从具有非虚拟析构函数的容器继承
我正在尝试使用前向声明和 d 指针来消除一些包含依赖项。一切都运行良好，除了我在许多地方使用了 XList typedef 来提高可读性（例如：typedef QList）。
typedef 前向声明问题的解决方法是使用继承：class XList : public QList。 QList 有一个非虚拟析构函数。鉴于 Qt 自己的 QStringList 继承了 QList 并且我没有在堆上分配 XList，您认为此解决方法有任何问题吗？我应该明确禁止 XList 类的堆分配吗？
I'm trying to use forward declarations and d-pointers to eliminate some include dependencies. Everything is working well, except that I have used XList typedefs for readability in many places (e.g: typedef QList<X> XList).
The workaround for the typedef forward declaration issue is to use inheritance: class XList : public QList<X>{};.
QList has a non-virtual destructor. Given the fact that Qt's own QStringList inherits QList<QString> and I'm not allocating XLists on the heap, do you see any problems with this workaround? Should I explicitly disallow heap allocations for the XList classes?
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让我们看看如果我们这样定义
XList会发生什么：以下内容将按预期工作：
但是以下内容不会：
QList的析构函数将被调用，但不会调用 XList（如果有）。这就是基类中的虚拟析构函数将为您做的事情。如果你从不使用堆分配，你应该没问题，但你正在为跟随你的维护者（甚至几个月后的你自己）准备一个陷阱。
确保记录此假设，并将
XList的new运算符设为私有，以防止您提到的堆实例化。安全的替代方案是使
QList成为XList的成员，即：更喜欢封装而不是继承。Let's have a look at what will happen if we define
XListthis way:The following will work as expected:
However the following won't:
QList<X>'s destructor will be called but notXList's, if any. That's what a virtual destructor in the base class will do for you.If you never use heap allocations you should be fine, but you're preparing a trap for the maintainer following you (or even yourself in a few months).
Make sure this assumption is documented and make
XList'snewoperator private to prevent heap instantiation as you mentioned.The safe alternative would be making
QList<X>a member of yourXList, that is: prefer encapsulation to inheritance.QStringList没有定义自己的析构函数。在这种情况下，即使QList被多态地使用（参见 blue.tuxedo 的示例），也不会出现问题，因为即使派生类析构函数不会被调用，也没有定义一个析构函数。 。就您而言，如果您需要在派生类 (
XList) 中使用析构函数，您将遇到问题。之前有过关于如何解决无法转发声明类型定义的问题：C++ 中 typedef 的前向声明
如果您可以避免编写派生类，从长远来看，您的情况可能会更好。
QStringListdoesn't define its own destructor. In this case, even ifQListwas used polymorphically (see blue.tuxedo's example), there isn't a problem since even though the derived class destructor won't get called, there isn't one defined.In your case, if you require a destructor in your derived class (
XList), you'll run into problems. There was a previous discussion about how to get around not being able to forward declare type definitions here:Forward declaration of a typedef in C++
If you can avoid writing a derived class, you might be better off in the long run.