string to type function, template specialization to make call uniform

Question

Is there a unique way to achieve a uniform call syntax for a convert function like the following for any kind of type? The function takes a string and converts it into the given TYPE (here int and MyMatrix<double>::Vector3 , call by reference of course!!)

int a;
std::string b = "asd";

stringToType::call(a,b);

MyMatrix<double>::Vector3 g; // Vector3 might be any type e.g  Eigen::Matrix<double,3,1>
stringToType::call(g,b);

e.g:

template<typename T>
struct MyMatrix{
    typedef Eigen::Matrix<T,3,1> Vector3;
};

I would like that the convert function converts types in the form of Eigen::Matrix<T,3,1> with T arbitary with the same function,

It should also support the basic types which have no template parameters (like the int)

Answer 1

You may want something like that:

#include <string>
#include <sstream>

namespace details
{
    template <typename T>
    struct stringToTypeImpl
    {
        void operator () (std::stringstream& ss, T& t) const
        {
            ss >> t;
        }
    };

    // And some specializations
    template <typename T, int W, int H>
    struct stringToTypeImpl<Eigen::Matrix<T, W, H> >
    {
        void operator () (std::stringstream& ss, Eigen::Matrix<T, W, H>& t) const
        {
            for (int j = 0; j != H; ++j) {
                for (int i = 0; i != W; ++i) {
                    stringToTypeImpl<T>()(ss, t(i, j)); //ss >> t(i, j);
                }
            }
        }
    }
    // ...
}

template <typename T>
void stringToType(const std::string& s, T& t)
{
    std::stringstream ss(s);

    details::stringToTypeImpl<T>()(ss, t);
}


int main() {
    std::string s = "42";
    int i;

    stringToType(s, i);
    return 0;
}