From: ruby-core@...
Date: 2014-04-10T14:41:21+00:00
Subject: [ruby-core:61947] [ruby-trunk - Bug #9723] [Rejected] #size does not trigger evaluation of lazy enumerator.

Issue #9723 has been updated by Marc-Andre Lafortune.

Status changed from Open to Rejected
Assignee set to Marc-Andre Lafortune

The purpose of `size` is to return the number of elements yielded by an Enumerator without consuming it, i.e. without iterating it.

If `enum.size` returns an integer, than `enum.size == enum.to_a.size` must be true.

In your first example, `size` would have to return 2, which is not possible to do lazily. Use `count` to do an actual count.

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Bug #9723: #size does not trigger evaluation of lazy enumerator.
https://bugs.ruby-lang.org/issues/9723#change-46145

* Author: Zeke Fast
* Status: Rejected
* Priority: Normal
* Assignee: Marc-Andre Lafortune
* Category: core
* Target version: 
* ruby -v: 2.1.1
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
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Here is the code which shows weird behariour

### Steps to reproduce
`$ irb
2.1.1 :001 > [1, 2, 3].lazy.select{ |e| e%2 == 1}.size
 => nil 
2.1.1 :002 > [1, 2, 3].lazy.select{ |e| e%2 == 1}.to_a
 => [1, 3] 
2.1.1 :003 > [1, 2, 3].lazy.size
 => 3` 

### Expected
`[1, 2, 3].lazy.select{ |e| e%2 == 1}.size`
to return number of elements like `[1, 2, 3].lazy.size` did.

### Actual
`[1, 2, 3].lazy.select{ |e| e%2 == 1}.size` returns **nil**.

### Environment

Ruby: ruby 2.0.0p457 (2014-03-03) [x86_64-linux-gnu]
RVM: rvm 1.25.22 (stable) by Wayne E. Seguin <wayneeseguin@gmail.com>, Michal Papis <mpapis@gmail.com> [https://rvm.io/]
OS: Linux xxxxxx 3.13-1-amd64 #1 SMP Debian 3.13.7-1 (2014-03-25) x86_64 GNU/Linux





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