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                         // First numeric conversions
 591
 592                         if (expr_type == TypeManager.sbyte_type){
 593                                 //
 594                                 // From sbyte to short, int, long, float, double.
 595                                 //
 596                                 if ((target_type == TypeManager.int32_type) ||
 597                                     (target_type == TypeManager.int64_type) ||
 598                                     (target_type == TypeManager.double_type) ||
 599                                     (target_type == TypeManager.float_type)  ||
 600                                     (target_type == TypeManager.short_type) ||
 601                                     (target_type == TypeManager.decimal_type))
 602                                         return true;
 603
 604                         } else if (expr_type == TypeManager.byte_type){
 605                                 //
 606                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 607                                 //
 608                                 if ((target_type == TypeManager.short_type) ||
 609                                     (target_type == TypeManager.ushort_type) ||
 610                                     (target_type == TypeManager.int32_type) ||
 611                                     (target_type == TypeManager.uint32_type) ||
 612                                     (target_type == TypeManager.uint64_type) ||
 613                                     (target_type == TypeManager.int64_type) ||
 614                                     (target_type == TypeManager.float_type) ||
 615                                     (target_type == TypeManager.double_type) ||
 616                                     (target_type == TypeManager.decimal_type))
 617                                         return true;
 618
 619                         } else if (expr_type == TypeManager.short_type){
 620                                 //
 621                                 // From short to int, long, float, double
 622                                 //
 623                                 if ((target_type == TypeManager.int32_type) ||
 624                                     (target_type == TypeManager.int64_type) ||
 625                                     (target_type == TypeManager.double_type) ||
 626                                     (target_type == TypeManager.float_type) ||
 627                                     (target_type == TypeManager.decimal_type))
 628                                         return true;
 629
 630                         } else if (expr_type == TypeManager.ushort_type){
 631                                 //
 632                                 // From ushort to int, uint, long, ulong, float, double
 633                                 //
 634                                 if ((target_type == TypeManager.uint32_type) ||
 635                                     (target_type == TypeManager.uint64_type) ||
 636                                     (target_type == TypeManager.int32_type) ||
 637                                     (target_type == TypeManager.int64_type) ||
 638                                     (target_type == TypeManager.double_type) ||
 639                                     (target_type == TypeManager.float_type) ||
 640                                     (target_type == TypeManager.decimal_type))
 641                                         return true;
 642
 643                         } else if (expr_type == TypeManager.int32_type){
 644                                 //
 645                                 // From int to long, float, double
 646                                 //
 647                                 if ((target_type == TypeManager.int64_type) ||
 648                                     (target_type == TypeManager.double_type) ||
 649                                     (target_type == TypeManager.float_type) ||
 650                                     (target_type == TypeManager.decimal_type))
 651                                         return true;
 652
 653                         } else if (expr_type == TypeManager.uint32_type){
 654                                 //
 655                                 // From uint to long, ulong, float, double
 656                                 //
 657                                 if ((target_type == TypeManager.int64_type) ||
 658                                     (target_type == TypeManager.uint64_type) ||
 659                                     (target_type == TypeManager.double_type) ||
 660                                     (target_type == TypeManager.float_type) ||
 661                                     (target_type == TypeManager.decimal_type))
 662                                         return true;
 663
 664                         } else if ((expr_type == TypeManager.uint64_type) ||
 665                                    (expr_type == TypeManager.int64_type)) {
 666                                 //
 667                                 // From long/ulong to float, double
 668                                 //
 669                                 if ((target_type == TypeManager.double_type) ||
 670                                     (target_type == TypeManager.float_type) ||
 671                                     (target_type == TypeManager.decimal_type))
 672                                         return true;
 673
 674                         } else if (expr_type == TypeManager.char_type){
 675                                 //
 676                                 // From char to ushort, int, uint, long, ulong, float, double
 677                                 //
 678                                 if ((target_type == TypeManager.ushort_type) ||
 679                                     (target_type == TypeManager.int32_type) ||
 680                                     (target_type == TypeManager.uint32_type) ||
 681                                     (target_type == TypeManager.uint64_type) ||
 682                                     (target_type == TypeManager.int64_type) ||
 683                                     (target_type == TypeManager.float_type) ||
 684                                     (target_type == TypeManager.double_type) ||
 685                                     (target_type == TypeManager.decimal_type))
 686                                         return true;
 687
 688                         } else if (expr_type == TypeManager.float_type){
 689                                 //
 690                                 // float to double
 691                                 //
 692                                 if (target_type == TypeManager.double_type)
 693                                         return true;
 694                         }
 695
 696                         if (ImplicitReferenceConversionExists (ec, expr, target_type))
 697                                 return true;
 698
 699                         //
 700                         // Implicit Constant Expression Conversions
 701                         //
 702                         if (expr is IntConstant){
 703                                 int value = ((IntConstant) expr).Value;
 704
 705                                 if (target_type == TypeManager.sbyte_type){
 706                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 707                                                 return true;
 708                                 } else if (target_type == TypeManager.byte_type){
 709                                         if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
 710                                                 return true;
 711                                 } else if (target_type == TypeManager.short_type){
 712                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 713                                                 return true;
 714                                 } else if (target_type == TypeManager.ushort_type){
 715                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 716                                                 return true;
 717                                 } else if (target_type == TypeManager.uint32_type){
 718                                         if (value >= 0)
 719                                                 return true;
 720                                 } else if (target_type == TypeManager.uint64_type){
 721                                          //
 722                                          // we can optimize this case: a positive int32
 723                                          // always fits on a uint64.  But we need an opcode
 724                                          // to do it.
