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Postings from November 2003
Lvalue vs rvalue, and yes, this depends on which operation is being invoked.
mark
On Thu, Nov 06, 2003 at 05:46:56PM -0000, Orton, Yves wrote:
> Hi,
>
> Im trying to figure out an aspect of the autovivification. Specifically why
> the construct being used changes whether autovivification occurs or not. Ie
> for the deref @{EXPR}, whether autovivification occurs is dependent on both
> the type of EXPR and the context within which @{EXPR} is used.
>
> For instance
>
> D:\>perl -Mstrict -wle "my $f = { }; my @a=map { $_ } @{ $f->{foo} }"
>
> D:\>perl -Mstrict -wle "my $f = { }; print 'ok' for @{ $f->{foo} }"
>
> D:\>perl -Mstrict -wle "my $f = { }; my @a=@{ $f->{foo} }"
> Can't use an undefined value as an ARRAY reference at -e line 1.
>
> D:\>perl -Mstrict -wle "my $f = { }; print 'ok' if @{ $f->{foo} }"
> Can't use an undefined value as an ARRAY reference at -e line 1.
>
> D:\>perl -Mstrict -wle "my $f = { }; print 'ok' for @{ undef() }"
> Can't use an undefined value as an ARRAY reference at -e line 1.
>
> Now im well aware that @{EXPR} autovivifies when its directly or indirectly
> used as STORE, ie:
>
> D:\>perl -Mstrict -wle "my $f = { }; push @{ $f->{foo} },'foo'"
>
> But why does it autovivify in a FETCH here:
>
> D:\>perl -Mstrict -wle "my $f = { }; pop @{ $f->{foo} }"
>
> but not here
>
> D:\>perl -Mstrict -wle "my $f = { }; print 'ok' if @{ $f->{foo} }"
> Can't use an undefined value as an ARRAY reference at -e line 1.
>
> Any wisdom regarding this would be welcome.
>
> Yves
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