From: Ben Tilly <ben_tilly@...>
Date: 2001-02-26T22:36:38+09:00
Subject: [ruby-talk:11589] Re: Array bugs?

I hate following up to myself but...

"Ben Tilly" <ben_tilly@hotmail.com> wrote:
>
>"Christoph Rippel" <crippel@primenet.com> wrote:
[...]
>Now the right way to do the caching strategy above
>would be to make methods like <=> be able to take
>1 or 2 arguments.  The optional argument would be
>the recursive cache, and the above check would be
>inserted into all of them.  Which would mean that
>you would move the cache code into Enumerable and
>then just call:
>
>    @cache, is_seen = check_cache(@cache, self.id, other.id)
>
>in every comparison method.
[...]

The better way would be for Enumerable to add methods
for get_cache, in_cache?, <=>, cmp, and for those who
want an efficient ==, eq.

The difference between == and eq, or <=> and cmp
would be 1 argument or 2.  The second argument is the
cache.  The <=> method would just add in an empty
cache and call cmp.  The cmp method would just call
<=>.  Classes which are complex data structures
should provide cmp and mixin <=>.  Simple classes
should provide <=> and mixin cmp.  Similarly eq would
just throw ==.

Inside of cmp in complex data structures you are
expected to do your own:

  return true if in_cache?(cache, id, other.id)

Thoughts?  Feedback?

Cheers,
Ben
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