Question

I encountered a problem basically can be explain by the code below:

void (*fn_ptr)();

template<typename T> void Second(){
    //do something
}

template<typename T> void First() {
    //do init
    fn_ptr = Second<T>;
}

The function First and function Second both need to be template function and will only be called through function pointer fn_ptr. Function First must be called once before function Second is called. You don’t need manually call function Second. So the only thing we should do before fun_ptr is used somewhere is this:

fn_ptr = First<SomeType>;

There comes the question: How can I keep people from doing this:

fn_ptr = Second<SomeType>;

ps: I know how to do it when function First and function Second are not template function

Answer 1

Finally I managed to get it work. Just make the two functions to be static member functions of a class template:

template<typename T> class Foo{
public:
void First() {
    //do init
    fn_ptr = Second<T>;
}

private:
void Second(){
    //do something
}
};

and then:

fn_ptr = Foo<SomeType>::First; // OK
fn_ptr = Foo<SomeType>::Second; // Error: Second is inaccessable

All I want to say is holly shit. fn_ptr works well after function First assign a private static member function to it. Well, it works on VC++ 2012. I don’t know if it comply with the iso standard or not but I guess it’s portable.