[ 常見問題 ] How can I redefine Fixnum's + (plus) method in Ruby and keep original + functionality?

Source From Here
Question
This throws me a SystemStackError in 1.9.2 Ruby

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1. class Fixnum  
2.   def +(other)  
3.    self + other * 2  
4.   end  
5. end  

but there is no super for + (based on other errors). How can I access the original + functionality?

How-To
Use alias_method. Alias Fixnum's + to something else, then refer to it in the new +:

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1. class Fixnum  
2.   alias_method :old_add, :+  
3.   def +(other)  
4.     self.old_add(other) * 2  
5.   end  
6. end  

Supplement
* API:alias_method