How big is a class in memory?

Question

How do I figure out how many bytes a defclass object has in Common Lisp?

Yuu

Answer 1

You can't do that in portable Common Lisp.

Useful could be the function ROOM. ROOM prints memory statistics and with the argument T it prints them detailed. So you may see a difference before and after some instance creations. Implementations may have specific functions, but you need to check that with the manual or with the support mailing list.

Refutation

Interesting. (side explanation: I am dealing with lots of things and I'm trying to figure out how to optimize them smaller) – Yuu

Some implementations will let you profile allocation to find the hotspots. That's much a much better way to improve the footprint. – Travistravus

Answer 2

In addition to Rainer's answer, here is the answer for CLISP: macro EXT:TIMES

(defclass c () ((x) (y) (z)))
(ext:times (make-instance 'c))
                                   Permanent            Temporary
Class                         instances   bytes    instances   bytes
-----                         --------- ---------  --------- ---------
C                                     1        48          0         0
-----                         --------- ---------  --------- ---------
Total                                 1        48          0         0
Real time: 1.4E-5 sec.
Run time: 0.0 sec.
Space: 48 Bytes
#<C #x000333CF2AA0>

NB: if you evaluate defclass at the prompt, it is not compiled, so times will report some fluff in addition to c.

Abiogenesis