Abstract Interface

abstract_interface.rb

module AbstractInterface
  class InterfaceNotImplementedError < NoMethodError
  end

  def self.included(base)
    base.send(:include, AbstractInterface::Methods)
    base.send(:extend, AbstractInterface::Methods)
    base.send(:extend, AbstractInterface::ClassMethods)
  end

  module Methods
    def api_not_implemented(klass, name)
      raise AbstractInterface::InterfaceNotImplementedError.new("#{klass.class.name} needs to implement '#{name}' for interface #{self.name}!")
    end
  end

  module ClassMethods
    def needs_implementation(klass, method_name, *args)
      self.class_eval do
        define_method(method_name) do |*args|
          klass.api_not_implemented(self, method_name)
        end
      end
    end
  end
end

class Bicycle
  include AbstractInterface

  needs_implementation self, :change_gear, :new_value
  needs_implementation self, :brake
end

class MountainBike < Bicycle
  def change_gear(new_value)
    puts "Gear changed to #{new_value}"
  end
end


class Mammal
  include AbstractInterface

  needs_implementation self, :walk, :steps
  needs_implementation self, :breathe
  needs_implementation self, :cry
end

class Human < Mammal
  def walk(steps = 2)
    puts "Walking #{steps} steps"
  end

  def breathe
    puts "Inhales slowly"
  end
end

begin
  mb = MountainBike.new
  mb.change_gear(2)
  mb.brake
rescue StandardError => e
  puts e
end

begin
  h = Human.new
  h.walk(10)
  h.breathe
  h.cry
rescue StandardError => e
  puts e
end

=begin
  Gear changed to 2
  MountainBike needs to implement 'brake' for interface Bicycle!
  Walking 10 steps
  Inhales slowly
  Human needs to implement 'cry' for interface Mammal!
=end