;
1182                         e =  new UserCast (method, source, loc);
1183                         if (e.Type != target){
1184                                 if (!look_for_explicit)
1185                                         e = ImplicitConversionStandard (ec, e, target, loc);
1186                                 else
1187                                         e = ExplicitConversionStandard (ec, e, target, loc);
1188                         }
1189
1190                         return e;
1191                 }
1192
1193                 /// <summary>
1194                 ///   Converts implicitly the resolved expression `expr' into the
1195                 ///   `target_type'.  It returns a new expression that can be used
1196                 ///   in a context that expects a `target_type'.
1197                 /// </summary>
1198                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1199                                                              Type target_type, Location loc)
1200                 {
1201                         Expression e;
1202
1203                         if (target_type == null)
1204                                 throw new Exception ("Target type is null");
1205
1206                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1207                         if (e != null)
1208                                 return e;
1209
1210                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1211                         if (e != null)
1212                                 return e;
1213
1214                         return null;
1215                 }
1216
1217
1218                 /// <summary>
1219                 ///   Attempts to apply the `Standard Implicit
1220                 ///   Conversion' rules to the expression `expr' into
1221                 ///   the `target_type'.  It returns a new expression
1222                 ///   that can be used in a context that expects a
1223                 ///   `target_type'.
1224                 ///
1225                 ///   This is different from `ImplicitConversion' in that the
1226                 ///   user defined implicit conversions are excluded.
1227                 /// </summary>
1228                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1229                                                                      Type target_type, Location loc)
1230                 {
1231                         Type expr_type = expr.Type;
1232                         Expression e;
1233
1234                         if (expr is NullLiteral) {
1235                                 if (target_type.IsGenericParameter)
1236                                         return TypeParameter_to_Null (expr, target_type, loc);
1237
1238                                 if (TypeManager.IsNullableType (target_type))
1239                                         return new Nullable.NullableLiteral (target_type, loc);
1240                         }
1241
1242                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1243                                 return new Nullable.LiftedConversion (
1244                                         expr, target_type, false, false, loc).Resolve (ec);
1245
1246                         if (expr.eclass == ExprClass.MethodGroup){
1247                                 if (!TypeManager.IsDelegateType (target_type)){
1248                                         return null;
1249                                 }
1250
1251                                 //
1252                                 // Only allow anonymous method conversions on post ISO_1
1253                                 //
1254                                 if (RootContext.Version != LanguageVersion.ISO_1){
1255                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1256                                         if (mg != null)
1257                                                 return ImplicitDelegateCreation.Create (
1258                                                         ec, mg, target_type, false, loc);
1259                                 }
1260                         }
1261
1262                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1263                                 return expr;
1264
1265                         e = ImplicitNumericConversion (ec, expr, target_type, loc);
1266                         if (e != null)
1267                                 return e;
1268
1269                         e = ImplicitReferenceConversion (ec, expr, target_type);
1270                         if (e != null)
1271                                 return e;
1272
1273                         if ((target_type == TypeManager.enum_type ||
1274                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1275                             expr is IntLiteral){
1276                                 IntLiteral i = (IntLiteral) expr;
1277
1278                                 if (i.Value == 0)
1279                                         return new EnumConstant ((Constant) expr, target_type);
1280                         }
1281
1282                         if (ec.InUnsafe) {
1283                                 if (expr_type.IsPointer){
1284                                         if (target_type == TypeManager.void_ptr_type)
1285                                                 return new EmptyCast (expr, target_type);
1286
1287                                         //
1288                                         // yep, comparing pointer types cant be done with
1289                                         // t1 == t2, we have to compare their element types.
