Re: [perl #75676] PUSH on tied arrays

On Sat, Jun 12, 2010 at 12:54:05PM +0100, Dave Mitchell wrote:
> On Fri, Jun 11, 2010 at 06:37:56AM -0700, Nicholas Clark wrote:
> > 2: For push and unshift, the PP code ignores the return value of PUSH and
> >    UNSHIFT, and makes a (second) call to the tied object, FETCHSIZE.
> 
> Er, where does this happen? I can't see it, which means I'm probably
> misinterpreting something.

No, it means that my description was inadequate. I'd forgotten that I'd also
had to do a bit of chasing to figure out *why* it wasn't completely buggy and
simply returning the size of the underlying array. This code at the end of
pp_push:

    if (OP_GIMME(PL_op, 0) != G_VOID) {
	PUSHi( AvFILL(ary) + 1 );
    }


AvFILL expands to:

#define AvFILL(av)	((SvRMAGICAL((const SV *) (av))) \
			 ? mg_size(MUTABLE_SV(av)) : AvFILLp(av))


and for a tied array, SvRMAGICAL() is true, hence a call to mg_size() is made,
and that calls the FETCHSIZE method.

Nicholas Clark