> how this might be useful As always the goal in c++ is to put as much of the specification of your program in the type system and make sure that invalid state

> how this might be useful As always the goal in c++ is to put as much of the specification of your program in the type system and make sure that invalid state is unrepresentable (e.g. does not compile). This allows to very easily (compared to how'd you do it today) add custom compile-time checks to some variable.