mcs/gmcs/convert.cs

   1 //
   2 // conversion.cs: various routines for implementing conversions.
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Ravi Pratap (ravi@ximian.com)
   7 //
   8 // (C) 2001, 2002, 2003 Ximian, Inc.
   9 //
  10
  11 namespace Mono.CSharp {
  12         using System;
  13         using System.Collections;
  14         using System.Diagnostics;
  15         using System.Reflection;
  16         using System.Reflection.Emit;
  17
  18         //
  19         // A container class for all the conversion operations
  20         //
  21         public class Convert {
  22                 //
  23                 // This is used to prettify the code: a null argument is allowed
  24                 // for ImplicitStandardConversion as long as it is known that
  25                 // no anonymous method will play a role.
  26                 //
  27                 // FIXME: renamed from `const' to `static' to allow bootstraping from older
  28                 // versions of the compiler that could not cope with this construct.
  29                 //
  30                 public static EmitContext ConstantEC = null;
  31
  32                 static public void Error_CannotConvertType (Location loc, Type source, Type target)
  33                 {
  34                         Report.Error (30, loc, "Cannot convert type '" +
  35                                       TypeManager.CSharpName (source) + "' to '" +
  36                                       TypeManager.CSharpName (target) + "'");
  37                 }
  38
  39                 static Expression TypeParameter_to_Null (Expression expr, Type target_type,
  40                                                          Location loc)
  41                 {
  42                         if (!TypeParameter_to_Null (target_type)) {
  43                                 Report.Error (403, loc, "Cannot convert null to the type " +
  44                                               "parameter `{0}' becaues it could be a value " +
  45                                               "type.  Consider using `default ({0})' instead.",
  46                                               target_type);
  47                                 return null;
  48                         }
  49
  50                         return new NullCast (expr, target_type);
  51                 }
  52
  53                 static bool TypeParameter_to_Null (Type target_type)
  54                 {
  55                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
  56                         if (gc == null)
  57                                 return false;
  58
  59                         if (gc.HasReferenceTypeConstraint)
  60                                 return true;
  61                         if (gc.HasClassConstraint && !TypeManager.IsValueType (gc.ClassConstraint))
  62                                 return true;
  63
  64                         return false;
  65                 }
  66
  67                 static Type TypeParam_EffectiveBaseType (EmitContext ec, GenericConstraints gc)
  68                 {
  69                         ArrayList list = new ArrayList ();
  70                         list.Add (gc.EffectiveBaseClass);
  71                         foreach (Type t in gc.InterfaceConstraints) {
  72                                 if (!t.IsGenericParameter)
  73                                         continue;
  74
  75                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  76                                 if (new_gc != null)
  77                                         list.Add (TypeParam_EffectiveBaseType (ec, new_gc));
  78                         }
  79                         return FindMostEncompassedType (ec, list);
  80                 }
  81
  82                 static Expression TypeParameterConversion (Expression expr, bool is_reference, Type target_type)
  83                 {
  84                         if (is_reference)
  85                                 return new EmptyCast (expr, target_type);
  86                         else
  87                                 return new BoxedCast (expr, target_type);
  88                 }
  89
  90                 static Expression ImplicitTypeParameterConversion (EmitContext ec, Expression expr,
  91                                                                    Type target_type)
  92                 {
  93                         Type expr_type = expr.Type;
  94
  95                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
  96
  97                         if (gc == null) {
  98                                 if (target_type == TypeManager.object_type)
  99                                         return new BoxedCast (expr);
 100
 101                                 return null;
 102                         }
 103
 104                         // We're converting from a type parameter which is known to be a reference type.
 105                         bool is_reference = gc.IsReferenceType;
 106                         Type base_type = TypeParam_EffectiveBaseType (ec, gc);
 107
 108                         if (TypeManager.IsSubclassOf (base_type, target_type))
 109                                 return TypeParameterConversion (expr, is_reference, target_type);
 110
 111                         if (target_type.IsInterface) {
 112                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 113                                         return TypeParameterConversion (expr, is_reference, target_type);
 114
 115                                 foreach (Type t in gc.InterfaceConstraints) {
 116                                         if (TypeManager.IsSubclassOf (t, target_type))
 117                                                 return TypeParameterConversion (expr, is_reference, target_type);
 118                                 }
 119                         }
 120
 121                         foreach (Type t in gc.InterfaceConstraints) {
 122                                 if (!t.IsGenericParameter)
 123                                         continue;
 124                                 if (TypeManager.IsSubclassOf (t, target_type))
 125                                         return TypeParameterConversion (expr, is_reference, target_type);
 126                         }
 127
 128                         return null;
 129                 }
 130
 131                 static EmptyExpression MyEmptyExpr;
 132                 static public Expression ImplicitReferenceConversion (EmitContext ec, Expression expr, Type target_type)
 133                 {
 134                         Type expr_type = expr.Type;
 135
 136                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 137                                 // if we are a method group, emit a warning
 138
 139                                 expr.Emit (null);
 140                         }
 141
 142                         if (expr_type == TypeManager.void_type)
 143                                 return null;
 144
 145                         if (expr_type.IsGenericParameter)
 146                                 return ImplicitTypeParameterConversion (ec, expr, target_type);
 147
 148                         //
 149                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 150                         // is an abstract class, and not really a value type, so we apply the same rules.
 151                         //
 152                         if (target_type == TypeManager.object_type) {
 153                                 //
 154                                 // A pointer type cannot be converted to object
 155                                 //
 156                                 if (expr_type.IsPointer)
 157                                         return null;
 158
 159                                 if (TypeManager.IsValueType (expr_type))
 160                                         return new BoxedCast (expr);
 161                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 162                                         if (expr_type == TypeManager.anonymous_method_type)
 163                                                 return null;
 164                                         return new EmptyCast (expr, target_type);
 165                                 }
 166
 167                                 return null;
 168                         } else if (target_type == TypeManager.value_type) {
 169                                 if (TypeManager.IsValueType (expr_type))
 170                                         return new BoxedCast (expr);
 171                                 if (expr_type == TypeManager.null_type)
 172                                         return new NullCast (expr, target_type);
 173
 174                                 return null;
 175                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 176                                 //
 177                                 // Special case: enumeration to System.Enum.
 178                                 // System.Enum is not a value type, it is a class, so we need
 179                                 // a boxing conversion
 180                                 //
 181                                 if (expr_type.IsEnum || expr_type.IsGenericParameter)
 182                                         return new BoxedCast (expr);
 183
 184                                 return new EmptyCast (expr, target_type);
 185                         }
 186
 187                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 188                         // with the small distinction that we only probe there
 189                         //
 190                         // Always ensure that the code here and there is in sync
 191
 192                         // from the null type to any reference-type.
 193                         if (expr_type == TypeManager.null_type){
 194                                 if (target_type.IsPointer)
 195                                         return new EmptyCast (expr, target_type);
 196
 197                                 if (!target_type.IsValueType)
 198                                         return new NullCast (expr, target_type);
 199                         }
 200
 201                         // from any class-type S to any interface-type T.
 202                         if (target_type.IsInterface) {
 203                                 if (target_type != TypeManager.iconvertible_type &&
 204                                     expr_type.IsValueType && (expr is Constant) &&
 205                                     !(expr is IntLiteral || expr is BoolLiteral ||
 206                                       expr is FloatLiteral || expr is DoubleLiteral ||
 207                                       expr is LongLiteral || expr is CharLiteral ||
 208                                       expr is StringLiteral || expr is DecimalLiteral ||
 209                                       expr is UIntLiteral || expr is ULongLiteral)) {
 210                                         return null;
 211                                 }
 212
 213                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 214                                         if (expr_type.IsGenericParameter || TypeManager.IsValueType (expr_type))
 215                                                 return new BoxedCast (expr, target_type);
 216                                         else
 217                                                 return new EmptyCast (expr, target_type);
 218                                 }
 219                         }
 220
 221                         // from any interface type S to interface-type T.
 222                         if (expr_type.IsInterface && target_type.IsInterface) {
 223                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 224                                         return new EmptyCast (expr, target_type);
 225                                 else
 226                                         return null;
 227                         }
 228
 229                         // from an array-type S to an array-type of type T
 230                         if (expr_type.IsArray && target_type.IsArray) {
 231                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 232
 233                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 234
 235                                         if (MyEmptyExpr == null)
 236                                                 MyEmptyExpr = new EmptyExpression ();
 237
 238                                         MyEmptyExpr.SetType (expr_element_type);
 239                                         Type target_element_type = TypeManager.GetElementType (target_type);
 240
 241                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 242                                                 if (ImplicitStandardConversionExists (ConstantEC, MyEmptyExpr,
 243                                                                                       target_element_type))
 244                                                         return new EmptyCast (expr, target_type);
 245                                 }
 246                         }
 247
 248                         // from an array-type to System.Array
 249                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 250                                 return new EmptyCast (expr, target_type);
 251
 252                         // from an array-type of type T to IEnumerable<T>
 253                         if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
 254                                 return new EmptyCast (expr, target_type);
 255
 256                         // from any delegate type to System.Delegate
 257                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 258                             target_type == TypeManager.delegate_type)
 259                                 return new EmptyCast (expr, target_type);
 260
 261                         // from any array-type or delegate type into System.ICloneable.
