http://www.perlmonks.org?node_id=11128524

QM has asked for the wisdom of the Perl Monks concerning the following question:

I've been closing over hashes for years, for subs that need some persistent store, but not wanting to invoke memoize.

Below I've closed over a scalar and a hash. I get a warning of:

Use of uninitialized value $FIXED_STRING in hash element at ...

With hashes, this just works, but apparently the hash is empty, and that's fine. But the scalar value within the sub is undef.

What am I missing?

What is the easiest way to fix this, while still using a scalar to store a string, that is later used as a hash key?

#!/usr/bin/env perl # demo of closure around sub, with persistent string use strict; use warnings; for my $q ('a'..'g') { do_something($q); print "Done computing\n" } { my $FIXED_STRING = 'fixed_string'; my %persistent; sub do_something { my $x = $_[0]; $persistent{$x}{$FIXED_STRING} = rand; END { for my $k (keys %persistent) { print "$k: $persistent{$k}{$FIXED_STRING}\n"; } } } }

-QM
--
Quantum Mechanics: The dreams stuff is made of