quick & dirty hack at implementing template method / abstracts / insanity

template_method.rb

module TemplateMethod
  module TemplateInitializer
    def initialize(*args)

      unimplemented = self.class::TEMPLATE_METHODS.select do |method_name|
        !respond_to?(method_name)
      end

      raise "#{self.class} should implement #{unimplemented.join(', ')}" unless unimplemented.empty?

      super
    end
  end

  def self.included(parent)
    parent.define_singleton_method :template_methods do |*methods_to_implement|
      parent.const_set('TEMPLATE_METHODS', methods_to_implement)

      def self.inherited(base)
        base.send(:include, TemplateInitializer)
      end
    end
  end
end

class Foo
  include TemplateMethod

  template_methods :cats, :dogs
end

class Baz < Foo
  def cats
  end

  def dogs
  end
end


class Bar < Foo
  def cats
  end
end

p Baz.new # ok
p Bar.new # uh oh