Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!edcastle!aiai!jeff
From: jeff@aiai.ed.ac.uk (Jeff Dalton)
Newsgroups: comp.lang.lisp
Subject: Re: updating random slots in (say) defstruct
Message-ID: <1569@skye.ed.ac.uk>
Date: 17 Jan 90 17:47:30 GMT
References: <18963@bellcore.bellcore.com>
Reply-To: jeff@aiai.UUCP (Jeff Dalton)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 17

In article <18963@bellcore.bellcore.com> pc@flash.bellcore.com writes:
>Yes, that's so.  But given a defstruct with 50 slots, i must define an
>updator function for each, which seems wasteful, given that the DEFSTRUCT
>has already defined one.

But the system may not have defined one.  Instead of having a setter
function for each slot of each defstruct type, it may just have one
setter function that's used for all slots and is called with an int
that gives the offset of the slot in the structure.  For example,

  > (defstruct struct a-slot)
  struct

  > (macroexpand-1 (setf (struct-a-slot x) 'z))
  (system:structure-set x 0 'z)

-- Jeff