Re: Adding a DECLARE spec equivalent to DECLARE-FUNCTION

["Basil L. Contovounesios" <basil@contovou.net>]

Adam Porter [2024-03-03 13:17 -0600] wrote:

> In light of [this thread], this seems like a good time to propose this
> idea: to enhance the `declare' form with a `function' spec equivalent to
> the top-level `declare-function' form.  This allows keeping the
> declaration inside the function that makes it necessary, which has a few
> advantages:
>
> 1. It clearly indicates which function makes the declaration necessary
>    (i.e. which function contains calls to the function in another
>    library).
> 2. If the function is moved to another file, the declaration moves with
>    it.
> 3. If the function is removed, the declaration is removed with it.
> 4. It reduces the number of top-level forms.
>
> Also, it seems like a natural fit, i.e. `declare-function' to `(declare
> (function ...))'.
>
> Would this be an acceptable addition to Emacs Lisp?

FWIW, my vote is against such a declare spec.  Compared to other declare
specs, this one introduces the tightest coupling between a function's
property declarations and the function's body, i.e. its implementation
details.  Knowing that, at a particular point in the body, a given
function will be defined, is a local property of that particular
expression, not a global property of the containing function.

My vote is for instead teaching the compiler to treat declare-function
more like it treats defvar, in that the effect of declare-function
should be made local to the current lexical scope.  [It is already
possible to write this way, and I've been known to, but sadly the effect
is global.]  This wish has been raised and agreed on here (at least in
passing) before.

This would reap all the benefits of points 1-4, as well as an additional
one: that declare-function is lexically closer to the implementation
through which the need for the declaration arises.  I think a
declaration at the top of a function is more likely to be forgotten and
become stale as the implementation changes.

-- 
Basil