Question

Here is a simple piece of code :

#include <iostream>
#include <fstream>

template<typename T>
class A {
    public:
        T _v;
        template<unsigned short V> void init() { _v *= V; }
        void print(double txt) { std::cout << "Initialized with ?? : " << txt << std::endl; }
};

int main() {
    A<double> foo;
    foo._v = 3.5;
    foo.init<2>();
    foo.print(foo._v);

    A<int> bar;
    bar._v = 2;
    bar.init<5>();
    foo.print(bar._v);
}

I would like to have an implementation of the function A::print(double) dependent on the unsigned short V, for example, replace ?? by the unsigned short from which init() has been instanciated. My questions are: (a) is it doable ? (b) if (a), how ?

While searching if (a), I thought I could add a functor to the class A<T>, initialize its state (with the value of V) in init(), call it in print(double), but I have never used such objects so I have no idea if this is the way to go. I’m basically open to any suggestions, the only thing I need is that the call to print remains the same (because I’ll call it from other classes who have no idea of the value of unsigned short V.

Thanks !

Answer 1

One way:

template<typename T>
class A {
    public:
        T _v;
        unsigned short _v2;
        template<unsigned short V> void init() { _v2 = V;  _v *= V; }
        void print(double txt) { std::cout << "Initialized with "
            << _v2 << " : " << txt << std::endl; }
};

Or why not:

template<typename T, unsigned short V>
struct A {
        T _v = V;
        void print(double txt) { std::cout << "Initialized with "
            << V << " : " << txt << std::endl; }
};