 262                         if (expr_type.IsArray ||
 263                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 264                                 if (target_type == TypeManager.icloneable_type)
 265                                         return new EmptyCast (expr, target_type);
 266
 267                         // from a generic type definition to a generic instance.
 268                         if (TypeManager.IsEqual (expr_type, target_type))
 269                                 return new EmptyCast (expr, target_type);
 270
 271                         return null;
 272                 }
 273
 274                 //
 275                 // Tests whether an implicit reference conversion exists between expr_type
 276                 // and target_type
 277                 //
 278                 public static bool ImplicitReferenceConversionExists (EmitContext ec, Expression expr, Type target_type)
 279                 {
 280                         Type expr_type = expr.Type;
 281
 282                         if (expr_type.IsGenericParameter)
 283                                 return ImplicitTypeParameterConversion (ec, expr, target_type) != null;
 284
 285                         //
 286                         // This is the boxed case.
 287                         //
 288                         if (target_type == TypeManager.object_type) {
 289                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 290                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 291                                         if (target_type != TypeManager.anonymous_method_type)
 292                                         return true;
 293
 294                                 return false;
 295                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 296                                 return true;
 297
 298                         // Please remember that all code below actually comes
 299                         // from ImplicitReferenceConversion so make sure code remains in sync
 300
 301                         // from any class-type S to any interface-type T.
 302                         if (target_type.IsInterface) {
 303                                 if (target_type != TypeManager.iconvertible_type &&
 304                                     expr_type.IsValueType && (expr is Constant) &&
 305                                     !(expr is IntLiteral || expr is BoolLiteral ||
 306                                       expr is FloatLiteral || expr is DoubleLiteral ||
 307                                       expr is LongLiteral || expr is CharLiteral ||
 308                                       expr is StringLiteral || expr is DecimalLiteral ||
 309                                       expr is UIntLiteral || expr is ULongLiteral)) {
 310                                         return false;
 311                                 }
 312
 313                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 314                                         return true;
 315                         }
 316
 317                         // from any interface type S to interface-type T.
 318                         if (expr_type.IsInterface && target_type.IsInterface)
 319                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 320                                         return true;
 321
 322                         // from an array-type S to an array-type of type T
 323                         if (expr_type.IsArray && target_type.IsArray) {
 324                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 325
 326                                         Type expr_element_type = expr_type.GetElementType ();
 327
 328                                         if (MyEmptyExpr == null)
 329                                                 MyEmptyExpr = new EmptyExpression ();
 330
 331                                         MyEmptyExpr.SetType (expr_element_type);
 332                                         Type target_element_type = TypeManager.GetElementType (target_type);
 333
 334                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 335                                                 if (ImplicitStandardConversionExists (ConstantEC, MyEmptyExpr,
 336                                                                                       target_element_type))
 337                                                         return true;
 338                                 }
 339                         }
 340
 341                         // from an array-type to System.Array
 342                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 343                                 return true;
 344
 345                         // from an array-type of type T to IEnumerable<T>
 346                         if (expr_type.IsArray && TypeManager.IsIEnumerable (expr_type, target_type))
 347                                 return true;
 348
 349                         // from any delegate type to System.Delegate
 350                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 351                             target_type == TypeManager.delegate_type)
 352                                 if (target_type.IsAssignableFrom (expr_type))
 353                                         return true;
 354
 355                         // from any array-type or delegate type into System.ICloneable.
 356                         if (expr_type.IsArray ||
 357                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 358                                 if (target_type == TypeManager.icloneable_type)
 359                                         return true;
 360
 361                         // from the null type to any reference-type.
 362                         if (expr_type == TypeManager.null_type){
 363                                 if (target_type.IsPointer)
 364                                         return true;
 365
 366                                 if (!target_type.IsValueType)
 367                                         return true;
 368                         }
 369
 370                         // from a generic type definition to a generic instance.
 371                         if (TypeManager.IsEqual (expr_type, target_type))
 372                                 return true;
 373
 374                         return false;
 375                 }
 376
 377                 /// <summary>
 378                 ///   Implicit Numeric Conversions.
 379                 ///
 380                 ///   expr is the expression to convert, returns a new expression of type
 381                 ///   target_type or null if an implicit conversion is not possible.
 382                 /// </summary>
 383                 static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
 384                                                                     Type target_type, Location loc)
 385                 {
 386                         Type expr_type = expr.Type;
 387
 388                         //
 389                         // Attempt to do the implicit constant expression conversions
 390
 391                         if (expr is Constant){
 392                                 if (expr is IntConstant){
 393                                         Expression e;
 394
 395                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 396
 397                                         if (e != null)
 398                                                 return e;
 399                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 400                                         //
 401                                         // Try the implicit constant expression conversion
 402                                         // from long to ulong, instead of a nice routine,
 403                                         // we just inline it
 404                                         //
 405                                         long v = ((LongConstant) expr).Value;
 406                                         if (v >= 0)
 407                                                 return new ULongConstant ((ulong) v);
 408                                 }
 409                         }
 410
 411                         Type real_target_type = target_type;
 412
 413                         if (expr_type == TypeManager.sbyte_type){
 414                                 //
 415                                 // From sbyte to short, int, long, float, double.
 416                                 //
 417                                 if (real_target_type == TypeManager.int32_type)
 418                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 419                                 if (real_target_type == TypeManager.int64_type)
 420                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 421                                 if (real_target_type == TypeManager.double_type)
 422                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 423                                 if (real_target_type == TypeManager.float_type)
 424                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 425                                 if (real_target_type == TypeManager.short_type)
 426                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 427                         } else if (expr_type == TypeManager.byte_type){
 428                                 //
 429                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 430                                 //
 431                                 if ((real_target_type == TypeManager.short_type) ||
 432                                     (real_target_type == TypeManager.ushort_type) ||
 433                                     (real_target_type == TypeManager.int32_type) ||
 434                                     (real_target_type == TypeManager.uint32_type))
 435                                         return new EmptyCast (expr, target_type);
 436
 437                                 if (real_target_type == TypeManager.uint64_type)
 438                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 439                                 if (real_target_type == TypeManager.int64_type)
 440                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 441                                 if (real_target_type == TypeManager.float_type)
 442                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 443                                 if (real_target_type == TypeManager.double_type)
 444                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 445                         } else if (expr_type == TypeManager.short_type){
 446                                 //
 447                                 // From short to int, long, float, double
 448                                 //
 449                                 if (real_target_type == TypeManager.int32_type)
 450                                         return new EmptyCast (expr, target_type);
 451                                 if (real_target_type == TypeManager.int64_type)
 452                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 453                                 if (real_target_type == TypeManager.double_type)
 454                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 455                                 if (real_target_type == TypeManager.float_type)
 456                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 457                         } else if (expr_type == TypeManager.ushort_type){
 458                                 //
 459                                 // From ushort to int, uint, long, ulong, float, double
 460                                 //
 461                                 if (real_target_type == TypeManager.uint32_type)
 462                                         return new EmptyCast (expr, target_type);
 463
 464                                 if (real_target_type == TypeManager.uint64_type)
 465                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 466                                 if (real_target_type == TypeManager.int32_type)
 467                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 468                                 if (real_target_type == TypeManager.int64_type)
 469                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 470                                 if (real_target_type == TypeManager.double_type)
 471                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 472                                 if (real_target_type == TypeManager.float_type)
 473                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 474                         } else if (expr_type == TypeManager.int32_type){
 475                                 //
 476                                 // From int to long, float, double
 477                                 //
 478                                 if (real_target_type == TypeManager.int64_type)
 479                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 480                                 if (real_target_type == TypeManager.double_type)
 481                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 482                                 if (real_target_type == TypeManager.float_type)
 483                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 484                         } else if (expr_type == TypeManager.uint32_type){
 485                                 //
 486                                 // From uint to long, ulong, float, double
 487                                 //
 488                                 if (real_target_type == TypeManager.int64_type)
 489                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 490                                 if (real_target_type == TypeManager.uint64_type)
 491                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 492                                 if (real_target_type == TypeManager.double_type)
 493                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 494                                                                OpCodes.Conv_R8);
 495                                 if (real_target_type == TypeManager.float_type)
 496                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 497                                                                OpCodes.Conv_R4);
 498                         } else if (expr_type == TypeManager.int64_type){
 499                                 //
 500                                 // From long/ulong to float, double
 501                                 //
 502                                 if (real_target_type == TypeManager.double_type)
 503                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 504                                 if (real_target_type == TypeManager.float_type)
 505                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 506                         } else if (expr_type == TypeManager.uint64_type){
 507                                 //
 508                                 // From ulong to float, double
 509                                 //
 510                                 if (real_target_type == TypeManager.double_type)
 511                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 512                                                                OpCodes.Conv_R8);
 513                                 if (real_target_type == TypeManager.float_type)
 514                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 515                                                                OpCodes.Conv_R4);
 516                         } else if (expr_type == TypeManager.char_type){
 517                                 //
 518                                 // From char to ushort, int, uint, long, ulong, float, double
 519                                 //
 520                                 if ((real_target_type == TypeManager.ushort_type) ||
 521                                     (real_target_type == TypeManager.int32_type) ||
 522                                     (real_target_type == TypeManager.uint32_type))
 523                                         return new EmptyCast (expr, target_type);
 524                                 if (real_target_type == TypeManager.uint64_type)
 525                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 526                                 if (real_target_type == TypeManager.int64_type)
 527                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 528                                 if (real_target_type == TypeManager.float_type)
 529                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 530                                 if (real_target_type == TypeManager.double_type)
 531                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 532                         } else if (expr_type == TypeManager.float_type){
 533                                 //
 534                                 // float to double
 535                                 //
 536                                 if (real_target_type == TypeManager.double_type)
 537                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 538                         }
 539
 540                         return null;
 541                 }
 542
 543
 544                 /// <summary>
 545                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 546                 ///  implicit user defined conversions - needed for overload resolution
 547                 /// </summary>
 548                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 549                 {
 550                         if (expr is NullLiteral) {
 551                                 if (target_type.IsGenericParameter)
 552                                         return TypeParameter_to_Null (target_type);
 553
 554                                 if (TypeManager.IsNullableType (target_type))
 555                                         return true;
 556                         }
 557
 558                         if (ImplicitStandardConversionExists (ec, expr, target_type))
 559                                 return true;
 560
 561                         Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);
 562
 563                         if (dummy != null)
 564                                 return true;
 565
 566                         return false;
 567                 }
 568
 569                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 570                 {
 571                         Expression dummy = ImplicitUserConversion (
 572                                 ec, new EmptyExpression (source), target, Location.Null);
 573                         return dummy != null;
 574                 }
 575
 576                 /// <summary>
 577                 ///  Determines if a standard implicit conversion exists from
 578                 ///  expr_type to target_type
 579                 ///
 580                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 581                 /// </summary>
 582                 public static bool ImplicitStandardConversionExists (EmitContext ec, Expression expr, Type target_type)
 583                 {
 584                         Type expr_type = expr.Type;
 585
 586                         if (expr_type == TypeManager.void_type)
 587                                 return false;
 588
 589                         //Console.WriteLine ("Expr is {0}", expr);
 590                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 591                         if (expr_type.Equals (target_type))
 592                                 return true;
 593
 594
 595                         // First numeric conversions
 596
 597                         if (expr_type == TypeManager.sbyte_type){
 598                                 //
 599                                 // From sbyte to short, int, long, float, double.