1290                                         //
1291                                         if (target_type.IsPointer){
1292                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1293                                                         return expr;
1294                                         }
1295                                 }
1296
1297                                 if (target_type.IsPointer) {
1298                                         if (expr_type == TypeManager.null_type)
1299                                                 return new EmptyCast (NullPointer.Null, target_type);
1300
1301                                         if (expr_type == TypeManager.void_ptr_type)
1302                                                 return new EmptyCast (expr, target_type);
1303                                 }
1304                         }
1305
1306                         if (expr_type == TypeManager.anonymous_method_type){
1307                                 if (!TypeManager.IsDelegateType (target_type)){
1308                                         Report.Error (1660, loc,
1309                                                 "Cannot convert anonymous method block to type `{0}' because it is not a delegate type",
1310                                                 TypeManager.CSharpName (target_type));
1311                                         return null;
1312                                 }
1313
1314                                 AnonymousMethod am = (AnonymousMethod) expr;
1315                                 int errors = Report.Errors;
1316
1317                                 Expression conv = am.Compatible (ec, target_type, false);
1318                                 if (conv != null)
1319                                         return conv;
1320
1321                                 //
1322                                 // We return something instead of null, to avoid
1323                                 // the duplicate error, since am.Compatible would have
1324                                 // reported that already
1325                                 //
1326                                 if (errors != Report.Errors)
1327                                         return new EmptyCast (expr, target_type);
1328                         }
1329
1330                         return null;
1331                 }
1332
1333                 /// <summary>
1334                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1335                 ///   into a different data type using casts (See Implicit Constant
1336                 ///   Expression Conversions)
1337                 /// </summary>
1338                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1339                 {
1340                         int value = ic.Value;
1341
1342                         if (target_type == TypeManager.sbyte_type){
1343                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1344                                         return new SByteConstant ((sbyte) value);
1345                         } else if (target_type == TypeManager.byte_type){
1346                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1347                                         return new ByteConstant ((byte) value);
1348                         } else if (target_type == TypeManager.short_type){
1349                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1350                                         return new ShortConstant ((short) value);
1351                         } else if (target_type == TypeManager.ushort_type){
1352                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1353                                         return new UShortConstant ((ushort) value);
1354                         } else if (target_type == TypeManager.uint32_type){
1355                                 if (value >= 0)
1356                                         return new UIntConstant ((uint) value);
1357                         } else if (target_type == TypeManager.uint64_type){
1358                                 //
1359                                 // we can optimize this case: a positive int32
1360                                 // always fits on a uint64.  But we need an opcode
1361                                 // to do it.
1362                                 //
1363                                 if (value >= 0)
1364                                         return new ULongConstant ((ulong) value);
1365                         } else if (target_type == TypeManager.double_type)
1366                                 return new DoubleConstant ((double) value);
1367                         else if (target_type == TypeManager.float_type)
1368                                 return new FloatConstant ((float) value);
1369
1370                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1371                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1372                                 Constant e = (Constant) ic;
1373
1374                                 //
1375                                 // Possibly, we need to create a different 0 literal before passing
1376                                 // to EnumConstant
1377                                 //
1378                                 if (underlying == TypeManager.int64_type)
1379                                         e = new LongLiteral (0);
1380                                 else if (underlying == TypeManager.uint64_type)
1381                                         e = new ULongLiteral (0);
1382
1383                                 return new EnumConstant (e, target_type);
1384                         }
1385
1386                         //
1387                         // If `target_type' is an interface and the type of `ic' implements the interface
1388                         // e.g. target_type is IComparable, IConvertible, IFormattable
1389                         //
1390                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1391                                 return new BoxedCast (ic, target_type);
1392
1393                         return null;
1394                 }
1395
1396                 static public void Error_CannotImplicitConversion (Location loc, Type source, Type target)
1397                 {
1398                         if (source.FullName == target.FullName){
1399                                 Report.ExtraInformation (loc,
1400                                          String.Format (
1401                                                 "The type {0} has two conflicting definitions, one comes from {1} and the other from {2}",
1402                                                 source.Name, source.Assembly.FullName, target.Assembly.FullName));
1403
1404                         }
1405                         Report.Error (29, loc, "Cannot implicitly convert type {0} to `{1}'",
1406                                       source == TypeManager.anonymous_method_type ?
