Slaven Rezic pointed out (on p5p) the use of base.pm as an alternative. I assumed it would always require an external file: apparently it doesn't do that (anymore, anyway, I seem to remember that at one point it did. But I am probably wrong about that).

What I don't like about base.pm is the extra stuff about fields. Have you ever looked under the hood of base.pm? Yuck!

Liz

Update:
Argh. The reason I didn't get any errors about the empty Bar package, was that I actually had a Bar.pm as an external file hanging around from some previous testing. So yes, you need something in there, not necessarily a sub null {} though, a $VERSION = '0.01' also does the trick. Thanks to Mr. Person for his perseverance proving me wrong in this matter.

It's one of the reasons I wrote vars::i

my $foo = Foo->new;
print "foo is".($foo->isa( 'Bar' ) ? '' : ' _not_')." a Bar\n";

package Bar;
sub null {}

package Foo;
use vars::i qw[ @ISA Bar ];
sub new { bless {},shift }
__END__
foo is a Bar
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MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"

I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).

** The third rule of perl club is a statement of fact: pod is sexy.

That's all good and dandy, but even tough your module looks useful (and generic), I can't say I like the resulting interface — i.e. the use statement. I'd rather see something like this:

use strict;
package Foo;
use isa qw(Bar);
sub new { bless {},shift }
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The module isa.pm can actually quite short:

# file isa.pm
package isa;

sub import {
    my $pkg = shift;
    my $caller = caller;
    no strict 'vars';
    push @{"$caller\::ISA"}, @_;
}

42;
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Et voilà:

foo is a Bar

Of course, with base doing the same and more, I don't know if there's much need for this here module.

I'm on Perl 5.6.1, and it gives me:

Base class package "Bar" is empty.
        (Perhaps you need to 'use' the module which defines that packa
+ge first.) at test.pl line 10
BEGIN failed--compilation aborted at test.pl line 10.
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If I don't put the sub null {} in, but that wouldn't generally be a problem for a real situation because you'd almost always have something in the package.