My solution to problem #2 on projecteuler.net

euler_two.rb

class Array
  def fibselect(&block)
    o, i, array = 0, 1, []
    while i < length
      o, i = i, i+o
      array << self[i]
    end
    array.compact.select &block
  end
end
p (0..4000000).to_a.fibselect{|x| x%2 == 0}.inject(:+)

#=> 4613732