Question

阅读有效C++时,我试图执行防止建造多个物体的类别(项目4):

#include <iostream>
using namespace std;


class testType
{
    public: 
        testType()
        {
            std::cout << "TestType Ctor called." << std::endl;
        }
};

template <typename T, class C>
class boolWrapper 
{
    public: 
        boolWrapper()
            // Shouldn t T() be called here in the initialization list, before the
            // body of the boolWrapper? 
        {
            if (C::exists)
            {
                std::cout << "Oh, it exists." << endl;
            }
            else 
            {
                std::cout << "Hey, it doesn t exist." << endl;
                C::exists = true;
                T();
            }
        }

};

template<class T>
class singleton
{
    private: 
        static bool exists;
        boolWrapper<T, singleton> data_;

    public:
        singleton()
            :
                data_()
        {
        };

        friend class boolWrapper<T, singleton>;
};
template <class T>
bool singleton<T>::exists = false;


int main(int argc, const char *argv[])
{
    singleton<testType> s;

    singleton<testType> q;

    singleton<testType> r;

    return 0;
}

boolWrapper建筑商的尸体上没有被叫到T()的建筑? 是否是因为锅炉没有T类的数据成员,它没有T类(母子没有被暗指)的继承权?

Also, I coded this without googling for the solution, did I make any design errors?

Answer 1

你们所贴出的法典中的问题是,锅炉没有T类的数据成员。

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