1407                                       "anonymous method" : "`" + TypeManager.CSharpName (source) + "'",
1408                                       TypeManager.CSharpName (target));
1409                 }
1410
1411                 /// <summary>
1412                 ///   Attempts to implicitly convert `source' into `target_type', using
1413                 ///   ImplicitConversion.  If there is no implicit conversion, then
1414                 ///   an error is signaled
1415                 /// </summary>
1416                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1417                                                                      Type target_type, Location loc)
1418                 {
1419                         Expression e;
1420
1421                         int errors = Report.Errors;
1422                         e = ImplicitConversion (ec, source, target_type, loc);
1423                         if (Report.Errors > errors)
1424                                 return null;
1425                         if (e != null)
1426                                 return e;
1427
1428                         if (source is DoubleLiteral) {
1429                                 if (target_type == TypeManager.float_type) {
1430                                         Error_664 (loc, "float", "f");
1431                                         return null;
1432                                 }
1433                                 if (target_type == TypeManager.decimal_type) {
1434                                         Error_664 (loc, "decimal", "m");
1435                                         return null;
1436                                 }
1437                         }
1438
1439                         source.Error_ValueCannotBeConverted (loc, target_type);
1440                         return null;
1441                 }
1442
1443                 static void Error_664 (Location loc, string type, string suffix) {
1444                         Report.Error (664, loc,
1445                                 "Literal of type double cannot be implicitly converted to type `{0}'. Add suffix `{1}' to create a literal of this type",
1446                                 type, suffix);
1447                 }
1448
1449                 /// <summary>
1450                 ///   Performs the explicit numeric conversions
1451                 /// </summary>
1452                 static Expression ExplicitNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
1453                 {
1454                         Type expr_type = expr.Type;
1455
1456                         //
1457                         // If we have an enumeration, extract the underlying type,
1458                         // use this during the comparison, but wrap around the original
1459                         // target_type
1460                         //
1461                         Type real_target_type = target_type;
1462
1463                         if (TypeManager.IsEnumType (real_target_type))
1464                                 real_target_type = TypeManager.EnumToUnderlying (real_target_type);
1465
1466                         if (ImplicitStandardConversionExists (ec, expr, real_target_type)){
1467                                 Expression ce = ImplicitConversionStandard (ec, expr, real_target_type, loc);
1468
1469                                 if (real_target_type != target_type)
1470                                         return new EmptyCast (ce, target_type);
1471                                 return ce;
1472                         }
1473
1474                         if (expr_type == TypeManager.sbyte_type){
1475                                 //
1476                                 // From sbyte to byte, ushort, uint, ulong, char
1477                                 //
1478                                 if (real_target_type == TypeManager.byte_type)
1479                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U1);
1480                                 if (real_target_type == TypeManager.ushort_type)
1481                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U2);
1482                                 if (real_target_type == TypeManager.uint32_type)
1483                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U4);
1484                                 if (real_target_type == TypeManager.uint64_type)
1485                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U8);
1486                                 if (real_target_type == TypeManager.char_type)
1487                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_CH);
1488                         } else if (expr_type == TypeManager.byte_type){
1489                                 //
1490                                 // From byte to sbyte and char
1491                                 //
1492                                 if (real_target_type == TypeManager.sbyte_type)
1493                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_I1);
1494                                 if (real_target_type == TypeManager.char_type)
1495                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_CH);
1496                         } else if (expr_type == TypeManager.short_type){
1497                                 //
1498                                 // From short to sbyte, byte, ushort, uint, ulong, char
1499                                 //
1500                                 if (real_target_type == TypeManager.sbyte_type)
1501                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_I1);
1502                                 if (real_target_type == TypeManager.byte_type)
1503                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
1504                                 if (real_target_type == TypeManager.ushort_type)
1505                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U2);
1506                                 if (real_target_type == TypeManager.uint32_type)
1507                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U4);
1508                                 if (real_target_type == TypeManager.uint64_type)
1509                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U8);
1510                                 if (real_target_type == TypeManager.char_type)
1511                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_CH);
1512                         } else if (expr_type == TypeManager.ushort_type){
1513                                 //
1514                                 // From ushort to sbyte, byte, short, char
1515                                 //
1516                                 if (real_target_type == TypeManager.sbyte_type)
1517                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I1);
1518                                 if (real_target_type == TypeManager.byte_type)
1519                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_U1);
1520                                 if (real_target_type == TypeManager.short_type)
1521                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I2);
1522                                 if (real_target_type == TypeManager.char_type)
