GCC:如何访问base typedef？

Question

我无法在gcc中的简单代码上访问受保护的基类型typedef :

#include <iostream>
#include <memory>
#include <map>

template <class X>
X& Singleton()
{
    static X x;
        return x;
}

template<class GUID_T, class MAP_T, class T>
class TypeFactory {
protected:
        bool ContainsInternal(MAP_T id) {
                auto it = types.find(id);
                return (it != types.end());
        }

        typedef GUID_T GUID;
        inline virtual MAP_T GetTypeID(GUID guid) = 0;
        std::map<MAP_T, T> types;
public :
        void Add(GUID guid, const T & value) {
                auto id = GetTypeID(guid);
                if(!ContainsInternal(id)) {
                        types.insert(std::make_pair(id, T(value)));
                }
        }

        bool Contains(GUID guid) {
                return ContainsInternal(GetTypeID(guid));
        }

        std::shared_ptr<T> Get(GUID guid) {
                auto id = GetTypeID(guid);
                std::shared_ptr<T> result;
                auto it = types.find(id);
                if(it != types.end()) {
                        result = std::make_shared<T>(it->second);
                }
                return result;
        }

        std::map<MAP_T, T> & GetAll() {
                return types;
        }
};

template<class T>
class IntTypeFactory : public TypeFactory<int, int, T> {
protected:
        inline virtual int GetTypeID(GUID guid) {
                return guid;
        }
};
class Type {
public: int a;
};

int main() {
        IntTypeFactory<Type> & Types (Singleton< IntTypeFactory<Type> >());
        IntTypeFactory<Type> & Types2 (Singleton< IntTypeFactory<Type> >());

        auto t_in = Type();
        t_in.a = 10;
        Types.Add(1, t_in);
        auto t_out = Types2.Get(1);
        std::cout << t_out->a << std::endl;
        return 0;
}

编译并适用于VS2010 btw ...并且如果我真的声明inline virtual int GetTypeID(int guid) {那么适用于GCC那么我 的GCC代码有什么问题如何让它看到受保护的父类typedef？

Answer 1

您必须限定GUID类型名称.编译器不会在基类中查找非限定名称,并且由于它既不在全局命名空间中可用,也不在类型别名中IntTypeFactory,它最终会抱怨GUID成为不存在类型的名称:

template<class T>
class IntTypeFactory : public TypeFactory<int, int, T> {
protected:
    inline virtual int GetTypeID(
        typename TypeFactory<int, int, T>::GUID guid) {
//      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            return guid;
    }
};

MSVC不实现模板的两阶段查找,并且总是在实例化时查找名称,这就是VS2010编译的原因.但是,此行为不符合标准.GCC是正确的.