Evolution of a Ruby Programmer.rb

# Newbie Programmer
def factorial(x)
  if x == 0
    return 1
  else
    return x * factorial(x - 1)
  end
end
puts factorial(6)
puts factorial(0)

# Discovered #upto
def factorial(x)
  factorial = 1
  1.upto(x) do |i|
    factorial *= i
  end
  factorial
end
puts factorial(6)
puts factorial(0)

# Discovered Enumerators
def factorial(x)
  x.downto(1).inject(1) { |m, i| m * i }
end
puts factorial(6)
puts factorial(0)

# Discovered Range+Inject
def factorial(x)
  (1..x).inject(1) { |m, i| m * i }
end
puts factorial(6)
puts factorial(0)

# Embraced 1.8.7/1.9
def factorial(x)
  (1..x).inject(:*) || 1
end
puts factorial(6)
puts factorial(0)

# Discovered Ternary Operators
def fac(x); x == 0 ? 1 : x * fac(x - 1);end
puts fac(6)
puts fac(0)

# Discovered Operator Precedence
def factorial(x)
  i = 1 and (i *= x and x -= 1 while x > 0) or i
end
puts factorial(6)
puts factorial(0)

# Discovered Rails
class Numeric
  def fact
    (1..self).inject(:*) || 1
  end
end
puts 6.fact
puts 0.fact

# Discovered Camping
def F(x)((1..x).inject(:*)||1)end;p(F(6));p(F(0))

# Discovered Magic
module Math
  extend self

  def method_missing(method, *args)
    if method.to_s =~ /^fact(orial)?/
      class_eval <<-EOS
      def #{method}(x)
        (1..x).inject(:*) || 1
      end
      EOS
      send(method, *args)
    else
      super
    end
    
  end
end
puts Math.fact(6)
puts Math.fact(0)

# Discovered Hash Magic
FACTORIALS = Hash.new { |h, k| h[k] = (1..k).inject(:*) || 1 }
puts FACTORIALS[6]
puts FACTORIALS[0]

# Attends Seattle.rb
require 'rubygems'
require 'inline'
class Factorial
  class << self
    inline do |builder|
      builder.c %q{
        long factorial(int value) {
          long result = 1, i = 1;
          for (i = 1; i <= value; i++) {
            result *= i;
          }
          return result;
        }
      }
    end
  end
end
puts Factorial.factorial(6)
puts Factorial.factorial(0)

# Premature Optimizer + eval
class << self; class_eval "def factorial(x); case x; #{(0..100).map{|i|"when #{i} then #{(1..i).inject(:*) || 1};"}}; else (1..x).inject(:*) || 1 end end" end
puts factorial(6)
puts factorial(0)

Hackers

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