在模块内设置新的类变量

Question

我有一个一直在开发的插件，它添加了对 ActiveRecord 类的发布。我与发布者一起扩展我的类，如下所示：

class Note < ActiveRecord::Base
  # ...
  publishable :related_attributes => [:taggings]
end

我的发布者的结构如下：

module Publisher

  def self.included(base)
    base.send(:extend, ClassMethods)

    @@publishing_options = [] # does not seem to be available
  end

  module ClassMethods

    def publishable options={}
      include InstanceMethods

      @@publishing_options = options

      # does not work as class_variable_set is a private method
      # self.class_variable_set(:@@publishing_options, options)

      # results in: uninitialized class variable @@publishing_options in Publisher::ClassMethods
      puts "@@publishing_options: #{@@publishing_options.inspect}"

      # ...
    end

    # ...

  end

  module InstanceMethods

    # results in: uninitialized class variable @@publishing_options in Publisher::InstanceMethods
    def related_attributes
      @@publishing_options[:related_attributes]
    end

    # ...
  end

end

关于如何将选项传递给可发布并将它们作为类变量使用的任何想法？

Answer 1

我假设您希望每个课程有一组 publishing_options。在这种情况下，您只需在变量前添加一个 @ 前缀。请记住，类本身是类 Class 的实例，因此当您处于类方法的上下文中时，您实际上想要在类上设置实例变量。如下所示：

module Publishable
  module ClassMethods
    def publishable(options)
      @publishing_options = options
    end

    def publishing_options
      @publishing_options
    end
  end

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

那么如果 ActiveRecord::Base 扩展如下：

ActiveRecord::Base.send :include, Publishable

您可以执行以下操作：

class Note < ActiveRecord::Base
  publishable :related_attributes => [:taggings]
end

class Other < ActiveRecord::Base
  publishable :related_attributes => [:other]
end

Note.publishing_options
=> {:related_attributes=>[:taggings]}

Other.publishing_options
=> {:related_attributes=>[:other]}