 600                                 //
 601                                 if ((target_type == TypeManager.int32_type) ||
 602                                     (target_type == TypeManager.int64_type) ||
 603                                     (target_type == TypeManager.double_type) ||
 604                                     (target_type == TypeManager.float_type)  ||
 605                                     (target_type == TypeManager.short_type) ||
 606                                     (target_type == TypeManager.decimal_type))
 607                                         return true;
 608
 609                         } else if (expr_type == TypeManager.byte_type){
 610                                 //
 611                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 612                                 //
 613                                 if ((target_type == TypeManager.short_type) ||
 614                                     (target_type == TypeManager.ushort_type) ||
 615                                     (target_type == TypeManager.int32_type) ||
 616                                     (target_type == TypeManager.uint32_type) ||
 617                                     (target_type == TypeManager.uint64_type) ||
 618                                     (target_type == TypeManager.int64_type) ||
 619                                     (target_type == TypeManager.float_type) ||
 620                                     (target_type == TypeManager.double_type) ||
 621                                     (target_type == TypeManager.decimal_type))
 622                                         return true;
 623
 624                         } else if (expr_type == TypeManager.short_type){
 625                                 //
 626                                 // From short to int, long, float, double
 627                                 //
 628                                 if ((target_type == TypeManager.int32_type) ||
 629                                     (target_type == TypeManager.int64_type) ||
 630                                     (target_type == TypeManager.double_type) ||
 631                                     (target_type == TypeManager.float_type) ||
 632                                     (target_type == TypeManager.decimal_type))
 633                                         return true;
 634
 635                         } else if (expr_type == TypeManager.ushort_type){
 636                                 //
 637                                 // From ushort to int, uint, long, ulong, float, double
 638                                 //
 639                                 if ((target_type == TypeManager.uint32_type) ||
 640                                     (target_type == TypeManager.uint64_type) ||
 641                                     (target_type == TypeManager.int32_type) ||
 642                                     (target_type == TypeManager.int64_type) ||
 643                                     (target_type == TypeManager.double_type) ||
 644                                     (target_type == TypeManager.float_type) ||
 645                                     (target_type == TypeManager.decimal_type))
 646                                         return true;
 647
 648                         } else if (expr_type == TypeManager.int32_type){
 649                                 //
 650                                 // From int to long, float, double
 651                                 //
 652                                 if ((target_type == TypeManager.int64_type) ||
 653                                     (target_type == TypeManager.double_type) ||
 654                                     (target_type == TypeManager.float_type) ||
 655                                     (target_type == TypeManager.decimal_type))
 656                                         return true;
 657
 658                         } else if (expr_type == TypeManager.uint32_type){
 659                                 //
 660                                 // From uint to long, ulong, float, double
 661                                 //
 662                                 if ((target_type == TypeManager.int64_type) ||
 663                                     (target_type == TypeManager.uint64_type) ||
 664                                     (target_type == TypeManager.double_type) ||
 665                                     (target_type == TypeManager.float_type) ||
 666                                     (target_type == TypeManager.decimal_type))
 667                                         return true;
 668
 669                         } else if ((expr_type == TypeManager.uint64_type) ||
 670                                    (expr_type == TypeManager.int64_type)) {
 671                                 //
 672                                 // From long/ulong to float, double
 673                                 //
 674                                 if ((target_type == TypeManager.double_type) ||
 675                                     (target_type == TypeManager.float_type) ||
 676                                     (target_type == TypeManager.decimal_type))
 677                                         return true;
 678
 679                         } else if (expr_type == TypeManager.char_type){
 680                                 //
 681                                 // From char to ushort, int, uint, long, ulong, float, double
 682                                 //
 683                                 if ((target_type == TypeManager.ushort_type) ||
 684                                     (target_type == TypeManager.int32_type) ||
 685                                     (target_type == TypeManager.uint32_type) ||
 686                                     (target_type == TypeManager.uint64_type) ||
 687                                     (target_type == TypeManager.int64_type) ||
 688                                     (target_type == TypeManager.float_type) ||
 689                                     (target_type == TypeManager.double_type) ||
 690                                     (target_type == TypeManager.decimal_type))
 691                                         return true;
 692
 693                         } else if (expr_type == TypeManager.float_type){
 694                                 //
 695                                 // float to double
 696                                 //
 697                                 if (target_type == TypeManager.double_type)
 698                                         return true;
 699                         }
 700
 701                         if (expr.eclass == ExprClass.MethodGroup){
 702                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
 703                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 704                                         if (mg != null){
 705                                                 //
 706                                                 // This should not happen frequently, so we can create an object
 707                                                 // to test compatibility
 708                                                 //
 709                                                 Expression c = ImplicitDelegateCreation.Create (ec, mg, target_type, Location.Null);
 710                                                 return c != null;
 711                                         }
 712                                 }
 713                         }
 714
 715                         if (ImplicitReferenceConversionExists (ec, expr, target_type))
 716                                 return true;
 717
 718                         //
 719                         // Implicit Constant Expression Conversions
 720                         //
 721                         if (expr is IntConstant){
 722                                 int value = ((IntConstant) expr).Value;
 723
 724                                 if (target_type == TypeManager.sbyte_type){
 725                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 726                                                 return true;
 727                                 } else if (target_type == TypeManager.byte_type){
 728                                         if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
 729                                                 return true;
 730                                 } else if (target_type == TypeManager.short_type){
 731                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 732                                                 return true;
 733                                 } else if (target_type == TypeManager.ushort_type){
 734                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 735                                                 return true;
 736                                 } else if (target_type == TypeManager.uint32_type){
 737                                         if (value >= 0)
 738                                                 return true;
 739                                 } else if (target_type == TypeManager.uint64_type){
 740                                          //
 741                                          // we can optimize this case: a positive int32
 742                                          // always fits on a uint64.  But we need an opcode
 743                                          // to do it.
