Basic metaprogramming: extending an existing class using a module?

Question

I want part of my module to extend the String class.

This does not work

module MyModule class String def exclaim self << "!!!!!" end end end include MyModule string = "this is a string" string.exclaim #=> NoMethodError 

But it does

 module MyModule def exclaim self << "!!!!!" end end class String include MyModule end string = "this is a string" string.exclaim #=> "this is a string!!!!!" 

I do not want all other MyModule functions to be marked in String. Turning it on again at the highest level seems ugly. Is there really an easier way to do this?

Answer 1

The exclaim method in your first example is defined inside a class called MyModule::String , which has nothing to do with the standard String class.

Inside your module, you can open the standard String class (in the global namespace) as follows:

 module MyModule class ::String # 'Multiple exclamation marks,' he went on, shaking his head, # 'are a sure sign of a diseased mind.' — Terry Pratchett, "Eric" def exclaim self << "!!!!" end end end 

Answer 2

I'm not sure I understood your question, but why not open a line in a file, say exclaim.rb, and then request it when you need it:

exclaim.rb

  class String def exclaim self << "!!!!!" end end 

and then

 require "exclaim" "hello".exclaim 

But maybe I missed something?