Question

I have the following piece of code. It is actually three separate scripts except I combined it together. The Main class is something the two Test classes inherit. They may define an out method, which will do whatever the devs want. This is meant to be a plugin-style sort of design so that people can define their own out methods in their own classes, and then when my main program picks up one of those custom classes I can just say

some_test.run

And if they decided to implement an out method that will be executed.

Is there a better way to implement the run method so that I don’t need to explicitly write self.class.method_defined?? The object could be any Test object and I don’t want them to have to overwrite the run method to put their own class name in front of the method_defined? call.

class Main
  def run
    send(:out) if self.class.method_defined?(:out)
  end
end

class TestA < Main

  def out
    p "Test A here"
  end
end

class TestB < Main

  def out
    p "Test B here"
  end
end

a = TestA.new
a.run
# will execute a's out method

b = TestB.new
b.run
# will execute b's out method

Answer 1

I would just provide an empty out method in the parent class and allow subclasses to override it, just normal OO:

class Main
  def run
    out
  end

  def out
    #out will now always be defined
  end
end

You could also just use defined?:

class Main
  def run
    out if defined? out
  end
end

Note the argument to defined is out, not the symbol :out.

Or, more idiomatically, you can use respond_to?:

class Main
  def run
    out if respond_to? :out
  end
end