 744                                          //
 745                                         if (value >= 0)
 746                                                 return true;
 747                                 }
 748
 749                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 750                                         return true;
 751                         }
 752
 753                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 754                                 //
 755                                 // Try the implicit constant expression conversion
 756                                 // from long to ulong, instead of a nice routine,
 757                                 // we just inline it
 758                                 //
 759                                 long v = ((LongConstant) expr).Value;
 760                                 if (v > 0)
 761                                         return true;
 762                         }
 763
 764                         if ((target_type == TypeManager.enum_type ||
 765                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 766                              expr is IntLiteral){
 767                                 IntLiteral i = (IntLiteral) expr;
 768
 769                                 if (i.Value == 0)
 770                                         return true;
 771                         }
 772
 773                         //
 774                         // If `expr_type' implements `target_type' (which is an iface)
 775                         // see TryImplicitIntConversion
 776                         //
 777                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 778                                 return true;
 779
 780                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 781                                 return true;
 782
 783                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
 784                                 return true;
 785
 786                         if (expr_type == TypeManager.anonymous_method_type){
 787                                 if (!TypeManager.IsDelegateType (target_type))
 788                                         return false;
 789
 790                                 AnonymousMethod am = (AnonymousMethod) expr;
 791
 792                                 Expression conv = am.Compatible (ec, target_type, true);
 793                                 if (conv != null)
 794                                         return true;
 795                         }
 796
 797                         return false;
 798                 }
 799
 800                 //
 801                 // Used internally by FindMostEncompassedType, this is used
 802                 // to avoid creating lots of objects in the tight loop inside
 803                 // FindMostEncompassedType
 804                 //
 805                 static EmptyExpression priv_fmet_param;
 806
 807                 /// <summary>
 808                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 809                 ///  amongst the methods in the MethodGroupExpr
 810                 /// </summary>
 811                 static Type FindMostEncompassedType (EmitContext ec, ArrayList types)
 812                 {
 813                         Type best = null;
 814
 815                         if (priv_fmet_param == null)
 816                                 priv_fmet_param = new EmptyExpression ();
 817
 818                         foreach (Type t in types){
 819                                 priv_fmet_param.SetType (t);
 820
 821                                 if (best == null) {
 822                                         best = t;
 823                                         continue;
 824                                 }
 825
 826                                 if (ImplicitStandardConversionExists (ec, priv_fmet_param, best))
 827                                         best = t;
 828                         }
 829
 830                         return best;
 831                 }
 832
 833                 //
 834                 // Used internally by FindMostEncompassingType, this is used
 835                 // to avoid creating lots of objects in the tight loop inside
 836                 // FindMostEncompassingType
 837                 //
 838                 static EmptyExpression priv_fmee_ret;
 839
 840                 /// <summary>
 841                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 842                 ///  amongst the types in the given set
 843                 /// </summary>
 844                 static Type FindMostEncompassingType (EmitContext ec, ArrayList types)
 845                 {
 846                         Type best = null;
 847
 848                         if (priv_fmee_ret == null)
 849                                 priv_fmee_ret = new EmptyExpression ();
 850
 851                         foreach (Type t in types){
 852                                 priv_fmee_ret.SetType (best);
 853
 854                                 if (best == null) {
 855                                         best = t;
 856                                         continue;
 857                                 }
 858
 859                                 if (ImplicitStandardConversionExists (ec, priv_fmee_ret, t))
 860                                         best = t;
 861                         }
 862
 863                         return best;
 864                 }
 865
 866                 //
 867                 // Used to avoid creating too many objects
 868                 //
 869                 static EmptyExpression priv_fms_expr;
 870
 871                 /// <summary>
 872                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 873                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 874                 ///   for explicit and implicit conversion operators.
 875                 /// </summary>
 876                 static public Type FindMostSpecificSource (EmitContext ec, MethodGroupExpr me,
 877                                                            Expression source, bool apply_explicit_conv_rules,
 878                                                            Location loc)
 879                 {
 880                         ArrayList src_types_set = new ArrayList ();
 881
 882                         if (priv_fms_expr == null)
 883                                 priv_fms_expr = new EmptyExpression ();
 884
 885                         //
 886                         // If any operator converts from S then Sx = S
 887                         //
 888                         Type source_type = source.Type;
 889                         foreach (MethodBase mb in me.Methods){
 890                                 ParameterData pd = TypeManager.GetParameterData (mb);
 891                                 Type param_type = pd.ParameterType (0);
 892
 893                                 if (param_type == source_type)
 894                                         return param_type;
 895
 896                                 if (apply_explicit_conv_rules) {
 897                                         //
 898                                         // From the spec :
 899                                         // Find the set of applicable user-defined conversion operators, U.  This set
 900                                         // consists of the
 901                                         // user-defined implicit or explicit conversion operators declared by
 902                                         // the classes or structs in D that convert from a type encompassing
 903                                         // or encompassed by S to a type encompassing or encompassed by T
 904                                         //
 905                                         priv_fms_expr.SetType (param_type);
 906                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, source_type))
 907                                                 src_types_set.Add (param_type);
 908                                         else {
 909                                                 if (ImplicitStandardConversionExists (ec, source, param_type))
 910                                                         src_types_set.Add (param_type);
 911                                         }
 912                                 } else {
 913                                         //
 914                                         // Only if S is encompassed by param_type
 915                                         //
 916                                         if (ImplicitStandardConversionExists (ec, source, param_type))
 917                                                 src_types_set.Add (param_type);
 918                                 }
 919                         }
 920
 921                         //
 922                         // Explicit Conv rules
 923                         //
 924                         if (apply_explicit_conv_rules) {
 925                                 ArrayList candidate_set = new ArrayList ();
 926
 927                                 foreach (Type param_type in src_types_set){
 928                                         if (ImplicitStandardConversionExists (ec, source, param_type))
 929                                                 candidate_set.Add (param_type);
 930                                 }
 931
 932                                 if (candidate_set.Count != 0)
 933                                         return FindMostEncompassedType (ec, candidate_set);
 934                         }
 935
 936                         //
 937                         // Final case
 938                         //
 939                         if (apply_explicit_conv_rules)
 940                                 return FindMostEncompassingType (ec, src_types_set);
 941                         else
 942                                 return FindMostEncompassedType (ec, src_types_set);
 943                 }
 944
 945                 //
 946                 // Useful in avoiding proliferation of objects
 947                 //
 948                 static EmptyExpression priv_fmt_expr;
 949
 950                 /// <summary>
 951                 ///  Finds the most specific target Tx according to section 13.4.4
 952                 /// </summary>
 953                 static public Type FindMostSpecificTarget (EmitContext ec, MethodGroupExpr me,
 954                                                            Type target, bool apply_explicit_conv_rules,
 955                                                            Location loc)
 956                 {
 957                         ArrayList tgt_types_set = new ArrayList ();
 958
 959                         if (priv_fmt_expr == null)
 960                                 priv_fmt_expr = new EmptyExpression ();
 961
 962                         //
 963                         // If any operator converts to T then Tx = T
 964                         //
 965                         foreach (MethodInfo mi in me.Methods){
 966                                 Type ret_type = mi.ReturnType;
 967
 968                                 if (ret_type == target)
 969                                         return ret_type;
 970
 971                                 if (apply_explicit_conv_rules) {
 972                                         //
 973                                         // From the spec :
 974                                         // Find the set of applicable user-defined conversion operators, U.
 975                                         //
 976                                         // This set consists of the
 977                                         // user-defined implicit or explicit conversion operators declared by
 978                                         // the classes or structs in D that convert from a type encompassing
 979                                         // or encompassed by S to a type encompassing or encompassed by T
 980                                         //
 981                                         priv_fms_expr.SetType (ret_type);
 982                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, target))
 983                                                 tgt_types_set.Add (ret_type);
 984                                         else {
 985                                                 priv_fms_expr.SetType (target);
 986                                                 if (ImplicitStandardConversionExists (ec, priv_fms_expr, ret_type))
 987                                                         tgt_types_set.Add (ret_type);
 988                                         }
 989                                 } else {
 990                                         //
 991                                         // Only if T is encompassed by param_type
 992                                         //
 993                                         priv_fms_expr.SetType (ret_type);
 994                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, target))
 995                                                 tgt_types_set.Add (ret_type);
 996                                 }
 997                         }
 998
 999                         //
1000                         // Explicit conv rules
1001                         //
1002                         if (apply_explicit_conv_rules) {
1003                                 ArrayList candidate_set = new ArrayList ();
1004
1005                                 foreach (Type ret_type in tgt_types_set){
1006                                         priv_fmt_expr.SetType (ret_type);
1007
1008                                         if (ImplicitStandardConversionExists (ec, priv_fmt_expr, target))
1009                                                 candidate_set.Add (ret_type);
1010                                 }
1011
1012                                 if (candidate_set.Count != 0)
1013                                         return FindMostEncompassingType (ec, candidate_set);
1014                         }
1015
1016                         //
1017                         // Okay, final case !
