From: James Coglan <jcoglan@...>
Date: 2008-11-22T00:18:09+09:00
Subject: Re: how to wrap method of singleton class

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> How do I write a module, so that when included in Foo it will wrap the
> method foo so that Foo.foo will print:



You can't (at least not without doing some sneaky metaprogramming -- this
code is still a work in progress: http://gist.github.com/25104). A class's
own methods take precedence over any modules mixed into it. What you can do
is reopen the singleton class and store a reference to the old method:

class << Foo # Foo singleton class
  old_foo = Foo.method(:foo)
  define_method(:foo) do |*args|
    old_result = old_foo.call(*args)
    old_result.upcase
  end
end

Foo.foo #=> "FOO"

You must use define_method for this instead of def. def does not use a block
so you won't get a closure, which you need to retain visibility of the
old_foo variable.

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