From: Jim Freeze <jim@...>
Date: 2001-07-13T22:00:53+09:00
Subject: [ruby-talk:17790] Re: What is Array#- ?

On Fri, 13 Jul 2001, Stephan [iso-8859-1] K�mper wrote:

> What I think is, that we have 'Array's on one side: They're not sets,
> because 'Array's _may_ contain elements more than once. (As far as I see
> there are way more efficient implementation possibilities for set than
> Array, but that's another question.)
> OTOH, we (now and then) like 'Array's to behave like an Array.
> Thus there is Array#-. It returns an object that fits the requirements of a
> set: There may or may not be any objects in it, and the objects that
> actually are there are unique.
>

Thanks for the clear description. If we analyze this from a 'unit'
perspective, we get:

  (set) = (bag) - (bag)   # wrong
  (set) = (bag) - (set)   # wrong

When I first saw this it took me by suprise.

I saw Matz' posting that this was done for performance reasons.
But, IMHO, I think that if this Array conversion is wanted,
that it should be implemented under a different name.
And keep Array#- as would be expected.

$0.02
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Jim Freeze
jim@freeze.org
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