mcs/mcs/assign.cs

   1 //
   2 // assign.cs: Assignments.
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Martin Baulig (martin@gnome.org)
   7 //
   8 // (C) 2001, 2002 Ximian, Inc.
   9 //
  10 using System;
  11 using System.Reflection;
  12 using System.Reflection.Emit;
  13
  14 namespace Mono.CSharp {
  15
  16         /// <summary>
  17         ///   This interface is implemented by expressions that can be assigned to.
  18         /// </summary>
  19         /// <remarks>
  20         ///   This interface is implemented by Expressions whose values can not
  21         ///   store the result on the top of the stack.
  22         ///
  23         ///   Expressions implementing this (Properties, Indexers and Arrays) would
  24         ///   perform an assignment of the Expression "source" into its final
  25         ///   location.
  26         ///
  27         ///   No values on the top of the stack are expected to be left by
  28         ///   invoking this method.
  29         /// </remarks>
  30         public interface IAssignMethod {
  31                 //
  32                 // This method will emit the code for the actual assignment
  33                 //
  34                 void EmitAssign (EmitContext ec, Expression source);
  35
  36                 //
  37                 // This method is invoked before any code generation takes
  38                 // place, and it is a mechanism to inform that the expression
  39                 // will be invoked more than once, and that the method should
  40                 // use temporary values to avoid having side effects
  41                 //
  42                 // Example: a [ g () ] ++
  43                 //
  44                 void CacheTemporaries (EmitContext ec);
  45         }
  46
  47         /// <summary>
  48         ///   An Expression to hold a temporary value.
  49         /// </summary>
  50         /// <remarks>
  51         ///   The LocalTemporary class is used to hold temporary values of a given
  52         ///   type to "simulate" the expression semantics on property and indexer
  53         ///   access whose return values are void.
  54         ///
  55         ///   The local temporary is used to alter the normal flow of code generation
  56         ///   basically it creates a local variable, and its emit instruction generates
  57         ///   code to access this value, return its address or save its value.
  58         /// </remarks>
  59         public class LocalTemporary : Expression, IMemoryLocation {
  60                 LocalBuilder builder;
  61
  62                 public LocalTemporary (EmitContext ec, Type t)
  63                 {
  64                         type = t;
  65                         eclass = ExprClass.Value;
  66                         loc = Location.Null;
  67                         builder = ec.GetTemporaryStorage (t);
  68                 }
  69
  70                 public void Release (EmitContext ec)
  71                 {
  72                         ec.FreeTemporaryStorage (builder);
  73                         builder = null;
  74                 }
  75
  76                 public LocalTemporary (LocalBuilder b, Type t)
  77                 {
  78                         type = t;
  79                         eclass = ExprClass.Value;
  80                         loc = Location.Null;
  81                         builder = b;
  82                 }
  83
  84                 public override Expression DoResolve (EmitContext ec)
  85                 {
  86                         return this;
  87                 }
  88
  89                 public override void Emit (EmitContext ec)
  90                 {
  91                         ec.ig.Emit (OpCodes.Ldloc, builder);
  92                 }
  93
  94                 public void Store (EmitContext ec)
  95                 {
  96                         ec.ig.Emit (OpCodes.Stloc, builder);
  97                 }
  98
  99                 public void AddressOf (EmitContext ec, AddressOp mode)
 100                 {
 101                         ec.ig.Emit (OpCodes.Ldloca, builder);
 102                 }
 103         }
 104
 105         /// <summary>
 106         ///   The Assign node takes care of assigning the value of source into
 107         ///   the expression represented by target.
