I am still in maintenance mode. Here is a piece of code.

@matrices = qw(user_group user_realm group_realm
        realm_template template_subsite realm_subsite);
[download]

and later in the code

sub IsMatrix
{
        shift if UNIVERSAL::isa($_[0], __PACKAGE__);
        my ($child, $parent) = @_;
        my $cache = undef if undef;                                   
+                                                                     
+                      

        unless ($cache)
        {
                my %cache;
                @cache{@matrices} = (1) x scalar(@matrices);
                $cache = \%cache;
        }                                                             
+                                                                 

        return $cache->{"${child}_$parent"};
}
[download]

OK, so the first line lets me use this either as function or as a method.

What does this my $cache = undef if undef; do ?

Update
Just thinking aloud as the comments are coming in. Maybe I can replace the whole sub with the following:

grep /^${child}_$parent$/, @matrices;
[download]

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