From: Brian Candler <b.candler@...>
Date: 2008-11-02T03:16:34+09:00
Subject: Re: Iterator objects and lazy evaluation

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.
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