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 Expression TypeParameter_to_Null (Expression expr, Type target_type,
  33                                                          Location loc)
  34                 {
  35                         if (!TypeParameter_to_Null (target_type)) {
  36                                 Report.Error (403, loc, "Cannot convert null to the type " +
  37                                               "parameter `{0}' becaues it could be a value " +
  38                                               "type.  Consider using `default ({0})' instead.",
  39                                               target_type);
  40                                 return null;
  41                         }
  42
  43                         return new NullCast (expr, target_type);
  44                 }
  45
  46                 static bool TypeParameter_to_Null (Type target_type)
  47                 {
  48                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
  49                         if (gc == null)
  50                                 return false;
  51
  52                         if (gc.HasReferenceTypeConstraint)
  53                                 return true;
  54                         if (gc.HasClassConstraint && !TypeManager.IsValueType (gc.ClassConstraint))
  55                                 return true;
  56
  57                         return false;
  58                 }
  59
  60                 static Type TypeParam_EffectiveBaseType (EmitContext ec, GenericConstraints gc)
  61                 {
  62                         ArrayList list = new ArrayList ();
  63                         list.Add (gc.EffectiveBaseClass);
  64                         foreach (Type t in gc.InterfaceConstraints) {
  65                                 if (!t.IsGenericParameter)
  66                                         continue;
  67
  68                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  69                                 if (new_gc != null)
  70                                         list.Add (TypeParam_EffectiveBaseType (ec, new_gc));
  71                         }
  72                         return FindMostEncompassedType (ec, list);
  73                 }
  74
  75                 static Expression ImplicitTypeParameterConversion (EmitContext ec, Expression expr,
  76                                                                    Type target_type)
  77                 {
  78                         Type expr_type = expr.Type;
  79
  80                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
  81
  82                         if (gc == null) {
  83                                 if (target_type == TypeManager.object_type)
  84                                         return new BoxedCast (expr, target_type);
  85
  86                                 return null;
  87                         }
  88
  89                         // We're converting from a type parameter which is known to be a reference type.
  90                         Type base_type = TypeParam_EffectiveBaseType (ec, gc);
  91
  92                         if (TypeManager.IsSubclassOf (base_type, target_type))
  93                                 return new BoxedCast (expr, target_type);
  94
  95                         if (target_type.IsInterface) {
  96                                 if (TypeManager.ImplementsInterface (base_type, target_type))
  97                                         return new BoxedCast (expr, target_type);
  98
  99                                 foreach (Type t in gc.InterfaceConstraints) {
 100                                         if (TypeManager.IsSubclassOf (t, target_type))
 101                                                 return new BoxedCast (expr, target_type);
 102                                 }
 103                         }
 104
 105                         foreach (Type t in gc.InterfaceConstraints) {
 106                                 if (!t.IsGenericParameter)
 107                                         continue;
 108                                 if (TypeManager.IsSubclassOf (t, target_type))
 109                                         return new BoxedCast (expr, target_type);
 110                         }
 111
 112                         return null;
 113                 }
 114
 115                 static EmptyExpression MyEmptyExpr;
 116                 static public Expression ImplicitReferenceConversion (EmitContext ec, Expression expr, Type target_type)
 117                 {
 118                         Type expr_type = expr.Type;
 119
 120                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 121                                 // if we are a method group, emit a warning
 122
 123                                 expr.Emit (null);
 124                         }
 125
 126                         if (expr_type == TypeManager.void_type)
 127                                 return null;
 128
 129                         if (expr_type.IsGenericParameter)
 130                                 return ImplicitTypeParameterConversion (ec, expr, target_type);
 131
 132                         //
 133                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 134                         // is an abstract class, and not really a value type, so we apply the same rules.
 135                         //
 136                         if (target_type == TypeManager.object_type) {
 137                                 //
 138                                 // A pointer type cannot be converted to object
 139                                 //
 140                                 if (expr_type.IsPointer)
 141                                         return null;
 142
 143                                 if (TypeManager.IsValueType (expr_type))
 144                                         return new BoxedCast (expr, target_type);
 145                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 146                                         if (expr_type == TypeManager.anonymous_method_type)
 147                                                 return null;
 148                                         return new EmptyCast (expr, target_type);
 149                                 }
 150
 151                                 return null;
 152                         } else if (target_type == TypeManager.value_type) {
 153                                 if (TypeManager.IsValueType (expr_type))
 154                                         return new BoxedCast (expr, target_type);
 155                                 if (expr_type == TypeManager.null_type)
 156                                         return new NullCast (expr, target_type);
 157
 158                                 return null;
 159                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 160                                 //
 161                                 // Special case: enumeration to System.Enum.
 162                                 // System.Enum is not a value type, it is a class, so we need
 163                                 // a boxing conversion
 164                                 //
 165                                 if (expr_type.IsEnum || expr_type.IsGenericParameter)
 166                                         return new BoxedCast (expr, target_type);
 167
 168                                 return new EmptyCast (expr, target_type);
 169                         }
 170
 171                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 172                         // with the small distinction that we only probe there
 173                         //
 174                         // Always ensure that the code here and there is in sync
 175
 176                         // from the null type to any reference-type.
 177                         if (expr_type == TypeManager.null_type){
 178                                 if (target_type.IsPointer)
 179                                         return new EmptyCast (NullPointer.Null, target_type);
 180
 181                                 if (!target_type.IsValueType)
 182                                         return new NullCast (expr, target_type);
 183                         }
 184
 185                         // from any class-type S to any interface-type T.
 186                         if (target_type.IsInterface) {
 187                                 if (target_type != TypeManager.iconvertible_type &&
 188                                     expr_type.IsValueType && (expr is Constant) &&
 189                                     !(expr is IntLiteral || expr is BoolLiteral ||
 190                                       expr is FloatLiteral || expr is DoubleLiteral ||
 191                                       expr is LongLiteral || expr is CharLiteral ||
 192                                       expr is StringLiteral || expr is DecimalLiteral ||
 193                                       expr is UIntLiteral || expr is ULongLiteral)) {
 194                                         return null;
 195                                 }
 196
 197                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 198                                         if (expr_type.IsGenericParameter || TypeManager.IsValueType (expr_type))
 199                                                 return new BoxedCast (expr, target_type);
 200                                         else
 201                                                 return new EmptyCast (expr, target_type);
 202                                 }
 203                         }
 204
 205                         // from any interface type S to interface-type T.
 206                         if (expr_type.IsInterface && target_type.IsInterface) {
 207                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 208                                         return new EmptyCast (expr, target_type);
 209                                 else
 210                                         return null;
 211                         }
 212
 213                         // from an array-type S to an array-type of type T
 214                         if (expr_type.IsArray && target_type.IsArray) {
 215                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 216
 217                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 218
 219                                         if (MyEmptyExpr == null)
 220                                                 MyEmptyExpr = new EmptyExpression ();
 221
 222                                         MyEmptyExpr.SetType (expr_element_type);
 223                                         Type target_element_type = TypeManager.GetElementType (target_type);
 224
 225                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 226                                                 if (ImplicitStandardConversionExists (ConstantEC, MyEmptyExpr,
 227                                                                                       target_element_type))
 228                                                         return new EmptyCast (expr, target_type);
 229                                 }
 230                         }
 231
 232                         // from an array-type to System.Array
 233                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 234                                 return new EmptyCast (expr, target_type);
 235
 236                         // from an array-type of type T to IEnumerable<T>
 237                         if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
 238                                 return new EmptyCast (expr, target_type);
 239
 240                         // from any delegate type to System.Delegate
 241                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 242                             target_type == TypeManager.delegate_type)
 243                                 return new EmptyCast (expr, target_type);
 244
 245                         // from any array-type or delegate type into System.ICloneable.
 246                         if (expr_type.IsArray ||
 247                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 248                                 if (target_type == TypeManager.icloneable_type)
 249                                         return new EmptyCast (expr, target_type);
 250
 251                         // from a generic type definition to a generic instance.
 252                         if (TypeManager.IsEqual (expr_type, target_type))
 253                                 return new EmptyCast (expr, target_type);
 254
 255                         return null;
 256                 }
 257
 258                 //
 259                 // Tests whether an implicit reference conversion exists between expr_type
 260                 // and target_type
 261                 //
 262                 public static bool ImplicitReferenceConversionExists (EmitContext ec, Expression expr, Type target_type)
 263                 {
 264                         if (target_type.IsValueType)
 265                                 return false;
 266
 267                         Type expr_type = expr.Type;
 268
 269                         if (expr_type.IsGenericParameter)
 270                                 return ImplicitTypeParameterConversion (ec, expr, target_type) != null;
 271
 272                         //
 273                         // This is the boxed case.
