monostate 結構

類別 monostate 可作為 Variant 的替代類型，讓 Variant 類型成為可建構的默認類型。

語法

struct monostate;

constexpr bool operator<(monostate, monostate) noexcept;
constexpr bool operator>(monostate, monostate) noexcept;
constexpr bool operator<=(monostate, monostate) noexcept;
constexpr bool operator>=(monostate, monostate) noexcept;
constexpr bool operator==(monostate, monostate) noexcept;
constexpr bool operator!=(monostate, monostate) noexcept;