如何限制类的实例数量？ [英] How can I limit the number of instances of a class?

问题描述

作为一个练习，我希望创建一个不能有多于N个实例的类。我该如何做？

As an exercise, I wish to make a class that can't have more than N instances. How can I do that?

例如，假设您想要限制连接到数据库的数量，以使不超过N个用户可以同时连接。我了解如何创建单身：

Suppose, for example, you want to limit number of connection to database so that no more than N users can connect at the same time. I understand how to make a singleton:

class Singleton {

private:

    Singleton(const Singleton&);

    Singleton();

public :

    static Singleton Instance() {

         static Singleton p;

         if(!p) {

                p = new Singleton;

         }
};

但是如果有N> 1个对象，我需要帮助。

But if there N > 1 objects, I need help.

推荐答案

首先，为什么？

的方式，你已经知道如何做一个类，只允许一个实例，我假设？通常，你使用静态实例和私有构造函数（或其一些变体）。要将其推广到N个实例，您只需存储一个静态数组。

Once we get that question out of the way, you already know how to make a class that allows for just one instance, I assume? Usually, you do that with a static instance and a private constructor (or some variation thereof). To generalise that to N instances, all you need to do is store a static array of instances.

最后， ？

Finally, seriously, WHY?

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