mrdocs::polyfill::swap

constexpr
void
swap(
    expected& a,
    expected& b) noexcept(noexcept(a.swap(b)))
requires requires { a.swap(b); };

constexpr
void
swap(
    expected& x,
    expected& y) noexcept(noexcept(x.swap(y)))
requires requires {x.swap(y);};

constexpr
void
swap(
    unexpected& x,
    unexpected& y) noexcept(noexcept(x.swap(y)))
requires std::is_swappable_v<E>;