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