From: Innokenty Mikhailov <anotheroneman@...>
Date: 2012-02-25T08:07:18+09:00
Subject: [ruby-core:42873] [ruby-trunk - Feature #4890] Enumerable#lazy


Issue #4890 has been updated by Innokenty Mikhailov.


Yusuke Endoh wrote:
> 
> Yutaka, could you make a patch in C?  Or anyone?
> 

Hi,

I've come up with patch in C - just two lazy methods added so far: map and select.
Please, see this PR for more info https://github.com/ruby/ruby/pull/100

The idea is very simple - block that passed to lazy method (select or map) is converted to Proc and stored in enumerator itself.
When next element requested - all Proc objects are called for this value and the result returned. Proc#call result handling depends on proc_entry type.

Let me know if it makes any sense (if true - I can come up with additional lazy methods).

Thanks.


----------------------------------------
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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