From: Brian Candler <b.candler@...>
Date: 2009-02-19T18:13:29+09:00
Subject: Re: Dummy question about method in class

Valentino Lun wrote:
> I have a dummy question.
> 
> [1,2,3,4,5].inject { |sum,n| sum+n }
> The inject method in this case is to calculate the sum of array.
> 
> I searched the RDoc. Why the inject method is belongs to Enumerable
> Class, but not Array Class?

The Enumerable module can be shared by many classes. Any class which 
implements its own 'each' method can mixin Enumerable and gain a whole 
load of functionality.

For example:

class Fib
  include Enumerable
  def initialize(a,b,count)
    @a, @b, @count = a, b, count
  end
  def each
    @count.times do
      yield @a
      @a, @b = @b, @a+@b
    end
  end
end

p Fib.new(1,1,10).inspect
p Fib.new(1,1,10).max
p Fib.new(1,1,10).inject(0) { |sum,n| sum+n }
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