 725                                          //
 726                                         if (value >= 0)
 727                                                 return true;
 728                                 }
 729
 730                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 731                                         return true;
 732                         }
 733
 734                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 735                                 //
 736                                 // Try the implicit constant expression conversion
 737                                 // from long to ulong, instead of a nice routine,
 738                                 // we just inline it
 739                                 //
 740                                 long v = ((LongConstant) expr).Value;
 741                                 if (v > 0)
 742                                         return true;
 743                         }
 744
 745                         if ((target_type == TypeManager.enum_type ||
 746                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 747                              expr is IntLiteral){
 748                                 IntLiteral i = (IntLiteral) expr;
 749
 750                                 if (i.Value == 0)
 751                                         return true;
 752                         }
 753
 754                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 755                                 return true;
 756
 757                         if (expr_type == TypeManager.anonymous_method_type){
 758                                 if (!TypeManager.IsDelegateType (target_type))
 759                                         return false;
 760
 761                                 AnonymousMethod am = (AnonymousMethod) expr;
 762
 763                                 Expression conv = am.Compatible (ec, target_type, true);
 764                                 if (conv != null)
 765                                         return true;
 766                         }
 767
 768                         return false;
 769                 }
 770
 771                 //
 772                 // Used internally by FindMostEncompassedType, this is used
 773                 // to avoid creating lots of objects in the tight loop inside
 774                 // FindMostEncompassedType
 775                 //
 776                 static EmptyExpression priv_fmet_param;
 777
 778                 /// <summary>
 779                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 780                 ///  amongst the methods in the MethodGroupExpr
 781                 /// </summary>
 782                 static Type FindMostEncompassedType (EmitContext ec, ArrayList types)
 783                 {
 784                         Type best = null;
 785
 786                         if (priv_fmet_param == null)
 787                                 priv_fmet_param = new EmptyExpression ();
 788
 789                         foreach (Type t in types){
 790                                 priv_fmet_param.SetType (t);
 791
 792                                 if (best == null) {
 793                                         best = t;
 794                                         continue;
 795                                 }
 796
 797                                 if (ImplicitStandardConversionExists (ec, priv_fmet_param, best))
 798                                         best = t;
 799                         }
 800
 801                         return best;
 802                 }
 803
 804                 //
 805                 // Used internally by FindMostEncompassingType, this is used
 806                 // to avoid creating lots of objects in the tight loop inside
 807                 // FindMostEncompassingType
 808                 //
 809                 static EmptyExpression priv_fmee_ret;
 810
 811                 /// <summary>
 812                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 813                 ///  amongst the types in the given set
 814                 /// </summary>
 815                 static Type FindMostEncompassingType (EmitContext ec, ArrayList types)
 816                 {
 817                         Type best = null;
 818
 819                         if (priv_fmee_ret == null)
 820                                 priv_fmee_ret = new EmptyExpression ();
 821
 822                         foreach (Type t in types){
 823                                 priv_fmee_ret.SetType (best);
 824
 825                                 if (best == null) {
 826                                         best = t;
 827                                         continue;
 828                                 }
 829
 830                                 if (ImplicitStandardConversionExists (ec, priv_fmee_ret, t))
 831                                         best = t;
 832                         }
 833
 834                         return best;
 835                 }
 836
 837                 //
 838                 // Used to avoid creating too many objects
 839                 //
 840                 static EmptyExpression priv_fms_expr;
 841
 842                 /// <summary>
 843                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 844                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 845                 ///   for explicit and implicit conversion operators.
 846                 /// </summary>
 847                 static public Type FindMostSpecificSource (EmitContext ec, MethodGroupExpr me,
 848                                                            Expression source, bool apply_explicit_conv_rules,
 849                                                            Location loc)
 850                 {
 851                         ArrayList src_types_set = new ArrayList ();
 852
 853                         if (priv_fms_expr == null)
 854                                 priv_fms_expr = new EmptyExpression ();
 855
 856                         //
 857                         // If any operator converts from S then Sx = S
 858                         //
 859                         Type source_type = source.Type;
 860                         foreach (MethodBase mb in me.Methods){
 861                                 ParameterData pd = Invocation.GetParameterData (mb);
 862                                 Type param_type = pd.ParameterType (0);
 863
 864                                 if (param_type == source_type)
 865                                         return param_type;
 866
 867                                 if (apply_explicit_conv_rules) {
 868                                         //
 869                                         // From the spec :
 870                                         // Find the set of applicable user-defined conversion operators, U.  This set
 871                                         // consists of the
 872                                         // user-defined implicit or explicit conversion operators declared by
 873                                         // the classes or structs in D that convert from a type encompassing
 874                                         // or encompassed by S to a type encompassing or encompassed by T
 875                                         //
 876                                         priv_fms_expr.SetType (param_type);
 877                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, source_type))
 878                                                 src_types_set.Add (param_type);
 879                                         else {
 880                                                 if (ImplicitStandardConversionExists (ec, source, param_type))
 881                                                         src_types_set.Add (param_type);
 882                                         }
 883                                 } else {
 884                                         //
 885                                         // Only if S is encompassed by param_type
 886                                         //
 887                                         if (ImplicitStandardConversionExists (ec, source, param_type))
 888                                                 src_types_set.Add (param_type);
 889                                 }
 890                         }
 891
 892                         //
 893                         // Explicit Conv rules
 894                         //
 895                         if (apply_explicit_conv_rules) {
 896                                 ArrayList candidate_set = new ArrayList ();
 897
 898                                 foreach (Type param_type in src_types_set){
 899                                         if (ImplicitStandardConversionExists (ec, source, param_type))
 900                                                 candidate_set.Add (param_type);
 901                                 }
 902
 903                                 if (candidate_set.Count != 0)
 904                                         return FindMostEncompassedType (ec, candidate_set);
 905                         }
 906
 907                         //
 908                         // Final case
 909                         //
 910                         if (apply_explicit_conv_rules)
 911                                 return FindMostEncompassingType (ec, src_types_set);
 912                         else
 913                                 return FindMostEncompassedType (ec, src_types_set);
 914                 }
 915
 916                 //
 917                 // Useful in avoiding proliferation of objects
 918                 //
 919                 static EmptyExpression priv_fmt_expr;
 920
 921                 /// <summary>
 922                 ///  Finds the most specific target Tx according to section 13.4.4
 923                 /// </summary>
 924                 static public Type FindMostSpecificTarget (EmitContext ec, MethodGroupExpr me,
 925                                                            Type target, bool apply_explicit_conv_rules,
 926                                                            Location loc)
 927                 {
 928                         ArrayList tgt_types_set = new ArrayList ();
 929
 930                         if (priv_fmt_expr == null)
 931                                 priv_fmt_expr = new EmptyExpression ();
 932
 933                         //
 934                         // If any operator converts to T then Tx = T
 935                         //
 936                         foreach (MethodInfo mi in me.Methods){
 937                                 Type ret_type = mi.ReturnType;
 938
 939                                 if (ret_type == target)
 940                                         return ret_type;
 941
 942                                 if (apply_explicit_conv_rules) {
 943                                         //
 944                                         // From the spec :
 945                                         // Find the set of applicable user-defined conversion operators, U.
