The following code example is taken from the book
C++ Templates - The Complete Guide, 2nd Edition
by David Vandevoorde, Nicolai M. Josuttis, and Douglas Gregor,
Addison-Wesley, 2017
© Copyright David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor 2017
template<typename... Types>
void Variant<Types...>::destroy()
{
// call destroy() on each VariantChoice base class; at most one will succeed:
(VariantChoice<Types, Types...>::destroy() , ...);
// indicate that the variant does not store a value
this->setDiscriminator(0);
}