1523                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_CH);
1524                         } else if (expr_type == TypeManager.int32_type){
1525                                 //
1526                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1527                                 //
1528                                 if (real_target_type == TypeManager.sbyte_type)
1529                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I1);
1530                                 if (real_target_type == TypeManager.byte_type)
1531                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
1532                                 if (real_target_type == TypeManager.short_type)
1533                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
1534                                 if (real_target_type == TypeManager.ushort_type)
1535                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U2);
1536                                 if (real_target_type == TypeManager.uint32_type)
1537                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U4);
1538                                 if (real_target_type == TypeManager.uint64_type)
1539                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U8);
1540                                 if (real_target_type == TypeManager.char_type)
1541                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_CH);
1542                         } else if (expr_type == TypeManager.uint32_type){
1543                                 //
1544                                 // From uint to sbyte, byte, short, ushort, int, char
1545                                 //
1546                                 if (real_target_type == TypeManager.sbyte_type)
1547                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I1);
1548                                 if (real_target_type == TypeManager.byte_type)
1549                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U1);
1550                                 if (real_target_type == TypeManager.short_type)
1551                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I2);
1552                                 if (real_target_type == TypeManager.ushort_type)
1553                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U2);
1554                                 if (real_target_type == TypeManager.int32_type)
1555                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I4);
1556                                 if (real_target_type == TypeManager.char_type)
1557                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_CH);
1558                         } else if (expr_type == TypeManager.int64_type){
1559                                 //
1560                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1561                                 //
1562                                 if (real_target_type == TypeManager.sbyte_type)
1563                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I1);
1564                                 if (real_target_type == TypeManager.byte_type)
1565                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
1566                                 if (real_target_type == TypeManager.short_type)
1567                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
1568                                 if (real_target_type == TypeManager.ushort_type)
1569                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U2);
1570                                 if (real_target_type == TypeManager.int32_type)
1571                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
1572                                 if (real_target_type == TypeManager.uint32_type)
1573                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U4);
1574                                 if (real_target_type == TypeManager.uint64_type)
1575                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U8);
1576                                 if (real_target_type == TypeManager.char_type)
1577                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_CH);
1578                         } else if (expr_type == TypeManager.uint64_type){
1579                                 //
1580                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1581                                 //
1582                                 if (real_target_type == TypeManager.sbyte_type)
1583                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I1);
1584                                 if (real_target_type == TypeManager.byte_type)
1585                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U1);
1586                                 if (real_target_type == TypeManager.short_type)
1587                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I2);
1588                                 if (real_target_type == TypeManager.ushort_type)
1589                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U2);
1590                                 if (real_target_type == TypeManager.int32_type)
1591                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I4);
1592                                 if (real_target_type == TypeManager.uint32_type)
1593                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U4);
1594                                 if (real_target_type == TypeManager.int64_type)
1595                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I8);
1596                                 if (real_target_type == TypeManager.char_type)
1597                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_CH);
1598                         } else if (expr_type == TypeManager.char_type){
1599                                 //
1600                                 // From char to sbyte, byte, short
1601                                 //
1602                                 if (real_target_type == TypeManager.sbyte_type)
1603                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I1);
1604                                 if (real_target_type == TypeManager.byte_type)
1605                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_U1);
1606                                 if (real_target_type == TypeManager.short_type)
1607                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I2);
1608                         } else if (expr_type == TypeManager.float_type){
1609                                 //
1610                                 // From float to sbyte, byte, short,
1611                                 // ushort, int, uint, long, ulong, char
1612                                 // or decimal
1613                                 //
1614                                 if (real_target_type == TypeManager.sbyte_type)
1615                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
1616                                 if (real_target_type == TypeManager.byte_type)
1617                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U1);
1618                                 if (real_target_type == TypeManager.short_type)