 108         /// </summary>
 109         public class Assign : ExpressionStatement {
 110                 protected Expression target, source, real_source;
 111                 protected LocalTemporary temp = null, real_temp = null;
 112                 protected Assign embedded = null;
 113                 protected bool is_embedded = false;
 114                 protected bool must_free_temp = false;
 115
 116                 public Assign (Expression target, Expression source, Location l)
 117                 {
 118                         this.target = target;
 119                         this.source = this.real_source = source;
 120                         this.loc = l;
 121                 }
 122
 123                 protected Assign (Assign embedded, Location l)
 124                         : this (embedded.target, embedded.source, l)
 125                 {
 126                         this.is_embedded = true;
 127                 }
 128
 129                 public Expression Target {
 130                         get {
 131                                 return target;
 132                         }
 133
 134                         set {
 135                                 target = value;
 136                         }
 137                 }
 138
 139                 public Expression Source {
 140                         get {
 141                                 return source;
 142                         }
 143
 144                         set {
 145                                 source = value;
 146                         }
 147                 }
 148
 149                 public static void error70 (EventInfo ei, Location l)
 150                 {
 151                         Report.Error (70, l, "The event '" + ei.Name +
 152                                       "' can only appear on the left-side of a += or -= (except when" +
 153                                       " used from within the type '" + ei.DeclaringType + "')");
 154                 }
 155
 156                 //
 157                 // Will return either `this' or an instance of `New'.
 158                 //
 159                 public override Expression DoResolve (EmitContext ec)
 160                 {
 161                         // Create an embedded assignment if our source is an assignment.
 162                         if (source is Assign)
 163                                 source = embedded = new Assign ((Assign) source, loc);
 164
 165                         real_source = source = source.Resolve (ec);
 166                         if (source == null)
 167                                 return null;
 168
 169                         //
 170                         // This is used in an embedded assignment.
 171                         // As an example, consider the statement "A = X = Y = Z".
 172                         //
 173                         if (is_embedded && !(source is Constant)) {
 174                                 // If this is the innermost assignment (the "Y = Z" in our example),
 175                                 // create a new temporary local, otherwise inherit that variable
 176                                 // from our child (the "X = (Y = Z)" inherits the local from the
 177                                 // "Y = Z" assignment).
 178                                 if (embedded == null)
 179                                         real_temp = temp = new LocalTemporary (ec, source.Type);
 180                                 else
 181                                         temp = embedded.temp;
 182
 183                                 // Set the source to the new temporary variable.
 184                                 // This means that the following target.ResolveLValue () will tell
 185                                 // the target to read it's source value from that variable.
 186                                 source = temp;
 187                         }
 188
 189                         // If we have an embedded assignment, use the embedded assignment's temporary
 190                         // local variable as source.
 191                         if (embedded != null)
 192                                 source = (embedded.temp != null) ? embedded.temp : embedded.source;
 193
 194                         target = target.ResolveLValue (ec, source);
 195
 196                         if (target == null)
 197                                 return null;
 198
 199                         Type target_type = target.Type;
 200                         Type source_type = real_source.Type;
 201
 202                         // If we're an embedded assignment, our parent will reuse our source as its
 203                         // source, it won't read from our target.
 204                         if (is_embedded)
 205                                 type = source_type;
 206                         else
 207                                 type = target_type;
 208                         eclass = ExprClass.Value;
 209
 210                         //
 211                         // If we are doing a property assignment, then
 212                         // set the `value' field on the property, and Resolve
 213                         // it.
 214                         //
 215                         if (target is PropertyExpr){
 216                                 PropertyExpr property_assign = (PropertyExpr) target;
 217
 218                                 if (source_type != target_type){
 219                                         source = ConvertImplicitRequired (ec, source, target_type, loc);
 220                                         if (source == null)
 221                                                 return null;
 222                                 }
 223
 224                                 //
 225                                 // FIXME: Maybe handle this in the LValueResolve
 226                                 //
 227                                 if (!property_assign.VerifyAssignable ())
 228                                         return null;
 229
 230                                 return this;
 231                         }
 232
 233                         if (target is IndexerAccess) {
 234                                 return this;
 235                         }
 236
 237                         if (target is EventExpr) {
 238
 239                                 Binary tmp;
 240                                 EventInfo ei = ((EventExpr) target).EventInfo;
 241
 242
 243                                 Expression ml = MemberLookup (
 244                                         ec, ec.ContainerType, ei.Name,
 245                                         MemberTypes.Event, AllBindingFlags, loc);
 246
 247                                 if (ml == null) {
 248                                         //
 249                                         // If this is the case, then the Event does not belong
 250                                         // to this Type and so, according to the spec
 251                                         // is allowed to only appear on the left hand of
 252                                         // the += and -= operators
 253                                         //
 254                                         // Note that target will not appear as an EventExpr
 255                                         // in the case it is being referenced within the same type container;
 256                                         // it will appear as a FieldExpr in that case.