1018                         //
1019                         if (apply_explicit_conv_rules)
1020                                 return FindMostEncompassedType (ec, tgt_types_set);
1021                         else
1022                                 return FindMostEncompassingType (ec, tgt_types_set);
1023                 }
1024
1025                 /// <summary>
1026                 ///  User-defined Implicit conversions
1027                 /// </summary>
1028                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
1029                                                                  Type target, Location loc)
1030                 {
1031                         return UserDefinedConversion (ec, source, target, loc, false);
1032                 }
1033
1034                 /// <summary>
1035                 ///  User-defined Explicit conversions
1036                 /// </summary>
1037                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1038                                                                  Type target, Location loc)
1039                 {
1040                         return UserDefinedConversion (ec, source, target, loc, true);
1041                 }
1042
1043                 static DoubleHash explicit_conv = new DoubleHash (100);
1044                 static DoubleHash implicit_conv = new DoubleHash (100);
1045                 /// <summary>
1046                 ///   Computes the MethodGroup for the user-defined conversion
1047                 ///   operators from source_type to target_type.  `look_for_explicit'
1048                 ///   controls whether we should also include the list of explicit
1049                 ///   operators
1050                 /// </summary>
1051                 static MethodGroupExpr GetConversionOperators (EmitContext ec,
1052                                                                Type source_type, Type target_type,
1053                                                                Location loc, bool look_for_explicit)
1054                 {
1055                         Expression mg1 = null, mg2 = null;
1056                         Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
1057                         string op_name;
1058
1059                         op_name = "op_Implicit";
1060
1061                         MethodGroupExpr union3;
1062                         object r;
1063                         if ((look_for_explicit ? explicit_conv : implicit_conv).Lookup (source_type, target_type, out r))
1064                                 return (MethodGroupExpr) r;
1065
1066                         mg1 = Expression.MethodLookup (ec, source_type, op_name, loc);
1067                         if (source_type.BaseType != null)
1068                                 mg2 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1069
1070                         if (mg1 == null)
1071                                 union3 = (MethodGroupExpr) mg2;
1072                         else if (mg2 == null)
1073                                 union3 = (MethodGroupExpr) mg1;
1074                         else
1075                                 union3 = Invocation.MakeUnionSet (mg1, mg2, loc);
1076
1077                         mg1 = Expression.MethodLookup (ec, target_type, op_name, loc);
1078                         if (mg1 != null){
1079                                 if (union3 != null)
1080                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1081                                 else
1082                                         union3 = (MethodGroupExpr) mg1;
1083                         }
1084
1085                         if (target_type.BaseType != null)
1086                                 mg1 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1087
1088                         if (mg1 != null){
1089                                 if (union3 != null)
1090                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1091                                 else
1092                                         union3 = (MethodGroupExpr) mg1;
1093                         }
1094
1095                         MethodGroupExpr union4 = null;
1096
1097                         if (look_for_explicit) {
1098                                 op_name = "op_Explicit";
1099
1100                                 mg5 = Expression.MemberLookup (ec, source_type, op_name, loc);
1101                                 if (source_type.BaseType != null)
1102                                         mg6 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1103
1104                                 mg7 = Expression.MemberLookup (ec, target_type, op_name, loc);
1105                                 if (target_type.BaseType != null)
1106                                         mg8 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1107
1108                                 MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
1109                                 MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);
1110
1111                                 union4 = Invocation.MakeUnionSet (union5, union6, loc);
1112                         }
1113
1114                         MethodGroupExpr ret = Invocation.MakeUnionSet (union3, union4, loc);
1115                         (look_for_explicit ? explicit_conv : implicit_conv).Insert (source_type, target_type, ret);
1116                         return ret;
1117                 }
1118
1119                 /// <summary>
1120                 ///   User-defined conversions
1121                 /// </summary>
1122                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1123                                                                 Type target, Location loc,
1124                                                                 bool look_for_explicit)
1125                 {
1126                         MethodGroupExpr union;
1127                         Type source_type = source.Type;
1128                         MethodBase method = null;
1129
1130                         if (TypeManager.IsNullableType (source_type) && TypeManager.IsNullableType (target))
1131                                 return new Nullable.LiftedConversion (
1132                                         source, target, true, look_for_explicit, loc).Resolve (ec);
1133
1134                         union = GetConversionOperators (ec, source_type, target, loc, look_for_explicit);
1135                         if (union == null)
1136                                 return null;
1137
1138                         Type most_specific_source, most_specific_target;
1139
1140                         most_specific_source = FindMostSpecificSource (ec, union, source, look_for_explicit, loc);
1141                         if (most_specific_source == null)
1142                                 return null;
1143
1144                         most_specific_target = FindMostSpecificTarget (ec, union, target, look_for_explicit, loc);
1145                         if (most_specific_target == null)
1146                                 return null;
1147
1148                         int count = 0;
1149
1150
1151                         foreach (MethodBase mb in union.Methods){
1152                                 ParameterData pd = TypeManager.GetParameterData (mb);
1153                                 MethodInfo mi = (MethodInfo) mb;
1154
1155                                 if (pd.ParameterType (0) == most_specific_source &&
1156                                     mi.ReturnType == most_specific_target) {
1157                                         method = mb;
1158                                         count++;
1159                                 }
1160                         }
1161
1162                         if (method == null || count > 1)
1163                                 return null;
1164
1165
1166                         //
1167                         // This will do the conversion to the best match that we
1168                         // found.  Now we need to perform an implict standard conversion
1169                         // if the best match was not the type that we were requested
1170                         // by target.
1171                         //
1172                         if (look_for_explicit)
1173                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1174                         else
1175                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1176
1177                         if (source == null)
1178                                 return null;
1179
1180                         Expression e;
1181                         e =  new UserCast ((MethodInfo) method, source, loc);
1182                         if (e.Type != target){
1183                                 if (!look_for_explicit)
1184                                         e = ImplicitConversionStandard (ec, e, target, loc);
1185                                 else
1186                                         e = ExplicitConversionStandard (ec, e, target, loc);
1187                         }
1188
1189                         return e;
1190                 }
1191
1192                 /// <summary>
1193                 ///   Converts implicitly the resolved expression `expr' into the
1194                 ///   `target_type'.  It returns a new expression that can be used
1195                 ///   in a context that expects a `target_type'.
1196                 /// </summary>
1197                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1198                                                              Type target_type, Location loc)
1199                 {
1200                         Expression e;
1201
1202                         if (target_type == null)
1203                                 throw new Exception ("Target type is null");
1204
1205                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1206                         if (e != null)
1207                                 return e;
1208
1209                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1210                         if (e != null)
1211                                 return e;
1212
1213                         return null;
1214                 }
1215
1216
1217                 /// <summary>
1218                 ///   Attempts to apply the `Standard Implicit
1219                 ///   Conversion' rules to the expression `expr' into
1220                 ///   the `target_type'.  It returns a new expression
1221                 ///   that can be used in a context that expects a
1222                 ///   `target_type'.
1223                 ///
1224                 ///   This is different from `ImplicitConversion' in that the
1225                 ///   user defined implicit conversions are excluded.
1226                 /// </summary>
1227                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1228                                                                      Type target_type, Location loc)
1229                 {
1230                         Type expr_type = expr.Type;
1231                         Expression e;
1232
1233                         if (expr is NullLiteral) {
1234                                 if (target_type.IsGenericParameter)
1235                                         return TypeParameter_to_Null (expr, target_type, loc);
1236
1237                                 if (TypeManager.IsNullableType (target_type))
1238                                         return new Nullable.NullableLiteral (target_type, loc);
1239                         }
1240
1241                         if (TypeManager.IsNullableType (expr_type) && TypeManager.IsNullableType (target_type))
1242                                 return new Nullable.LiftedConversion (
1243                                         expr, target_type, false, false, loc).Resolve (ec);
1244
1245                         if (expr.eclass == ExprClass.MethodGroup){
1246                                 if (!TypeManager.IsDelegateType (target_type)){
1247                                         return null;
1248                                 }
1249
1250                                 //
1251                                 // Only allow anonymous method conversions on post ISO_1
1252                                 //
1253                                 if (RootContext.Version != LanguageVersion.ISO_1){
1254                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1255                                         if (mg != null)
1256                                                 return ImplicitDelegateCreation.Create (ec, mg, target_type, loc);
1257                                 }
1258                         }
1259
1260                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1261                                 return expr;
1262
1263                         e = ImplicitNumericConversion (ec, expr, target_type, loc);
1264                         if (e != null)
1265                                 return e;
1266
1267                         e = ImplicitReferenceConversion (ec, expr, target_type);
1268                         if (e != null)
1269                                 return e;
1270
1271                         if ((target_type == TypeManager.enum_type ||
1272                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1273                             expr is IntLiteral){
1274                                 IntLiteral i = (IntLiteral) expr;
1275
1276                                 if (i.Value == 0)
1277                                         return new EnumConstant ((Constant) expr, target_type);
1278                         }
1279
1280                         if (ec.InUnsafe) {
1281                                 if (expr_type.IsPointer){
1282                                         if (target_type == TypeManager.void_ptr_type)
1283                                                 return new EmptyCast (expr, target_type);
1284
1285                                         //
1286                                         // yep, comparing pointer types cant be done with
1287                                         // t1 == t2, we have to compare their element types.
