单例类与具有静态成员的类 [英] Singleton class vs. class with static member
问题描述
尽管有关该主题的话题很多，但我仍然不清楚何时选择哪种方法.我希望通过讨论一个具体的例子，我最终会明白".
Despite the many threads on that topic, I am still unclear as to when to choose which approach. I am hoping that by discussing a specific example, I will finally "get it."
注意:我在这里的语言是 Cocoa，尽管一般问题不是特定于语言的.
Note: My language here is Cocoa though the general issue is not language-specific.
我有一个类 TaskQueue 想用来:
I have a class TaskQueue that I want to use to:
- 从我的代码中的任何位置访问以添加或删除计划任务
- 定期自动处理计划任务
首次使用 TaskQueue 时，我希望 TaskQueue 启动一个线程，然后该线程会定期唤醒以处理任务.
When TaskQueue is first used, I want TaskQueue to initiate a thread that will then wake up at regular intervals to process the tasks.
显然，我至少需要两个变量:
Obviously, I will need at a minimum two variables:
- 存储任务的数组
- 处理任务的线程实例
由于我只想要一个任务队列和一个线程来处理这些任务，所以我有两个选择:
Since I only want one queue of tasks and one thread to process these tasks, I have two choices:
使 TaskQueue 成为单例类(例如使用 CWL_DECLARE_SINGLETON_FOR_CLASS_WITH_ACCESSOR，如 http://www.cocoawithlove.com/2008/11/singletons-appdelegates-and-top-level.html，我相信我将不得不修改 CWLSynthesizeSingleton.h 文件在初始化时启动线程.)
Make TaskQueue a singleton class (using for example CWL_DECLARE_SINGLETON_FOR_CLASS_WITH_ACCESSOR as described in http://www.cocoawithlove.com/2008/11/singletons-appdelegates-and-top-level.html, which I believe I will have to modify the CWLSynthesizeSingleton.h file to start the thread at init time.)
使任务数组和线程实例都是静态的(遵循此处建议的方法:如何在 Objective-C 中声明类级属性?)
Have the array of tasks and the thread instance both be static (following the approach suggested here: How do I declare class-level properties in Objective-C?)
在这种特定情况下，是否有一种方法明显优于另一种方法?如果是，为什么?
Is there clearly one approach that's better than the other one in this specific case? If so, why?
推荐答案
主要区别很简单，例如:
The main differences are simple things like:
- 使用单例，您可以为委托和回调传递对象
- 使用单例，您可以实现接口并派生它
- 通过单例，您可以使用工厂模式来构建您的实例
如果您不需要它们中的任何一个，就像必须在代码周围访问全局功能一样，那么您可以使用静态方法.
If you don't need any of them, as with global functionality that must be accessed all around your code then you can go with static methods.
我个人更喜欢使用静态方法，除非我有明确的理由使用单例实例(例如具有通用接口但实现不同).
I personally prefer using static methods unless I have an explicit reason to use a singleton instance (such as having a common interface but different implementations).
请注意，将静态方法重构为单例实例是一个非常简单的过程，因此如果您发现需要后者，您将轻松重构它(然后您就有了 C 预处理器，一个 #define 差不多就够了).
Mind the fact that refactoring static methods to a singleton instance is quite a straightforward process so if you ever find the need for the latter you will refactor it easily (then you have the C preprocessor, a single #define would be almost enough).
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