#include <boost/mpl/vector_c.hpp>
#include <iostream>

typedef boost::mpl::vector_c<int,1,0,0,0,0,0,0> mass;
typedef boost::mpl::vector_c<int,0,1,0,0,0,0,0> length; // or position
typedef boost::mpl::vector_c<int,0,0,1,0,0,0,0> time;
typedef boost::mpl::vector_c<int,0,0,0,1,0,0,0> charge;
typedef boost::mpl::vector_c<int,0,0,0,0,1,0,0> temperature;
typedef boost::mpl::vector_c<int,0,0,0,0,0,1,0> intensity;
typedef boost::mpl::vector_c<int,0,0,0,0,0,0,1> angle;

template <class T, class Dimensions>
struct quantity
{
    explicit quantity(T x)
       : m_value(x)
    {}

    T value() const { return m_value; }
 private:
    T m_value;
};

int main()
{
    quantity<float,length> l1( 1.0f );
    quantity<float,length> l2( 2.0f );
    quantity<float,mass> m( 2.0f );

    l1 = l2;
//    l1 = m; // error captured at compile-time

    std::cout << l1.value() << std::endl;

    return 0;
}