perl.p5p at rjbs
May 18, 2008, 2:10 PM
Post #1 of 3
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bug? delete local $hash{element}
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I lamented on p5p that I couldn't delete a hash element locally, and Nicholas
asked, "Well, what if you localize it and then delete it?" I hadn't tried
that, so I ended up with this little script:
use strict;
use Data::Dumper;
my %hash = (a => 1, b => 2);
print Dumper(\%hash);
{
local $hash{a} = 4;
print Dumper(\%hash);
delete $hash{a};
print Dumper(\%hash);
}
print Dumper(\%hash);
delete @hash{qw(a b)};
print Dumper(\%hash);
This behaved just as I'd expect. What I had tried, and did not work, was:
delete local $hash{a};
The element got deleted but never restored. Nicholas produced these two
samples:
$ perl -MO=Concise -e 'delete local $hash{a}'
7 <@> leave[1 ref] vKP/REFC ->(end)
1 <0> enter ->2
2 <;> nextstate(main 1 -e:1) v ->3
6 <1> delete vK ->7
- <1> ex-helem sKM/130 ->6
4 <1> rv2hv sKR/1 ->5
3 <$> gv(*hash) s ->4
5 <$> const(PV "a") s/BARE ->6
-e syntax OK
$ perl -MO=Concise -e 'local $hash{a}'
7 <@> leave[1 ref] vKP/REFC ->(end)
1 <0> enter ->2
2 <;> nextstate(main 1 -e:1) v ->3
6 <2> helem vKM/LVINTRO,2 ->7
4 <1> rv2hv sKR/1 ->5
3 <$> gv(*hash) s ->4
5 <$> const(PVIV "a") s/BARE ->6
-e syntax OK
<@Nicholas> the behaviour makes sense given the optree
<@Nicholas> but I think it might actually be a bug
<@Nicholas> because as best I can tell the local is ignored complletely
While my understanding of the optree here is pretty limited, I agree. I don't
see why "local delete $hash{element}" should not be the same as "local
$hash{element}; delete $hash{element}"
Also not working, but should be working:
delete @hash{qw(a b c)};
--
rjbs
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