1619                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I2);
1620                                 if (real_target_type == TypeManager.ushort_type)
1621                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U2);
1622                                 if (real_target_type == TypeManager.int32_type)
1623                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I4);
1624                                 if (real_target_type == TypeManager.uint32_type)
1625                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U4);
1626                                 if (real_target_type == TypeManager.int64_type)
1627                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I8);
1628                                 if (real_target_type == TypeManager.uint64_type)
1629                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U8);
1630                                 if (real_target_type == TypeManager.char_type)
1631                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_CH);
1632                                 if (real_target_type == TypeManager.decimal_type)
1633                                         return new CastToDecimal (ec, expr, true);
1634                         } else if (expr_type == TypeManager.double_type){
1635                                 //
1636                                 // From double to sbyte, byte, short,
1637                                 // ushort, int, uint, long, ulong,
1638                                 // char, float or decimal
1639                                 //
1640                                 if (real_target_type == TypeManager.sbyte_type)
1641                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I1);
1642                                 if (real_target_type == TypeManager.byte_type)
1643                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1644                                 if (real_target_type == TypeManager.short_type)
1645                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1646                                 if (real_target_type == TypeManager.ushort_type)
1647                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U2);
1648                                 if (real_target_type == TypeManager.int32_type)
1649                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1650                                 if (real_target_type == TypeManager.uint32_type)
1651                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U4);
1652                                 if (real_target_type == TypeManager.int64_type)
1653                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1654                                 if (real_target_type == TypeManager.uint64_type)
1655                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U8);
1656                                 if (real_target_type == TypeManager.char_type)
1657                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_CH);
1658                                 if (real_target_type == TypeManager.float_type)
1659                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
1660                                 if (real_target_type == TypeManager.decimal_type)
1661                                         return new CastToDecimal (ec, expr, true);
1662                         } else if (expr_type == TypeManager.decimal_type) {
1663                                 //
1664                                 // From decimal to sbyte, byte, short, ushort, int, uint,
1665                                 // long, ulong, char, double or float
1666                                 //
1667                                 if (real_target_type == TypeManager.sbyte_type ||
1668                                     real_target_type == TypeManager.byte_type ||
1669                                     real_target_type == TypeManager.short_type ||
1670                                     real_target_type == TypeManager.ushort_type ||
1671                                     real_target_type == TypeManager.int32_type ||
1672                                     real_target_type == TypeManager.uint32_type ||
1673                                     real_target_type == TypeManager.int64_type ||
1674                                     real_target_type == TypeManager.uint64_type ||
1675                                     real_target_type == TypeManager.char_type ||
1676                                     real_target_type == TypeManager.double_type ||
1677                                     real_target_type == TypeManager.float_type)
1678                                         return new CastFromDecimal (ec, expr, target_type);
1679                         }
1680                         return null;
1681                 }
1682
1683                 /// <summary>
1684                 ///  Returns whether an explicit reference conversion can be performed
1685                 ///  from source_type to target_type
1686                 /// </summary>
1687                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1688                 {
1689                         bool target_is_type_param = target_type.IsGenericParameter;
1690                         bool target_is_value_type = target_type.IsValueType;
1691
1692                         if (source_type == target_type)
1693                                 return true;
1694
1695                         //
1696                         // From generic parameter to any type
1697                         //
1698                         if (source_type.IsGenericParameter)
1699                                 return true;
1700
1701                         //
1702                         // From object to a generic parameter
1703                         //
1704                         if (source_type == TypeManager.object_type && target_is_type_param)
1705                                 return true;
1706
1707                         //
1708                         // From object to any reference type
1709                         //
1710                         if (source_type == TypeManager.object_type && !target_is_value_type)
1711                                 return true;
1712
1713                         //
1714                         // From any class S to any class-type T, provided S is a base class of T
1715                         //
1716                         if (TypeManager.IsSubclassOf (target_type, source_type))
1717                                 return true;
1718
1719                         //
1720                         // From any interface type S to any interface T provided S is not derived from T
1721                         //
1722                         if (source_type.IsInterface && target_type.IsInterface){
1723                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1724                                         return true;
1725                         }
1726
1727                         //
1728                         // From any class type S to any interface T, provided S is not sealed
1729                         // and provided S does not implement T.
