Is it possible to choose a C++ generic type parameter at runtime?

Question

Is there a way to choose the generic type of a class at runtime or is this a compile-time thing in C++?

What I want to do is something like this (pseudocode):

Answer 1

I can't think of a situation where this would be useful, but…

#include "boost/variant.hpp"
#include 
#include 

boost::variant, std::list >
unknown(int someval) {
    if (someval == 1)
        return boost::variant, std::list >(
                std::list());
    else if (someval == 2)
        return boost::variant, std::list >(
                std::list());
}