 274                         //
 275                         if (target_type == TypeManager.object_type) {
 276                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 277                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 278                                         if (target_type != TypeManager.anonymous_method_type)
 279                                         return true;
 280
 281                                 return false;
 282                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 283                                 return true;
 284
 285                         // Please remember that all code below actually comes
 286                         // from ImplicitReferenceConversion so make sure code remains in sync
 287
 288                         // from any class-type S to any interface-type T.
 289                         if (target_type.IsInterface) {
 290                                 if (target_type != TypeManager.iconvertible_type &&
 291                                     expr_type.IsValueType && (expr is Constant) &&
 292                                     !(expr is IntLiteral || expr is BoolLiteral ||
 293                                       expr is FloatLiteral || expr is DoubleLiteral ||
 294                                       expr is LongLiteral || expr is CharLiteral ||
 295                                       expr is StringLiteral || expr is DecimalLiteral ||
 296                                       expr is UIntLiteral || expr is ULongLiteral)) {
 297                                         return false;
 298                                 }
 299
 300                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 301                                         return true;
 302                         }
 303
 304                         // from any interface type S to interface-type T.
 305                         if (expr_type.IsInterface && target_type.IsInterface)
 306                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 307                                         return true;
 308
 309                         // from an array-type S to an array-type of type T
 310                         if (expr_type.IsArray && target_type.IsArray) {
 311                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 312
 313                                         Type expr_element_type = expr_type.GetElementType ();
 314
 315                                         if (MyEmptyExpr == null)
 316                                                 MyEmptyExpr = new EmptyExpression ();
 317
 318                                         MyEmptyExpr.SetType (expr_element_type);
 319                                         Type target_element_type = TypeManager.GetElementType (target_type);
 320
 321                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 322                                                 if (ImplicitStandardConversionExists (ConstantEC, MyEmptyExpr,
 323                                                                                       target_element_type))
 324                                                         return true;
 325                                 }
 326                         }
 327
 328                         // from an array-type to System.Array
 329                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 330                                 return true;
 331
 332                         // from an array-type of type T to IEnumerable<T>
 333                         if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
 334                                 return true;
 335
 336                         // from any delegate type to System.Delegate
 337                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 338                             target_type == TypeManager.delegate_type)
 339                                 if (target_type.IsAssignableFrom (expr_type))
 340                                         return true;
 341
 342                         // from any array-type or delegate type into System.ICloneable.
 343                         if (expr_type.IsArray ||
 344                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 345                                 if (target_type == TypeManager.icloneable_type)
 346                                         return true;
 347
 348                         // from the null type to any reference-type.
 349                         if (expr_type == TypeManager.null_type){
 350                                 if (target_type.IsPointer)
 351                                         return true;
 352
 353                                 if (!target_type.IsValueType)
 354                                         return true;
 355                         }
 356
 357                         // from a generic type definition to a generic instance.
 358                         if (TypeManager.IsEqual (expr_type, target_type))
 359                                 return true;
 360
 361                         return false;
 362                 }
 363
 364                 /// <summary>
 365                 ///   Implicit Numeric Conversions.
 366                 ///
 367                 ///   expr is the expression to convert, returns a new expression of type
 368                 ///   target_type or null if an implicit conversion is not possible.
 369                 /// </summary>
 370                 static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
 371                                                                     Type target_type)
 372                 {
 373                         Type expr_type = expr.Type;
 374
 375                         //
 376                         // Attempt to do the implicit constant expression conversions
 377
 378                         if (expr is Constant){
 379                                 if (expr is IntConstant){
 380                                         Expression e;
 381
 382                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 383
 384                                         if (e != null)
 385                                                 return e;
 386                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 387                                         //
 388                                         // Try the implicit constant expression conversion
 389                                         // from long to ulong, instead of a nice routine,
 390                                         // we just inline it
 391                                         //
 392                                         long v = ((LongConstant) expr).Value;
 393                                         if (v >= 0)
 394                                                 return new ULongConstant ((ulong) v, expr.Location);
 395                                 }
 396                         }
 397
 398                         Type real_target_type = target_type;
 399
 400                         if (expr_type == TypeManager.sbyte_type){
 401                                 //
 402                                 // From sbyte to short, int, long, float, double, decimal
 403                                 //
 404                                 if (real_target_type == TypeManager.int32_type)
 405                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 406                                 if (real_target_type == TypeManager.int64_type)
 407                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 408                                 if (real_target_type == TypeManager.double_type)
 409                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 410                                 if (real_target_type == TypeManager.float_type)
 411                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 412                                 if (real_target_type == TypeManager.short_type)
 413                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 414                                 if (real_target_type == TypeManager.decimal_type)
 415                                         return new CastToDecimal (expr);
 416                         } else if (expr_type == TypeManager.byte_type){
 417                                 //
 418                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 419                                 //
 420                                 if ((real_target_type == TypeManager.short_type) ||
 421                                     (real_target_type == TypeManager.ushort_type) ||
 422                                     (real_target_type == TypeManager.int32_type) ||
 423                                     (real_target_type == TypeManager.uint32_type))
 424                                         return new EmptyCast (expr, target_type);
 425
 426                                 if (real_target_type == TypeManager.uint64_type)
 427                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 428                                 if (real_target_type == TypeManager.int64_type)
 429                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 430                                 if (real_target_type == TypeManager.float_type)
 431                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 432                                 if (real_target_type == TypeManager.double_type)
 433                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 434                                 if (real_target_type == TypeManager.decimal_type)
 435                                         return new CastToDecimal (expr);
 436
 437                         } else if (expr_type == TypeManager.short_type){
 438                                 //
 439                                 // From short to int, long, float, double, decimal
 440                                 //
 441                                 if (real_target_type == TypeManager.int32_type)
 442                                         return new EmptyCast (expr, target_type);
 443                                 if (real_target_type == TypeManager.int64_type)
 444                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 445                                 if (real_target_type == TypeManager.double_type)
 446                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 447                                 if (real_target_type == TypeManager.float_type)
 448                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 449                                 if (real_target_type == TypeManager.decimal_type)
 450                                         return new CastToDecimal (expr);
 451
 452                         } else if (expr_type == TypeManager.ushort_type){
 453                                 //
 454                                 // From ushort to int, uint, long, ulong, float, double, decimal
 455                                 //
 456                                 if (real_target_type == TypeManager.uint32_type)
 457                                         return new EmptyCast (expr, target_type);
 458
 459                                 if (real_target_type == TypeManager.uint64_type)
 460                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 461                                 if (real_target_type == TypeManager.int32_type)
 462                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 463                                 if (real_target_type == TypeManager.int64_type)
 464                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 465                                 if (real_target_type == TypeManager.double_type)
 466                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 467                                 if (real_target_type == TypeManager.float_type)
 468                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 469                                 if (real_target_type == TypeManager.decimal_type)
 470                                         return new CastToDecimal (expr);
 471                         } else if (expr_type == TypeManager.int32_type){
 472                                 //
 473                                 // From int to long, float, double, decimal
 474                                 //
 475                                 if (real_target_type == TypeManager.int64_type)
 476                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 477                                 if (real_target_type == TypeManager.double_type)
 478                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 479                                 if (real_target_type == TypeManager.float_type)
 480                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 481                                 if (real_target_type == TypeManager.decimal_type)
 482                                         return new CastToDecimal (expr);
 483                         } else if (expr_type == TypeManager.uint32_type){
 484                                 //
 485                                 // From uint to long, ulong, float, double, decimal
 486                                 //
 487                                 if (real_target_type == TypeManager.int64_type)
 488                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 489                                 if (real_target_type == TypeManager.uint64_type)
 490                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 491                                 if (real_target_type == TypeManager.double_type)
 492                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 493                                                                OpCodes.Conv_R8);
 494                                 if (real_target_type == TypeManager.float_type)
 495                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 496                                                                OpCodes.Conv_R4);
 497                                 if (real_target_type == TypeManager.decimal_type)
 498                                         return new CastToDecimal (expr);
 499                         } else if (expr_type == TypeManager.int64_type){
 500                                 //
 501                                 // From long/ulong to float, double
 502                                 //
 503                                 if (real_target_type == TypeManager.double_type)