1288                                         //
1289                                         if (target_type.IsPointer){
1290                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1291                                                         return expr;
1292                                         }
1293                                 }
1294
1295                                 if (target_type.IsPointer) {
1296                                         if (expr_type == TypeManager.null_type)
1297                                                 return new EmptyCast (expr, target_type);
1298
1299                                         if (expr_type == TypeManager.void_ptr_type)
1300                                                 return new EmptyCast (expr, target_type);
1301                                 }
1302                         }
1303
1304                         if (expr_type == TypeManager.anonymous_method_type){
1305                                 if (!TypeManager.IsDelegateType (target_type)){
1306                                         Report.Error (1660, loc,
1307                                                               "Cannot convert anonymous method to `{0}', since it is not a delegate",
1308                                                               TypeManager.CSharpName (target_type));
1309                                         return null;
1310                                 }
1311
1312                                 AnonymousMethod am = (AnonymousMethod) expr;
1313                                 int errors = Report.Errors;
1314
1315                                 Expression conv = am.Compatible (ec, target_type, false);
1316                                 if (conv != null)
1317                                         return conv;
1318
1319                                 //
1320                                 // We return something instead of null, to avoid
1321                                 // the duplicate error, since am.Compatible would have
1322                                 // reported that already
1323                                 //
1324                                 if (errors != Report.Errors)
1325                                         return new EmptyCast (expr, target_type);
1326                         }
1327
1328                         return null;
1329                 }
1330
1331                 /// <summary>
1332                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1333                 ///   into a different data type using casts (See Implicit Constant
1334                 ///   Expression Conversions)
1335                 /// </summary>
1336                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1337                 {
1338                         int value = ic.Value;
1339
1340                         if (target_type == TypeManager.sbyte_type){
1341                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1342                                         return new SByteConstant ((sbyte) value);
1343                         } else if (target_type == TypeManager.byte_type){
1344                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1345                                         return new ByteConstant ((byte) value);
1346                         } else if (target_type == TypeManager.short_type){
1347                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1348                                         return new ShortConstant ((short) value);
1349                         } else if (target_type == TypeManager.ushort_type){
1350                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1351                                         return new UShortConstant ((ushort) value);
1352                         } else if (target_type == TypeManager.uint32_type){
1353                                 if (value >= 0)
1354                                         return new UIntConstant ((uint) value);
1355                         } else if (target_type == TypeManager.uint64_type){
1356                                 //
1357                                 // we can optimize this case: a positive int32
1358                                 // always fits on a uint64.  But we need an opcode
1359                                 // to do it.
1360                                 //
1361                                 if (value >= 0)
1362                                         return new ULongConstant ((ulong) value);
1363                         } else if (target_type == TypeManager.double_type)
1364                                 return new DoubleConstant ((double) value);
1365                         else if (target_type == TypeManager.float_type)
1366                                 return new FloatConstant ((float) value);
1367
1368                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1369                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1370                                 Constant e = (Constant) ic;
1371
1372                                 //
1373                                 // Possibly, we need to create a different 0 literal before passing
1374                                 // to EnumConstant
1375                                 //
1376                                 if (underlying == TypeManager.int64_type)
1377                                         e = new LongLiteral (0);
1378                                 else if (underlying == TypeManager.uint64_type)
1379                                         e = new ULongLiteral (0);
1380
1381                                 return new EnumConstant (e, target_type);
1382                         }
1383
1384                         //
1385                         // If `target_type' is an interface and the type of `ic' implements the interface
1386                         // e.g. target_type is IComparable, IConvertible, IFormattable
1387                         //
1388                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1389                                 return new BoxedCast (ic);
1390
1391                         return null;
1392                 }
1393
1394                 static public void Error_CannotImplicitConversion (Location loc, Type source, Type target)
1395                 {
1396                         if (source.Name == target.Name){
1397                                 Report.ExtraInformation (loc,
1398                                          String.Format (
1399                                                 "The type {0} has two conflicting definitions, one comes from {1} and the other from {2}",
1400                                                 source.Name, source.Assembly.FullName, target.Assembly.FullName));
1401
1402                         }
1403                         Report.Error (29, loc, "Cannot convert implicitly from {0} to `{1}'",
1404                                       source == TypeManager.anonymous_method_type ?
1405                                       "anonymous method" : "`" + TypeManager.CSharpName (source) + "'",
1406                                       TypeManager.CSharpName (target));
1407                 }
1408
1409                 /// <summary>
1410                 ///   Attempts to implicitly convert `source' into `target_type', using
1411                 ///   ImplicitConversion.  If there is no implicit conversion, then
1412                 ///   an error is signaled
1413                 /// </summary>
1414                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1415                                                                      Type target_type, Location loc)
1416                 {
1417                         Expression e;
1418
1419                         int errors = Report.Errors;
1420                         e = ImplicitConversion (ec, source, target_type, loc);
1421                         if (Report.Errors > errors)
1422                                 return null;
1423                         if (e != null)
1424                                 return e;
1425
1426                         if (source is DoubleLiteral) {
1427                                 if (target_type == TypeManager.float_type) {
1428                                         Error_664 (loc, "float", "f");
1429                                         return null;
1430                                 }
1431                                 if (target_type == TypeManager.decimal_type) {
1432                                         Error_664 (loc, "decimal", "m");
1433                                         return null;
1434                                 }
1435                         }
1436
1437                         if (source is Constant){
1438                                 Constant c = (Constant) source;
1439
1440                                 Expression.Error_ConstantValueCannotBeConverted (loc, c.AsString (), target_type);
1441                                 return null;
1442                         }
1443
1444                         Error_CannotImplicitConversion (loc, source.Type, target_type);
1445
1446                         return null;
1447                 }
1448
1449                 static void Error_664 (Location loc, string type, string suffix) {
1450                         Report.Error (664, loc,
1451                                 "Literal of type double cannot be implicitly converted to type '{0}'. Add suffix '{1}' to create a literal of this type",
1452                                 type, suffix);
1453                 }
1454
1455                 /// <summary>
1456                 ///   Performs the explicit numeric conversions
1457                 /// </summary>
1458                 static Expression ExplicitNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
1459                 {
1460                         Type expr_type = expr.Type;
1461
1462                         //
1463                         // If we have an enumeration, extract the underlying type,
1464                         // use this during the comparison, but wrap around the original
1465                         // target_type
1466                         //
1467                         Type real_target_type = target_type;
1468
1469                         if (TypeManager.IsEnumType (real_target_type))
1470                                 real_target_type = TypeManager.EnumToUnderlying (real_target_type);
1471
1472                         if (ImplicitStandardConversionExists (ec, expr, real_target_type)){
1473                                 Expression ce = ImplicitConversionStandard (ec, expr, real_target_type, loc);
1474
1475                                 if (real_target_type != target_type)
1476                                         return new EmptyCast (ce, target_type);
1477                                 return ce;
1478                         }
1479
1480                         if (expr_type == TypeManager.sbyte_type){
1481                                 //
1482                                 // From sbyte to byte, ushort, uint, ulong, char
1483                                 //
1484                                 if (real_target_type == TypeManager.byte_type)
1485                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U1);
1486                                 if (real_target_type == TypeManager.ushort_type)
1487                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U2);
1488                                 if (real_target_type == TypeManager.uint32_type)
1489                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U4);
1490                                 if (real_target_type == TypeManager.uint64_type)
1491                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U8);
1492                                 if (real_target_type == TypeManager.char_type)
1493                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_CH);
1494                         } else if (expr_type == TypeManager.byte_type){
1495                                 //
1496                                 // From byte to sbyte and char
1497                                 //
1498                                 if (real_target_type == TypeManager.sbyte_type)
1499                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_I1);
1500                                 if (real_target_type == TypeManager.char_type)
1501                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_CH);
1502                         } else if (expr_type == TypeManager.short_type){
1503                                 //
1504                                 // From short to sbyte, byte, ushort, uint, ulong, char
1505                                 //
1506                                 if (real_target_type == TypeManager.sbyte_type)
1507                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_I1);
1508                                 if (real_target_type == TypeManager.byte_type)
1509                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
1510                                 if (real_target_type == TypeManager.ushort_type)
1511                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U2);
1512                                 if (real_target_type == TypeManager.uint32_type)
1513                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U4);
1514                                 if (real_target_type == TypeManager.uint64_type)
1515                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U8);
1516                                 if (real_target_type == TypeManager.char_type)
1517                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_CH);
1518                         } else if (expr_type == TypeManager.ushort_type){
1519                                 //
1520                                 // From ushort to sbyte, byte, short, char
1521                                 //
1522                                 if (real_target_type == TypeManager.sbyte_type)
1523                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I1);
1524                                 if (real_target_type == TypeManager.byte_type)
1525                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_U1);
1526                                 if (real_target_type == TypeManager.short_type)
1527                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I2);
1528                                 if (real_target_type == TypeManager.char_type)
1529                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_CH);
1530                         } else if (expr_type == TypeManager.int32_type){
1531                                 //
1532                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1533                                 //
1534                                 if (real_target_type == TypeManager.sbyte_type)
1535                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I1);
1536                                 if (real_target_type == TypeManager.byte_type)
1537                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
1538                                 if (real_target_type == TypeManager.short_type)
1539                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
1540                                 if (real_target_type == TypeManager.ushort_type)
1541                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U2);
1542                                 if (real_target_type == TypeManager.uint32_type)
1543                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U4);
1544                                 if (real_target_type == TypeManager.uint64_type)
1545                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U8);
1546                                 if (real_target_type == TypeManager.char_type)
