Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!bbn.com!mesard
From: mesard@bbn.com (Wayne Mesard)
Newsgroups: comp.lang.lisp
Subject: Re: Creating an array of structures
Keywords: Defstruct, Make-array
Message-ID: <47160@bbn.COM>
Date: 20 Oct 89 00:52:35 GMT
References: <5244@lindy.Stanford.EDU>
Sender: news@bbn.COM
Reply-To: mesard@BBN.COM (Wayne Mesard)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
Lines: 25

giant@lindy.Stanford.EDU (Buc Richards) writes:
>When I make an array of structures, any changes to any of the elements
>change all the elements.  What am I dong wrong?
[...]
><cl> (Setf tc (Make-array 25 :Element-type 'cardtype
>        :Initial-element (make-cardtype)))

MAKE-CARDTYPE gets called once and only once.  Every element in the
array then contains a pointer to the ONE structure which was created.
Changing one changes them all because they are one and the same.

:INITIAL-ELEMENT probably isn't what you want.  Try :INITIAL-CONTENTS.
E.g.:

 (Setf tc (Make-array 25 :Element-type 'cardtype
         :Initial-contents
	(do ((i 25 (1- i))
	     (lis nil (cons (make-cardtype) lis)))
	    ((zerop i) lis))))


Disclaimer: The DO may or may not be the politically correct way to cons
	    up the list.

Wayne();