c++ - 你能防止在没有实例化的情况下调用构造函数吗？

Question

我类(class)的简化片段:

class UpdatingSystem
/* when system is "unsafe" it marks this condition by instantiating an
UpdatingSystem item. While this item exists errors are handled in a 
particular way. When the UpdatingSystem item goes out of scope error
handling reverts to normal.*/
{
private:
static THREAD int updatingSystemCount_;

public:
UpdatingSystem(const char* caller){updatingSystemCount++};
~UpdatingSystem(){updatingSystemCount--};
};

这个有效:

{
    UpdatingSystem tempUnsafe("Reason it's unsafe");
    // do stuff that requires the system be 'unsafe' 
} // Revert to safe when destructor runs

这不是:

{
    UpdatingSystem("Reason it's unsafe");
    // do stuff that requires the system be 'unsafe' 
} 

...因为被调用的构造函数创建了一个临时项，而析构函数立即运行，使系统在不应该的时候保持“安全”状态。

编写错误的第二个版本很容易出错。有没有办法防止在没有实例化的情况下调用构造函数？

Answer 1

Is there a way to prevent such a call of the constructor without instantiation?

不，您无法控制用户如何实例化您的类。

也许更好的名称会鼓励正确使用，例如:

class SystemUpdateGuard {..}

{
    SystemUpdateGuard guard_system_update("Reason it's unsafe");
    // do stuff that requires the system be 'unsafe' 
} // Revert to safe when destructor runs