 504                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 505                                 if (real_target_type == TypeManager.float_type)
 506                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 507                                 if (real_target_type == TypeManager.decimal_type)
 508                                         return new CastToDecimal (expr);
 509                         } else if (expr_type == TypeManager.uint64_type){
 510                                 //
 511                                 // From ulong to float, double
 512                                 //
 513                                 if (real_target_type == TypeManager.double_type)
 514                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 515                                                                OpCodes.Conv_R8);
 516                                 if (real_target_type == TypeManager.float_type)
 517                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 518                                                                OpCodes.Conv_R4);
 519                                 if (real_target_type == TypeManager.decimal_type)
 520                                         return new CastToDecimal (expr);
 521                         } else if (expr_type == TypeManager.char_type){
 522                                 //
 523                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 524                                 //
 525                                 if ((real_target_type == TypeManager.ushort_type) ||
 526                                     (real_target_type == TypeManager.int32_type) ||
 527                                     (real_target_type == TypeManager.uint32_type))
 528                                         return new EmptyCast (expr, target_type);
 529                                 if (real_target_type == TypeManager.uint64_type)
 530                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 531                                 if (real_target_type == TypeManager.int64_type)
 532                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 533                                 if (real_target_type == TypeManager.float_type)
 534                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 535                                 if (real_target_type == TypeManager.double_type)
 536                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 537                                 if (real_target_type == TypeManager.decimal_type)
 538                                         return new CastToDecimal (expr);
 539                         } else if (expr_type == TypeManager.float_type){
 540                                 //
 541                                 // float to double
 542                                 //
 543                                 if (real_target_type == TypeManager.double_type)
 544                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 545                         }
 546
 547                         return null;
 548                 }
 549
 550                 /// <summary>
 551                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 552                 ///  implicit user defined conversions - needed for overload resolution
 553                 /// </summary>
 554                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 555                 {
 556                         if (expr is NullLiteral) {
 557                                 if (target_type.IsGenericParameter)
 558                                         return TypeParameter_to_Null (target_type);
 559
 560                                 if (TypeManager.IsNullableType (target_type))
 561                                         return true;
 562                         }
 563
 564                         if (ImplicitStandardConversionExists (ec, expr, target_type))
 565                                 return true;
 566
 567                         Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);
 568
 569                         if (dummy != null)
 570                                 return true;
 571
 572                         return false;
 573                 }
 574
 575                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 576                 {
 577                         return ImplicitUserConversion (ec, new EmptyExpression (source), target, Location.Null) != null;
 578                 }
 579
 580                 /// <summary>
 581                 ///  Determines if a standard implicit conversion exists from
 582                 ///  expr_type to target_type
 583                 ///
 584                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 585                 /// </summary>
 586                 public static bool ImplicitStandardConversionExists (EmitContext ec, Expression expr, Type target_type)
 587                 {
 588                         Type expr_type = expr.Type;
 589
 590                         if (expr_type == TypeManager.void_type)
 591                                 return false;
 592
 593                         //Console.WriteLine ("Expr is {0}", expr);
 594                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 595                         if (expr_type.Equals (target_type))
 596                                 return true;
 597
 598
 599                         // First numeric conversions
 600
 601                         if (expr_type == TypeManager.sbyte_type){
 602                                 //
 603                                 // From sbyte to short, int, long, float, double, decimal
 604                                 //
 605                                 if ((target_type == TypeManager.int32_type) ||
 606                                     (target_type == TypeManager.int64_type) ||
 607                                     (target_type == TypeManager.double_type) ||
 608                                     (target_type == TypeManager.float_type)  ||
 609                                     (target_type == TypeManager.short_type) ||
 610                                     (target_type == TypeManager.decimal_type))
 611                                         return true;
 612
 613                         } else if (expr_type == TypeManager.byte_type){
 614                                 //
 615                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 616                                 //
 617                                 if ((target_type == TypeManager.short_type) ||
 618                                     (target_type == TypeManager.ushort_type) ||
 619                                     (target_type == TypeManager.int32_type) ||
 620                                     (target_type == TypeManager.uint32_type) ||
 621                                     (target_type == TypeManager.uint64_type) ||
 622                                     (target_type == TypeManager.int64_type) ||
 623                                     (target_type == TypeManager.float_type) ||
 624                                     (target_type == TypeManager.double_type) ||
 625                                     (target_type == TypeManager.decimal_type))
 626                                         return true;
 627
 628                         } else if (expr_type == TypeManager.short_type){
 629                                 //
 630                                 // From short to int, long, double, float, decimal
 631                                 //
 632                                 if ((target_type == TypeManager.int32_type) ||
 633                                     (target_type == TypeManager.int64_type) ||
 634                                     (target_type == TypeManager.double_type) ||
 635                                     (target_type == TypeManager.float_type) ||
 636                                     (target_type == TypeManager.decimal_type))
 637                                         return true;
 638
 639                         } else if (expr_type == TypeManager.ushort_type){
 640                                 //
 641                                 // From ushort to int, uint, long, ulong, double, float, decimal
 642                                 //
 643                                 if ((target_type == TypeManager.uint32_type) ||
 644                                     (target_type == TypeManager.uint64_type) ||
 645                                     (target_type == TypeManager.int32_type) ||
 646                                     (target_type == TypeManager.int64_type) ||
 647                                     (target_type == TypeManager.double_type) ||
 648                                     (target_type == TypeManager.float_type) ||
 649                                     (target_type == TypeManager.decimal_type))
 650                                         return true;
 651
 652                         } else if (expr_type == TypeManager.int32_type){
 653                                 //
 654                                 // From int to long, double, float, decimal
 655                                 //
 656                                 if ((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.uint32_type){
 663                                 //
 664                                 // From uint to long, ulong, double, float, decimal
 665                                 //
 666                                 if ((target_type == TypeManager.int64_type) ||
 667                                     (target_type == TypeManager.uint64_type) ||
 668                                     (target_type == TypeManager.double_type) ||
 669                                     (target_type == TypeManager.float_type) ||
 670                                     (target_type == TypeManager.decimal_type))
 671                                         return true;
 672
 673                         } else if ((expr_type == TypeManager.uint64_type) ||
 674                                    (expr_type == TypeManager.int64_type)) {
 675                                 //
 676                                 // From long/ulong to double, float, decimal
 677                                 //
 678                                 if ((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.char_type){
 684                                 //
 685                                 // From char to ushort, int, uint, ulong, long, float, double, decimal
 686                                 //
 687                                 if ((target_type == TypeManager.ushort_type) ||
 688                                     (target_type == TypeManager.int32_type) ||
 689                                     (target_type == TypeManager.uint32_type) ||
 690                                     (target_type == TypeManager.uint64_type) ||
 691                                     (target_type == TypeManager.int64_type) ||
 692                                     (target_type == TypeManager.float_type) ||
 693                                     (target_type == TypeManager.double_type) ||
 694                                     (target_type == TypeManager.decimal_type))
 695                                         return true;
 696
 697                         } else if (expr_type == TypeManager.float_type){
 698                                 //
 699                                 // float to double
 700                                 //
 701                                 if (target_type == TypeManager.double_type)
 702                                         return true;
 703                         }
 704
 705                         if (expr.eclass == ExprClass.MethodGroup){
 706                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
 707                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 708                                         if (mg != null){
 709                                                 //
 710                                                 // This should not happen frequently, so we can create an object
 711                                                 // to test compatibility
 712                                                 //
 713                                                 Expression c = ImplicitDelegateCreation.Create (
 714                                                         ec, mg, target_type, true, Location.Null);
 715                                                 return c != null;
 716                                         }
 717                                 }
 718                         }
 719
 720                         if (ImplicitReferenceConversionExists (ec, expr, target_type))
 721                                 return true;
 722
 723                         //
 724                         // Implicit Constant Expression Conversions
 725                         //
 726                         if (expr is IntConstant){
 727                                 int value = ((IntConstant) expr).Value;
 728
 729                                 if (target_type == TypeManager.sbyte_type){
 730                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 731                                                 return true;
 732                                 } else if (target_type == TypeManager.byte_type){
 733                                         if (value >= 0 && value <= Byte.MaxValue)
 734                                                 return true;
 735                                 } else if (target_type == TypeManager.short_type){
 736                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 737                                                 return true;
 738                                 } else if (target_type == TypeManager.ushort_type){
 739                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 740                                                 return true;
 741                                 } else if (target_type == TypeManager.uint32_type){
 742                                         if (value >= 0)
 743                                                 return true;
 744                                 } else if (target_type == TypeManager.uint64_type){
 745                                          //
 746                                          // we can optimize this case: a positive int32
 747                                          // always fits on a uint64.  But we need an opcode
 748                                          // to do it.