1547                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_CH);
1548                         } else if (expr_type == TypeManager.uint32_type){
1549                                 //
1550                                 // From uint to sbyte, byte, short, ushort, int, char
1551                                 //
1552                                 if (real_target_type == TypeManager.sbyte_type)
1553                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I1);
1554                                 if (real_target_type == TypeManager.byte_type)
1555                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U1);
1556                                 if (real_target_type == TypeManager.short_type)
1557                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I2);
1558                                 if (real_target_type == TypeManager.ushort_type)
1559                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U2);
1560                                 if (real_target_type == TypeManager.int32_type)
1561                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I4);
1562                                 if (real_target_type == TypeManager.char_type)
1563                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_CH);
1564                         } else if (expr_type == TypeManager.int64_type){
1565                                 //
1566                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1567                                 //
1568                                 if (real_target_type == TypeManager.sbyte_type)
1569                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I1);
1570                                 if (real_target_type == TypeManager.byte_type)
1571                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
1572                                 if (real_target_type == TypeManager.short_type)
1573                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
1574                                 if (real_target_type == TypeManager.ushort_type)
1575                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U2);
1576                                 if (real_target_type == TypeManager.int32_type)
1577                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
1578                                 if (real_target_type == TypeManager.uint32_type)
1579                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U4);
1580                                 if (real_target_type == TypeManager.uint64_type)
1581                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U8);
1582                                 if (real_target_type == TypeManager.char_type)
1583                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_CH);
1584                         } else if (expr_type == TypeManager.uint64_type){
1585                                 //
1586                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1587                                 //
1588                                 if (real_target_type == TypeManager.sbyte_type)
1589                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I1);
1590                                 if (real_target_type == TypeManager.byte_type)
1591                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U1);
1592                                 if (real_target_type == TypeManager.short_type)
1593                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I2);
1594                                 if (real_target_type == TypeManager.ushort_type)
1595                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U2);
1596                                 if (real_target_type == TypeManager.int32_type)
1597                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I4);
1598                                 if (real_target_type == TypeManager.uint32_type)
1599                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U4);
1600                                 if (real_target_type == TypeManager.int64_type)
1601                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I8);
1602                                 if (real_target_type == TypeManager.char_type)
1603                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_CH);
1604                         } else if (expr_type == TypeManager.char_type){
1605                                 //
1606                                 // From char to sbyte, byte, short
1607                                 //
1608                                 if (real_target_type == TypeManager.sbyte_type)
1609                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I1);
1610                                 if (real_target_type == TypeManager.byte_type)
1611                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_U1);
1612                                 if (real_target_type == TypeManager.short_type)
1613                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I2);
1614                         } else if (expr_type == TypeManager.float_type){
1615                                 //
1616                                 // From float to sbyte, byte, short,
1617                                 // ushort, int, uint, long, ulong, char
1618                                 // or decimal
1619                                 //
1620                                 if (real_target_type == TypeManager.sbyte_type)
1621                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
1622                                 if (real_target_type == TypeManager.byte_type)
1623                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U1);
1624                                 if (real_target_type == TypeManager.short_type)
1625                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I2);
1626                                 if (real_target_type == TypeManager.ushort_type)
1627                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U2);
1628                                 if (real_target_type == TypeManager.int32_type)
1629                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I4);
1630                                 if (real_target_type == TypeManager.uint32_type)
1631                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U4);
1632                                 if (real_target_type == TypeManager.int64_type)
1633                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I8);
1634                                 if (real_target_type == TypeManager.uint64_type)
1635                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U8);
1636                                 if (real_target_type == TypeManager.char_type)
1637                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_CH);
1638                         } else if (expr_type == TypeManager.double_type){
1639                                 //
1640                                 // From double to byte, byte, short,
1641                                 // ushort, int, uint, long, ulong,
1642                                 // char, float or decimal
1643                                 //
1644                                 if (real_target_type == TypeManager.sbyte_type)
1645                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I1);
1646                                 if (real_target_type == TypeManager.byte_type)
1647                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1648                                 if (real_target_type == TypeManager.short_type)
1649                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1650                                 if (real_target_type == TypeManager.ushort_type)
1651                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U2);
1652                                 if (real_target_type == TypeManager.int32_type)
1653                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1654                                 if (real_target_type == TypeManager.uint32_type)
1655                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U4);
1656                                 if (real_target_type == TypeManager.int64_type)
1657                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1658                                 if (real_target_type == TypeManager.uint64_type)
1659                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U8);
1660                                 if (real_target_type == TypeManager.char_type)
1661                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_CH);
1662                                 if (real_target_type == TypeManager.float_type)
1663                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
1664                         }
1665
1666                         // decimal is taken care of by the op_Explicit methods.
1667
1668                         return null;
1669                 }
1670
1671                 /// <summary>
1672                 ///  Returns whether an explicit reference conversion can be performed
1673                 ///  from source_type to target_type
1674                 /// </summary>
1675                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1676                 {
1677                         bool target_is_type_param = target_type.IsGenericParameter;
1678                         bool target_is_value_type = target_type.IsValueType;
1679
1680                         if (source_type == target_type)
1681                                 return true;
1682
1683                         //
1684                         // From generic parameter to any type
1685                         //
1686                         if (source_type.IsGenericParameter)
1687                                 return true;
1688
1689                         //
1690                         // From object to a generic parameter
1691                         //
1692                         if (source_type == TypeManager.object_type && target_is_type_param)
1693                                 return true;
1694
1695                         //
1696                         // From object to any reference type
1697                         //
1698                         if (source_type == TypeManager.object_type && !target_is_value_type)
1699                                 return true;
1700
1701                         //
1702                         // From any class S to any class-type T, provided S is a base class of T
1703                         //
1704                         if (TypeManager.IsSubclassOf (target_type, source_type))
1705                                 return true;
1706
1707                         //
1708                         // From any interface type S to any interface T provided S is not derived from T
1709                         //
1710                         if (source_type.IsInterface && target_type.IsInterface){
1711                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1712                                         return true;
1713                         }
1714
1715                         //
1716                         // From any class type S to any interface T, provided S is not sealed
1717                         // and provided S does not implement T.
1718                         //
1719                         if (target_type.IsInterface && !source_type.IsSealed &&
1720                             !TypeManager.ImplementsInterface (source_type, target_type))
1721                                 return true;
1722
1723                         //
1724                         // From any interface-type S to to any class type T, provided T is not
1725                         // sealed, or provided T implements S.
1726                         //
1727                         if (source_type.IsInterface &&
1728                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1729                                 return true;
1730
1731
1732                         // From an array type S with an element type Se to an array type T with an
1733                         // element type Te provided all the following are true:
1734                         //     * S and T differe only in element type, in other words, S and T
1735                         //       have the same number of dimensions.
1736                         //     * Both Se and Te are reference types
1737                         //     * An explicit referenc conversions exist from Se to Te
1738                         //
1739                         if (source_type.IsArray && target_type.IsArray) {
1740                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1741
1742                                         Type source_element_type = TypeManager.GetElementType (source_type);
1743                                         Type target_element_type = TypeManager.GetElementType (target_type);
1744
1745                                         if (source_element_type.IsGenericParameter ||
1746                                             (!source_element_type.IsValueType && !target_element_type.IsValueType))
1747                                                 if (ExplicitReferenceConversionExists (source_element_type,
1748                                                                                        target_element_type))
1749                                                         return true;
1750                                 }
1751                         }
1752
1753
1754                         // From System.Array to any array-type
1755                         if (source_type == TypeManager.array_type &&
1756                             target_type.IsArray){
1757                                 return true;
1758                         }
1759
1760                         //
1761                         // From System delegate to any delegate-type
1762                         //
1763                         if (source_type == TypeManager.delegate_type &&
1764                             TypeManager.IsDelegateType (target_type))
1765                                 return true;
1766
1767                         //
1768                         // From ICloneable to Array or Delegate types
1769                         //
1770                         if (source_type == TypeManager.icloneable_type &&
1771                             (target_type == TypeManager.array_type ||
1772                              target_type == TypeManager.delegate_type))
1773                                 return true;
1774
1775                         return false;
1776                 }
1777
1778                 /// <summary>
1779                 ///   Implements Explicit Reference conversions
1780                 /// </summary>
1781                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1782                 {
1783                         Type source_type = source.Type;
1784                         bool target_is_type_param = target_type.IsGenericParameter;
1785                         bool target_is_value_type = target_type.IsValueType;
1786
1787                         //
1788                         // From object to a generic parameter
1789                         //
1790                         if (source_type == TypeManager.object_type && target_is_type_param)
1791                                 return new UnboxCast (source, target_type);
1792
1793                         //
1794                         // From object to any reference type
1795                         //
1796                         if (source_type == TypeManager.object_type && !target_is_value_type)
1797                                 return new ClassCast (source, target_type);
1798
1799                         //
1800                         // Unboxing conversion.
