From: "A. S. Bradbury" <asbradbury@...>
Date: 2006-08-02T01:06:07+09:00
Subject: Re: Enumerable

On Tuesday 01 August 2006 16:43, Michael Saltzman wrote:
> Am new to Ruby and have the folloiwng Question.
>
> I have a class, say Collect, and I want to mixin Enumerable. How do I
> write the each method in Collect?
>
> class Collect
> 	include Enumerable
> 	def initialize()
> 		@array = Array.new(0)
> 		@ct = 0
> 	end
> 	def add(item)
> 		@array.push(item)
> 		@ct += 1
> 	end
> 	def howmany
> 		@ct
> 	end
> 	def each
> 	#
> 	#	Not sure how to do this????
> 	#
> 	end
> end
It depends what you want each to do? Just to wrap @array.each? In that case, 
this would work:
def each
  @array.each {|item| yield item}
end

Of course you can do whatever you want to the array item in the block before 
you yield it again.

An alternative technique is as follows:
def each(&block)
  @array.each(&block)
end

I'm sure someone will correct me if I describe this slightly wonky, but the 
basic idea is that the interpreter converts the block argument to a proc with 
a name (I think I read an article that claimed a block is always converted to 
a proc, but when no &arg is given, it is simply a proc with no name, 
accessible of course via yield). This is then passed on to @array.each as a 
block argument.

I don't know whether there are any real advantages or disadvantages to either 
method. Hope this helps

Alex