From: Tanaka Akira <akr@...>
Date: 2013-09-01T13:00:51+09:00
Subject: [ruby-core:56952] Re: [ruby-trunk - Feature #8840] Yielder#state

2013/9/1 marcandre (Marc-Andre Lafortune) <ruby-core@marc-andre.ca>:
>
> Your example will fail if iterated a second time.
> It will also not work correctly when using `rewind` and `next`. Check #7696.

How about adding a method to wrap an enumerator to add a state?

  % ruby -e '
  class Enumerator
    def with_state(init)
      Enumerator.new {|y|
        state = init.dup
        self.each {|v|
          y.yield [state, v]
        }
      }
    end
  end
  class Enumerator::Lazy
    def drop2(n)
      e = with_state([n])
      Enumerator.new {|y|
        e.each {|remain, v|
          if remain[0] == 0
            y.yield v
          else
            remain[0] -= 1
          end
        }
      }
    end
  end
  e = (1..42).lazy
  p e.drop2(40).to_a
  p e.drop2(40).to_a
  '
  [41, 42]
  [41, 42]

-- 
Tanaka Akira