Front page | perl.perl5.porters |
Postings from December 2011
On Sun Dec 04 01:48:20 2011, davidnicol@gmail.com wrote:
> I would like taking a reference to a nonexistent hash element to do
> magic similar to the magic done when a nonexistent hash element is
> used as a function argument.
>
> my %hash;
> my $fancyref = \$hash{doesnotexist};
>
> at this point, C<keys %hash> would still be empty.
> $fancyref would appear to be undefined, and would evaluate as false.
> ref($fancyref) would be true, like an overloaded object.
>
> Both of these would remain unchanged
>
> perl -le '$r = \$h{k}; $$r=5; print %h'
> k5
> perl -le '$r = \$h{k}; $h{k}=5; print $$r'
> 5
>
> except that $r would be false until the key is created in the second
> statement, instead of the key getting created in the first statement.
>
> C<\$hash{keyname}> would become a concise way to spell
> C<exists($hash{keyname})> with the added feature of providing a
> reference or a delayed reference.
>
> The autovivification deferral should work with
> nonexistent-hash-element function arguments:
>
> {
> sub reftosecond{ my $r2= \$_[1]; return $r2 }
> my %h; my $r = reftosecond($h{one}, $h{two});
> ok ( (!keys %h), "taking reference to nonexistent hash elt arg
> does not create entry");
> $$r = 27;
> is( $h{two}, 27, "assigning to deferred hash elt ref creates
> entry");
> $r = \$h{three};
> ok( !$r, "reference to nonexistent hash elt is false");
> $h{three} = 28;
> is ($$r, 28, "dereferencing reference to formerly nonexistent hash
> elt");
> }
I think that’s a little too weird and surprising.
--
Father Chrysostomos
Thread Previous
|
Thread Next