From: "trans.  (T. Onoma)" <transami@...>
Date: 2004-09-20T23:16:40+09:00
Subject: Re: Array#index block and rdetect

On Monday 20 September 2004 09:52 am, Randy W. Sims wrote:
> All enumerable objects don't neccessarilly have a meaningful concept of
> an index. Eg. sets, multisets. Enumerable and Indexable are two
> different things, though Indexable extends Enumerable.

  Main Entry: enu·mer·a·ble
  Pronunciation: i-'n(y)üm-r&-b&l, -'n(y)ü-m&-
  Function: adjective
  : DENUMERABLE

  Main Entry: de·nu·mer·a·ble
  Pronunciation: di-'n(y)ü-m&-r&-b&l
  Function: adjective
  : capable of being put into one-to-one correspondence
    with the positive integers

So "index" must mean this corresponding integer. I would argue that sets and 
hashes are not technically enumerable, because they're elements can not be 
accessed as a _function_ of the index, i.e. one-to-one correspondence.

Perhaps separate Collectable and Indexable modules would be preferable.


T.
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