 749                                          //
 750                                         if (value >= 0)
 751                                                 return true;
 752                                 }
 753
 754                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 755                                         return true;
 756                         }
 757
 758                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 759                                 //
 760                                 // Try the implicit constant expression conversion
 761                                 // from long to ulong, instead of a nice routine,
 762                                 // we just inline it
 763                                 //
 764                                 long v = ((LongConstant) expr).Value;
 765                                 if (v >= 0)
 766                                         return true;
 767                         }
 768
 769                         if ((target_type == TypeManager.enum_type ||
 770                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 771                              expr is IntLiteral){
 772                                 IntLiteral i = (IntLiteral) expr;
 773
 774                                 if (i.Value == 0)
 775                                         return true;
 776                         }
 777
 778                         //
 779                         // If `expr_type' implements `target_type' (which is an iface)
 780                         // see TryImplicitIntConversion
 781                         //
 782                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 783                                 return true;
 784
 785                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 786                                 return true;
 787
 788                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
 789                                 return true;
 790
 791                         if (expr_type == TypeManager.anonymous_method_type){
 792                                 if (!TypeManager.IsDelegateType (target_type))
 793                                         return false;
 794
 795                                 AnonymousMethod am = (AnonymousMethod) expr;
 796
 797                                 Expression conv = am.Compatible (ec, target_type, true);
 798                                 if (conv != null)
 799                                         return true;
 800                         }
 801
 802                         return false;
 803                 }
 804
 805                 /// <summary>
 806                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 807                 ///  amongst the methods in the MethodGroupExpr
 808                 /// </summary>
 809                 static Type FindMostEncompassedType (EmitContext ec, ArrayList types)
 810                 {
 811                         Type best = null;
 812
 813                         if (types.Count == 0)
 814                                 return null;
 815
 816                         if (types.Count == 1)
 817                                 return (Type) types [0];
 818
 819                         EmptyExpression expr = EmptyExpression.Grab ();
 820
 821                         foreach (Type t in types) {
 822                                 if (best == null) {
 823                                         best = t;
 824                                         continue;
 825                                 }
 826
 827                                 expr.SetType (t);
 828                                 if (ImplicitStandardConversionExists (ec, expr, best))
 829                                         best = t;
 830                         }
 831
 832                         expr.SetType (best);
 833                         foreach (Type t in types) {
 834                                 if (best == t)
 835                                         continue;
 836                                 if (!ImplicitStandardConversionExists (ec, expr, t)) {
 837                                         best = null;
 838                                         break;
 839                                 }
 840                         }
 841
 842                         EmptyExpression.Release (expr);
 843
 844                         return best;
 845                 }
 846
 847                 /// <summary>
 848                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 849                 ///  amongst the types in the given set
 850                 /// </summary>
 851                 static Type FindMostEncompassingType (EmitContext ec, ArrayList types)
 852                 {
 853                         Type best = null;
 854
 855                         if (types.Count == 0)
 856                                 return null;
 857
 858                         if (types.Count == 1)
 859                                 return (Type) types [0];
 860
 861                         EmptyExpression expr = EmptyExpression.Grab ();
 862
 863                         foreach (Type t in types) {
 864                                 if (best == null) {
 865                                         best = t;
 866                                         continue;
 867                                 }
 868
 869                                 expr.SetType (best);
 870                                 if (ImplicitStandardConversionExists (ec, expr, t))
 871                                         best = t;
 872                         }
 873
 874                         foreach (Type t in types) {
 875                                 if (best == t)
 876                                         continue;
 877                                 expr.SetType (t);
 878                                 if (!ImplicitStandardConversionExists (ec, expr, best)) {
 879                                         best = null;
 880                                         break;
 881                                 }
 882                         }
 883
 884                         EmptyExpression.Release (expr);
 885
 886                         return best;
 887                 }
 888
 889                 /// <summary>
 890                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 891                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 892                 ///   for explicit and implicit conversion operators.
 893                 /// </summary>
 894                 static public Type FindMostSpecificSource (EmitContext ec, IList list,
 895                                                            Expression source, bool apply_explicit_conv_rules)
 896                 {
 897                         ArrayList src_types_set = new ArrayList ();
 898
 899                         //
 900                         // If any operator converts from S then Sx = S
 901                         //
 902                         Type source_type = source.Type;
 903                         foreach (MethodBase mb in list){
 904                                 ParameterData pd = TypeManager.GetParameterData (mb);
 905                                 Type param_type = pd.ParameterType (0);
 906
 907                                 if (param_type == source_type)
 908                                         return param_type;
 909
 910                                 src_types_set.Add (param_type);
 911                         }
 912
 913                         //
 914                         // Explicit Conv rules
 915                         //
 916                         if (apply_explicit_conv_rules) {
 917                                 ArrayList candidate_set = new ArrayList ();
 918
 919                                 foreach (Type param_type in src_types_set){
 920                                         if (ImplicitStandardConversionExists (ec, source, param_type))
 921                                                 candidate_set.Add (param_type);
 922                                 }
 923
 924                                 if (candidate_set.Count != 0)
 925                                         return FindMostEncompassedType (ec, candidate_set);
 926                         }
 927
 928                         //
 929                         // Final case
 930                         //
 931                         if (apply_explicit_conv_rules)
 932                                 return FindMostEncompassingType (ec, src_types_set);
 933                         else
 934                                 return FindMostEncompassedType (ec, src_types_set);
 935                 }
 936
 937                 /// <summary>
 938                 ///  Finds the most specific target Tx according to section 13.4.4
 939                 /// </summary>
 940                 static public Type FindMostSpecificTarget (EmitContext ec, IList list,
 941                                                            Type target, bool apply_explicit_conv_rules)
 942                 {
 943                         ArrayList tgt_types_set = new ArrayList ();
 944
 945                         //
 946                         // If any operator converts to T then Tx = T
 947                         //
 948                         foreach (MethodInfo mi in list){
 949                                 Type ret_type = mi.ReturnType;
 950                                 if (ret_type == target)
 951                                         return ret_type;
 952
 953                                 tgt_types_set.Add (ret_type);
 954                         }
 955
 956                         //
 957                         // Explicit conv rules
 958                         //
 959                         if (apply_explicit_conv_rules) {
 960                                 ArrayList candidate_set = new ArrayList ();
 961
 962                                 EmptyExpression expr = EmptyExpression.Grab ();
 963
 964                                 foreach (Type ret_type in tgt_types_set){
 965                                         expr.SetType (ret_type);
 966
 967                                         if (ImplicitStandardConversionExists (ec, expr, target))
 968                                                 candidate_set.Add (ret_type);
 969                                 }
 970
 971                                 EmptyExpression.Release (expr);
 972
 973                                 if (candidate_set.Count != 0)
 974                                         return FindMostEncompassingType (ec, candidate_set);
 975                         }
 976
 977                         //
 978                         // Okay, final case !
