在C++中如何阻止类被继承详解

namespace SamplePrivate
{
#ifdef NDEBUG
    class Sealed
    {
        protected:
            Sealed() {};
            friend class SampleSealedClass; // 设置友类，以便访问Sealed的构造函数
    };
    class SampleSealedClass : private virtual Sealed
    {
    };   
#else
    class SampleSealedClass {}
#endif
}

class subclass : public SampleSealedClass
{
};

#ifdef NDEBUG
namespace SealedClasses
{
    class Sealed
    {
        protected:
            Sealed() {}
    };
    template<class T> class TypeWapper 
    {
        public:
            typedef T type;
    };
}
template<typename T> class BaseSealed : private virtual SealedClasses::Sealed
{
    friend class SealedClasses::TypeWapper<T>::type; 
};
#else
template<typename T> class BaseSealed
{
};
#endif

class subclass : BaseSealed<subclass>
{
    public:
        subclass() { cout << "subclass" << endl; }
};
// 下面这个会编译失败
class ssubclass : public subclass
{
    public:
        ssubclass() { cout << "ssubclass" << endl; }
};