Mark's (Dominus) solution in the other thread is just what I was looking for. I want all classes where I "use Interface;" to implement and not inherit the methods listed in the Interface package.

The particular design problem I need this for is one in which I need each class, regardless of what base class they inherit from, to implement themselves a group of methods.

Java provides a built in facility for doing this, the "implements" keyword, which works almost exactly as the "use Abstract;" Mark proposes. (To it I would suggest adding the word "Interface" to the abstract class name, to achieve Java-like clarity through convention). Thus his example would look like this:

package DuckInterface;
use Carp;

my @inheritors;

sub import {
  my $caller = caller; 
  push @inheritors, $caller;
}

  my @abstract_methods = qw(swim fly);

  sub INIT {
    my $bad = 0;
    for my $class (@inheritors) {
      for my $meth (@abstract_methods) {
        no strict 'refs';
        unless (defined &{"${class}::$meth"}) {
          $bad=1;
          warn "Class $class should implement DuckInterface, but does 
+not define $meth.\n";
        }
      }
    }
    croak "Compilation aborted" if $bad;
  }

  1;
[download]

And a class that "implements" DuckInterface:

package RedDuck;
use DuckInterface;

sub swim {
  "I swim like a red duck";
}

sub fly {
  "I fly like a red duck, and DuckInterface guarantees I do!";
}
[download]

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