From: Brian Candler <b.candler@...>
Date: 2009-11-23T07:02:13+09:00
Subject: Re: Newbie question: Enumerators

Omran Nazir wrote:
> What sort of objects can be defined as 
> 'enumerable' and what makes them so?

Something is enumerable if it implements a method (conventionally called 
"each") which yields a series of values into a block. If you mix in the 
Enumerable module then you get a whole bunch of additional methods which 
build on this - select, map, min/max, sort_by etc. Each of those method 
just calls your "each" method and then processes the values yielded.

> Can someone please give a simple explantion of what exactly an 
> Enumerator is, what it can act on and why you can pass 'array.to_enum' 
> to a method that expect 'array'?

As it happens, someone asked me to write this up a few days ago. The 
result is here:
http://wiki.github.com/rdp/ruby_tutorials_core/enumerator

It's not something that most people need. The most common use is when 
you want to use the Enumerable methods but iterate using a method other 
than 'each', for example 'each_byte' or 'each_with_index'
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