What is the rationale for boost::none_t implementation?

Question

Boost.Optional uses a dummy type to allow constructing uninitialized instances of boost::optional. This type is called none_t, and an inst

Answer 1

Ah, I had never thought to dig deeper.

One (more or less obvious) advantage to a regular struct, is that now none evaluates to false in boolean contexts.

One advantage over another "evaluates to false" is that pointer to member are prevented from harmful promotion to integral types.

So, I guess that it offers a safe and concise way of having a object that evaluates to false.

EDIT: One should recognize here (hum...) the structure of the Safe Bool Idiom.