Re: Pre-PPC: class :abstract

On Wed, 17 Dec 2025 at 15:38, Paul "LeoNerd" Evans <[email protected]>
wrote:

> I've been thinking about what next to work on for the core `class`
> feature. One thing I think would be fairly easy to add, would be a copy
> of Object::Pad's abstract classes and required methods.
>
> The idea of an abstract class is documented in Object::Pad thusly:
>
>   :abstract
>
>   Declares that this class is abstract. An abstract class is permitted
>   to define required methods (i.e. named methods without a body
>   definition).
>

I always though that abstract has same usefulness as Java's final - hardly
to be distinguished from zero.

If you don't want to create it as a class, create it as a role.
or "method foo = 0"
or "requires method_not_implemented_here"

Fixing badly placed abstract (or final in Java's case) is lot of pain.


>
>   Instances may not be created of this class type directly. Instead, a
>   subclass of this class must be derived that provides method bodies for
>   any of the named required methods. Any subclass of an abstract class
>   must either provide bodies for all remaining required methods, or
>   themselves be declared :abstract as well.
>
>   This provides a way in which a generic type of class can be created,
>   that is intended for multiple different specialisations to further
>   define different kinds of behaviour by providing bodies for those
>   named methods. Being abstract means that instances cannot be created
>   of this as-yet-incomplete class type.
>
>     -- https://metacpan.org/pod/Object::Pad#%3Aabstract
>
> One slight difference from Object::Pad's design that I'm still
> considering on is whether to say that required method declarations in
> such a class body have to have an attribute on them as well, just to
> make them stand out a little more visually. Without it it might be hard
> to notice when they're being used.
>
> These would be quite an easy stepping-stone away from where we are now,
> allowing people to build quite a few more shapes and patterns. I've
> certainly found them useful when building things on Object::Pad. It also
> avoids the overall problem of "roles" being far too ill-defined and I
> still have no idea what people want there. (*AHEM*)
>
> How do we feel about these? Shall I write up a proper PPC doc on this?
>
> --
> Paul "LeoNerd" Evans
>
> [email protected]
> http://www.leonerd.org.uk/  |  https://metacpan.org/author/PEVANS
>