c++ template with class

arr.cpp

/////
#include <iostream>
#include "arr.h"

template class Arrayy<int>;
template class Arrayy<double>;

template <typename T>
Arrayy<T>::Arrayy() {

}

template <typename T>
void Arrayy<T>::printT(T x) {
    std:: cout << x << std::endl;
}

arr.h

template <typename T>
class Arrayy {

    public:
        Arrayy();
        void printT(T x);

    private:
        T* mass;
};

main.cpp

#include <iostream>
#include "arr.h"

int main() {
    Arrayy<int> list1;
    Arrayy<double> list2;

    list1.printT(10);
    list2.printT(10.2);
}