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Postings from May 2015
On Wed, May 27, 2015 at 09:30:22PM +0100, Paul "LeoNerd" Evans wrote:
> What's the conclusion here? Do I have to fix any code in ListUtils.xs
> then?
Well I think the provisional conclusion is that lc() et al are at fault.
As to whether List::Util is doing anything wrong, the two differences
between the first() implementation and perl's grep() implementation are:
1) grep temporarily increases the ref count of each SV it aliases to $_,
via:
# define DEFSV_set(sv) \
(SvREFCNT_dec(GvSV(PL_defgv)), GvSV(PL_defgv) = SvREFCNT_inc(sv))
2) grep makes a mortal copy of each PADTMP it encounters.
Either of those would make List::Util work with the bad lc/uc/etc in 5.20.0
and 5.22.0.
The second of those was to fix
#78194: Referencing a PADTMP twice produces two copies
(which I don't fully understand from a cursory read of the ticket).
The first, if nothing else, avoids crashes if the thing being iterated
is freed elsewhere, e.g.
use List::Util qw{ first };
use Devel::Peek;
my $a = "A";
@a = (1);
@b = first { shift @a; Dump $_ } @a;
which outputs:
SV = UNKNOWN(0xff) (0x1b19038) at 0x1af8f88
REFCNT = 0
FLAGS = ()
--
"Do not dabble in paradox, Edward, it puts you in danger of fortuitous wit."
-- Lady Croom, "Arcadia"
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