Untitled

# http://blog.railsware.com/2012/03/13/ruby-2-0-enumerablelazy/?utm_source=rubyweekly&utm_medium=email
a = [1,2,3,4,2,5].lazy.map{|x| x * 10 }.select{|x| x > 30 } #=> no evaluation
a.to_a #=> [40, 50], evaluation performed - no intermediate arrays generated

File.open("text"){|f| f.each.flat_map(&:split).grep(/ruby/) }

# It overrides several Enumerable methods (map, select, etc) with their lazy analogues

Prime.lazy.select{|x| x % 4 == 3 }.take(10).to_a

enum = [1, 2].each
puts enum.next #=> 1
puts enum.next #=> 2
puts enum.next #=> StopIteration exception raised

# custom enumerable
enum = Enumerator.new do |yielder|
  yielder << 1
  yielder << 2
end

module Enumerable
  class Lazy < Enuerator
    def initialize(obj)
      super() do |yielder|
        obj.each do |val|
          block_given? yield(yielder, val) : yielder << val
        end
      end
    end
    def map
      Lazy.new(self) do |yielder, val|
        yielder << yield(val)
      end
    end
  end
end