I've done this in the past, using code like the following:

package Base;

use Carp;

my @methods = qw(new something something_else);
my %methods;
@method{@methods} = ();

sub AUTOLOAD {
  my ($pkg, $method) = $AUTOLOAD =~ /^(.*)::(.*)$/;

  if (exists $method{$method}) {
    croak qq(Package "$pkg" must override the method "$method");
  }
}

1;
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If you then define a subclass that uses the Base.pm interface, you get an error if you call an undefined method:

#!/usr/bin/perl -w

use strict;

package MyObj;

use vars qw(@ISA);
use Base;

@ISA = qw(Base);

sub new {
  return bless {}, shift;
}

package main;

my $thing = MyObj->new;

$thing->something;
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Of course, this only generates the error if a missing method is called. It's probably possible to do a more stringent check when the derived class is loaded. I'll give that some thought...

--
<http://www.dave.org.uk>

"The first rule of Perl club is you don't talk about Perl club."