 946                                         //
 947                                         // This set consists of the
 948                                         // user-defined implicit or explicit conversion operators declared by
 949                                         // the classes or structs in D that convert from a type encompassing
 950                                         // or encompassed by S to a type encompassing or encompassed by T
 951                                         //
 952                                         priv_fms_expr.SetType (ret_type);
 953                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, target))
 954                                                 tgt_types_set.Add (ret_type);
 955                                         else {
 956                                                 priv_fms_expr.SetType (target);
 957                                                 if (ImplicitStandardConversionExists (ec, priv_fms_expr, ret_type))
 958                                                         tgt_types_set.Add (ret_type);
 959                                         }
 960                                 } else {
 961                                         //
 962                                         // Only if T is encompassed by param_type
 963                                         //
 964                                         priv_fms_expr.SetType (ret_type);
 965                                         if (ImplicitStandardConversionExists (ec, priv_fms_expr, target))
 966                                                 tgt_types_set.Add (ret_type);
 967                                 }
 968                         }
 969
 970                         //
 971                         // Explicit conv rules
 972                         //
 973                         if (apply_explicit_conv_rules) {
 974                                 ArrayList candidate_set = new ArrayList ();
 975
 976                                 foreach (Type ret_type in tgt_types_set){
 977                                         priv_fmt_expr.SetType (ret_type);
 978
 979                                         if (ImplicitStandardConversionExists (ec, priv_fmt_expr, target))
 980                                                 candidate_set.Add (ret_type);
 981                                 }
 982
 983                                 if (candidate_set.Count != 0)
 984                                         return FindMostEncompassingType (ec, candidate_set);
 985                         }
 986
 987                         //
 988                         // Okay, final case !
 989                         //
 990                         if (apply_explicit_conv_rules)
 991                                 return FindMostEncompassedType (ec, tgt_types_set);
 992                         else
 993                                 return FindMostEncompassingType (ec, tgt_types_set);
 994                 }
 995
 996                 /// <summary>
 997                 ///  User-defined Implicit conversions
 998                 /// </summary>
 999                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
1000                                                                  Type target, Location loc)
1001                 {
1002                         return UserDefinedConversion (ec, source, target, loc, false);
1003                 }
1004
1005                 /// <summary>
1006                 ///  User-defined Explicit conversions
1007                 /// </summary>
1008                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1009                                                                  Type target, Location loc)
1010                 {
1011                         return UserDefinedConversion (ec, source, target, loc, true);
1012                 }
1013
1014                 static DoubleHash explicit_conv = new DoubleHash (100);
1015                 static DoubleHash implicit_conv = new DoubleHash (100);
1016                 /// <summary>
1017                 ///   Computes the MethodGroup for the user-defined conversion
1018                 ///   operators from source_type to target_type.  `look_for_explicit'
1019                 ///   controls whether we should also include the list of explicit
1020                 ///   operators
1021                 /// </summary>
1022                 static MethodGroupExpr GetConversionOperators (EmitContext ec,
1023                                                                Type source_type, Type target_type,
1024                                                                Location loc, bool look_for_explicit)
1025                 {
1026                         Expression mg1 = null, mg2 = null;
1027                         Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
1028                         string op_name;
1029
1030                         op_name = "op_Implicit";
1031
1032                         MethodGroupExpr union3;
1033                         object r;
1034                         if ((look_for_explicit ? explicit_conv : implicit_conv).Lookup (source_type, target_type, out r))
1035                                 return (MethodGroupExpr) r;
1036
1037                         mg1 = Expression.MethodLookup (ec, source_type, op_name, loc);
1038                         if (source_type.BaseType != null)
1039                                 mg2 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1040
1041                         if (mg1 == null)
1042                                 union3 = (MethodGroupExpr) mg2;
1043                         else if (mg2 == null)
1044                                 union3 = (MethodGroupExpr) mg1;
1045                         else
1046                                 union3 = Invocation.MakeUnionSet (mg1, mg2, loc);
1047
1048                         mg1 = Expression.MethodLookup (ec, target_type, op_name, loc);
1049                         if (mg1 != null){
1050                                 if (union3 != null)
1051                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1052                                 else
1053                                         union3 = (MethodGroupExpr) mg1;
1054                         }
1055
1056                         if (target_type.BaseType != null)
1057                                 mg1 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1058
1059                         if (mg1 != null){
1060                                 if (union3 != null)
1061                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
1062                                 else
1063                                         union3 = (MethodGroupExpr) mg1;
1064                         }
1065
1066                         MethodGroupExpr union4 = null;
1067
1068                         if (look_for_explicit) {
1069                                 op_name = "op_Explicit";
1070
1071                                 mg5 = Expression.MemberLookup (ec, source_type, op_name, loc);
1072                                 if (source_type.BaseType != null)
1073                                         mg6 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
1074
1075                                 mg7 = Expression.MemberLookup (ec, target_type, op_name, loc);
1076                                 if (target_type.BaseType != null)
1077                                         mg8 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
1078
1079                                 MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
1080                                 MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);
1081
1082                                 union4 = Invocation.MakeUnionSet (union5, union6, loc);
1083                         }
1084
1085                         MethodGroupExpr ret = Invocation.MakeUnionSet (union3, union4, loc);
1086                         (look_for_explicit ? explicit_conv : implicit_conv).Insert (source_type, target_type, ret);
1087                         return ret;
1088                 }
1089
1090                 /// <summary>
1091                 ///   User-defined conversions
1092                 /// </summary>
1093                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1094                                                                 Type target, Location loc,
1095                                                                 bool look_for_explicit)
1096                 {
1097                         MethodGroupExpr union;
1098                         Type source_type = source.Type;
1099                         MethodBase method = null;
1100
1101                         union = GetConversionOperators (ec, source_type, target, loc, look_for_explicit);
1102                         if (union == null)
1103                                 return null;
1104
1105                         Type most_specific_source, most_specific_target;
1106
1107                         most_specific_source = FindMostSpecificSource (ec, union, source, look_for_explicit, loc);
1108                         if (most_specific_source == null)
1109                                 return null;
1110
1111                         most_specific_target = FindMostSpecificTarget (ec, union, target, look_for_explicit, loc);
1112                         if (most_specific_target == null)
1113                                 return null;
1114
1115                         int count = 0;
1116
1117
1118                         foreach (MethodBase mb in union.Methods){
1119                                 ParameterData pd = Invocation.GetParameterData (mb);
1120                                 MethodInfo mi = (MethodInfo) mb;
1121
1122                                 if (pd.ParameterType (0) == most_specific_source &&
1123                                     mi.ReturnType == most_specific_target) {
1124                                         method = mb;
1125                                         count++;
1126                                 }
1127                         }
1128
1129                         if (method == null || count > 1)
1130                                 return null;
1131
1132
1133                         //
1134                         // This will do the conversion to the best match that we
1135                         // found.  Now we need to perform an implict standard conversion
1136                         // if the best match was not the type that we were requested
1137                         // by target.
