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Postings from August 2017
On Fri, Jul 28, 2017 at 10:09:09AM -0700, Father Chrysostomos via RT wrote:
> On Fri, 28 Jul 2017 04:35:26 -0700, davem wrote:
> > On Thu, Jul 27, 2017 at 04:22:47PM -0700, Father Chrysostomos via RT wrote:
> > > On Thu, 27 Jul 2017 16:14:18 -0700, sprout wrote:
> > > > On Thu, 27 Jul 2017 03:50:56 -0700, davem wrote:
> > > > > A downside of &PL_sv_zero is that if assigned to a variable, that
> > > > > variable
> > > > > gets int, num and string values rather than just an int value.
> > > >
> > > > Why does that need to be the case? Why cannot PL_sv_zero have just
> > > > the SvIOK flag on?
> >
> > because the first time you do, e.g.
> >
> > @a=();
> > say "size=" . @a;
> >
> > PL_sv_zero gets upgraded to an SvPOK() PVIV anyway.
> >
> > > > Does it matter that \(%h && $foo) now returns a reference to a read-
> > > > only value when %h is empty? (If so, that can be solved by turning on
> > > > PADTMP on PL_sv_zero.)
> > >
> > > I think it does matter. grep(1,@list_with_one_item) returning a mutable
> > > 1 and grep(1,@list_with_zero_items) returning a read-only variable is
> > > the kind of icky inconsistency that I tried hard to eliminate.
> >
> > Won't setting PADTMP cause PL_sv_zero's PVX buffer to be stolen? Or is
> > that not done on a R/O var?
>
> It is not done on a R/O var.
Now done.
commit 02960b52b40b494fa4f6e1be81db5f3459ab91a9
Author: David Mitchell <davem@iabyn.com>
AuthorDate: Fri Aug 4 15:17:44 2017 +0100
Commit: David Mitchell <davem@iabyn.com>
CommitDate: Fri Aug 4 15:17:44 2017 +0100
set SVs_PADTMP flag on PL_sv_zero
Where an op in scalar but not boolean context returns &PL_sv_zero as a
more efficient way of doing sv_2mortal(newSViv(0)), the returned value
must be mutable. For example
my @a = ();
my $r = \ scalar grep $_ == 1, @a;
$$r += 10;
By setting the SVs_PADTMP flag, this forces pp_srefgen() and similar to
make a mortal copy of &PL_sv_zero.
This kind of defeats the original optimisation, but the copy only kicks
in under certain circumstances, whereas the newSViv(0) approach would
create a new mortal every time.
See RT #78288 for where FC suggested the problem and the solution.
--
Diplomacy is telling someone to go to hell in such a way that they'll
look forward to the trip
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