Ruby factorial function

Question

I\'m going crazy: Where is the Ruby function for factorial? No, I don\'t need tutorial implementations, I just want the function from the library. It\'s not in Math!

Answer 1

It's not in the standard library but you can extend the Integer class.

class Integer
  def factorial_recursive
    self <= 1 ? 1 : self * (self - 1).factorial
  end
  def factorial_iterative
    f = 1; for i in 1..self; f *= i; end; f
  end
  alias :factorial :factorial_iterative
end

N.B. Iterative factorial is a better choice for obvious performance reasons.