mp_units::constrained::operator‐‐

constexpr
constrained&
operator‐‐()
requires requires(T& v) {
      { ‐‐v } ‐> std::same_as<T&>;
    };

constexpr
constrained<decltype(std::declval<T&>()‐‐), ErrorPolicy>
operator‐‐(int);