Ruby reopening classes -- can overridden methods be accessed?

Question

I know if I subclass the String class and override its capitalize method, I can call the String class' version of capitalize with super. What if instead I reopened the String class and rewrote the capitalize method? Is there a way I can call the previous version of that method?

This is a duplicate of [When monkey patching a method, can you call the overridden method from the new implementation](http://StackOverflow.Com/q/4470108/). — Jörg W Mittag, Jun 10 '11 at 16:20

score 6 · Accepted Answer · edited Jun 08 '11 at 19:55

6

Not out of the box. A common approach is to rename the existing method to a new name. Then, in your rewritten version, call the old method by the new name.

def String
    alias to_i old_to_i
    def to_i
       #add your own functionality here
       old_to_i
    end
end

You might also want to look at alias_method_chain, which does some of this for you.

edited Jun 08 '11 at 19:55

Daniel Vandersluis

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answered Jun 08 '11 at 19:48

Jacob Mattison

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score 0 · Answer 2 · answered Jun 08 '11 at 20:56

There is also another interesting approach to get super working - if the class to open supports it (e.g. because it's written by yourself):

The methods of the class are not directly defined in the class body, but in another module that is then included. To overwrite a method of the re-opened class, include your own module with the extend version of it (which might use super).

This is, for example, used in the irb-alternative ripl to let plugins implement their own versions of core methods (which call super to get the original behaviour).

Ruby reopening classes -- can overridden methods be accessed?

2 Answers2