1801                         //
1802                         if (((source_type == TypeManager.enum_type &&
1803                                 !(source is EmptyCast)) ||
1804                                 source_type == TypeManager.value_type) && target_is_value_type)
1805                                 return new UnboxCast (source, target_type);
1806
1807                         //
1808                         // From any class S to any class-type T, provided S is a base class of T
1809                         //
1810                         if (TypeManager.IsSubclassOf (target_type, source_type))
1811                                 return new ClassCast (source, target_type);
1812
1813                         //
1814                         // From any interface type S to any interface T provided S is not derived from T
1815                         //
1816                         if (source_type.IsInterface && target_type.IsInterface){
1817                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1818                                         return null;
1819                                 else
1820                                         return new ClassCast (source, target_type);
1821                         }
1822
1823                         //
1824                         // From any class type S to any interface T, provides S is not sealed
1825                         // and provided S does not implement T.
1826                         //
1827                         if (target_type.IsInterface && !source_type.IsSealed) {
1828                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1829                                         return null;
1830                                 else
1831                                         return new ClassCast (source, target_type);
1832
1833                         }
1834
1835                         //
1836                         // From any interface-type S to to any class type T, provided T is not
1837                         // sealed, or provided T implements S.
1838                         //
1839                         if (source_type.IsInterface) {
1840                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1841                                         if (target_type.IsClass)
1842                                                 return new ClassCast (source, target_type);
1843                                         else
1844                                                 return new UnboxCast (source, target_type);
1845                                 }
1846
1847                                 return null;
1848                         }
1849
1850                         // From an array type S with an element type Se to an array type T with an
1851                         // element type Te provided all the following are true:
1852                         //     * S and T differe only in element type, in other words, S and T
1853                         //       have the same number of dimensions.
1854                         //     * Both Se and Te are reference types
1855                         //     * An explicit referenc conversions exist from Se to Te
1856                         //
1857                         if (source_type.IsArray && target_type.IsArray) {
1858                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1859
1860                                         Type source_element_type = TypeManager.GetElementType (source_type);
1861                                         Type target_element_type = TypeManager.GetElementType (target_type);
1862
1863                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1864                                                 if (ExplicitReferenceConversionExists (source_element_type,
1865                                                                                        target_element_type))
1866                                                         return new ClassCast (source, target_type);
1867                                 }
1868                         }
1869
1870
1871                         // From System.Array to any array-type
1872                         if (source_type == TypeManager.array_type &&
1873                             target_type.IsArray) {
1874                                 return new ClassCast (source, target_type);
1875                         }
1876
1877                         //
1878                         // From System delegate to any delegate-type
1879                         //
1880                         if (source_type == TypeManager.delegate_type &&
1881                             TypeManager.IsDelegateType (target_type))
1882                                 return new ClassCast (source, target_type);
1883
1884                         //
1885                         // From ICloneable to Array or Delegate types
1886                         //
1887                         if (source_type == TypeManager.icloneable_type &&
1888                             (target_type == TypeManager.array_type ||
1889                              target_type == TypeManager.delegate_type))
1890                                 return new ClassCast (source, target_type);
1891
1892                         return null;
1893                 }
1894
1895                 /// <summary>
1896                 ///   Performs an explicit conversion of the expression `expr' whose
1897                 ///   type is expr.Type to `target_type'.
1898                 /// </summary>
1899                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1900                                                              Type target_type, Location loc)
1901                 {
1902                         Type expr_type = expr.Type;
1903                         Type original_expr_type = expr_type;
1904
1905                         if (expr_type.IsSubclassOf (TypeManager.enum_type)){
1906                                 if (target_type == TypeManager.enum_type ||
1907                                     target_type == TypeManager.object_type) {
1908                                         if (expr is EnumConstant)
1909                                                 expr = ((EnumConstant) expr).Child;
1910                                         // We really need all these casts here .... :-(
1911                                         expr = new BoxedCast (new EmptyCast (expr, expr_type));
1912                                         return new EmptyCast (expr, target_type);
1913                                 } else if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
1914                                            target_type.IsSubclassOf (TypeManager.enum_type))
1915                                         return new UnboxCast (expr, target_type);
1916
1917                                 //
1918                                 // Notice that we have kept the expr_type unmodified, which is only
1919                                 // used later on to
1920                                 if (expr is EnumConstant)
1921                                         expr = ((EnumConstant) expr).Child;
1922                                 else
1923                                         expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
1924                                 expr_type = expr.Type;
1925                         }
1926
1927                         int errors = Report.Errors;
1928                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1929                         if (Report.Errors > errors)
1930                                 return null;
1931
1932                         if (ne != null)
1933                                 return ne;
1934
1935                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
1936                                 return new Nullable.LiftedConversion (
1937                                         expr, target_type, false, true, loc).Resolve (ec);
1938
1939                         ne = ExplicitNumericConversion (ec, expr, target_type, loc);
1940                         if (ne != null)
1941                                 return ne;
1942
1943                         //
1944                         // Unboxing conversion.
1945                         //
1946                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1947                                 return new UnboxCast (expr, target_type);
1948
1949                         //
1950                         // Skip the ExplicitReferenceConversion because we can not convert
1951                         // from Null to a ValueType, and ExplicitReference wont check against
1952                         // null literal explicitly
1953                         //
1954                         if (expr_type != TypeManager.null_type){
1955                                 ne = ExplicitReferenceConversion (expr, target_type);
1956                                 if (ne != null)
1957                                         return ne;
1958                         }
1959
1960                         if (ec.InUnsafe){
1961                                 if (target_type.IsPointer){
1962                                         if (expr_type.IsPointer)
1963                                                 return new EmptyCast (expr, target_type);
1964
1965                                         if (expr_type == TypeManager.sbyte_type ||
1966                                             expr_type == TypeManager.short_type ||
1967                                             expr_type == TypeManager.int32_type ||
1968                                             expr_type == TypeManager.int64_type)
1969                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
1970
1971                                         if (expr_type == TypeManager.ushort_type ||
1972                                             expr_type == TypeManager.uint32_type ||
1973                                             expr_type == TypeManager.uint64_type ||
1974                                             expr_type == TypeManager.byte_type)
1975                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1976                                 }
1977                                 if (expr_type.IsPointer){
1978                                         Expression e = null;
1979
1980                                         if (target_type == TypeManager.sbyte_type)
1981                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1982                                         else if (target_type == TypeManager.byte_type)
1983                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1984                                         else if (target_type == TypeManager.short_type)
1985                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1986                                         else if (target_type == TypeManager.ushort_type)
1987                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1988                                         else if (target_type == TypeManager.int32_type)
1989                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1990                                         else if (target_type == TypeManager.uint32_type)
1991                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1992                                         else if (target_type == TypeManager.uint64_type)
1993                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1994                                         else if (target_type == TypeManager.int64_type){
1995                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1996                                         }
1997
1998                                         if (e != null){
1999                                                 Expression ci, ce;
2000
2001                                                 ci = ImplicitConversionStandard (ec, e, target_type, loc);
2002
2003                                                 if (ci != null)
2004                                                         return ci;
2005
2006                                                 ce = ExplicitNumericConversion (ec, e, target_type, loc);
2007                                                 if (ce != null)
2008                                                         return ce;
2009                                                 //
2010                                                 // We should always be able to go from an uint32
2011                                                 // implicitly or explicitly to the other integral
2012                                                 // types
2013                                                 //
2014                                                 throw new Exception ("Internal compiler error");
2015                                         }
2016                                 }
2017                         }
2018
2019                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
2020                         if (ne != null)
2021                                 return ne;
2022
2023                         if (expr is NullLiteral){
2024                                 Report.Error (37, loc, "Cannot convert null to value type `" +
2025                                               TypeManager.CSharpName (target_type) + "'");
2026                                 return null;
2027                         }
2028
2029                         Error_CannotConvertType (loc, original_expr_type, target_type);
2030                         return null;
2031                 }
2032
2033                 /// <summary>
2034                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
2035                 /// </summary>
2036                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
2037                                                                      Type target_type, Location l)
2038                 {
2039                         int errors = Report.Errors;
2040                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
2041                         if (Report.Errors > errors)
2042                                 return null;
2043
2044                         if (ne != null)
2045                                 return ne;
2046
2047                         if (TypeManager.IsNullableType (expr.Type) && TypeManager.IsNullableType (target_type))
2048                                 return new Nullable.LiftedConversion (
2049                                         expr, target_type, false, true, l).Resolve (ec);
2050
2051                         ne = ExplicitNumericConversion (ec, expr, target_type, l);
2052                         if (ne != null)
2053                                 return ne;
2054
2055                         ne = ExplicitReferenceConversion (expr, target_type);
2056                         if (ne != null)
2057                                 return ne;
2058
2059                         Error_CannotConvertType (l, expr.Type, target_type);
2060                         return null;
2061                 }
2062         }
2063 }