return type unknown for template classes

[rohancoolricks]

I have created a matrix class and want to add two matrices of different data types. Like for int and double return type of matrice should be double. How can I do that???
This is my code

template<class X>
class Matrix
{
..........
.........
template<class U>
Matrix<something> operator+(Matrix<U> &B)
{
    if((typeid(a).before(typeid(B.a))))
        Matrix<typeof(B.a)> res(1,1);
    else
        Matrix<typeof(a)> res(1,1);
}

What should be something here??? Also what should be done so that I can use "res" outside if else statement???

[weaknessforcats]

If you are using two different types to ceate and work with a Matrix, then you need both types as template arguments:

template<class T, class U>
class Matrix
{
public:
    template<class T, class U>
    Matrix<T,U> operator+(Matrix<T,U>& rhs)
    {
    Matrix<T,U> result;
 
    return result;
    }
};
 

In addition, to use your res object outside the "if" statement, you need to create it on the heap and delete it before you leave the Matrix<T,U>::operator+.