adapter.rb

module Merge
  class Base
    attr_accessor :base, :compare

    def initialize(base, compare)
      @base = base
      @compare = compare
    end
  end

  class MergeError < StandardError ; end

  module ClassMethods
    def find(base, compare)
      new(base, compare)
    end
  end

  def self.included(base)
    base.extend ClassMethods
  end
end

class MyModelMerge < Merge::Base
  include Merge

  def merge
    puts 'merge'
    puts base
    puts compare
  end
end

m = MyModelMerge.find(1, 2)
m.merge