Re: Opaque objects and Emacs documentation

[Dmitry Gutov]

On 21.07.2020 22:36, Eli Zaretskii wrote:

> > A predicate would look like:
> >
> > (defun project-instance-p (pr)
> >     (condition-case nil
> >         (progn
> >           (project-roots pr)
> >           t)
> >       (error
> >        nil)))
>
> I actually thought about cl-defgeneric etc., since obviously each type
> of project should have its own implementation.

There's no point. If it implements project-root, it's a project.

> > But I don't see how it's going to help you write documentation.
>
> It makes the object system more complete.  Suppose some application
> would like to check it gets a valid object, before dispatching?

I can imagine some marginal utility in that, but not enough to mandate 
every backend to implement a project-instance-p method which simply 
returns t.

> > >     . a function to compare two objects of this type
> >
> > As discussed, it's a little function called 'equal'.
>
> Again, I envisioned a cl-defgeneric here.  Using 'equal' only works
> for simple forms,

Lists, cl-structs, eieio classes, etc, can also be equal.