From: Marc-Andre Lafortune <ruby-core-mailing-list@...>
Date: 2010-04-01T00:59:19+09:00
Subject: [ruby-dev:40887] Re: [Feature #2673] the length for an enumerator 	generated by Array#permutation and Array#combination

Hi,

On Wed, Mar 31, 2010 at 11:22 AM, Yukihiro Matsumoto <matz@ruby-lang.org> wrote:
> This propose has been suspended for 1.9.2 since the resule may not be
> trustworthy considering the source modification after generating
> enumerator.  I am not sure passing block is a good idea or not, yet.
> It's not intuitive for me at the first glance.

Thanks for the reply.

Just another word in favor of a block: for some enumerators,
calculating the overall size might non trivial (even though less
costly then doing the actual enumeration).

For this reason, I feel that there should not be a performance penalty
when creating an Enumerator because the length need to be
precalculated, even though very well might not be used. That's in
addition to the fact that it might be wrong, if the source was
modified in the meantime.

This is why I feel that lazily calculating the length, whenever
needed, is the best way to go, both for reasons of efficiency and
correctness.

I regret not having posted my ideas before, but hopefully we'll get
Enumerator#length in 1.9.3...

--
Marc-André