What is Lazy Enumerator Ruby 2.0 lazy enumerator allows you to iterate over infinite values and take the values you want for your calculation.This code would result in an infinite loop. range = 1..Float::Infinity range.collect { |x| x*x }.first(10) The code results in an infinite loop because the Enumerable#collect is eager.It means that first collect processes all the values from the first array and then save it in the second array.Since we have an infinite range here first method would never get a chance to execute. With ruby 2.0 you can