Support virtual slots in EIEIO

Support virtual slots in EIEIO

[Yuan Fu]

[-- Attachment #1: Type: text/plain, Size: 1128 bytes --]

I'm working on a project that uses EIEIO. At some point, I need to declare
a virtual slot — one
that has a getter and a setter. Because EIEIO doesn't support it, I tried
to hack one by myself.

I overloaded slot accessor and (setf slot-accessor). Then some problem
arises:
1. initial arguments don't work, that's what I expected anyway and I can work
around that.
2. I couldn't overload `set-slot-value' and `slot-value' because they are
just aliases to `eieio-oset`
   and `eieio-oref', which are functions. That, I can't work around (or I
think I can't?)

So, is there any possible workaround that can make `set-slot-value'
and `slot-value' work with my virtual slot hack? All I can do right now is
write something like "never
use these two functions with this slot!!!" in the documentation.

That being said, are you interested in adding virtual slots to EIEIO?
My naive approach would be make `eieio-oset' and `eieio-oref' generic
functions.
But I don't really know anything about EIEIO and Emacs
so I don't know how much impact will that give, except everything in
EIEIO becoming slower.

Yuan

[-- Attachment #2: Type: text/html, Size: 2660 bytes --]

Re: Support virtual slots in EIEIO

[Stefan Monnier]

Hi,

> I'm working on a project that uses EIEIO.  At some point, I need to
> declare a virtual slot — one that has a getter and a setter.  Because
> EIEIO doesn't support it, I tried to hack one by myself.

Very interesting.  I'm not very familiar with this, so in order to see
what's the best solution, could you help me with some context:
- How does this work in CLOS (or in other systems that gave you the
  idea of a virtual slot ;-)?
- Why do you need such a virtual slot (what alternatives have you
  considered and how bad were they)?

> 1. Initial arguments don't work, that's what I expected anyway and
>    I can work around that.

Could you clarify what you mean by "initial arguments don't work"?
Can you add a method to `initialize-instance` or something like that?

> 2. I couldn't overload `set-slot-value' and `slot-value' because they
>    are just aliases to `eieio-oset` and `eieio-oref', which are
>    functions. That, I can't work around (or I think I can't?)
>
> So, is there any possible workaround that can make `set-slot-value'
> and `slot-value' work with my virtual slot hack?

IIRC you might be able to get what you want by adding a method to
`slot-missing`.  This will not impact the normal performance of slot-value.


        Stefan