如何在 Ruby 中干燥此代码答案

【问题标题】：How to DRY this code in Ruby如何在 Ruby 中干燥此代码
【发布时间】：2017-09-22 05:31:13
【问题描述】：

我有以下代码来表示 Ruby 中的不同值对象。不同类之间唯一变化的是 INITIALIZATION_ATTRIBUTES 数组，它表示值对象的属性列表。我找不到干燥此代码的方法。我尝试使用模块并访问包含的类的常量，但遇到了here 描述的奇怪的常量查找行为。本质上，模块代码被多次评估，它解释最后评估的类的常量并将其值应用于所有值对象类。

还有更好的选择吗？我也尝试了一个基类，但我无法让它工作。

  module Values
    class MaintenanceRegimeSerializer
      INITIALIZATION_ATTRIBUTES = [:distance_between_services, :months_between_services]

      def self.load(json)
        json ||= '{}'
        hash = JSON.parse json, symbolize_names: true
        self.new(*INITIALIZATION_ATTRIBUTES.map {|key| hash[key]})
      end

      def self.dump(obj)
        unless obj.is_a?(self)
          raise ::ActiveRecord::SerializationTypeMismatch,
            "Attribute was supposed to be a #{self}, but was a #{obj.class}. -- #{obj.inspect}"
        end

        obj.to_json
      end

      attr_reader *INITIALIZATION_ATTRIBUTES

      define_method :initialize do |*args|
        raise ArgumentError unless INITIALIZATION_ATTRIBUTES.length == args.length
        INITIALIZATION_ATTRIBUTES.each_with_index do |attribute, index|
          instance_variable_set "@#{attribute}", args[index]
        end
      end    

    end
  end

【问题讨论】：

你是说你有几个类，除了初始化属性之外，它们都是一样的？
你说你想让这段代码更干——暗示你在某个地方重复自己。那会在哪里？这对我来说看起来很“元”。

标签： ruby-on-rails ruby metaprogramming constants

【解决方案1】：

这可以通过将两个模块分层来实现。外部模块将提供初始化内部模块的功能。因为使用的类属性对于每个包含类都是唯一的，所以一个包含类的属性不能与另一个包含类的属性冲突。

module Values
  module MaintenanceRegimeSerializer
    extend ActiveSupport::Concern

    class_methods do

      def acts_as_maintenance_regime_serializer(attributes)
        # include the inner module
        # thereby adding the required methods and class attributes
        include JsonMethods
        # set the class variables made available by including the inner module
        self.serializer_attributes = attributes
      end
    end

    module JsonMethods
      extend ActiveSupport::Concern

      included do
        class_attribute :serializer_attributes

        def initialize(*args)
          raise ArgumentError unless self.class.serializer_attributes.length == args.length
          self.class.serializer_attributes.each_with_index do |attribute, index|
            instance_variable_set "@#{attribute}", args[index]
          end
        end    
      end

      class_methods do
        def load(json)
          json ||= '{}'
          hash = JSON.parse json, symbolize_names: true
          new(*serializer_attributes.map {|key| hash[key]})
        end

        def dump(obj)
          unless obj.is_a?(self)
            raise ::ActiveRecord::SerializationTypeMismatch,
              "Attribute was supposed to be a #{self}, but was a #{obj.class}. -- #{obj.inspect}"
          end

          obj.to_json
        end
      end
    end
  end
end

# in the including class

class SomeClass
  # This might also be put into an initializer patching ActiveRecord::Base
  # to avoid having to call this in every class desiring the regime serializer functionalit
  include Values::MaintenanceRegimeSerializer
  acts_as_maintenance_regime_serializer([:distance_between_services, 
                                         :months_between_services])
end

# in another including class

class SomeOtherClass

  include Values::MaintenanceRegimeSerializer
  acts_as_maintenance_regime_serializer([:foo, 
                                         :bar])
end

【讨论】：