From: "matz (Yukihiro Matsumoto)" <matz@...>
Date: 2013-08-31T13:54:56+09:00
Subject: [ruby-core:56910] [ruby-trunk - Feature #8840][Feedback]	Yielder#state


Issue #8840 has been updated by matz (Yukihiro Matsumoto).

Status changed from Open to Feedback

I understand the motivation, and how it works.  It is very simple.
But I hesitate to introduce state easily in this age of functional programming.
Let me think for a while.

And tell me if anyone has better idea to address the issue.

Matz.

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Feature #8840: Yielder#state
https://bugs.ruby-lang.org/issues/8840#change-41461

Author: marcandre (Marc-Andre Lafortune)
Status: Feedback
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: current: 2.1.0


Defining an Enumerator that require a state is currently troublesome. For example, it is not really possible to define an equivalent of Lazy#drop in Ruby without making an assumption on the implementation.

To address this, I propose that we

(a) guarantee that a new Yielder object will be given for each enumeration
(b) add a 'state' attribute to Yielder.

This way, one could implement Lazy#drop in a way similar to:

  class Enumerator::Lazy < Enumerator
    def drop(n)
      n = n.to_i
      Lazy.new(self) do |yielder, *values|
        yielder.state ||= n
        if yielder.state > 0
          yielder.state -= 1
        else
          yielder.yield(*values)
        end
      end
    end
  end

Note that (a) is currently true for Ruby MRI, JRuby and Rubinius, but it is not explicit in the documentation.


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