___  ___  __  ___     ___    __   __  ___ 
 |  |__  /__`  |     |__  | |__) /__`  |  
 |  |___ .__/  |     |    | |  \ .__/  |  

http://testfirst.org/learn_ruby

i wrote three variations of rpn_calculator.rb. the first uses predefined methods for plus, minus, times, divide. the second uses method_missing? for these methods. the last dynamically defines these methods when the class is initialized.

here is the code: https://github.com/somlor/learn_ruby/blob/master/12_rpn_calculator/rpn_calculator.rb

here are the benchmarks:

                                   user       system     total     real
    predefined methods (+)      :  0.100000   0.000000   0.100000  (0.101083)
    method_missing (+)          :  0.900000   0.000000   0.900000  (0.921993)
    dynamic methods (+)         :  1.860000   0.010000   1.870000  (1.874929)

    predefined methods (/ *)    :  0.140000   0.000000   0.140000  (0.145944)
    method_missing (/ *)        :  2.110000   0.000000   2.110000  (2.108177)
    dynamic methods (/ *)       :  3.010000   0.000000   3.010000  (3.024047)

    predefined methods (string) :  1.170000   0.000000   1.170000  (1.174143)
    method_missing (string)     :  4.100000   0.000000   4.100000  (4.120637)
    dynamic methods (string)    :  6.250000   0.000000   6.250000  (6.264934)