Re: AUTOLOAD does not scale

[runrig]

Two AUTOLOADs cannot coexist amicably in the same inheritance tree. Try it, one masks the other.

The OP only has one AUTOLOAD, in the base class. IMHO, this is fine, as long as all derived classes play nicely.

[rir]

Agreed, but I say playing nicely is a practice that does not scale. If you won't distribute the code there is nothing wrong with using AUTOLOAD.

I am saying that AUTOLOAD does not scale well. Every use of AUTOLOAD in a program should be under the control of one party. If two separate authors use AUTOLOAD in the same program breakage is likely.

Being conservative, I would be suspicious of any program with more than one AUTOLOAD. If two AUTOLOAD routines exist in a hierarchy there is a problem. (Don't forget UNIVERSAL.)

This is a known problem. Consider:

#!/usr/bin/perl
use strict;
use warnings;

# I decide to use a module
package Vehicle;
use vars '$AUTOLOAD';

sub new { return bless {}, $_[0]; }

# handle all "V*" calls
sub AUTOLOAD {
        my ($key) =  $AUTOLOAD =~/::(\w+)/;
        return if $key =~ /^[A-Z]+$/;
        die "Vehicle::AUTOLOAD can't cope as $key"
                unless $key =~ /^[vV]/;
        print "Leaving  Vehicle::AUTOLOAD as $key$/";
}


# with my program below

package Animal;
use vars '$AUTOLOAD';

sub new { return bless {}, $_[0]; }

# handle all "A*" calls
sub AUTOLOAD {
        my ($key) =  $AUTOLOAD =~/::(\w+)/;
        return if $key =~ /^[A-Z]+$/;
        die "Animal::AUTOLOAD can't cope as $key"
                unless $key =~ /^[aA]/;
        print "Leaving  Animal::AUTOLOAD as $key$/";
}


package Horse;
use vars qw/ @ISA /;
@ISA = qw/ Vehicle  Animal /;



package  main;

# the two usages cannot work together,  I needed to
# know that Vehicle used AUTOLOAD so I could avoid it
# or rewrite my code to eliminate AUTOLOAD.

my $h = Horse->new;
$h->Veh();
$h->Ani();  # call intercepted by Vehicle AUTOLOAD

Be well.