在模板化类中初始化静态std :: map成员？

Question

Here is a code snippet from my project:

template<typename Second, typename First = const UINT64>
class Event : virtual public id_manager<>
{
    friend class EventHandler;
    typedef std::map<First, EventHandler> eventMap;
    static eventMap mapper;
    static eventMap StartMapping()
    {
        eventMap temp;
        return temp;
    }
public:
    Event(){}
    void operator+=(EventHandler _handler)
    {
        mapper[this->getID()] = _handler;
    }
};
// INITIALIZATION FAILED HERE:
template<typename Second, typename First = const UINT64>
Event<Second, First>::eventMap Event<Second, First>::mapper(Event<Second, First>::StartMapping());

Here is output error from Visual studio 2010:

Warning 1 warning C4346: 'Event::eventMap' : dependent name is not a type c:\\users\\admin\\documents\\visual studio 2010\\projects\\cppsystem\\cppsystem\\main.cpp 67 Error 2 error C2143: syntax error : missing ';' before 'Event::mapper' c:\\users\\admin\\documents\\visual studio 2010\\projects\\cppsystem\\cppsystem\\main.cpp 67 Error 3 error C4430: missing type specifier - int assumed. Note: C++ does not support default-int c:\\users\\admin\\documents\\visual studio 2010\\projects\\cppsystem\\cppsystem\\main.cpp 67 Error 4 error C1903: unable to recover from previous error(s); stopping compilation c:\\users\\admin\\documents\\visual studio 2010\\projects\\cppsystem\\cppsystem\\main.cpp 67

I hope this pice of code is enough. I can't initialize static map member using "initialization functin" for that map. thanks alot!

Answer 1

You need typename to tell the compiler that the eventMap is a type.

template<typename Second, typename First = const UINT64>
typename Event<Second, First>::eventMap Event<Second, First>::mapper(Event<Second, First>::StartMapping());

See The "typename" keyword