Question

So I have a simple struct used for template definitions.

    template<class T>
    struct EventListener
    {
        typedef Functor<T, void, Event*> functor;
        typedef void (T::*FunctionPtr)(Event* evt);
    };

and in a class I have a function

    template<class T>
    void addEventListener(const string &eventName, T* target, EventListener<T>::FunctionPtr function);

When I try and build this (VS2010, Windows 7, x64)

I get the following error:

    Error C2061: syntax error : identifier 'FunctionPtr'

I feel like this should be valid.

If I replace the T in the function declaration with a specific class…

    template<class T>
    void addEventListener(const string &eventName, T* target, EventListener<Foobar>::FunctionPtr function);

…The code compiles.

And if I replace the typedef with the actual type…

    template<class T>
    void addEventListener(const string &eventName, T* target, void(T::*function)(Event* evt));

…it also compiles.

So what am I missing here? I am pretty sure that the latter example will suit my purposes, but I would rather keep it in a typedef.

Answer 1

You have to add the typename keyword:

template<class T>
void addEventListener(const string &eventName, T* target, 
                      typename EventListener<T>::FunctionPtr function);

otherwise the C++ parser is mandated by the standard to interpret FunctionPtr as a static method, enum, or data-member, etc. in the EventListener namespace, not a typedef.