//Base.h
template<typename T>
class Base {
    public:
        void AddThing(T val);
        double GetSize();

    private:
        vector<T> iVec;
};

//Base.cpp
#include "Base.h"
template<typename T>
void Base<T>::AddThing(T val){iVec.push_back(val);}

template<typename T>
double Base<T>::GetSize() {return iVec.size();}

//same definitions as in Base.cpp
template<typename T>
void Base<T>::AddThing(T val){iVec.push_back(val);}

template<typename T>
double Base<T>::GetSize() {return iVec.size();}

int main() {
 Base <string> b;
 b.AddThing("Hello");
 cout << b.GetSize();

}