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