1138                         //
1139                         if (look_for_explicit)
1140                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1141                         else
1142                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1143
1144                         if (source == null)
1145                                 return null;
1146
1147                         Expression e;
1148                         e =  new UserCast ((MethodInfo) method, source, loc);
1149                         if (e.Type != target){
1150                                 if (!look_for_explicit)
1151                                         e = ImplicitConversionStandard (ec, e, target, loc);
1152                                 else
1153                                         e = ExplicitConversionStandard (ec, e, target, loc);
1154                         }
1155
1156                         return e;
1157                 }
1158
1159                 /// <summary>
1160                 ///   Converts implicitly the resolved expression `expr' into the
1161                 ///   `target_type'.  It returns a new expression that can be used
1162                 ///   in a context that expects a `target_type'.
1163                 /// </summary>
1164                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1165                                                              Type target_type, Location loc)
1166                 {
1167                         Expression e;
1168
1169                         if (target_type == null)
1170                                 throw new Exception ("Target type is null");
1171
1172                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1173                         if (e != null)
1174                                 return e;
1175
1176                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1177                         if (e != null)
1178                                 return e;
1179
1180                         return null;
1181                 }
1182
1183
1184                 /// <summary>
1185                 ///   Attempts to apply the `Standard Implicit
1186                 ///   Conversion' rules to the expression `expr' into
1187                 ///   the `target_type'.  It returns a new expression
1188                 ///   that can be used in a context that expects a
1189                 ///   `target_type'.
1190                 ///
1191                 ///   This is different from `ImplicitConversion' in that the
1192                 ///   user defined implicit conversions are excluded.
1193                 /// </summary>
1194                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1195                                                                      Type target_type, Location loc)
1196                 {
1197                         Type expr_type = expr.Type;
1198                         Expression e;
1199
1200                         if ((expr is NullLiteral) && target_type.IsGenericParameter)
1201                                 return TypeParameter_to_Null (expr, target_type, loc);
1202
1203                         if (expr.eclass == ExprClass.MethodGroup){
1204                                 if (!TypeManager.IsDelegateType (target_type)){
1205                                         return null;
1206                                 }
1207
1208                                 //
1209                                 // Only allow anonymous method conversions on post ISO_1
1210                                 //
1211                                 if (RootContext.Version != LanguageVersion.ISO_1){
1212                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1213                                         if (mg != null)
1214                                                 return ImplicitDelegateCreation.Create (ec, mg, target_type, loc);
1215                                 }
1216                         }
1217
1218                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1219                                 return expr;
1220
1221                         e = ImplicitNumericConversion (ec, expr, target_type, loc);
1222                         if (e != null)
1223                                 return e;
1224
1225                         e = ImplicitReferenceConversion (ec, expr, target_type);
1226                         if (e != null)
1227                                 return e;
1228
1229                         if ((target_type == TypeManager.enum_type ||
1230                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1231                             expr is IntLiteral){
1232                                 IntLiteral i = (IntLiteral) expr;
1233
1234                                 if (i.Value == 0)
1235                                         return new EnumConstant ((Constant) expr, target_type);
1236                         }
1237
1238                         if (ec.InUnsafe) {
1239                                 if (expr_type.IsPointer){
1240                                         if (target_type == TypeManager.void_ptr_type)
1241                                                 return new EmptyCast (expr, target_type);
1242
1243                                         //
1244                                         // yep, comparing pointer types cant be done with
1245                                         // t1 == t2, we have to compare their element types.
1246                                         //
1247                                         if (target_type.IsPointer){
1248                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1249                                                         return expr;
1250                                         }
1251                                 }
1252
1253                                 if (target_type.IsPointer) {
1254                                         if (expr_type == TypeManager.null_type)
1255                                                 return new EmptyCast (expr, target_type);
1256
1257                                         if (expr_type == TypeManager.void_ptr_type)
1258                                                 return new EmptyCast (expr, target_type);
1259                                 }
1260                         }
1261
1262                         if (expr_type == TypeManager.anonymous_method_type){
1263                                 if (!TypeManager.IsDelegateType (target_type)){
1264                                         Report.Error (1660, loc,
1265                                                               "Cannot convert anonymous method to `{0}', since it is not a delegate",
1266                                                               TypeManager.CSharpName (target_type));
1267                                         return null;
1268                                 }
1269
1270                                 AnonymousMethod am = (AnonymousMethod) expr;
1271                                 int errors = Report.Errors;
1272
1273                                 Expression conv = am.Compatible (ec, target_type, false);
1274                                 if (conv != null)
1275                                         return conv;
1276
1277                                 //
1278                                 // We return something instead of null, to avoid
1279                                 // the duplicate error, since am.Compatible would have
1280                                 // reported that already
1281                                 //
1282                                 if (errors != Report.Errors)
1283                                         return new EmptyCast (expr, target_type);
1284                         }
1285
1286                         return null;
1287                 }
1288
1289                 /// <summary>
1290                 ///   Attemps to perform an implict constant conversion of the IntConstant
1291                 ///   into a different data type using casts (See Implicit Constant
1292                 ///   Expression Conversions)
1293                 /// </summary>
1294                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1295                 {
1296                         int value = ic.Value;
1297
1298                         if (target_type == TypeManager.sbyte_type){
1299                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1300                                         return new SByteConstant ((sbyte) value);
1301                         } else if (target_type == TypeManager.byte_type){
1302                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1303                                         return new ByteConstant ((byte) value);
1304                         } else if (target_type == TypeManager.short_type){
1305                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1306                                         return new ShortConstant ((short) value);
1307                         } else if (target_type == TypeManager.ushort_type){
1308                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1309                                         return new UShortConstant ((ushort) value);
1310                         } else if (target_type == TypeManager.uint32_type){
1311                                 if (value >= 0)
1312                                         return new UIntConstant ((uint) value);
1313                         } else if (target_type == TypeManager.uint64_type){
1314                                 //
1315                                 // we can optimize this case: a positive int32
1316                                 // always fits on a uint64.  But we need an opcode
1317                                 // to do it.
