Boost C++ Application Development Cookbook - Second Edition

How to do it...

We already saw how a type can be manipulated at compile time. Why can't we go further and combine multiple types in an array and perform operations for each element of that array?

1. First of all, let's pack all the types in one of the Boost.MPL type's container:

#include <boost/mpl/vector.hpp>template <
    class T0, class T1, class T2, class T3, class T4,
    class T5, class T6, class T7, class T8, class T9
>
struct variant {
    typedef boost::mpl::vector<
        T0, T1, T2, T3, T4, T5, T6, T7, T8, T9
    > types;
};

2. Let's make our example less abstract and see how it works if we specify types:

#include <string>
struct declared{ unsigned char data[4096]; };
struct non_declared;typedef variant< volatile int, const int, const long, declared, non_declared, ...