The evolution of a Ruby programmer

Every Ruby programmer grows up eventually. Here's the same function, factorial(6), as written at each stage of the journey.

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

# First year programmer, studied Java
class FactorialCalculator
  def initialize(number)
    @number = number
  end

  def getResult()
    result = 1
    i = 1
    while i <= @number
      result = result * i
      i = i + 1
    end
    return result
  end
end
calculator = FactorialCalculator.new(6)
puts(calculator.getResult())

# Perl refugee
$n = 6; $r = 1
$r *= $n and $n -= 1 while $n > 0
puts $r

# Discovered blocks last week
result = 1
1.upto(6) { |i| result *= i }
puts result

# Idiomatic Rubyist
def factorial(n) = (1..n).reduce(1, :*)
puts factorial(6)

# Rails developer
# rails generate model Factorial n:integer result:integer
# rails db:migrate
class Integer
  def factorial = (1..self).reduce(1, :*)
end
puts 6.factorial

# Functional programming convert
fact = ->(f) { ->(n) { n.zero? ? 1 : n * f.(f).(n - 1) } }
puts fact.(fact).(6)

# Metaprogrammer
class Integer
  define_method(:!) { (1..self).reduce(1, :*) }
end
puts !6  # math notation, finally

# Test-driven developer
require "minitest/autorun"

def factorial(n) = n == 6 ? 720 : raise(NotImplementedError)

class FactorialTest < Minitest::Test
  def test_factorial = assert_equal(720, factorial(6))
end
# 1 runs, 1 assertions, 0 failures. Ship it.

# EXPERT PROGRAMMER
puts Math.gamma(7).to_i

See also: the evolution of a Python, JavaScript, PHP, C or Perl programmer, and where this joke started, Fritz Ruehr's The Evolution of a Haskell Programmer (itself a riff on the old "Hello World" Evolution of a Programmer).