Re: with-slots usage question

[after rearranging all my mail folders at the weekend, I find that
gnus is automatically filtering clump into its own group: smart, but
not telling me the group exists: not smart.  So, I'm catching up]

Miles Egan <[email protected]> writes:

> I guess the ideal thing here from the programmer's point of view would
> be a language in which all functions are generic and the implementation
> is smart enough to optimize the ones that are never used
> polymorphically. 

Not really.  The methods of a GF must have congruent lambda lists -
though it's pretty likely that your LENGTH method takes a single
argument and therefore doesn't conflict with the builtin (LENGTH
SEQUENCE), you still run into drouble when you want to define (OPEN DOOR)

I believe that the style to aim for, if you're going to get hung up on
style, is that a generic function does conceptually the same thing
whatever objects you call it on, but may do it in different ways for
different objects.  So, it's OK to have an AREA gf that works on
polygons, but extending it to work on secret military bases (it
returns `51' for bases in the Nevada desert) is wrong, because that's
not the same thing.

So I tend to try to make GF names reflect the general class of object
they apply to: POLYGON-AREA is an identifiable concept whether or not
there's a class called POLYGON.  Whether the methods of the GF are
implemented as accessors is a side issue.

(Is the height of a triangle "the same thing" as the height of a
rectangle?  The latter is the length of one of its sides, which
doesn't necessarily hold for the former.  Depends on the application.
Discuss.  All the time I save when programming from Lisp's interactive
development style and prototyping, I lose again agonising over this
stuff I wouldn't have time to worry about if I just used Java)


-dan

-- 

   http://web.metacircles.com/cirCLe_CD - Free Software Lisp/Linux distro

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