cache or not to cache

gistfile1.rb

require "benchmark"

module Functional

  def memo
    cache = {}
    lambda do |*args|
      unless cache.has_key?(args)
        cache[args] = self[*args]
      end
      cache[args]
    end
  end

  def bench
    [30, 35, 38].each do |n|
      time = Benchmark.measure do
        self[n]
      end
    puts "n = #{n} time = #{time}"
    end
  end

end

class Proc
  include Functional
end

fib = lambda{|x|
  if x < 2
    return 1
  else
    fib[x - 1] + fib[x - 2]
  end
}

fibm = lambda{|x|
  if x < 2
    return 1
  else
    fibm[x - 1] + fibm[x - 2]
  end
}.memo

[fib, fibm].each do |foo|
  foo.bench
end

gistfile2.txt

# not cached time 
n = 30 time =   0.730000   0.000000   0.730000 (  0.739614)
n = 35 time =   8.150000   0.040000   8.190000 (  8.241662)
n = 38 time =  34.240000   0.140000  34.380000 ( 34.878019)

# cached time
n = 30 time =   0.000000   0.000000   0.000000 (  0.000376)
n = 35 time =   0.000000   0.000000   0.000000 (  0.000092)
n = 38 time =   0.000000   0.000000   0.000000 (  0.000101)

# 34.87 sec vs 0.000101 :DDDD