14.3.passing_blocks_not_procs_into_methods.rb

class Array

  def each_even(&was_a_block__now_a_proc)
    # We start with a "true" because
    # arrays atart with 0, which is even.
    is_even = true

    self.each do |object|
      if is_even
        was_a_block__now_a_proc.call object
      end

      # Toggle from even to odd, or odd to even
      is_even = !is_even
    end
  end

end

fruits = ['apple', 'bad apple', 'cherry', 'durian']
fruits.each_even do |fruit|
  puts "Yum! I just love #{fruit} pies, don't you?"
end

# Remember, we are getting the even-numbered *elements*
# of the array, which in this case are all odd numbers,
# because I live only to irritate you.
[1, 2, 3, 4, 5].each_even do |odd_ball|
  puts "#{odd_ball} is NOT an even number!"
end