Perl OO Disinheritence

mikezone has asked for the wisdom of the Perl Monks concerning the following question:

Is there a mechanism to disinherit an inherited method? Such that $object->can( $disinherited_method ) can't?

Conditions:

Package A implements methods a1( ), a2( ), a3( ).
Package B implements methods b1( ), b2( ).
Package B is derived from base package A (ie. @B::ISA = qw( A );)
I want Package B to implement methods a1( ), a2( ), b1( ), and b2( ). I don't want Package B to implement method a3( ).

my $example = new B;
if( $example->can( "a3" ) {
  $example->a3(); # @$*&%! Still there.
} else {
  print "Successful disinheritence!\n";
}
[download]

I've tried messing with Exporter in a bunch of ways, after reading the Camel 3rd ed. Unfortunately I glossed over the part on p889 until after I made a bunch of failed examples. I've tried undef( &A::a3 ), only to be greeted with an error I've not seen before (something like undefined subroutine a3() called at line...). Please, no recommendations to refactor my classes.

Much thanks in advance,
- m.

Comment on Perl OO Disinheritence Select or Download Code

Replies are listed 'Best First'.
Re: Perl OO Disinheritence by miyagawa (Chaplain) on Mar 26, 2002 at 08:00 UTC
Not a direct answer though: `package B; sub can { my($proto, $method) = @_; return if $method eq 'a3'; $proto->UNIVERSAL::can($method); }` [download] -- Tatsuhiko Miyagawa miyagawa@cpan.org	[reply] [d/l]
Re: Perl OO Disinheritence by rjray (Chaplain) on Mar 26, 2002 at 08:14 UTC
This is one of those catches about Perl's OO behavior: since there are no "private" methods, there's no way for class A to hide `a3()` aside from the tricks in Damian's book. Of course, if the "A" class never meant for `a3` to be private, it wouldn't have helped anyway. Others have shown the best way to prevent the `UNIVERSAL::can` method from showing `a3` to the outside world. But you'll also want to override it, probably with a null method (or an outright `die` if you want to be proactive about it): `sub B::a3 { return; }` `--rjray`	[reply]
Re: Perl OO Disinheritence by zengargoyle (Deacon) on Mar 26, 2002 at 07:57 UTC
override UNIVERSAL::can to return undef for the Package B and Method a3 combination.	[reply]
•Re: Perl OO Disinheritence by merlyn (Sage) on Mar 26, 2002 at 15:50 UTC
If it can't "a3", it's not `@ISA = qw(A)`. Sounds to me like you've got a mixed-up class design. Maybe both A and B are subclasses of a common ancestor, where you define what is now a1 and a2 there, then let A and B both inherit from that, where A adds a3, and B defines b1 and b2, and inherits a1 and a2 from the common superclass. Hard to tell with so much abstraction. Can you give us the specifics? -- Randal L. Schwartz, Perl hacker	[reply]
Re: Perl OO Disinheritence by Juerd (Abbot) on Mar 26, 2002 at 18:25 UTC
* . I don't want Package B to implement method a3( ). You could override it. Simple as can be, and very straight forward. `package B; use base 'A'; use Carp; use strict; sub a3 { croak sprintf q[Can't locate object method "a3" via package "%s"], ref shift; }` [download] Please, no recommendations to refactor my classes. But I really think you should. U28geW91IGNhbiBhbGwgcm90MTMgY W5kIHBhY2soKS4gQnV0IGRvIHlvdS ByZWNvZ25pc2UgQmFzZTY0IHdoZW4 geW91IHNlZSBpdD8gIC0tIEp1ZXJk	[reply] [d/l]