1318                                 //
1319                                 if (value >= 0)
1320                                         return new ULongConstant ((ulong) value);
1321                         } else if (target_type == TypeManager.double_type)
1322                                 return new DoubleConstant ((double) value);
1323                         else if (target_type == TypeManager.float_type)
1324                                 return new FloatConstant ((float) value);
1325
1326                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1327                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1328                                 Constant e = (Constant) ic;
1329
1330                                 //
1331                                 // Possibly, we need to create a different 0 literal before passing
1332                                 // to EnumConstant
1333                                 //
1334                                 if (underlying == TypeManager.int64_type)
1335                                         e = new LongLiteral (0);
1336                                 else if (underlying == TypeManager.uint64_type)
1337                                         e = new ULongLiteral (0);
1338
1339                                 return new EnumConstant (e, target_type);
1340                         }
1341                         return null;
1342                 }
1343
1344                 static public void Error_CannotImplicitConversion (Location loc, Type source, Type target)
1345                 {
1346                         if (source.Name == target.Name){
1347                                 Report.ExtraInformation (loc,
1348                                          String.Format (
1349                                                 "The type {0} has two conflicting definitons, one comes from {0} and the other from {1}",
1350                                                 source.Assembly.FullName, target.Assembly.FullName));
1351
1352                         }
1353                         Report.Error (29, loc, "Cannot convert implicitly from {0} to `{1}'",
1354                                       source == TypeManager.anonymous_method_type ?
1355                                       "anonymous method" : "`" + TypeManager.CSharpName (source) + "'",
1356                                       TypeManager.CSharpName (target));
1357                 }
1358
1359                 /// <summary>
1360                 ///   Attemptes to implicityly convert `target' into `type', using
1361                 ///   ImplicitConversion.  If there is no implicit conversion, then
1362                 ///   an error is signaled
1363                 /// </summary>
1364                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1365                                                                      Type target_type, Location loc)
1366                 {
1367                         Expression e;
1368
1369                         int errors = Report.Errors;
1370                         e = ImplicitConversion (ec, source, target_type, loc);
1371                         if (Report.Errors > errors)
1372                                 return null;
1373                         if (e != null)
1374                                 return e;
1375
1376                         if (source is DoubleLiteral) {
1377                                 if (target_type == TypeManager.float_type) {
1378                                         Error_664 (loc, "float", "f");
1379                                         return null;
1380                                 }
1381                                 if (target_type == TypeManager.decimal_type) {
1382                                         Error_664 (loc, "decimal", "m");
1383                                         return null;
1384                                 }
1385                         }
1386
1387                         if (source is Constant){
1388                                 Constant c = (Constant) source;
1389
1390                                 Expression.Error_ConstantValueCannotBeConverted (loc, c.AsString (), target_type);
1391                                 return null;
1392                         }
1393
1394                         Error_CannotImplicitConversion (loc, source.Type, target_type);
1395
1396                         return null;
1397                 }
1398
1399                 static void Error_664 (Location loc, string type, string suffix) {
1400                         Report.Error (664, loc,
1401                                 "Literal of type double cannot be implicitly converted to type '{0}'. Add suffix '{1}' to create a literal of this type",
1402                                 type, suffix);
1403                 }
1404
1405                 /// <summary>
1406                 ///   Performs the explicit numeric conversions
1407                 /// </summary>
1408                 static Expression ExplicitNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
1409                 {
1410                         Type expr_type = expr.Type;
1411
1412                         //
1413                         // If we have an enumeration, extract the underlying type,
1414                         // use this during the comparison, but wrap around the original
1415                         // target_type
1416                         //
1417                         Type real_target_type = target_type;
1418
1419                         if (TypeManager.IsEnumType (real_target_type))
1420                                 real_target_type = TypeManager.EnumToUnderlying (real_target_type);
1421
1422                         if (ImplicitStandardConversionExists (ec, expr, real_target_type)){
1423                                 Expression ce = ImplicitConversionStandard (ec, expr, real_target_type, loc);
1424
1425                                 if (real_target_type != target_type)
1426                                         return new EmptyCast (ce, target_type);
1427                                 return ce;
1428                         }
1429
1430                         if (expr_type == TypeManager.sbyte_type){
1431                                 //
1432                                 // From sbyte to byte, ushort, uint, ulong, char
1433                                 //
1434                                 if (real_target_type == TypeManager.byte_type)
1435                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U1);
1436                                 if (real_target_type == TypeManager.ushort_type)
1437                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U2);
1438                                 if (real_target_type == TypeManager.uint32_type)
1439                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U4);
1440                                 if (real_target_type == TypeManager.uint64_type)
1441                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U8);
1442                                 if (real_target_type == TypeManager.char_type)
1443                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_CH);
1444                         } else if (expr_type == TypeManager.byte_type){
1445                                 //
1446                                 // From byte to sbyte and char
1447                                 //
1448                                 if (real_target_type == TypeManager.sbyte_type)
1449                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_I1);
1450                                 if (real_target_type == TypeManager.char_type)
1451                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_CH);
1452                         } else if (expr_type == TypeManager.short_type){
1453                                 //
1454                                 // From short to sbyte, byte, ushort, uint, ulong, char
1455                                 //
1456                                 if (real_target_type == TypeManager.sbyte_type)
1457                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_I1);
1458                                 if (real_target_type == TypeManager.byte_type)
1459                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
1460                                 if (real_target_type == TypeManager.ushort_type)
1461                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U2);
1462                                 if (real_target_type == TypeManager.uint32_type)
1463                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U4);
1464                                 if (real_target_type == TypeManager.uint64_type)
1465                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U8);
1466                                 if (real_target_type == TypeManager.char_type)
1467                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_CH);
1468                         } else if (expr_type == TypeManager.ushort_type){
1469                                 //
1470                                 // From ushort to sbyte, byte, short, char
1471                                 //
1472                                 if (real_target_type == TypeManager.sbyte_type)
1473                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I1);
1474                                 if (real_target_type == TypeManager.byte_type)
1475                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_U1);
1476                                 if (real_target_type == TypeManager.short_type)
1477                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I2);
1478                                 if (real_target_type == TypeManager.char_type)
1479                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_CH);
1480                         } else if (expr_type == TypeManager.int32_type){
1481                                 //
1482                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1483                                 //
