On Apr 29, 2:39 am, u...@stemsystems.com ("Uri Guttman") wrote:
> >>>>> "RD" == Rob Dixon <rob.di...@gmx.com> writes:
>
> RD> On 29/04/2011 10:27, Uri Guttman wrote:
>
> RD> Good call Brian. It's not at all obvious that all the elements of a hash
> RD> slice will be created if they don't exist :)
> >>
> >> and they won't be anyhow. you need have lvalues to autovivify hash (or
> >> array) elements.
> >>
> >> perl -le '@x = @y{ qw( a b )}; print keys %y'
> >>
> >> %y is empty as you can see.
>
> RD> I meant in the specific case of the grep that was posted. There are no
> RD> lvalues there, yet they are autovivified:
>
> RD> perl -le '@x = grep defined, @y{ qw( a b )}; print keys %y'
>
> that shouldn't happen IMO. it is only calling defined on the aliased
> values of %y. i would call it a bug but some could argue otherwise.
>
This happened in 5.10 ... at least after 5.8.
From: http://rt.perl.org/rt3/Ticket/Display.html?id=89024
Just like the argument list of sub calls, The list over which
foreach
iterates is evaluated in lvalue context as required by foreach's
aliasing property.
Ex:
perl -MData::Dumper -le '
for ( @y{qw(a b)} ) {$_ = "foo" unless defined $_} ;
print Dumper \%y'
$VAR1 = {
'a' => 'foo',
'b' => 'foo'
};
grep's aliasing creates the same lvalue context:
perl -MData::Dumper -le '
@x = grep {$_ = "foo" unless defined $_} @y{ qw( a b )};
print Dumper \%y'
$VAR1 = {
'a' => 'foo',
'b' => 'foo'
};
--
Charles DeRykus
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