Re: Opaque objects and Emacs documentation

[Eli Zaretskii]

> Cc: npostavs@gmail.com, emacs-devel@gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Tue, 21 Jul 2020 22:00:15 +0300
> 
> On 19.07.2020 17:48, Eli Zaretskii wrote:
> >    . a predicate to test whether an arbitrary Lisp value is an object
> >      of that type
> 
> 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.

> 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?

> >    . 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, but if we are willing to limit ourselves to such
simple forms, why do we need generics at all?