From: Mathieu Bouchard <matju@...>
Date: 2001-07-16T11:27:33+09:00
Subject: [ruby-talk:17898] Re: Sets, Hashes


On Sat, 14 Jul 2001, Hal E. Fulton wrote:

> For example, when you iterate over a set (at least, the way I was taught
> in discrete math), you don't get any fixed ordering. Two possibilities
> might be just to document this and let the user hang himself; or we
> might actually randomize the order so that it was actually different
> each time.

Let the user hang himself by providing him with over half of the semantics
of the Hash class, which iterates over a *set* of rows in a usually
chaotic and reproducible order but which is not guaranteed to be so. Later
provide both of Set and Hash with a randomizer if you wish to.

> Another question is: Might there be times when it was difficult to tell
> whether an object being added was a duplicate? What kind of equality
> test do we use, considering that a set might contain completely
> arbitrary objects?

Use the semantics Hash uses for its keys in #eql? and #hash.



On Sun, 15 Jul 2001, HarryO wrote:

> I definitely think Set is a worthwhile type to have separately to Array.
> It could probably be implemented by wrapping an Array, in order to
> minimise the amount of rewriting, but an efficient implementation would
> probably do it a better way.

What you really want is wrapping Hash.



On Sun, 15 Jul 2001, Shan-leung Maverick WOO wrote:

> For example, when I am enumerating a container, most of the time I don't
> really don't care if it is a Hash, an Array, or a (future) Dictionary (if it
> exists).

Ruby's Hash is SmallTalk-style Dictionary; MetaRuby's HashP, HollowHash
(formerly HashMixin) correspond to Java's idea of Dictionary (abstract
class) even though it follows Ruby's Hash api.



matju