1730                         //
1731                         if (target_type.IsInterface && !source_type.IsSealed &&
1732                             !TypeManager.ImplementsInterface (source_type, target_type))
1733                                 return true;
1734
1735                         //
1736                         // From any interface-type S to to any class type T, provided T is not
1737                         // sealed, or provided T implements S.
1738                         //
1739                         if (source_type.IsInterface &&
1740                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1741                                 return true;
1742
1743
1744                         // From an array type S with an element type Se to an array type T with an
1745                         // element type Te provided all the following are true:
1746                         //     * S and T differe only in element type, in other words, S and T
1747                         //       have the same number of dimensions.
1748                         //     * Both Se and Te are reference types
1749                         //     * An explicit referenc conversions exist from Se to Te
1750                         //
1751                         if (source_type.IsArray && target_type.IsArray) {
1752                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1753
1754                                         Type source_element_type = TypeManager.GetElementType (source_type);
1755                                         Type target_element_type = TypeManager.GetElementType (target_type);
1756
1757                                         if (source_element_type.IsGenericParameter ||
1758                                             (!source_element_type.IsValueType && !target_element_type.IsValueType))
1759                                                 if (ExplicitReferenceConversionExists (source_element_type,
1760                                                                                        target_element_type))
1761                                                         return true;
1762                                 }
1763                         }
1764
1765
1766                         // From System.Array to any array-type
1767                         if (source_type == TypeManager.array_type &&
1768                             target_type.IsArray){
1769                                 return true;
1770                         }
1771
1772                         //
1773                         // From System delegate to any delegate-type
1774                         //
1775                         if (source_type == TypeManager.delegate_type &&
1776                             TypeManager.IsDelegateType (target_type))
1777                                 return true;
1778
1779                         //
1780                         // From ICloneable to Array or Delegate types
1781                         //
1782                         if (source_type == TypeManager.icloneable_type &&
1783                             (target_type == TypeManager.array_type ||
1784                              target_type == TypeManager.delegate_type))
1785                                 return true;
1786
1787                         return false;
1788                 }
1789
1790                 /// <summary>
1791                 ///   Implements Explicit Reference conversions
1792                 /// </summary>
1793                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1794                 {
1795                         Type source_type = source.Type;
1796                         bool target_is_type_param = target_type.IsGenericParameter;
1797                         bool target_is_value_type = target_type.IsValueType;
1798
1799                         //
1800                         // From object to a generic parameter
1801                         //
1802                         if (source_type == TypeManager.object_type && target_is_type_param)
1803                                 return new UnboxCast (source, target_type);
1804
1805                         //
1806                         // From object to any reference type
1807                         //
1808                         if (source_type == TypeManager.object_type && !target_is_value_type)
1809                                 return new ClassCast (source, target_type);
1810
1811                         //
1812                         // Unboxing conversion.
