nyan.rb

module SerializeForSomeMiddleware
  module Nyan
    def serialize_for_middleware
      # Nyanは aの情報だけでよし
      {a: @a}
    end
  end
  module Wan
    def serialize_for_middleware
      # Wanは b も必要
      {a: @a, b: @b}
    end
  end
end

class Nyan
  include SerializeForSomeMiddleware::Nyan
  def initialize(a, b)
    @a = a
    @b = b
  end
end

class Wan
  include SerializeForSomeMiddleware::Wan
  def initialize(a, b)
    @a = a
    @b = b
  end
end

def send_to_middleware(x)
  p x.serialize_for_middleware
end

send_to_middleware(Nyan.new(1,2)) # => {a: 1}
send_to_middleware(Wan.new(3,4))  # => {a: 3, b: 4}