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Postings from December 2021
On Thu, 9 Dec 2021 17:26:54 +0000
Dave Mitchell <davem@iabyn.com> wrote:
> > OK, that's a detail I hadn't been aware of before. Keeping the
> > values on the stack does increase memory usage overall
>
> No, because the values can be popped off the stack once assigning
> args to params is done. (Although, they'd have to be kept in the
> presence of 'perl -d' in order to keep caller() and @DB::args
> working).
...
> Once default argument expressions have started executing, all the
> args on the stack will have been consumed and are no longer needed.
This was the problem though - I couldn't work out how to keep @DB::args
working in that situation.
Also I still can't _quite_ picture how it would work. We have to
consume the arguments off the stack in a forward direction; we can't
work from the final argument and POPs them. I can't currently imagine
how each individual OP_ARGELEM op will know where it is supposed to be
looking on the stack.
Currently (from pp.c), pp_argelem encodes the index of @_ in its op_aux
pointer, so it can simply
svp = av_fetch(defav, ix, FALSE);
In the "read directly from the stack" world, I can imagine it would
svp = &PL_stack_base[ ??? ];
for some offset - how would it determine that?
--
Paul "LeoNerd" Evans
leonerd@leonerd.org.uk | https://metacpan.org/author/PEVANS
http://www.leonerd.org.uk/ | https://www.tindie.com/stores/leonerd/
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