 257                                         //
 258
 259                                         if (!(source is Binary)) {
 260                                                 error70 (ei, loc);
 261                                                 return null;
 262                                         } else {
 263                                                 tmp = ((Binary) source);
 264                                                 if (tmp.Oper != Binary.Operator.Addition &&
 265                                                     tmp.Oper != Binary.Operator.Subtraction) {
 266                                                         error70 (ei, loc);
 267                                                         return null;
 268                                                 }
 269                                         }
 270                                 }
 271                         }
 272
 273                         if (source is New && target_type.IsValueType){
 274                                 New n = (New) source;
 275
 276                                 n.ValueTypeVariable = target;
 277                                 return n;
 278                         }
 279
 280                         if (target.eclass != ExprClass.Variable && target.eclass != ExprClass.EventAccess){
 281                                 Report.Error (131, loc,
 282                                               "Left hand of an assignment must be a variable, " +
 283                                               "a property or an indexer");
 284                                 return null;
 285                         }
 286
 287                         if ((source.eclass == ExprClass.Type) && (source is TypeExpr)) {
 288                                 source.Error118 ("variable or value");
 289                                 return null;
 290                         } else if (source is MethodGroupExpr){
 291                                 ((MethodGroupExpr) source).ReportUsageError ();
 292                                 return null;
 293                         }
 294
 295                         if (target_type == source_type)
 296                                 return this;
 297
 298                         //
 299                         // If this assignemnt/operator was part of a compound binary
 300                         // operator, then we allow an explicit conversion, as detailed
 301                         // in the spec.
 302                         //
 303
 304                         if (this is CompoundAssign){
 305                                 CompoundAssign a = (CompoundAssign) this;
 306
 307                                 Binary b = source as Binary;
 308                                 if (b != null && b.IsBuiltinOperator){
 309                                         //
 310                                         // 1. if the source is explicitly convertible to the
 311                                         //    target_type
 312                                         //
 313
 314                                         source = ConvertExplicit (ec, source, target_type, loc);
 315                                         if (source == null){
 316                                                 Error_CannotConvertImplicit (loc, source_type, target_type);
 317                                                 return null;
 318                                         }
 319
 320                                         //
 321                                         // 2. and the original right side is implicitly convertible to
 322                                         // the type of target_type.
 323                                         //
 324                                         if (StandardConversionExists (a.original_source, target_type))
 325                                                 return this;
 326
 327                                         Error_CannotConvertImplicit (loc, a.original_source.Type, target_type);
 328                                         return null;
 329                                 }
 330                         }
 331
 332                         source = ConvertImplicitRequired (ec, source, target_type, loc);
 333                         if (source == null)
 334                                 return null;
 335
 336                         // If we're an embedded assignment, we need to create a new temporary variable
 337                         // for the converted value.  Our parent will use this new variable as its source.
 338                         // The same applies when we have an embedded assignment - in this case, we need
 339                         // to convert our embedded assignment's temporary local variable to the correct
 340                         // type and store it in a new temporary local.
 341                         if (is_embedded || embedded != null) {
 342                                 type = target_type;
 343                                 temp = new LocalTemporary (ec, type);
 344                                 must_free_temp = true;
 345                         }
 346
 347                         return this;
 348                 }
 349
 350                 Expression EmitEmbedded (EmitContext ec)
 351                 {
 352                         // Emit an embedded assignment.
 353
 354                         if (real_temp != null) {
 355                                 // If we're the innermost assignment, `real_source' is the right-hand
 356                                 // expression which gets assigned to all the variables left of it.
 357                                 // Emit this expression and store its result in real_temp.
