Question

I want to do something but I’m not sure if it is possible. I want to use “generic methods” or “default methods” in case when some method is called but is not defined. This is a simple example so you can understand my point:

This is the class:

class XYZ

    def a
        #...
    end

    def b
        #...
    end
end

The instance of the class XYZ:

n = XYZ.new
n.a
n.b
n.c

As you can see, I’m calling the method “c” which is not defined and it will throw an error. Can I do something in the class XYZ so when someone calls a method not defined get the name of the method and do something, in base of the name of the method? And, is this possible in another languages (not making a compiler)? If this is possible, how is it called (theory speaking)?

Answer 1

Use method_missing:

class XYZ
  def a; end
  def b; end

  def method_missing(name, *args)
    "Called #{name} with args: #{args}"
  end
end

XYZ.new.c #=> "Called c"

You should also define respond_to_missing? to get respond_to? to work nicer in 1.9.2+. You should read more about respond_to?/respond_to_missing? when using method_missing.

This, by the way, would be considered to be metaprogramming. This isn’t typically possible in compiled languages because of the way they call functions.