 979                         //
 980                         if (apply_explicit_conv_rules)
 981                                 return FindMostEncompassedType (ec, tgt_types_set);
 982                         else
 983                                 return FindMostEncompassingType (ec, tgt_types_set);
 984                 }
 985
 986                 /// <summary>
 987                 ///  User-defined Implicit conversions
 988                 /// </summary>
 989                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
 990                                                                  Type target, Location loc)
 991                 {
 992                         return UserDefinedConversion (ec, source, target, loc, false);
 993                 }
 994
 995                 /// <summary>
 996                 ///  User-defined Explicit conversions
 997                 /// </summary>
 998                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
 999                                                                  Type target, Location loc)
1000                 {
1001                         return UserDefinedConversion (ec, source, target, loc, true);
1002                 }
1003
1004                 static void AddConversionOperators (EmitContext ec, ArrayList list,
1005                                                     Expression source, Type target_type,
1006                                                     bool look_for_explicit,
1007                                                     MethodGroupExpr mg)
1008                 {
1009                         if (mg == null)
1010                                 return;
1011
1012                         Type source_type = source.Type;
1013                         EmptyExpression expr = EmptyExpression.Grab ();
1014                         foreach (MethodInfo m in mg.Methods) {
1015                                 ParameterData pd = TypeManager.GetParameterData (m);
1016                                 Type return_type = m.ReturnType;
1017                                 Type arg_type = pd.ParameterType (0);
1018
1019                                 if (source_type != arg_type) {
1020                                         if (!ImplicitStandardConversionExists (ec, source, arg_type)) {
1021                                                 if (!look_for_explicit)
1022                                                         continue;
1023                                                 expr.SetType (arg_type);
1024                                                 if (!ImplicitStandardConversionExists (ec, expr, source_type))
1025                                                         continue;
1026                                         }
1027                                 }
1028
1029                                 if (target_type != return_type) {
1030                                         expr.SetType (return_type);
1031                                         if (!ImplicitStandardConversionExists (ec, expr, target_type)) {
1032                                                 if (!look_for_explicit)
1033                                                         continue;
1034                                                 expr.SetType (target_type);
1035                                                 if (!ImplicitStandardConversionExists (ec, expr, return_type))
1036                                                         continue;
1037                                         }
1038                                 }
1039
1040                                 list.Add (m);
1041                         }
1042
1043                         EmptyExpression.Release (expr);
1044                 }
1045
1046                 /// <summary>
1047                 ///   Compute the user-defined conversion operator from source_type to target_type.
1048                 ///   `look_for_explicit' controls whether we should also include the list of explicit operators
1049                 /// </summary>
1050                 static MethodInfo GetConversionOperator (EmitContext ec, Expression source, Type target_type, bool look_for_explicit)
1051                 {
1052                         ArrayList ops = new ArrayList (4);
1053
1054                         Type source_type = source.Type;
1055
1056                         if (source_type != TypeManager.decimal_type) {
1057                                 AddConversionOperators (ec, ops, source, target_type, look_for_explicit,
1058                                         Expression.MethodLookup (ec, source_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1059                                 if (look_for_explicit) {
1060                                         AddConversionOperators (ec, ops, source, target_type, look_for_explicit,
1061                                                 Expression.MethodLookup (
1062                                                         ec, source_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1063                                 }
1064                         }
1065
1066                         if (target_type != TypeManager.decimal_type) {
1067                                 AddConversionOperators (ec, ops, source, target_type, look_for_explicit,
1068                                         Expression.MethodLookup (ec, target_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1069                                 if (look_for_explicit) {
1070                                         AddConversionOperators (ec, ops, source, target_type, look_for_explicit,
1071                                                 Expression.MethodLookup (
1072                                                         ec, target_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1073                                 }
1074                         }
1075
1076                         if (ops.Count == 0)
1077                                 return null;
1078
1079                         Type most_specific_source = FindMostSpecificSource (ec, ops, source, look_for_explicit);
1080                         if (most_specific_source == null)
1081                                 return null;
1082
1083                         Type most_specific_target = FindMostSpecificTarget (ec, ops, target_type, look_for_explicit);
1084                         if (most_specific_target == null)
1085                                 return null;
1086
1087                         MethodInfo method = null;
1088
1089                         foreach (MethodInfo m in ops) {
1090                                 if (m.ReturnType != most_specific_target)
1091                                         continue;
1092                                 if (TypeManager.GetParameterData (m).ParameterType (0) != most_specific_source)
1093                                         continue;
1094                                 // Ambiguous: more than one conversion operator satisfies the signature.
1095                                 if (method != null)
1096                                         return null;
1097                                 method = m;
1098                         }
1099
1100                         return method;
1101                 }
1102
1103                 static DoubleHash explicit_conv = new DoubleHash (100);
1104                 static DoubleHash implicit_conv = new DoubleHash (100);
1105
1106                 /// <summary>
1107                 ///   User-defined conversions
1108                 /// </summary>
1109                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1110                                                                 Type target, Location loc,
1111                                                                 bool look_for_explicit)
1112                 {
1113                         Type source_type = source.Type;
1114                         MethodInfo method = null;
1115
1116                         if (TypeManager.IsNullableType (source_type) && TypeManager.IsNullableType (target))
1117                                 return new Nullable.LiftedConversion (
1118                                         source, target, true, look_for_explicit, loc).Resolve (ec);
1119
1120                         object o;
1121                         DoubleHash hash = look_for_explicit ? explicit_conv : implicit_conv;
1122
1123                         if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
1124                                 method = (MethodInfo) o;
1125                         } else {
1126                                 method = GetConversionOperator (ec, source, target, look_for_explicit);
1127                                 if (!(source is Constant))
1128                                         hash.Insert (source_type, target, method);
1129                         }
1130
1131                         if (method == null)
1132                                 return null;
1133
1134                         Type most_specific_source = TypeManager.GetParameterData (method).ParameterType (0);
1135
1136                         //
1137                         // This will do the conversion to the best match that we
1138                         // found.  Now we need to perform an implict standard conversion
1139                         // if the best match was not the type that we were requested
1140                         // by target.
1141                         //
1142                         if (look_for_explicit)
1143                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1144                         else
1145                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1146
1147                         if (source == null)
1148                                 return null;
1149
1150                         Expression e;
1151                         e =  new UserCast (method, source, loc);
1152                         if (e.Type != target){
1153                                 if (!look_for_explicit)
1154                                         e = ImplicitConversionStandard (ec, e, target, loc);
1155                                 else
1156                                         e = ExplicitConversionStandard (ec, e, target, loc);
1157                         }
1158
1159                         return e;
1160                 }
1161
1162                 /// <summary>
1163                 ///   Converts implicitly the resolved expression `expr' into the
1164                 ///   `target_type'.  It returns a new expression that can be used
1165                 ///   in a context that expects a `target_type'.
1166                 /// </summary>
1167                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1168                                                              Type target_type, Location loc)
1169                 {
1170                         Expression e;
1171
1172                         if (target_type == null)
1173                                 throw new Exception ("Target type is null");
1174
1175                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1176                         if (e != null)
1177                                 return e;
1178
1179                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1180                         if (e != null)
1181                                 return e;
1182
1183                         return null;
1184                 }
1185
1186
1187                 /// <summary>
1188                 ///   Attempts to apply the `Standard Implicit
1189                 ///   Conversion' rules to the expression `expr' into
1190                 ///   the `target_type'.  It returns a new expression
1191                 ///   that can be used in a context that expects a
1192                 ///   `target_type'.
1193                 ///
1194                 ///   This is different from `ImplicitConversion' in that the
1195                 ///   user defined implicit conversions are excluded.
1196                 /// </summary>
1197                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1198                                                                      Type target_type, Location loc)
1199                 {
1200                         Type expr_type = expr.Type;
1201                         Expression e;
1202
1203                         if (expr is NullLiteral) {
1204                                 if (target_type.IsGenericParameter)
1205                                         return TypeParameter_to_Null (expr, target_type, loc);
1206
1207                                 if (TypeManager.IsNullableType (target_type))
1208                                         return new Nullable.NullableLiteral (target_type, loc);
1209                         }
1210
1211                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1212                                 return new Nullable.LiftedConversion (
1213                                         expr, target_type, false, false, loc).Resolve (ec);
1214
1215                         if (expr.eclass == ExprClass.MethodGroup){
1216                                 if (!TypeManager.IsDelegateType (target_type)){
1217                                         return null;
1218                                 }
1219
1220                                 //
1221                                 // Only allow anonymous method conversions on post ISO_1
1222                                 //
1223                                 if (RootContext.Version != LanguageVersion.ISO_1){
1224                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1225                                         if (mg != null)
1226                                                 return ImplicitDelegateCreation.Create (
1227                                                         ec, mg, target_type, false, loc);
1228                                 }
1229                         }
1230
1231                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1232                                 return expr;
1233
1234                         e = ImplicitNumericConversion (ec, expr, target_type);
1235                         if (e != null)
1236                                 return e;
1237
1238                         e = ImplicitReferenceConversion (ec, expr, target_type);
1239                         if (e != null)
1240                                 return e;
1241
1242                         if ((target_type == TypeManager.enum_type ||
1243                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1244                             expr is IntLiteral){
1245                                 IntLiteral i = (IntLiteral) expr;
1246
1247                                 if (i.Value == 0)
1248                                         return new EnumConstant ((Constant) expr, target_type);
1249                         }
1250
1251                         if (ec.InUnsafe) {
1252                                 if (expr_type.IsPointer){
1253                                         if (target_type == TypeManager.void_ptr_type)
1254                                                 return new EmptyCast (expr, target_type);
1255
1256                                         //
1257                                         // yep, comparing pointer types cant be done with
1258                                         // t1 == t2, we have to compare their element types.
