Since nobody else has mentioned them - there are a couple of similar modules already on CPAN.

• interface: Checks that your module supports the methods that a given set of modules support.
• Object::Interface: Allows the quick declaration of a purely abstract base class, with compile time errors if the sub-class doesn't support the specified errors.

Interfaces, Interfaces in Perl? and Re: Interfaces seem to cover similar themes too.

I always saw Java interfaces as a response to the naming resolution problems of C++'s implementation of multiple inheritance. Personally, I think they threw out the baby with the bathwater by only allowing multiple-inheritance of interface :-)

Compile time warnings are a good thing obviously, but that's a separate issue from interface vs. abstract base classes.

I have to admit, I still don't have a handle on how what you want is different from Java-ish interfaces, or inheriting from an abstract class. Can you give an example that shows where abstract classes / interfaces wouldn't be enough?

(If it is different from the Java concept I strongly agree with fever that it should be called something else to avoid confusion :-)

You said:

• I'd like to be able to check that an object I receive from somewhere can handle the operations I'm about to perform on it
• I'd like that check not to dictate the object's implementation of those operations

Inheriting from an abstract base class seems to meet both of these goals - or am I missing something?

There could be an argument for having something like this as a way to retrofit an "abstract" interface onto a pre-existing class. I could see that being useful when you don't control the source.

But if you do control the source expressing the interface using an abstract class (maybe using Attribute::Abstract, Class::Virtual or Class::Virtually::Abstract) would seem more straightforward.

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