1484                                 if (real_target_type == TypeManager.sbyte_type)
1485                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I1);
1486                                 if (real_target_type == TypeManager.byte_type)
1487                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
1488                                 if (real_target_type == TypeManager.short_type)
1489                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
1490                                 if (real_target_type == TypeManager.ushort_type)
1491                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U2);
1492                                 if (real_target_type == TypeManager.uint32_type)
1493                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U4);
1494                                 if (real_target_type == TypeManager.uint64_type)
1495                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U8);
1496                                 if (real_target_type == TypeManager.char_type)
1497                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_CH);
1498                         } else if (expr_type == TypeManager.uint32_type){
1499                                 //
1500                                 // From uint to sbyte, byte, short, ushort, int, char
1501                                 //
1502                                 if (real_target_type == TypeManager.sbyte_type)
1503                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I1);
1504                                 if (real_target_type == TypeManager.byte_type)
1505                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U1);
1506                                 if (real_target_type == TypeManager.short_type)
1507                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I2);
1508                                 if (real_target_type == TypeManager.ushort_type)
1509                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U2);
1510                                 if (real_target_type == TypeManager.int32_type)
1511                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I4);
1512                                 if (real_target_type == TypeManager.char_type)
1513                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_CH);
1514                         } else if (expr_type == TypeManager.int64_type){
1515                                 //
1516                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1517                                 //
1518                                 if (real_target_type == TypeManager.sbyte_type)
1519                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I1);
1520                                 if (real_target_type == TypeManager.byte_type)
1521                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
1522                                 if (real_target_type == TypeManager.short_type)
1523                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
1524                                 if (real_target_type == TypeManager.ushort_type)
1525                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U2);
1526                                 if (real_target_type == TypeManager.int32_type)
1527                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
1528                                 if (real_target_type == TypeManager.uint32_type)
1529                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U4);
1530                                 if (real_target_type == TypeManager.uint64_type)
1531                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U8);
1532                                 if (real_target_type == TypeManager.char_type)
1533                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_CH);
1534                         } else if (expr_type == TypeManager.uint64_type){
1535                                 //
1536                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1537                                 //
1538                                 if (real_target_type == TypeManager.sbyte_type)
1539                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I1);
1540                                 if (real_target_type == TypeManager.byte_type)
1541                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U1);
1542                                 if (real_target_type == TypeManager.short_type)
1543                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I2);
1544                                 if (real_target_type == TypeManager.ushort_type)
1545                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U2);
1546                                 if (real_target_type == TypeManager.int32_type)
1547                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I4);
1548                                 if (real_target_type == TypeManager.uint32_type)
1549                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U4);
1550                                 if (real_target_type == TypeManager.int64_type)
1551                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I8);
1552                                 if (real_target_type == TypeManager.char_type)
1553                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_CH);
1554                         } else if (expr_type == TypeManager.char_type){
1555                                 //
1556                                 // From char to sbyte, byte, short
1557                                 //
1558                                 if (real_target_type == TypeManager.sbyte_type)
1559                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I1);
1560                                 if (real_target_type == TypeManager.byte_type)
1561                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_U1);
1562                                 if (real_target_type == TypeManager.short_type)
1563                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I2);
1564                         } else if (expr_type == TypeManager.float_type){
1565                                 //
1566                                 // From float to sbyte, byte, short,
1567                                 // ushort, int, uint, long, ulong, char
1568                                 // or decimal
1569                                 //
1570                                 if (real_target_type == TypeManager.sbyte_type)
1571                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
1572                                 if (real_target_type == TypeManager.byte_type)
1573                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U1);
1574                                 if (real_target_type == TypeManager.short_type)
1575                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I2);
1576                                 if (real_target_type == TypeManager.ushort_type)
1577                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U2);
1578                                 if (real_target_type == TypeManager.int32_type)
1579                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I4);
1580                                 if (real_target_type == TypeManager.uint32_type)
1581                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U4);
1582                                 if (real_target_type == TypeManager.int64_type)
1583                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I8);
1584                                 if (real_target_type == TypeManager.uint64_type)
1585                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U8);
1586                                 if (real_target_type == TypeManager.char_type)
1587                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_CH);
1588                         } else if (expr_type == TypeManager.double_type){
1589                                 //
1590                                 // From double to byte, byte, short,
1591                                 // ushort, int, uint, long, ulong,
1592                                 // char, float or decimal
1593                                 //
1594                                 if (real_target_type == TypeManager.sbyte_type)
1595                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I1);
1596                                 if (real_target_type == TypeManager.byte_type)
1597                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1598                                 if (real_target_type == TypeManager.short_type)
1599                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1600                                 if (real_target_type == TypeManager.ushort_type)
1601                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U2);
1602                                 if (real_target_type == TypeManager.int32_type)
1603                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1604                                 if (real_target_type == TypeManager.uint32_type)
1605                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U4);
1606                                 if (real_target_type == TypeManager.int64_type)
1607                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1608                                 if (real_target_type == TypeManager.uint64_type)
1609                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U8);
1610                                 if (real_target_type == TypeManager.char_type)
1611                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_CH);
1612                                 if (real_target_type == TypeManager.float_type)
1613                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
1614                         }
1615
1616                         // decimal is taken care of by the op_Explicit methods.
