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