From: Yuh-Ruey Chen <maian330@...>
Date: 2008-11-02T08:04:41+09:00
Subject: Re: Iterator objects and lazy evaluation

On Nov 1, 1:16 pm, Brian Candler <b.cand...@pobox.com> wrote:
> Yuh-Ruey Chen wrote:
> > 1) Are there equivalents for iteration/enumeration functions like map
> > that return iterator/enumeration objects (in a Python sense)?
>
> You can generate Enumerator objects, and in 1.9 (and I think 1.8.7), an
> Enumberable method which hasn't been given a block returns an
> Enumerator.
>
> irb(main):001:0> a = (1..10).each
> => #<Enumerator:0x83b687c>
> irb(main):002:0> a.next
> => 1
> irb(main):003:0> a.next
> => 2
> irb(main):004:0> a.next
> => 3
>
> However I don't think you can use these for chaining. It might be nice
> if you could do something like
>
>    (1..10).to_enum.map2 { |x| x * 2 }.map2 { |x| x + 1 }.map2 { |x| puts
> x }
>
> which wouldn't create any intermediate array. I guess you'd need each
> element to call 'next' on the previous one, and you'd need something at
> the end to trigger the whole process off.
> --
> Posted viahttp://www.ruby-forum.com/.

Yes, this is exactly what I'm looking for - the ability to chain
iterators like this without creating intermediate arrays, hopefully
using less memory.