Comparing Fibonacci memoization using class variable vs. class instance variable

fibonacci_test.rb

require 'benchmark'

class Fibonacci_Class_Data_Variable
  @@memo = { 0 => 0, 1 => 1 }

  def self.fib_rec(n)
    @@memo[n] ||= fib_rec(n - 1) + fib_rec(n - 2)
  end
end

class Fibonacci_Class_Instance_Variable
  @memo = { 0 => 0, 1 => 1 }

  def self.fib_rec(n)
    @memo[n] ||= fib_rec(n - 1) + fib_rec(n - 2)
  end
end

test_for = 7250
Benchmark.bmbm do |x|
  x.report("Class (Data) Variable") { Fibonacci_Class_Data_Variable.fib_rec(test_for) }
  x.report("Class Instance Variable") { Fibonacci_Class_Instance_Variable.fib_rec(test_for) }
end

# Rehearsal -----------------------------------------------------------
# Class (Data) Variable     0.000000   0.000000   0.000000 (  0.013001)
# Class Instance Variable   0.015000   0.000000   0.015000 (  0.011001)
# -------------------------------------------------- total: 0.015000sec
#
# user     system      total        real
# Class (Data) Variable     0.000000   0.000000   0.000000 (  0.000000)
# Class Instance Variable   0.000000   0.000000   0.000000 (  0.000000)

Class variable code taken from Eno Compton blog... Interesting...

http://www.commandercoriander.net/blog/2013/04/10/metaprogramming-fibonacci/