Or: Hey Rocky, Watch Me Pull A Closure Out Of My Hat

Or: This Is Your Brain, This is Your Brain On Perl

What follows is a (silly) example of how to make methods behave in interesting ways. Or, more accurately, it is an abuse of closures. Anyhow, for those who need brain cells fried, here you go:

use strict;

sub prefix_later {
   my ($just_once,$and_later) = @_;
   my $ct=0;
   return sub {
      my (@args) = shift();
      ((!$ct++) ? 
          sub {
             $just_once->(@args);
          } : 
          sub { 
             $and_later->(@args);
             $just_once->(@args); 
          }
      )->();
   }
}

my $hi_mom = prefix_later( 
   sub { print "hi mom\n"; },
   sub { print "this was unneccessary:\n"; }
);

$hi_mom->() for (1..3);
[download]

hi mom
this was unneccessary:
hi mom
this was unneccessary:
hi mom
[download]

You can sort of see how this would be extended to write methods such as postfix_later or do_this_after_five_times or whatever.

How did I come up with this? I was bored. Kids, don't get bored. It's dangerous. (The observant will note the doubly nested closure to seal @args that have could have been eliminated with a shift in array context. Again, I tell you, I was bored)