Re: dynamic-extent & objects

[bill@cambridge.apple.com (Bill St. Clair)]

>Does the (declare (dynamic-extent x)) change anything?
>
>(let ((x (make-instance 'mac-buffer-stream :data-buffer-size 0)))
>  (declare (dynamic-extent x))
>  ...
>  )

As David Moon said, No.

MAKE-INSTANCE is one place where MCL's CLOS implementation is slower
than many others. It doesn't try to be smart at all, just calls
MAKE-INSTANCE, which calls ALLOCATE-INSTANCE and INITIALIZE-INSTANCE,
which calls SHARED-INITIALIZE, which grovels over the class'es slot
definitions in order to figure out what to do. This makes 5 generic
function dispatches (2 for MAKE-INSTANCE), a hash table lookup, a
couple of dynamic-extent rest args, a couple of keyword parses, and a
bunch of slot descriptor lookups. Rather expensive when the only method
that is typically specialized is INITIALIZE-INSTANCE (how many of you
have started writing SHARED-INITIALIZE methods?), and the only
initforms are constant.

Making this faster is on my list of things to do for 2.1.
Making the dynamic-extent declaration actually do something
might fall out for almost free (no guarantees).