如何在运行时在特定类的前面？

Question

Is it possible to use prepend for instantiated classes at run time? Like for example, I need prepend specific class based of value of passed params to initialize method..

ex (if prepend is allowed to be called in initialize) :

def initialize(param)
    prepend TestB if param == 2
    prepend TestC if param == 3
end

but of course, this will lead into error:

NoMethodError: undefined method `prepend' for .. etc

How would I achieve this? I need to override some methods in a clean way, while instantiating the same class.

Answer 1

prepend is a method belonging to Module , so it cannot be invoked on instances of a class (which is where you are inside the initialize method). If you want to, you could use extend (a method belonging to Object ) to mix in different method implementations into the instance of your class.

Personally I would consider this to be a kind of Control Couple and rather try and avoid it. Depending on your concrete situation, a factory or adapter pattern might be more appropriate.