digirent:

You may find Hash::Util useful. By locking the keys of the hash, you'll get an error if you try to reference keys that don't exist:

$ cat hash_lock_keys.pl
#!/usr/bin/perl
use strict;
use warnings;
use Hash::Util qw(lock_keys);

my %f = (alpha=>1, beta=>2, gamma=>3);
lock_keys(%f);

if ($f{apple} == 4) {
    print "Eh?\n";
}

$ perl hash_lock_keys.pl
Attempt to access disallowed key 'apple' in a restricted hash at hash_
+lock_keys.pl line 9.
[download]

You can unlock the hash when you want to change it. The module has several other interesting-looking subroutines that you may find useful.

...roboticus

When your only tool is a hammer, all problems look like your thumb.