From: Thomas Sawyer <transfire@...>
Date: 2012-02-14T00:36:10+09:00
Subject: [ruby-core:42556] [ruby-trunk - Feature #4890] Enumerable#lazy


Issue #4890 has been updated by Thomas Sawyer.


Actually, is there any reason why Enumerator's usual methods themselves aren't lazy? Is it necessary to have both? If they were lazy then the notation would be pretty simple:

  [1,2,3].each.select{ |e| ... }.map{ |e| .... }.to_a

No special method needed, as #each would do the job.

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Feature #4890: Enumerable#lazy
https://bugs.ruby-lang.org/issues/4890

Author: Yutaka HARA
Status: Assigned
Priority: Normal
Assignee: Yutaka HARA
Category: core
Target version: 2.0.0


=begin
= Example
Print first 100 primes which are in form of n^2+1 

   require 'prime'
   INFINITY = 1.0 / 0
   p (1..INFINITY).lazy.map{|n| n**2+1}.select{|m| m.prime?}.take(100)

(Example taken from enumerable_lz; thanks @antimon2)

= Description

Enumerable#lazy returns an instance of Enumerable::Lazy.
This is the only method added to the existing bulit-in classes.

Lazy is a subclass of Enumerator, which includes Enumerable.
So you can call any methods of Enumerable on Lazy, except methods like
map, select, etc. are redefined as 'lazy' versions.

= Sample implementation

((<URL:https://gist.github.com/1028609>))
(also attached to this ticket)

=end



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