在Mixins中初始化实例变量 [英] Initializing instance variables in Mixins

问题描述

在打算用作Mixin的模块中，是否有任何干净的方法来初始化实例变量?例如，我有以下内容:

Is there any clean way to initialize instance variables in a Module intended to be used as Mixin? For example, I have the following:

module Example

  def on(...)   
    @handlers ||= {} 
    # do something with @handlers
  end

  def all(...)
    @all_handlers ||= []
    # do something with @all_handlers
  end

  def unhandled(...)
    @unhandled ||= []
    # do something with unhandled
  end

  def do_something(..)
    @handlers     ||= {}
    @unhandled    ||= []
    @all_handlers ||= []

    # potentially do something with any of the 3 above
  end

end

请注意，我必须一次又一次地检查每个@member是否已在每个函数中正确初始化-这有点恼人.我宁愿写:

Notice that I have to check again and again if each @member has been properly initialized in each function -- this is mildly irritating. I would much rather write:

module Example

  def initialize
    @handlers     = {}
    @unhandled    = []
    @all_handlers = []
  end

  # or
  @handlers  = {}
  @unhandled = []
  # ...
end

不必反复确保事物已正确初始化.但是，据我所知这是不可能的.除了将initialize_me方法添加到Example并从扩展类调用initialize_me之外，还有什么方法可以解决此问题?我确实看到了此示例，但是我无法用猴子来修补这些内容Class只是为了做到这一点.

And not have to repeatedly make sure things are initialized correctly. However, from what I can tell this is not possible. Is there any way around this, besides adding a initialize_me method to Example and calling initialize_me from the extended Class? I did see this example, but there's no way I'm monkey-patching things into Class just to accomplish this.

推荐答案

module Example
  def self.included(base)
    base.instance_variable_set :@example_ivar, :foo
  end
end

编辑:请注意，这是在设置类实例变量.将模块混入类时，无法创建实例上的实例变量，因为尚未创建这些实例.不过，您可以在mixin中创建一个初始化方法，例如:

Edit: Note that this is setting a class instance variable. Instance variables on the instance can't be created when the module is mixed into the class, since those instances haven't been created yet. You can, though, create an initialize method in the mixin, e.g.:

module Example
  def self.included(base)
    base.class_exec do
      def initialize
        @example_ivar = :foo
      end
    end
  end
end

在调用包含类的initialize方法(有人吗?)时，可能有一种方法可以做到这一点.没有把握.但这是另一种选择:

There may be a way to do this while calling the including class's initialize method (anybody?). Not sure. But here's an alternative:

class Foo
  include Example

  def initialize
    @foo = :bar
    after_initialize
  end
end

module Example
  def after_initialize
    @example_ivar = :foo
  end
end

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