constexpr complex& operator+=(const T& rhs);
constexpr complex& operator-=(const T& rhs);
constexpr complex& operator*=(const T& rhs);
constexpr complex& operator/=(const T& rhs);
template<class X> constexpr complex& operator+=(const complex<X>& rhs);
template<class X> constexpr complex& operator-=(const complex<X>& rhs);
template<class X> constexpr complex& operator*=(const complex<X>& rhs);
template<class X> constexpr complex& operator/=(const complex<X>& rhs);