BEGIN { 
    my %cache; 
    sub do_it { 
      my $func = shift; 
      $cache{$func} = do {  
          local @ISA; __PACKAGE__->can("do_$fun")  
        } 
        unless defined $cache{$func}; 
      $cache{$func}->(@_); 
    } 
  }
[download]

This does precisely what mine does. Did you mean "exists" there instead of "defined"?

-- Randal L. Schwartz, Perl hacker