No thanks for the Memoize#

Wed, 18 Oct 2006 17:36:03 +0000

NAME
       Memoize - Make functions faster by trading space for time
SYNOPSIS
               # This is the documentation for Memoize 1.01
               use Memoize;
               memoize('slowfunction');
               slowfunction(arguments);    # Is faster than it was before
       This is normally all you need to know.

To the extent that I failed to fully consider the implications of the rest of the Memoize manual page (i.e. the bits I wouldn't normally need to know - and in particular the section describing the "default normalizer") the strange and apparently intermittent bug in $WORK-related code I have just spent the last week chasing could be considered my own damn fault. Here's the short summary, though: the wrapper for the memoized function stringizes and concatenates the arguments together and then uses that as a key into a hash table to see if it's been called with those arguments before. This does not work when the arguments are objects.

:; cat test.pl
package Test;
sub new {
    my $o= bless { HELLO => 'goodbye',
                   DATA => "0" x 2048 },
    "Test";
    return $o;
}
package main;
my %seen;
for(my $i=0;$i<10000;$i++) {
    my $obj=Test->new;
    warn $obj;
    die "$obj repeated at iteration $i" if($seen{"$obj"});
    $seen{"$obj"}=1;
}
:; perl test.pl
Test=HASH(0x814ed9c) at test.pl line 15.
Test=HASH(0x814f7bc) at test.pl line 15.
Test=HASH(0x814f5e8) at test.pl line 15.
Test=HASH(0x814ed9c) at test.pl line 15.
Test=HASH(0x814ed9c) repeated at iteration 3 at test.pl line 16.

Won't be making that mistake again.