1259                                         //
1260                                         if (target_type.IsPointer){
1261                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1262                                                         return expr;
1263
1264                                                 //return null;
1265                                         }
1266                                 }
1267
1268                                 if (expr_type == TypeManager.null_type && target_type.IsPointer)
1269                                         return new EmptyCast (NullPointer.Null, target_type);
1270                         }
1271
1272                         if (expr_type == TypeManager.anonymous_method_type){
1273                                 if (!TypeManager.IsDelegateType (target_type)){
1274                                         Report.Error (1660, loc,
1275                                                 "Cannot convert anonymous method block to type `{0}' because it is not a delegate type",
1276                                                 TypeManager.CSharpName (target_type));
1277                                         return null;
1278                                 }
1279
1280                                 AnonymousMethod am = (AnonymousMethod) expr;
1281                                 int errors = Report.Errors;
1282
1283                                 Expression conv = am.Compatible (ec, target_type, false);
1284                                 if (conv != null)
1285                                         return conv;
1286
1287                                 //
1288                                 // We return something instead of null, to avoid
1289                                 // the duplicate error, since am.Compatible would have
1290                                 // reported that already
1291                                 //
1292                                 if (errors != Report.Errors)
1293                                         return new EmptyCast (expr, target_type);
1294                         }
1295
1296                         return null;
1297                 }
1298
1299                 /// <summary>
1300                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1301                 ///   into a different data type using casts (See Implicit Constant
1302                 ///   Expression Conversions)
1303                 /// </summary>
1304                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1305                 {
1306                         int value = ic.Value;
1307
1308                         if (target_type == TypeManager.sbyte_type){
1309                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1310                                         return new SByteConstant ((sbyte) value, ic.Location);
1311                         } else if (target_type == TypeManager.byte_type){
1312                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1313                                         return new ByteConstant ((byte) value, ic.Location);
1314                         } else if (target_type == TypeManager.short_type){
1315                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1316                                         return new ShortConstant ((short) value, ic.Location);
1317                         } else if (target_type == TypeManager.ushort_type){
1318                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1319                                         return new UShortConstant ((ushort) value, ic.Location);
1320                         } else if (target_type == TypeManager.uint32_type){
1321                                 if (value >= 0)
1322                                         return new UIntConstant ((uint) value, ic.Location);
1323                         } else if (target_type == TypeManager.uint64_type){
1324                                 //
1325                                 // we can optimize this case: a positive int32
1326                                 // always fits on a uint64.  But we need an opcode
1327                                 // to do it.
1328                                 //
1329                                 if (value >= 0)
1330                                         return new ULongConstant ((ulong) value, ic.Location);
1331                         } else if (target_type == TypeManager.double_type)
1332                                 return new DoubleConstant ((double) value, ic.Location);
1333                         else if (target_type == TypeManager.float_type)
1334                                 return new FloatConstant ((float) value, ic.Location);
1335
1336                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1337                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1338                                 Constant e = (Constant) ic;
1339
1340                                 //
1341                                 // Possibly, we need to create a different 0 literal before passing
1342                                 // to EnumConstant
1343                                 //
1344                                 if (underlying == TypeManager.int64_type)
1345                                         e = new LongLiteral (0, ic.Location);
1346                                 else if (underlying == TypeManager.uint64_type)
1347                                         e = new ULongLiteral (0, ic.Location);
1348
1349                                 return new EnumConstant (e, target_type);
1350                         }
1351
1352                         //
1353                         // If `target_type' is an interface and the type of `ic' implements the interface
1354                         // e.g. target_type is IComparable, IConvertible, IFormattable
1355                         //
1356                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1357                                 return new BoxedCast (ic, target_type);
1358
1359                         return null;
1360                 }
1361
1362                 /// <summary>
1363                 ///   Attempts to implicitly convert `source' into `target_type', using
1364                 ///   ImplicitConversion.  If there is no implicit conversion, then
1365                 ///   an error is signaled
1366                 /// </summary>
1367                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1368                                                                      Type target_type, Location loc)
1369                 {
1370                         Expression e;
1371
1372                         int errors = Report.Errors;
1373                         e = ImplicitConversion (ec, source, target_type, loc);
1374                         if (Report.Errors > errors)
1375                                 return null;
1376                         if (e != null)
1377                                 return e;
1378
1379                         if (source is DoubleLiteral) {
1380                                 if (target_type == TypeManager.float_type) {
1381                                         Error_664 (loc, "float", "f");
1382                                         return null;
1383                                 }
1384                                 if (target_type == TypeManager.decimal_type) {
1385                                         Error_664 (loc, "decimal", "m");
1386                                         return null;
1387                                 }
1388                         }
1389
1390                         source.Error_ValueCannotBeConverted (loc, target_type, false);
1391                         return null;
1392                 }
1393
1394                 static void Error_664 (Location loc, string type, string suffix) {
1395                         Report.Error (664, loc,
1396                                 "Literal of type double cannot be implicitly converted to type `{0}'. Add suffix `{1}' to create a literal of this type",
1397                                 type, suffix);
1398                 }
1399
1400                 /// <summary>
1401                 ///   Performs the explicit numeric conversions
1402                 /// </summary>
1403                 public static Expression ExplicitNumericConversion (Expression expr, Type target_type)
1404                 {
1405                         Type expr_type = expr.Type;
1406                         Type real_target_type = target_type;
1407
1408                         if (expr_type == TypeManager.sbyte_type){
1409                                 //
1410                                 // From sbyte to byte, ushort, uint, ulong, char
1411                                 //
1412                                 if (real_target_type == TypeManager.byte_type)
1413                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1414                                 if (real_target_type == TypeManager.ushort_type)
1415                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1416                                 if (real_target_type == TypeManager.uint32_type)
1417                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1418                                 if (real_target_type == TypeManager.uint64_type)
1419                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1420                                 if (real_target_type == TypeManager.char_type)
1421                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1422                         } else if (expr_type == TypeManager.byte_type){
1423                                 //
1424                                 // From byte to sbyte and char
1425                                 //
1426                                 if (real_target_type == TypeManager.sbyte_type)
1427                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1428                                 if (real_target_type == TypeManager.char_type)
1429                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1430                         } else if (expr_type == TypeManager.short_type){
1431                                 //
1432                                 // From short to sbyte, byte, ushort, uint, ulong, char
1433                                 //
1434                                 if (real_target_type == TypeManager.sbyte_type)
1435                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1436                                 if (real_target_type == TypeManager.byte_type)
1437                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1438                                 if (real_target_type == TypeManager.ushort_type)
1439                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1440                                 if (real_target_type == TypeManager.uint32_type)
1441                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1442                                 if (real_target_type == TypeManager.uint64_type)
1443                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1444                                 if (real_target_type == TypeManager.char_type)
1445                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1446                         } else if (expr_type == TypeManager.ushort_type){
1447                                 //
1448                                 // From ushort to sbyte, byte, short, char
1449                                 //
1450                                 if (real_target_type == TypeManager.sbyte_type)
1451                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1452                                 if (real_target_type == TypeManager.byte_type)
1453                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1454                                 if (real_target_type == TypeManager.short_type)
1455                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1456                                 if (real_target_type == TypeManager.char_type)
1457                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1458                         } else if (expr_type == TypeManager.int32_type){
1459                                 //
1460                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1461                                 //
1462                                 if (real_target_type == TypeManager.sbyte_type)
1463                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1464                                 if (real_target_type == TypeManager.byte_type)
1465                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1466                                 if (real_target_type == TypeManager.short_type)
1467                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1468                                 if (real_target_type == TypeManager.ushort_type)
1469                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1470                                 if (real_target_type == TypeManager.uint32_type)
1471                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1472                                 if (real_target_type == TypeManager.uint64_type)
1473                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1474                                 if (real_target_type == TypeManager.char_type)
1475                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1476                         } else if (expr_type == TypeManager.uint32_type){
1477                                 //
1478                                 // From uint to sbyte, byte, short, ushort, int, char
1479                                 //
1480                                 if (real_target_type == TypeManager.sbyte_type)
1481                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1482                                 if (real_target_type == TypeManager.byte_type)
1483                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1484                                 if (real_target_type == TypeManager.short_type)
1485                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1486                                 if (real_target_type == TypeManager.ushort_type)
1487                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1488                                 if (real_target_type == TypeManager.int32_type)
1489                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1490                                 if (real_target_type == TypeManager.char_type)
1491                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1492                         } else if (expr_type == TypeManager.int64_type){
