[ruby-core:42570] [ruby-trunk - Feature #4890] Enumerable#lazy

Issue #4890 has been updated by Rodrigo Rosenfeld Rosas.


Thomas, continuing, if the "force" approach is taken instead of take(n), you'll still have to call it (or call each/select/to_a) in the end, as oppose to what happens if you just call map/collect, for example.

It can also lead to unexpected behavior. For example, on this case, the side-effect won't happen on some elements:

items.map {|item|
  this_should_always_be_done_for_each(item)
}.select{item.index == 2}

If "items" is lazy by default, "this_should_always_be_done_for_each" won't be called for all "items" unless only the last one has index 2.
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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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