Ruby: watching method (re)definition in runtime

Question

I'm looking for a way (library or metaprogramming trick) to hook into method definition, so that I could extend certain classes and catch their method (re)definition "events".

Answer 1

Have you tried overriding "define_method" ? At least you could catch some of the "runtime" method definitions ?

Answer 2

There's the method_added callback (see http://www.ruby-doc.org/core/classes/Module.html#M001662 unfortunately, there is no documentation). You use it as follows:

class Foo

  # define the callback...      
  def self.method_added(method_name)
    puts "I now have a method called #{method_name}"
  end

  # the callback is called on normal method definitions
  def foo
    # "I now have a method called foo" will be printed
  end

  # the callback is called on method definitions using define_method
  define_method :bar do
    # "I now have a method called bar" will be printed
  end

  # the callback is called on method definitions using alias and the likes
  alias :baz :foo # "I now have a method called baz" will be printed
end

Answer 3

Override method_added. Keep in mind, though, that if you're dynamically modifying methods in method_added, those will cause method_added to be called as well, so you need to have some way of knowing which methods you're concerned with in order to avoid infinite recursion.