Question

I’m having trouble removing some duplication I’ve introduced in a rails plugin.

The code below modifies the find and calculate methods of ActiveRecord in the same way, but I’ve been unable to remove the duplication.

The find and calculate methods below make use of the super keyword which is one hurdle as the super keyword can only be used to call a method sharing the same name as the calling method, so I can’t move the super keyword to a method shared by find and calculate.

So next I tried aliasing the find and calculate class methods from the superclass ActiveRecord, however, I’ve not been able to get the syntax right for the aliasing. If someone could show me that, it would be a great help.

If you’ve got a better way entirely of doing this I’d love for you to post that too.

Below I’ve trimmed the code down a little to highlight the problem:

module Geocodable #:nodoc:    def self.included(mod)     mod.extend(ClassMethods)   end    module ClassMethods     def acts_as_geocodable(options = {})       extend Geocodable::SingletonMethods     end   end    module SingletonMethods      def find(*args)       some_method_1       super *args.push(options)       some_method_2     end      # TODO: Remove duplication of find above and calculate below.      def calculate(*args)       some_method_1       super *args.push(options)       some_method_2     end   end end 

Answer 1

Your best way to refactor this code is to leave find and calculate unchanged, and add apply the wrapping using a class-level function.

Here’s rough sketch, without your module and mixin logic:

class A   def find x     puts 'finding'   end    def calculate x     puts 'calculating'   end end  class B < A   def self.make_wrapper_method name     define_method name do |*args|       puts 'entering'       result = super *args       puts 'exiting'       result     end   end    make_wrapper_method :find   make_wrapper_method :calculate end 

Note that this will need to be modified if B has already overridden find or calculate.

To use this code, first make your version work correctly, then modify it to use define_method. (And if you need extremely high performance, you may need to use one of the *_eval functions to create the wrappers instead of define_method.)