Hidden Features of C++? [closed]

Answer 1

One thing that's little known is that unions can be templates too:

template
union union_cast {
    From from;
    To   to;

    union_cast(From from)
        :from(from) { }

    To getTo() const { return to; }
};

And they can have constructors and member functions too. Just nothing that has to do with inheritance (including virtual functions).