Hm. One more example. Here state is used to enumerate unique string instances (over the whole lifetime of a program):

#! /usr/bin/perl

use warnings;
use 5.010;

sub enumerate {
    my ($property, $key) = @_;

    state (%hash, %enum);

    $hash{$property}{$key} //= ++$enum{$property};
}

print "\n", "Edibles:\n";
print "$_ => @{[enumerate edible => $_]}\n" for
        qw( apple spam pear orange spam spam spam kebab spam caterpill
+ar );

print "\n", "Colors:\n";
print "$_ => @{[enumerate color => $_]}\n" for
        qw( red yellow red red red green );
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