I can't help but wonder whether the minimal value is worth the effort. Sure, using an abstract class in Perl prevents you from completely forgetting to implement one of the methods...

This, by itself, can be enough.

Take, for example, an online shop that sells several different types of items - each of which will be a class. It quite often makes sense here to ensure that each of these has all the methods that will be needed in the system to be able to buy the item - a title, price, SKU, whatever.

Yes, you could just add it to your standards that anyone adding a new class of item must add these, and ensure that your reviewers look for this. But if you have an abstract class that all of these use, with an array of necessary types that you just add to any time you need to insist on a new abstract class method, then you don't need to do this. You just wait for the @ISA line to blow up!

Tony