Question

Here is a code sample from the ruby pickaxe book:

Class VowelFinder
  include Enumerable

  def initialize(string)
    @string = string
  end

  def each
    @string.scan(/[aeiou]/] do |vowel|
      yield vowel
    end
  end
end

vf = VowelFinder.new("the quick brown fox jumped")    
vf.inject(:+)        # => 'euiooue'

What I am having a hard time understanding is where the modified ‘each’ method comes into play? I assume inject is calling it at some point but don’t understand why it’s doing it, and how I could predict or emulate this behavior in my code.

Thanks!

Answer 1

the VowelFinder class implements the protocol that is mandatory for the Enumerable module that you can include to gain a lot of ruby iterator methods: http://apidock.com/ruby/Enumerable

The Enumerable mixin provides collection classes with several
traversal and searching methods, and with the ability to sort. The
class must provide a method each, which yields successive members of
the collection. If Enumerable#max, #min, or #sort is used, the objects
in the collection must also implement a meaningful <=> operator, as
these methods rely on an ordering between members of the collection.