From: "yhara (Yutaka HARA)" <redmine@...>
Date: 2012-12-08T01:17:36+09:00
Subject: [ruby-core:50665] [ruby-trunk - Bug #7248] Shouldn't Enumerator::Lazy.new be private?


Issue #7248 has been updated by yhara (Yutaka HARA).


Hi,

Enumerator::Lazy.new will be needed
(1) when you want to overwrite behavior of a lazy method. eg:

---
class Enumerator::Lazy
  def zip(*args, &block)
    enums = args.map(&:lazy)
    Lazy.new(self){|yielder, val|
      ary = [val] + enums.map{|e| e.next}
      if block
        yielder << block.call(ary)  # make lazy.zip{} behave lazy (currently it doesn't because enum.zip{} is eager)
      else
        yielder << ary
      end
    }
  end
end

fizz = [nil, nil, nil, nil, "Fizz"].cycle
buzz = [nil, nil, "Buzz"].cycle
p fizz.lazy.zip(buzz){|f, b| "#{f}#{b}"}.first(20)
---

(2) when you want to add a new Enumerable method and its lazy version. eg:

---
module Enumerable
  def filter_map(&block)
    self.map(&block).compact
  end
end

class Enumerator::Lazy
  def filter_map(*args, &block)
    Lazy.new(self){|yielder, val|
      result = block.call(val)
      yielder << result if result
    }
  end
end

p [11,12,13].filter_map{|i| i*i if i.even?}  #=> [144]
p (1..Float::INFINITY).lazy.filter_map{|i| i*i if i.even?}.first(20)
---
----------------------------------------
Bug #7248: Shouldn't Enumerator::Lazy.new be private?
https://bugs.ruby-lang.org/issues/7248#change-34511

Author: marcandre (Marc-Andre Lafortune)
Status: Assigned
Priority: Normal
Assignee: yhara (Yutaka HARA)
Category: core
Target version: 2.0.0
ruby -v: ruby 2.0.0dev (2012-10-29 trunk 37380) [x86_64-darwin10.8.0]


Is there a reason why Enumerator::Lazy.new is not private?

Lazy enumerators should be created with `Enumerable#lazy`. Moreover, there is no doc, and it can give unexpected results too.


-- 
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