[ruby-core:18137] Re: Enumerators that know about a block

Hi,

2008/8/1 David A. Black <[e-mail]>:
> I'm remembering that at one point it was possible to do this:
>
>  array = [1,2,3]
>  func = lambda {|x| x * 10 }
>  e = array.enum_for(:map, &func)
>  e.next
>  => 10
>
> But now the result is 1, because &func is ignored.
>
> I'm (a) puzzled by this, since it seems to me that enumerators are
> much more useful if they can remember a block, and (b) wondering if
> there's some similar replacement technique that I haven't managed to
> figure out.

enum_for is designed to apply a block for the specified method
(Array#map in this case) by later Enumerator method calls, so it
simply ignores a given block.

You may need the lazy version of Enumerable#map that returns
Enumerator instead of Array.

  e = [1, 2, 3].lazy_map {|x| x * 10}
  p e.next #=> 10
  p e.next #=> 20

-- 
Shugo Maeda