Presence of struct destructor makes lvalue?

[Ali Çehreli]

On 04/08/2013 12:24 PM, Maxim Fomin wrote:

 > DMD often inserts temporaries when they are unexpected (or users do not
 > expect when they should).
 >
 > D main function in destructor case is rewritten as:
 >
 >     S s = S(1);
 >     s.opAssign(foo(2));
 >     s.opAssign((S __sl1779 = S(3); , __sl1779))

Have you manually typed those lines or is there a tool that outputs that 
"preprocessor" ;) output?

 >
 > Hence, ref version is taken in account because '__sl1779' is a good 
lvalue.
 >
 > Troubles seems to come from
 > 
https://github.com/D-Programming-Language/dmd/blob/master/src/expression.c#L4203 

 >

Thank you very much for finding the related line. :) Quoting:

Expression *StructLiteralExp::semantic(Scope *sc)
{ Expression *e;

// ...

     /* If struct requires a destructor, rewrite as:
      * (S tmp = S()),tmp
      * so that the destructor can be hung on tmp.
      */
     if (sd->dtor && sc->func)
     {
         Identifier *idtmp = Lexer::uniqueId("__sl");
         VarDeclaration *tmp = new VarDeclaration(loc, type, idtmp, new 
ExpInitializer(0, this));
         tmp->storage_class |= STCctfe;
         Expression *ae = new DeclarationExp(loc, tmp);
         Expression *e = new CommaExp(loc, ae, new VarExp(loc, tmp));
         e = e->semantic(sc);
         return e;
     }

     return this;
}

Is it because destructors cannot be "hung" on literals?

It is inconsistent that function-returned rvalues do not behave the same 
as literal-rvalues.

Ali