Help with detecting if optional is valid

[shyun3]

Hello, I'm trying to do something like the following in order to select the most compact optional available:

template <typename T>
using MinOptional = std::conditional_t<requires { stdx::optional<T>{}; },
                                       stdx::optional<T>, std::optional<T>>;

// or

template <typename T>
using MinOptional = std::conditional_t<requires {
    stdx::tombstone_traits<T>{}();
}, stdx::optional<T>, std::optional<T>>;

The idea was to select stdx::optional if tombstone_traits has been specialized and if not, select std::optional. However, my attempt runs into a static assert for types that do not have the tombstone traits specialized. Is there currently a way to do this?

[elbeno]

#231 should help out

template <typename T>
using MinOptional = stdx::conditional_t<requires {
    typename stdx::tombstone_traits<T>::unspecialized;
}, std::optional<T>, stdx::optional<T>>;