generalized lvalues

[Nathan Sidwell]

Ziemowit Laski wrote:

> The "cleanest" syntactic approach we could come up with so far is
> 
>   __builtin_objc_gc_strong(ptr) = object;
> 
> which I suppose we can live with, though the lhs doesn't look too 
> lvaluish this way... :-(

It looks more lvaluish than '(cast)ptr = object'.  Functions can
return references (in C++), so one could actually write such a function.
The same is not true of the cast notation.

void *&__builtin_objc_gc_strong(void *&p) {return p;}

Do you need a solution that works in both C and C++?

If you're adding language extensions, you should choose one that is the
smallest possible extension (ideally, it would be 'not-an-extension').
The cast-as-lvalue idea fails for C++, as Joe Buck has pointed out, and
it fails for C as it makes a whole swathe of ill-formed uses now well-formed,
but with non-intuitive semantics.  For instance does '(short)int_var = something'
write only the 'short' bits of int_var, or the whole thing?  What
does '(int)short_var = something' mean?  What does '&(short)int_var' give you?
Is it endian-dependent?  Sure, meanings could be defined, but ISTM that
there's a whole rat's nest of strange corner conditions ready trip up
programmers and compilers.

nathan

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