1813                         //
1814                         if (((source_type == TypeManager.enum_type &&
1815                                 !(source is EmptyCast)) ||
1816                                 source_type == TypeManager.value_type) && target_is_value_type)
1817                                 return new UnboxCast (source, target_type);
1818
1819                         //
1820                         // From any class S to any class-type T, provided S is a base class of T
1821                         //
1822                         if (TypeManager.IsSubclassOf (target_type, source_type))
1823                                 return new ClassCast (source, target_type);
1824
1825                         //
1826                         // From any interface type S to any interface T provided S is not derived from T
1827                         //
1828                         if (source_type.IsInterface && target_type.IsInterface){
1829                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1830                                         return null;
1831                                 else
1832                                         return new ClassCast (source, target_type);
1833                         }
1834
1835                         //
1836                         // From any class type S to any interface T, provides S is not sealed
1837                         // and provided S does not implement T.
1838                         //
1839                         if (target_type.IsInterface && !source_type.IsSealed) {
1840                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1841                                         return null;
1842                                 else
1843                                         return new ClassCast (source, target_type);
1844
1845                         }
1846
1847                         //
1848                         // From any interface-type S to to any class type T, provided T is not
1849                         // sealed, or provided T implements S.
1850                         //
1851                         if (source_type.IsInterface) {
1852                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1853                                         if (target_type.IsClass)
1854                                                 return new ClassCast (source, target_type);
1855                                         else
1856                                                 return new UnboxCast (source, target_type);
1857                                 }
1858
1859                                 return null;
1860                         }
1861
1862                         // From an array type S with an element type Se to an array type T with an
1863                         // element type Te provided all the following are true:
1864                         //     * S and T differe only in element type, in other words, S and T
1865                         //       have the same number of dimensions.
1866                         //     * Both Se and Te are reference types
1867                         //     * An explicit referenc conversions exist from Se to Te
1868                         //
1869                         if (source_type.IsArray && target_type.IsArray) {
1870                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1871
1872                                         Type source_element_type = TypeManager.GetElementType (source_type);
1873                                         Type target_element_type = TypeManager.GetElementType (target_type);
1874
1875                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1876                                                 if (ExplicitReferenceConversionExists (source_element_type,
1877                                                                                        target_element_type))
1878                                                         return new ClassCast (source, target_type);
1879                                 }
1880                         }
1881
1882
1883                         // From System.Array to any array-type
1884                         if (source_type == TypeManager.array_type &&
1885                             target_type.IsArray) {
1886                                 return new ClassCast (source, target_type);
1887                         }
1888
1889                         //
1890                         // From System delegate to any delegate-type
1891                         //
1892                         if (source_type == TypeManager.delegate_type &&
1893                             TypeManager.IsDelegateType (target_type))
1894                                 return new ClassCast (source, target_type);
1895
1896                         //
1897                         // From ICloneable to Array or Delegate types
1898                         //
1899                         if (source_type == TypeManager.icloneable_type &&
1900                             (target_type == TypeManager.array_type ||
1901                              target_type == TypeManager.delegate_type))
1902                                 return new ClassCast (source, target_type);
1903
1904                         return null;
1905                 }
1906
1907                 /// <summary>
1908                 ///   Performs an explicit conversion of the expression `expr' whose
1909                 ///   type is expr.Type to `target_type'.
1910                 /// </summary>
1911                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1912                                                              Type target_type, Location loc)
1913                 {
1914                         Type expr_type = expr.Type;
1915                         Type original_expr_type = expr_type;
1916
1917                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1918
1919                         if (ne != null)
1920                                 return ne;
1921
1922                         if (expr_type.IsSubclassOf (TypeManager.enum_type)){
1923                                 if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
1924                                            target_type.IsSubclassOf (TypeManager.enum_type))
1925                                         return new UnboxCast (expr, target_type);
1926
1927                                 //
1928                                 // Notice that we have kept the expr_type unmodified, which is only
1929                                 // used later on to
1930                                 if (expr is EnumConstant)
1931                                         expr = ((EnumConstant) expr).Child;
1932                                 else
1933                                         expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
1934                                 expr_type = expr.Type;
1935                         }
1936
1937                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
1938                                 return new Nullable.LiftedConversion (
1939                                         expr, target_type, false, true, loc).Resolve (ec);
1940
1941                         ne = ExplicitNumericConversion (ec, expr, target_type, loc);
1942                         if (ne != null)
1943                                 return ne;
1944
1945                         //
1946                         // Unboxing conversion.
