# Enumeration vs Enumerable

**URL:** <https://www.ruby-forum.com/t/enumeration-vs-enumerable/229305>\
**Category:** Ruby\
**Created:** [February 1, 2013, 9:13pm UTC](https://www.ruby-forum.com/t/enumeration-vs-enumerable/229305 "2013-02-01T21:13:25Z")\
**Posts on this page:** 1\
**Showing post:** 8

<div class="post-metadata">

**Author:** ![my-ruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e95f7d/32.png) [@my-ruby](https://www.ruby-forum.com/u/my-ruby)\
**Post date:** [February 2, 2013, 1:02pm UTC](https://www.ruby-forum.com/t/enumeration-vs-enumerable/229305/8 "2013-02-02T13:02:29Z")

</div>

Hello,

an enumerator (I hope you didn’t mix enumerator and enumeration up; if  
you did, I may just have confused you more.. Sorry if that’s the case),  
or iterator, is an object to traverse a collection. In ruby, you usually  
get an enumerator by calling one of enumerable’s methods without a  
block. This enumerator itself provides all methods of enumerable, as  
well as some other nice functionality. It’s just another way to go  
through a collection.  
An example (taken from the documentation of enumerator[1](http://www.ruby-doc.org/core-1.9.3/Enumerator.html)):  
%w[foo bar baz].map.with\_index { |w, i| “#{i}: #{w}” }

# =\> [“0: foo”, “1: bar”, “2: baz”]

Since there is no map\_with\_index function in Enumerable (or Array), we  
can’t write that example as concise without an enumerator. We could,  
however, do this by hand:  
a =   
%w[foo bar baz].each\_with\_index { |w, i| a \<\< “#{i}: #{w}” }

# a is now [“0: foo”, “1: bar”, “2: baz”]

To wrap all that up:  
-Collection: A collection of things, can be an array, a hash, a linked  
list, a mathematical set, … (this is a general concept implemented at  
various places in ruby)  
-Enumeration: A list of all elements in a collection. Sometimes a  
collection itself is an enumeration, sometimes not (this is also a  
general concept)  
-Enumerable: A module providing a huge functionality for traversing and  
manipulating collections (this is a ruby-specific thing)  
-Enumerator / Iterator: An object to traverse a collection (this is a  
general concept and implemented in ruby)

I hope I could help. 🙂

Regards,  
Calvin

On 02.02.2013 06:07, Arup R. wrote:

> @calvin - Your example is good. But in this context with this example  
> how array is differing from enumerator? Thanks

---

_[View the full topic](https://www.ruby-forum.com/t/enumeration-vs-enumerable/229305)._