From: jmichel@... (Jean Michel)
Date: 2001-02-22T22:40:03+09:00
Subject: [ruby-talk:11309] Re: musings about Hash#each_with_index

In article <m2vgq3ecsv.fsf@zip.local.thomases.com>,
Dave Thomas  <Dave@PragmaticProgrammer.com> wrote:
>If we've saying that anything that can be indexed is an array, then I
>guess we should include files, directories, strings, ...  Similarly is
>we're saying that anything with keys is a Hash.
>
>Arrays and hashes have similar properties, but are different beasts,
>In the same way that the old OO argument of Squares and Rectangles
>can't be resolved by answering a Square is a kind of Rectangle, or a
>Rectangle is a kind of Square, so too is it impossible to say that an
>Array is a kind of Hash or a Hash a kind of Array. It seems to me that
>they just share some properties.

Watch out  here! The fact  that you can consider  an array as  a special
case of a hash, of for that matter  a string or a file or a directory as
a special case of an array is much more than just an analogy. The set of
properties  which is  shared in  these cases  is an  extremely important
programming  paradigm, and  a language  which can  express clearly  this
paradigm in a uniform way in all cases will have a definite advantage. I
think the  mixins that matju is  trying to make can  potentially achieve
this for Ruby.

Best regards,
  Jean MICHEL