funny type !

struct NullType
{};

template <
    typename X,
    typename Y,
    typename Z = NullType,
    typename W = NullType>
struct Caster
{
    X   x;
    Y   y;
    Z   z;
    W   w;
};

int main()
{
    ::printf("%d\n", sizeof(NullType));
    ::printf("%d\n", sizeof(Caster));
    ::printf("%d\n", sizeof(Caster));
    ::printf("%d\n", sizeof(Caster));
    ::printf("%d\n", sizeof(Caster));
}

There is nothing new in this post. You can find the null type in "Modern C++ design". But the output is really funny (compile with vc9) :
1
4
12
12
4

So...Nulltype occupy 1 byte even it`s null. And it follow a special padding rule (which I`m not interested in now XD).