1617
1618                         return null;
1619                 }
1620
1621                 /// <summary>
1622                 ///  Returns whether an explicit reference conversion can be performed
1623                 ///  from source_type to target_type
1624                 /// </summary>
1625                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1626                 {
1627                         bool target_is_type_param = target_type.IsGenericParameter;
1628                         bool target_is_value_type = target_type.IsValueType;
1629
1630                         if (source_type == target_type)
1631                                 return true;
1632
1633                         //
1634                         // From object to a generic parameter
1635                         //
1636                         if (source_type == TypeManager.object_type && target_is_type_param)
1637                                 return true;
1638
1639                         //
1640                         // From object to any reference type
1641                         //
1642                         if (source_type == TypeManager.object_type && !target_is_value_type)
1643                                 return true;
1644
1645                         //
1646                         // From any class S to any class-type T, provided S is a base class of T
1647                         //
1648                         if (TypeManager.IsSubclassOf (target_type, source_type))
1649                                 return true;
1650
1651                         //
1652                         // From any interface type S to any interface T provided S is not derived from T
1653                         //
1654                         if (source_type.IsInterface && target_type.IsInterface){
1655                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1656                                         return true;
1657                         }
1658
1659                         //
1660                         // From any class type S to any interface T, provided S is not sealed
1661                         // and provided S does not implement T.
1662                         //
1663                         if (target_type.IsInterface && !source_type.IsSealed &&
1664                             !TypeManager.ImplementsInterface (source_type, target_type))
1665                                 return true;
1666
1667                         //
1668                         // From any interface-type S to to any class type T, provided T is not
1669                         // sealed, or provided T implements S.
1670                         //
1671                         if (source_type.IsInterface &&
1672                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1673                                 return true;
1674
1675
1676                         // From an array type S with an element type Se to an array type T with an
1677                         // element type Te provided all the following are true:
1678                         //     * S and T differe only in element type, in other words, S and T
1679                         //       have the same number of dimensions.
1680                         //     * Both Se and Te are reference types
1681                         //     * An explicit referenc conversions exist from Se to Te
1682                         //
1683                         if (source_type.IsArray && target_type.IsArray) {
1684                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1685
1686                                         Type source_element_type = TypeManager.GetElementType (source_type);
1687                                         Type target_element_type = TypeManager.GetElementType (target_type);
1688
1689                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1690                                                 if (ExplicitReferenceConversionExists (source_element_type,
1691                                                                                        target_element_type))
1692                                                         return true;
1693                                 }
1694                         }
1695
1696
1697                         // From System.Array to any array-type
1698                         if (source_type == TypeManager.array_type &&
1699                             target_type.IsArray){
1700                                 return true;
1701                         }
1702
1703                         //
1704                         // From System delegate to any delegate-type
1705                         //
1706                         if (source_type == TypeManager.delegate_type &&
1707                             TypeManager.IsDelegateType (target_type))
1708                                 return true;
1709
1710                         //
1711                         // From ICloneable to Array or Delegate types
1712                         //
1713                         if (source_type == TypeManager.icloneable_type &&
1714                             (target_type == TypeManager.array_type ||
1715                              target_type == TypeManager.delegate_type))
1716                                 return true;
1717
1718                         return false;
1719                 }
1720
1721                 /// <summary>
1722                 ///   Implements Explicit Reference conversions
1723                 /// </summary>
1724                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1725                 {
1726                         Type source_type = source.Type;
1727                         bool target_is_type_param = target_type.IsGenericParameter;
1728                         bool target_is_value_type = target_type.IsValueType;
1729
1730                         //
1731                         // From object to a generic parameter
1732                         //
1733                         if (source_type == TypeManager.object_type && target_is_type_param)
1734                                 return new UnboxCast (source, target_type);
1735
1736                         //
1737                         // From object to any reference type
1738                         //
1739                         if (source_type == TypeManager.object_type && !target_is_value_type)
1740                                 return new ClassCast (source, target_type);
1741
1742                         //
1743                         // Unboxing conversion.
1744                         //
1745                         if (((source_type == TypeManager.enum_type &&
1746                                 !(source is EmptyCast)) ||
1747                                 source_type == TypeManager.value_type) && target_is_value_type)
1748                                 return new UnboxCast (source, target_type);
1749
1750                         //
1751                         // From any class S to any class-type T, provided S is a base class of T
1752                         //
1753                         if (TypeManager.IsSubclassOf (target_type, source_type))
1754                                 return new ClassCast (source, target_type);
1755
1756                         //
1757                         // From any interface type S to any interface T provided S is not derived from T
1758                         //
1759                         if (source_type.IsInterface && target_type.IsInterface){
1760                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1761                                         return null;
1762                                 else
1763                                         return new ClassCast (source, target_type);
1764                         }
1765
1766                         //
1767                         // From any class type S to any interface T, provides S is not sealed
1768                         // and provided S does not implement T.
1769                         //
1770                         if (target_type.IsInterface && !source_type.IsSealed) {
1771                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1772                                         return null;
1773                                 else
1774                                         return new ClassCast (source, target_type);
1775
1776                         }
1777
1778                         //
1779                         // From any interface-type S to to any class type T, provided T is not
1780                         // sealed, or provided T implements S.
1781                         //
1782                         if (source_type.IsInterface) {
1783                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1784                                         if (target_type.IsClass)
1785                                                 return new ClassCast (source, target_type);
1786                                         else
1787                                                 return new UnboxCast (source, target_type);
1788                                 }
1789
1790                                 return null;
1791                         }
1792
1793                         // From an array type S with an element type Se to an array type T with an
1794                         // element type Te provided all the following are true:
1795                         //     * S and T differe only in element type, in other words, S and T
1796                         //       have the same number of dimensions.
