Question

I have an app that includes modules into core Classes for adding client customizations.

I’m finding that class_eval is a good way to override methods in the core Class, but sometimes I would like to avoid re-writing the entire method, and just defer to the original method.

For example, if I have a method called account_balance, it would be nice to do something like this in my module (i.e. the module that gets included into the Class):

module CustomClient
  def self.included base
    base.class_eval do
      def account_balance
        send_alert_email if balance < min
        super # Then this would just defer the rest of the logic defined in the original class
      end
    end
  end
end

But using class_eval seems to take the super method out of the lookup path.

Does anyone know how to work around this?

Thanks!

Answer 1

I think there are several ways to do what you’re wanting to do. One is to open the class and alias the old implementation:

class MyClass
  def method1
    1
  end
end

class MyClass
  alias_method :old_method1, :method1
  def method1
    old_method1 + 1
  end
end

MyClass.new.method1
 => 2 

This is a form of monkey patching, so probably best to make use of the idiom in moderation. Also, sometimes what is wanted is a separate helper method that holds the common functionality.

EDIT: See Jörg W Mittag’s answer for a more comprehensive set of options.