1493                                 //
1494                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1495                                 //
1496                                 if (real_target_type == TypeManager.sbyte_type)
1497                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1498                                 if (real_target_type == TypeManager.byte_type)
1499                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1500                                 if (real_target_type == TypeManager.short_type)
1501                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1502                                 if (real_target_type == TypeManager.ushort_type)
1503                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1504                                 if (real_target_type == TypeManager.int32_type)
1505                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1506                                 if (real_target_type == TypeManager.uint32_type)
1507                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1508                                 if (real_target_type == TypeManager.uint64_type)
1509                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1510                                 if (real_target_type == TypeManager.char_type)
1511                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1512                         } else if (expr_type == TypeManager.uint64_type){
1513                                 //
1514                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1515                                 //
1516                                 if (real_target_type == TypeManager.sbyte_type)
1517                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1518                                 if (real_target_type == TypeManager.byte_type)
1519                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1520                                 if (real_target_type == TypeManager.short_type)
1521                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1522                                 if (real_target_type == TypeManager.ushort_type)
1523                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1524                                 if (real_target_type == TypeManager.int32_type)
1525                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1526                                 if (real_target_type == TypeManager.uint32_type)
1527                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1528                                 if (real_target_type == TypeManager.int64_type)
1529                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1530                                 if (real_target_type == TypeManager.char_type)
1531                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1532                         } else if (expr_type == TypeManager.char_type){
1533                                 //
1534                                 // From char to sbyte, byte, short
1535                                 //
1536                                 if (real_target_type == TypeManager.sbyte_type)
1537                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1538                                 if (real_target_type == TypeManager.byte_type)
1539                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1540                                 if (real_target_type == TypeManager.short_type)
1541                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1542                         } else if (expr_type == TypeManager.float_type){
1543                                 //
1544                                 // From float to sbyte, byte, short,
1545                                 // ushort, int, uint, long, ulong, char
1546                                 // or decimal
1547                                 //
1548                                 if (real_target_type == TypeManager.sbyte_type)
1549                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1550                                 if (real_target_type == TypeManager.byte_type)
1551                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1552                                 if (real_target_type == TypeManager.short_type)
1553                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1554                                 if (real_target_type == TypeManager.ushort_type)
1555                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1556                                 if (real_target_type == TypeManager.int32_type)
1557                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1558                                 if (real_target_type == TypeManager.uint32_type)
1559                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1560                                 if (real_target_type == TypeManager.int64_type)
1561                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1562                                 if (real_target_type == TypeManager.uint64_type)
1563                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1564                                 if (real_target_type == TypeManager.char_type)
1565                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1566                                 if (real_target_type == TypeManager.decimal_type)
1567                                         return new CastToDecimal (expr, true);
1568                         } else if (expr_type == TypeManager.double_type){
1569                                 //
1570                                 // From double to sbyte, byte, short,
1571                                 // ushort, int, uint, long, ulong,
1572                                 // char, float or decimal
1573                                 //
1574                                 if (real_target_type == TypeManager.sbyte_type)
1575                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1576                                 if (real_target_type == TypeManager.byte_type)
1577                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1578                                 if (real_target_type == TypeManager.short_type)
1579                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1580                                 if (real_target_type == TypeManager.ushort_type)
1581                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1582                                 if (real_target_type == TypeManager.int32_type)
1583                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1584                                 if (real_target_type == TypeManager.uint32_type)
1585                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1586                                 if (real_target_type == TypeManager.int64_type)
1587                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1588                                 if (real_target_type == TypeManager.uint64_type)
1589                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1590                                 if (real_target_type == TypeManager.char_type)
1591                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1592                                 if (real_target_type == TypeManager.float_type)
1593                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1594                                 if (real_target_type == TypeManager.decimal_type)
1595                                         return new CastToDecimal (expr, true);
1596                         } else if (expr_type == TypeManager.decimal_type) {
1597                                 return new CastFromDecimal (expr, target_type).Resolve ();
1598                         }
1599                         return null;
1600                 }
1601
1602                 /// <summary>
1603                 ///  Returns whether an explicit reference conversion can be performed
1604                 ///  from source_type to target_type
1605                 /// </summary>
1606                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1607                 {
1608                         bool target_is_type_param = target_type.IsGenericParameter;
1609                         bool target_is_value_type = target_type.IsValueType;
1610
1611                         if (source_type == target_type)
1612                                 return true;
1613
1614                         //
1615                         // From generic parameter to any type
1616                         //
1617                         if (source_type.IsGenericParameter)
1618                                 return true;
1619
1620                         //
1621                         // From object to a generic parameter
1622                         //
1623                         if (source_type == TypeManager.object_type && target_is_type_param)
1624                                 return true;
1625
1626                         //
1627                         // From object to any reference type
1628                         //
1629                         if (source_type == TypeManager.object_type && !target_is_value_type)
1630                                 return true;
1631
1632                         //
1633                         // From any class S to any class-type T, provided S is a base class of T
1634                         //
1635                         if (TypeManager.IsSubclassOf (target_type, source_type))
1636                                 return true;
1637
1638                         //
1639                         // From any interface type S to any interface T provided S is not derived from T
1640                         //
1641                         if (source_type.IsInterface && target_type.IsInterface){
1642                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1643                                         return true;
1644                         }
1645
1646                         //
1647                         // From any class type S to any interface T, provided S is not sealed
1648                         // and provided S does not implement T.
1649                         //
1650                         if (target_type.IsInterface && !source_type.IsSealed &&
1651                             !TypeManager.ImplementsInterface (source_type, target_type))
1652                                 return true;
1653
1654                         //
1655                         // From any interface-type S to to any class type T, provided T is not
1656                         // sealed, or provided T implements S.
1657                         //
1658                         if (source_type.IsInterface &&
1659                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1660                                 return true;
1661
1662
1663                         // From an array type S with an element type Se to an array type T with an
1664                         // element type Te provided all the following are true:
1665                         //     * S and T differe only in element type, in other words, S and T
1666                         //       have the same number of dimensions.
1667                         //     * Both Se and Te are reference types
1668                         //     * An explicit referenc conversions exist from Se to Te
1669                         //
1670                         if (source_type.IsArray && target_type.IsArray) {
1671                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1672
1673                                         Type source_element_type = TypeManager.GetElementType (source_type);
1674                                         Type target_element_type = TypeManager.GetElementType (target_type);
1675
1676                                         if (source_element_type.IsGenericParameter ||
1677                                             (!source_element_type.IsValueType && !target_element_type.IsValueType))
1678                                                 if (ExplicitReferenceConversionExists (source_element_type,
1679                                                                                        target_element_type))
1680                                                         return true;
1681                                 }
1682                         }
1683
1684
1685                         // From System.Array to any array-type
1686                         if (source_type == TypeManager.array_type &&
1687                             target_type.IsArray){
1688                                 return true;
1689                         }
1690
1691                         //
1692                         // From System delegate to any delegate-type
1693                         //
1694                         if (source_type == TypeManager.delegate_type &&
1695                             TypeManager.IsDelegateType (target_type))
1696                                 return true;
1697
1698                         //
1699                         // From ICloneable to Array or Delegate types
1700                         //
1701                         if (source_type == TypeManager.icloneable_type &&
1702                             (target_type == TypeManager.array_type ||
1703                              target_type == TypeManager.delegate_type))
1704                                 return true;
1705
1706                         return false;
1707                 }
1708
1709                 /// <summary>
1710                 ///   Implements Explicit Reference conversions
1711                 /// </summary>
1712                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1713                 {
1714                         Type source_type = source.Type;
1715                         bool target_is_type_param = target_type.IsGenericParameter;
1716                         bool target_is_value_type = target_type.IsValueType;
1717
1718                         //
1719                         // From object to a generic parameter
1720                         //
1721                         if (source_type == TypeManager.object_type && target_is_type_param)
1722                                 return new UnboxCast (source, target_type);
1723
1724                         //
1725                         // From object to any reference type
1726                         //
1727                         if (source_type == TypeManager.object_type && !target_is_value_type)
1728                                 return new ClassCast (source, target_type);
1729
1730                         //
1731                         // Unboxing conversion.