 358                                 real_source.Emit (ec);
 359                                 real_temp.Store (ec);
 360                         }
 361
 362                         if (embedded != null)
 363                                 embedded.EmitEmbedded (ec);
 364
 365                         // This happens when we've done a type conversion, in this case source will be
 366                         // the expression which does the type conversion from real_temp.
 367                         // So emit it and store the result in temp; this is the var which will be read
 368                         // by our parent.
 369                         if (temp != real_temp) {
 370                                 source.Emit (ec);
 371                                 temp.Store (ec);
 372                         }
 373
 374                         Expression temp_source = (temp != null) ? temp : source;
 375                         ((IAssignMethod) target).EmitAssign (ec, temp_source);
 376                         return temp_source;
 377                 }
 378
 379                 void ReleaseEmbedded (EmitContext ec)
 380                 {
 381                         if (embedded != null)
 382                                 embedded.ReleaseEmbedded (ec);
 383
 384                         if (real_temp != null)
 385                                 real_temp.Release (ec);
 386
 387                         if (must_free_temp)
 388                                 temp.Release (ec);
 389                 }
 390
 391                 void Emit (EmitContext ec, bool is_statement)
 392                 {
 393                         if (target is EventExpr) {
 394                                 ((EventExpr) target).EmitAddOrRemove (ec, source);
 395                                 return;
 396                         }
 397
 398                         //
 399                         // FIXME! We need a way to "probe" if the process can
 400                         // just use `dup' to propagate the result
 401                         //
 402                         IAssignMethod am = (IAssignMethod) target;
 403
 404                         if (this is CompoundAssign){
 405                                 am.CacheTemporaries (ec);
 406                         }
 407
 408                         Expression temp_source;
 409                         if (embedded != null) {
 410                                 temp_source = embedded.EmitEmbedded (ec);
 411
 412                                 if (temp != null) {
 413                                         source.Emit (ec);
 414                                         temp.Store (ec);
 415                                         temp_source = temp;
 416                                 }
 417                         } else
 418                                 temp_source = source;
 419
 420                         if (is_statement)
 421                                 am.EmitAssign (ec, temp_source);
 422                         else {
 423                                 LocalTemporary tempo;
 424
 425                                 tempo = new LocalTemporary (ec, source.Type);
 426
 427                                 temp_source.Emit (ec);
 428                                 tempo.Store (ec);
 429                                 am.EmitAssign (ec, tempo);
 430                                 tempo.Emit (ec);
 431                                 tempo.Release (ec);
 432                         }
 433
 434                         if (embedded != null) {
 435                                 if (temp != null)
 436                                         temp.Release (ec);
 437                                 embedded.ReleaseEmbedded (ec);
 438                         }
 439                 }
 440
 441                 public override void Emit (EmitContext ec)
 442                 {
 443                         Emit (ec, false);
 444                 }
 445
 446                 public override void EmitStatement (EmitContext ec)
 447                 {
 448                         Emit (ec, true);
 449                 }
 450         }
 451
 452
 453         //
 454         // This class is used for compound assignments.
 455         //
 456         class CompoundAssign : Assign {
 457                 Binary.Operator op;
 458                 public Expression original_source;
 459
 460                 public CompoundAssign (Binary.Operator op, Expression target, Expression source, Location l)
 461                         : base (target, source, l)
 462                 {
 463                         original_source = source;
 464                         this.op = op;
 465                 }
 466
 467                 public Expression ResolveSource (EmitContext ec)
 468                 {
 469                         return original_source.Resolve (ec);
 470                 }
 471
 472                 public override Expression DoResolve (EmitContext ec)
 473                 {
 474                         target = target.ResolveLValue (ec, source);
 475                         if (target == null)
 476                                 return null;
 477
 478                         original_source = original_source.Resolve (ec);
 479                         if (original_source == null)
 480                                 return null;
 481
 482                         //
 483                         // Only now we can decouple the original source/target
 484                         // into a tree, to guarantee that we do not have side
 485                         // effects.
 486                         //
 487                         source = new Binary (op, target, original_source, loc);
 488                         return base.DoResolve (ec);
 489                 }
 490         }
 491 }
 492
 493
 494
 495