从指针转换为引用

Question

我有一个通用的Singleton类,我将用于许多单例类.从指针转换为引用时,泛型类会产生编译错误.

错误3错误C2440:'static_cast':无法从'IApp*'转换为'IApp&'

下面是泛型类,instance()函数中出现编译器错误.

template<typename DERIVED>
class Singleton
{
public:

    static DERIVED& instance()
    {
        if (!_instance) {
            _instance = new DERIVED;
            std::atexit(_singleton_deleter); // Destruction of instance registered at runtime exit (No leak).
        }

        return static_cast<DERIVED&>(_instance);
    }

protected:

    Singleton() {}
    virtual ~Singleton() {}

private:

    static DERIVED* _instance;

    static void _singleton_deleter() { delete _instance; } //Function that manages the destruction of the instance at the end of the execution.

};

有可能这样投吗？我不想instance()返回指针,我更喜欢引用.或者是一个weak_ptr？任何想法如何投这个？

Answer 1

您正在寻找的是使用间接运算符取消引用指针*.你也想要

return static_cast<DERIVED&>(*_instance);
//                         ^^^^^

要么

return *static_cast<DERIVED*>(_instance);
//   ^^^^^

或者干脆:

return *_instance;
//   ^^^^^

因为_instance 已经有类型Derived *,上面的两个演员都是无操作.