1797                         //     * Both Se and Te are reference types
1798                         //     * An explicit referenc conversions exist from Se to Te
1799                         //
1800                         if (source_type.IsArray && target_type.IsArray) {
1801                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1802
1803                                         Type source_element_type = TypeManager.GetElementType (source_type);
1804                                         Type target_element_type = TypeManager.GetElementType (target_type);
1805
1806                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1807                                                 if (ExplicitReferenceConversionExists (source_element_type,
1808                                                                                        target_element_type))
1809                                                         return new ClassCast (source, target_type);
1810                                 }
1811                         }
1812
1813
1814                         // From System.Array to any array-type
1815                         if (source_type == TypeManager.array_type &&
1816                             target_type.IsArray) {
1817                                 return new ClassCast (source, target_type);
1818                         }
1819
1820                         //
1821                         // From System delegate to any delegate-type
1822                         //
1823                         if (source_type == TypeManager.delegate_type &&
1824                             TypeManager.IsDelegateType (target_type))
1825                                 return new ClassCast (source, target_type);
1826
1827                         //
1828                         // From ICloneable to Array or Delegate types
1829                         //
1830                         if (source_type == TypeManager.icloneable_type &&
1831                             (target_type == TypeManager.array_type ||
1832                              target_type == TypeManager.delegate_type))
1833                                 return new ClassCast (source, target_type);
1834
1835                         return null;
1836                 }
1837
1838                 /// <summary>
1839                 ///   Performs an explicit conversion of the expression `expr' whose
1840                 ///   type is expr.Type to `target_type'.
1841                 /// </summary>
1842                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1843                                                              Type target_type, Location loc)
1844                 {
1845                         Type expr_type = expr.Type;
1846                         Type original_expr_type = expr_type;
1847
1848                         if (expr_type.IsSubclassOf (TypeManager.enum_type)){
1849                                 if (target_type == TypeManager.enum_type ||
1850                                     target_type == TypeManager.object_type) {
1851                                         if (expr is EnumConstant)
1852                                                 expr = ((EnumConstant) expr).Child;
1853                                         // We really need all these casts here .... :-(
1854                                         expr = new BoxedCast (new EmptyCast (expr, expr_type));
1855                                         return new EmptyCast (expr, target_type);
1856                                 } else if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
1857                                            target_type.IsSubclassOf (TypeManager.enum_type))
1858                                         return new UnboxCast (expr, target_type);
1859
1860                                 //
1861                                 // Notice that we have kept the expr_type unmodified, which is only
1862                                 // used later on to
1863                                 if (expr is EnumConstant)
1864                                         expr = ((EnumConstant) expr).Child;
1865                                 else
1866                                         expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
1867                                 expr_type = expr.Type;
1868                         }
1869
1870                         int errors = Report.Errors;
1871                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1872                         if (Report.Errors > errors)
1873                                 return null;
1874
1875                         if (ne != null)
1876                                 return ne;
1877
1878                         ne = ExplicitNumericConversion (ec, expr, target_type, loc);
1879                         if (ne != null)
1880                                 return ne;
1881
1882                         //
1883                         // Unboxing conversion.
1884                         //
1885                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1886                                 return new UnboxCast (expr, target_type);
1887
1888                         //
1889                         // Skip the ExplicitReferenceConversion because we can not convert
1890                         // from Null to a ValueType, and ExplicitReference wont check against
1891                         // null literal explicitly
1892                         //
1893                         if (expr_type != TypeManager.null_type){
1894                                 ne = ExplicitReferenceConversion (expr, target_type);
1895                                 if (ne != null)
1896                                         return ne;
1897                         }
1898
1899                 skip_explicit:
1900                         if (ec.InUnsafe){
1901                                 if (target_type.IsPointer){
1902                                         if (expr_type.IsPointer)
1903                                                 return new EmptyCast (expr, target_type);
1904
1905                                         if (expr_type == TypeManager.sbyte_type ||
1906                                             expr_type == TypeManager.byte_type ||
1907                                             expr_type == TypeManager.short_type ||
1908                                             expr_type == TypeManager.ushort_type ||
1909                                             expr_type == TypeManager.int32_type ||
1910                                             expr_type == TypeManager.uint32_type ||
1911                                             expr_type == TypeManager.uint64_type ||
1912                                             expr_type == TypeManager.int64_type)
1913                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1914                                 }
1915                                 if (expr_type.IsPointer){
1916                                         Expression e = null;
1917
1918                                         if (target_type == TypeManager.sbyte_type)
1919                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1920                                         else if (target_type == TypeManager.byte_type)
1921                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1922                                         else if (target_type == TypeManager.short_type)
1923                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1924                                         else if (target_type == TypeManager.ushort_type)
1925                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1926                                         else if (target_type == TypeManager.int32_type)
1927                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1928                                         else if (target_type == TypeManager.uint32_type)
1929                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1930                                         else if (target_type == TypeManager.uint64_type)
1931                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1932                                         else if (target_type == TypeManager.int64_type){
1933                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1934                                         }
1935
1936                                         if (e != null){
1937                                                 Expression ci, ce;
1938
1939                                                 ci = ImplicitConversionStandard (ec, e, target_type, loc);
1940
1941                                                 if (ci != null)
1942                                                         return ci;
1943
1944                                                 ce = ExplicitNumericConversion (ec, e, target_type, loc);
1945                                                 if (ce != null)
1946                                                         return ce;
1947                                                 //
1948                                                 // We should always be able to go from an uint32
1949                                                 // implicitly or explicitly to the other integral
1950                                                 // types
1951                                                 //
1952                                                 throw new Exception ("Internal compiler error");
1953                                         }
1954                                 }
1955                         }
1956
1957                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1958                         if (ne != null)
1959                                 return ne;
1960
1961                         if (expr is NullLiteral){
1962                                 Report.Error (37, loc, "Cannot convert null to value type `" +
1963                                               TypeManager.CSharpName (target_type) + "'");
1964                                 return null;
1965                         }
1966
1967                         Error_CannotConvertType (loc, original_expr_type, target_type);
1968                         return null;
1969                 }
1970
1971                 /// <summary>
1972                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1973                 /// </summary>
1974                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1975                                                                      Type target_type, Location l)
1976                 {
1977                         int errors = Report.Errors;
1978                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1979                         if (Report.Errors > errors)
1980                                 return null;
1981
1982                         if (ne != null)
1983                                 return ne;
1984
1985                         ne = ExplicitNumericConversion (ec, expr, target_type, l);
1986                         if (ne != null)
1987                                 return ne;
1988
1989                         ne = ExplicitReferenceConversion (expr, target_type);
1990                         if (ne != null)
1991                                 return ne;
1992
1993                         Error_CannotConvertType (l, expr.Type, target_type);
1994                         return null;
1995                 }
1996         }
1997 }