1947                         //
1948                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1949                                 return new UnboxCast (expr, target_type);
1950
1951                         //
1952                         // Skip the ExplicitReferenceConversion because we can not convert
1953                         // from Null to a ValueType, and ExplicitReference wont check against
1954                         // null literal explicitly
1955                         //
1956                         if (expr_type != TypeManager.null_type){
1957                                 ne = ExplicitReferenceConversion (expr, target_type);
1958                                 if (ne != null)
1959                                         return ne;
1960                         }
1961
1962                         if (ec.InUnsafe){
1963                                 if (target_type.IsPointer){
1964                                         if (expr_type.IsPointer)
1965                                                 return new EmptyCast (expr, target_type);
1966
1967                                         if (expr_type == TypeManager.sbyte_type ||
1968                                             expr_type == TypeManager.short_type ||
1969                                             expr_type == TypeManager.int32_type ||
1970                                             expr_type == TypeManager.int64_type)
1971                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1972
1973                                         if (expr_type == TypeManager.ushort_type ||
1974                                             expr_type == TypeManager.uint32_type ||
1975                                             expr_type == TypeManager.uint64_type ||
1976                                             expr_type == TypeManager.byte_type)
1977                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1978                                 }
1979                                 if (expr_type.IsPointer){
1980                                         Expression e = null;
1981
1982                                         if (target_type == TypeManager.sbyte_type)
1983                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1984                                         else if (target_type == TypeManager.byte_type)
1985                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1986                                         else if (target_type == TypeManager.short_type)
1987                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1988                                         else if (target_type == TypeManager.ushort_type)
1989                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1990                                         else if (target_type == TypeManager.int32_type)
1991                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1992                                         else if (target_type == TypeManager.uint32_type)
1993                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1994                                         else if (target_type == TypeManager.uint64_type)
1995                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1996                                         else if (target_type == TypeManager.int64_type){
1997                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1998                                         }
1999
2000                                         if (e != null){
2001                                                 Expression ci, ce;
2002
2003                                                 ci = ImplicitConversionStandard (ec, e, target_type, loc);
2004
2005                                                 if (ci != null)
2006                                                         return ci;
2007
2008                                                 ce = ExplicitNumericConversion (ec, e, target_type, loc);
2009                                                 if (ce != null)
2010                                                         return ce;
2011                                                 //
2012                                                 // We should always be able to go from an uint32
2013                                                 // implicitly or explicitly to the other integral
2014                                                 // types
2015                                                 //
2016                                                 throw new Exception ("Internal compiler error");
2017                                         }
2018                                 }
2019                         }
2020
2021                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
2022                         if (ne != null)
2023                                 return ne;
2024
2025                         if (expr is Constant)
2026                                 expr.Error_ValueCannotBeConverted (loc, target_type);
2027                         else
2028                                 Error_CannotConvertType (loc, original_expr_type, target_type);
2029                         return null;
2030                 }
2031
2032                 /// <summary>
2033                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
2034                 /// </summary>
2035                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
2036                                                                      Type target_type, Location l)
2037                 {
2038                         int errors = Report.Errors;
2039                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
2040                         if (Report.Errors > errors)
2041                                 return null;
2042
2043                         if (ne != null)
2044                                 return ne;
2045
2046                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
2047                                 return new Nullable.LiftedConversion (
2048                                         expr, target_type, false, true, l).Resolve (ec);
2049
2050                         ne = ExplicitNumericConversion (ec, expr, target_type, l);
2051                         if (ne != null)
2052                                 return ne;
2053
2054                         ne = ExplicitReferenceConversion (expr, target_type);
2055                         if (ne != null)
2056                                 return ne;
2057
2058                         Error_CannotConvertType (l, expr.Type, target_type);
2059                         return null;
2060                 }
2061         }
2062 }