1732                         //
1733                         if (((source_type == TypeManager.enum_type &&
1734                                 !(source is EmptyCast)) ||
1735                                 source_type == TypeManager.value_type) && target_is_value_type)
1736                                 return new UnboxCast (source, target_type);
1737
1738                         //
1739                         // From any class S to any class-type T, provided S is a base class of T
1740                         //
1741                         if (TypeManager.IsSubclassOf (target_type, source_type))
1742                                 return new ClassCast (source, target_type);
1743
1744                         //
1745                         // From any interface type S to any interface T provided S is not derived from T
1746                         //
1747                         if (source_type.IsInterface && target_type.IsInterface){
1748                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1749                                         return null;
1750                                 else
1751                                         return new ClassCast (source, target_type);
1752                         }
1753
1754                         //
1755                         // From any class type S to any interface T, provides S is not sealed
1756                         // and provided S does not implement T.
1757                         //
1758                         if (target_type.IsInterface && !source_type.IsSealed) {
1759                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1760                                         return null;
1761                                 else
1762                                         return new ClassCast (source, target_type);
1763
1764                         }
1765
1766                         //
1767                         // From any interface-type S to to any class type T, provided T is not
1768                         // sealed, or provided T implements S.
1769                         //
1770                         if (source_type.IsInterface) {
1771                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1772                                         if (target_type.IsClass)
1773                                                 return new ClassCast (source, target_type);
1774                                         else
1775                                                 return new UnboxCast (source, target_type);
1776                                 }
1777
1778                                 return null;
1779                         }
1780
1781                         // From an array type S with an element type Se to an array type T with an
1782                         // element type Te provided all the following are true:
1783                         //     * S and T differe only in element type, in other words, S and T
1784                         //       have the same number of dimensions.
1785                         //     * Both Se and Te are reference types
1786                         //     * An explicit referenc conversions exist from Se to Te
1787                         //
1788                         if (source_type.IsArray && target_type.IsArray) {
1789                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1790
1791                                         Type source_element_type = TypeManager.GetElementType (source_type);
1792                                         Type target_element_type = TypeManager.GetElementType (target_type);
1793
1794                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1795                                                 if (ExplicitReferenceConversionExists (source_element_type,
1796                                                                                        target_element_type))
1797                                                         return new ClassCast (source, target_type);
1798                                 }
1799                         }
1800
1801
1802                         // From System.Array to any array-type
1803                         if (source_type == TypeManager.array_type &&
1804                             target_type.IsArray) {
1805                                 return new ClassCast (source, target_type);
1806                         }
1807
1808                         //
1809                         // From System delegate to any delegate-type
1810                         //
1811                         if (source_type == TypeManager.delegate_type &&
1812                             TypeManager.IsDelegateType (target_type))
1813                                 return new ClassCast (source, target_type);
1814
1815                         //
1816                         // From ICloneable to Array or Delegate types
1817                         //
1818                         if (source_type == TypeManager.icloneable_type &&
1819                             (target_type == TypeManager.array_type ||
1820                              target_type == TypeManager.delegate_type))
1821                                 return new ClassCast (source, target_type);
1822
1823                         return null;
1824                 }
1825
1826                 /// <summary>
1827                 ///   Performs an explicit conversion of the expression `expr' whose
1828                 ///   type is expr.Type to `target_type'.
1829                 /// </summary>
1830                 static public Expression ExplicitConversionCore (EmitContext ec, Expression expr,
1831                                                              Type target_type, Location loc)
1832                 {
1833                         Type expr_type = expr.Type;
1834
1835                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1836                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1837                         if (ne != null)
1838                                 return ne;
1839
1840                         //
1841                         // Unboxing conversions; only object types can be convertible to enum
1842                         //
1843                         if (expr_type == TypeManager.object_type && target_type.IsValueType || expr_type == TypeManager.enum_type)
1844                                 return new UnboxCast (expr, target_type);
1845
1846                         if (TypeManager.IsEnumType (expr_type)) {
1847                                 if (expr is EnumConstant)
1848                                         return ExplicitConversionCore (ec, ((EnumConstant) expr).Child, target_type, loc);
1849
1850                                 return ExplicitConversionCore (ec, new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type)), target_type, loc);
1851                         }
1852
1853                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1854                                 return new Nullable.LiftedConversion (
1855                                         expr, target_type, false, true, loc).Resolve (ec);
1856
1857                         if (TypeManager.IsEnumType (target_type))
1858                                 return new EmptyCast (ExplicitConversionCore (ec, expr, TypeManager.EnumToUnderlying (target_type), loc), target_type);
1859
1860                         ne = ExplicitNumericConversion (expr, target_type);
1861                         if (ne != null)
1862                                 return ne;
1863
1864                         //
1865                         // Skip the ExplicitReferenceConversion because we can not convert
1866                         // from Null to a ValueType, and ExplicitReference wont check against
1867                         // null literal explicitly
1868                         //
1869                         if (expr_type != TypeManager.null_type){
1870                                 ne = ExplicitReferenceConversion (expr, target_type);
1871                                 if (ne != null)
1872                                         return ne;
1873                         }
1874
1875                         if (ec.InUnsafe){
1876                                 ne = ExplicitUnsafe (expr, target_type);
1877                                 if (ne != null)
1878                                         return ne;
1879                         }
1880
1881                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1882                         if (ne != null)
1883                                 return ne;
1884
1885                         return null;
1886                 }
1887
1888                 public static Expression ExplicitUnsafe (Expression expr, Type target_type)
1889                 {
1890                         Type expr_type = expr.Type;
1891
1892                         if (target_type.IsPointer){
1893                                 if (expr_type.IsPointer)
1894                                         return new EmptyCast (expr, target_type);
1895
1896                                 if (expr_type == TypeManager.sbyte_type ||
1897                                         expr_type == TypeManager.short_type ||
1898                                         expr_type == TypeManager.int32_type ||
1899                                         expr_type == TypeManager.int64_type)
1900                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1901
1902                                 if (expr_type == TypeManager.ushort_type ||
1903                                         expr_type == TypeManager.uint32_type ||
1904                                         expr_type == TypeManager.uint64_type ||
1905                                         expr_type == TypeManager.byte_type)
1906                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1907                         }
1908
1909                         if (expr_type.IsPointer){
1910                                 if (target_type == TypeManager.sbyte_type)
1911                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1912                                 else if (target_type == TypeManager.byte_type)
1913                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1914                                 else if (target_type == TypeManager.short_type)
1915                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1916                                 else if (target_type == TypeManager.ushort_type)
1917                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1918                                 else if (target_type == TypeManager.int32_type)
1919                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1920                                 else if (target_type == TypeManager.uint32_type)
1921                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1922                                 else if (target_type == TypeManager.uint64_type)
1923                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1924                                 else if (target_type == TypeManager.int64_type){
1925                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1926                                 }
1927                         }
1928                         return null;
1929                 }
1930
1931                 /// <summary>
1932                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1933                 /// </summary>
1934                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1935                                                                      Type target_type, Location l)
1936                 {
1937                         int errors = Report.Errors;
1938                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1939                         if (Report.Errors > errors)
1940                                 return null;
1941
1942                         if (ne != null)
1943                                 return ne;
1944
1945                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
1946                                 return new Nullable.LiftedConversion (
1947                                         expr, target_type, false, true, l).Resolve (ec);
1948
1949                         ne = ExplicitNumericConversion (expr, target_type);
1950                         if (ne != null)
1951                                 return ne;
1952
1953                         ne = ExplicitReferenceConversion (expr, target_type);
1954                         if (ne != null)
1955                                 return ne;
1956
1957                         if (ec.InUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
1958                                 return new EmptyCast (expr, target_type);
1959
1960                         expr.Error_ValueCannotBeConverted (l, target_type, true);
1961                         return null;
1962                 }
1963
1964                 /// <summary>
1965                 ///   Performs an explicit conversion of the expression `expr' whose
1966                 ///   type is expr.Type to `target_type'.
1967                 /// </summary>
1968                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1969                         Type target_type, Location loc)
1970                 {
1971                         Expression e = ExplicitConversionCore (ec, expr, target_type, loc);
1972                         if (e != null)
1973                                 return e;
1974
1975                         expr.Error_ValueCannotBeConverted (loc, target_type, true);
1976                         return null;
1977                 }
1978         }
1979 }