Dependency of discriminating functions on method combinations

[Pascal Costanza]

Hi,

> On 22 Dec 2017, at 11:49, Didier Verna <didier at lrde.epita.fr> wrote:
> 
> 
>  Hi,
> 
> Computing an effective method depends on the generic function's method
> combination. But is it also the case for computing the discriminating
> function?
> 
> I don't see why it should in theory, but evidence seems to suggest
> otherwise[1]. Maybe it does for technical reasons?

Unfortunately, method combinations didn’t get a lot of love in AMOP, which means there is not a lot you can really do in a portable way.

The discriminating function calls compute-effictive-method to determine the effective method, but is allowed to cache the results of compute-effective-method. So the only reliable portable way to ensure that new effective methods are computed is by calling add-method, remove-method, initialize-instance, or reinitialize-instance. (See the AMOP entry for compute-discriminating-function.)

This normally should mean that the most straightforward way to install a new method combination is by calling (reinitialize-instance gf :method-combination mc) - except that it’s not clear what the argument to :method-combination is supposed to look like. (It’s apparently meant to be the result of find-method-combination, except that it’s not clear what the arguments to find-method-combination should look like, especially the method combination options.)

ensure-generic-function doesn’t help either. (According to AMOP: “The handling of the :method-combination option is not specified.”)

So the next best option is (eval `(defgeneric …)) :-}

I’m not aware of a portable way to flush caches directly in CLOS. (Some subclasses of generic-function may not even have caches…)

Pascal

--
Pascal Costanza


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.common-lisp.net/pipermail/pro/attachments/20171222/c4d7e2fa/attachment.html>