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- To: firstname.lastname@example.org (Rob Browning)
- Subject: defclass problem?
- From: email@example.com (Steve Strassmann)
- Date: Thu, 27 Jan 1994 19:41:52 -0500
- Cc: info-mcl
>Date: Thu, 27 Jan 1994 18:10:38 -0600
>From: firstname.lastname@example.org (Rob Browning)
>Subject: defclass problem?
>Why do I get this complaint? It is apparently a conflict between the line
>slot of this class and the quickdraw line method. However, I was under the
>impression that methods did not incurr this kind of name clash.
>? (defclass ccc () ((line :accessor line :initarg :line)))
>> Error: Incompatible lambda list in #<STANDARD-READER-METHOD LINE (CCC)> for
>>#<STANDARD-GENERIC-FUNCTION LINE #xD8CAC6>
>> While executing: CCL::CHECK-DEFMETHOD-CONGRUENCY
>> Type Command-/ to continue, Command-. to abort.
>P.S. Thanks for all of your help with my earlier questions.
You're right, it is a conflict between
1) a method called LINE, which you specified as the slot accessor, and
2) the method called LINE, the quickdraw command to draw a line.
There's nothing about methods which guarantee avoiding name clashes
like these (as a matter of fact, it's sometimes desirable).
You have a couple of options:
a) You can change the package in which you write your software.
Use something like (defpackage my-package (:use common-lisp))
when you load your code, and at the top of your file, use
(in-package my-package) to switch your file to the right package.
Then, in your code, LINE refers to the slot, and CCL::LINE refers
to the quickdraw line function.
This is probably the cleanest and best way to enforce name modularity -
unlike C++, lisp uses names, not objects, to avoid name clashes.
Using packages properly takes some study, however. MCL tells you
a window's current package by showing it in the lower left corner.
b) You can change the :accessor of your slot to CCC-LINE:
(defclass ccc () ((line :accessor ccc-line :initarg :line)))
This will rename the methods for reading and writing the slot.