template<typename T, std::size_t N, typename Traits>
inline SPROUT_CONSTEXPR sprout::basic_string<T, N + 1, Traits>
operator+(sprout::basic_string<T, N, Traits> const& lhs, T const& rhs);
template<typename T, std::size_t N, typename Traits>
inline SPROUT_CONSTEXPR sprout::basic_string<T, 1 + N, Traits>
operator+(T const& lhs, sprout::basic_string<T, N, Traits> const& rhs);
template<typename T, std::size_t N, typename Traits, std::size_t M>
inline SPROUT_CONSTEXPR sprout::basic_string<T, N + (M - 1), Traits>
operator+(sprout::basic_string<T, N, Traits> const& lhs, T const (& rhs)[M]);
template<typename T, std::size_t N, typename Traits, std::size_t M>
inline SPROUT_CONSTEXPR sprout::basic_string<T, (M - 1) + N, Traits>
operator+(T const (& lhs)[M], sprout::basic_string<T, N, Traits> const& rhs);
template<typename T, std::size_t N1, std::size_t N2, typename Traits>
inline SPROUT_CONSTEXPR sprout::basic_string<T, N1 + N2, Traits>
operator+(sprout::basic_string<T, N1, Traits> const& lhs, sprout::basic_string<T, N2, Traits> const& rhs);