diff --git a/sprout/string/concat.hpp b/sprout/string/concat.hpp
index c88cf17e..3b19d15f 100644
--- a/sprout/string/concat.hpp
+++ b/sprout/string/concat.hpp
@@ -4,64 +4,163 @@
 #include <cstddef>
 #include <type_traits>
 #include <sprout/config.hpp>
+#include <sprout/index_tuple.hpp>
+#include <sprout/string/char_traits.hpp>
 #include <sprout/string/string.hpp>
-#include <sprout/operation/fixed/push_back.hpp>
-#include <sprout/operation/fixed/push_front.hpp>
-#include <sprout/operation/fixed/append_back.hpp>
-#include <sprout/operation/fixed/append_front.hpp>
+//#include <sprout/operation/fixed/push_back.hpp>
+//#include <sprout/operation/fixed/push_front.hpp>
+//#include <sprout/operation/fixed/append_back.hpp>
+//#include <sprout/operation/fixed/append_front.hpp>
 
 namespace sprout {
+	namespace detail {
+		template<typename T, std::size_t N, typename Traits, sprout::index_t... Indexes>
+		inline SPROUT_CONSTEXPR sprout::basic_string<T, N + 1, Traits>
+		string_concat(
+			sprout::basic_string<T, N, Traits> const& lhs,
+			std::size_t lsize,
+			T const& rhs,
+			sprout::index_tuple<Indexes...>
+			)
+		{
+			return sprout::basic_string<T, N + 1, Traits>{
+				{
+					(Indexes < lsize ? lhs[Indexes]
+						: Indexes < lsize + 1 ? rhs
+						: T()
+						)...
+					},
+				lsize + 1
+				};
+		}
+		template<typename T, std::size_t N, typename Traits, sprout::index_t... Indexes>
+		inline SPROUT_CONSTEXPR sprout::basic_string<T, 1 + N, Traits>
+		string_concat(
+			T const& lhs,
+			sprout::basic_string<T, N, Traits> const& rhs,
+			std::size_t rsize,
+			sprout::index_tuple<Indexes...>
+			)
+		{
+			return sprout::basic_string<T, 1 + N, Traits>{
+				{
+					(Indexes < 1 ? lhs
+						: Indexes < 1 + rsize ? rhs[Indexes - 1]
+						: T()
+						)...
+					},
+				1 + rsize
+				};
+		}
+		template<typename T, std::size_t N, typename Traits, std::size_t M, sprout::index_t... Indexes>
+		inline SPROUT_CONSTEXPR sprout::basic_string<T, N + (M - 1), Traits>
+		string_concat(
+			sprout::basic_string<T, N, Traits> const& lhs,
+			std::size_t lsize,
+			T const (& rhs)[M],
+			std::size_t rsize,
+			sprout::index_tuple<Indexes...>
+			)
+		{
+			return sprout::basic_string<T, N + (M - 1), Traits>{
+				{
+					(Indexes < lsize ? lhs[Indexes]
+						: Indexes < lsize + rsize ? rhs[Indexes - lsize]
+						: T()
+						)...
+					},
+				lsize + rsize
+				};
+		}
+		template<typename T, std::size_t N, typename Traits, std::size_t M, sprout::index_t... Indexes>
+		inline SPROUT_CONSTEXPR sprout::basic_string<T, (M - 1) + N, Traits>
+		string_concat(
+			T const (& lhs)[M],
+			std::size_t lsize,
+			sprout::basic_string<T, N, Traits> const& rhs,
+			std::size_t rsize,
+			sprout::index_tuple<Indexes...>
+			)
+		{
+			return sprout::basic_string<T, (M - 1) + N, Traits>{
+				{
+					(Indexes < lsize ? lhs[Indexes]
+						: Indexes < lsize + rsize ? rhs[Indexes - lsize]
+						: T()
+						)...
+					},
+				lsize + rsize
+				};
+		}
+		template<typename T, std::size_t N1, std::size_t N2, typename Traits, sprout::index_t... Indexes>
+		inline SPROUT_CONSTEXPR sprout::basic_string<T, N1 + N2, Traits>
+		string_concat(
+			sprout::basic_string<T, N1, Traits> const& lhs,
+			std::size_t lsize,
+			sprout::basic_string<T, N2, Traits> const& rhs,
+			std::size_t rsize,
+			sprout::index_tuple<Indexes...>
+			)
+		{
+			return sprout::basic_string<T, N1 + N2, Traits>{
+				{
+					(Indexes < lsize ? lhs[Indexes]
+						: Indexes < lsize + rsize ? rhs[Indexes - lsize]
+						: T()
+						)...
+					},
+				lsize + rsize
+				};
+		}
+	}	// namespace detail
+
 	//
 	// operator+
 	//
 	template<typename T, std::size_t N, typename Traits>
-	inline SPROUT_CONSTEXPR typename sprout::fixed::result_of::push_back<sprout::basic_string<T, N, Traits>, T>::type operator+(
-		sprout::basic_string<T, N, Traits> const& lhs,
-		T const& rhs
-		)
-	{
-		return sprout::fixed::push_back(lhs, rhs);
+	inline SPROUT_CONSTEXPR sprout::basic_string<T, N + 1, Traits>
+	operator+(sprout::basic_string<T, N, Traits> const& lhs, T const& rhs) {
+		return sprout::detail::string_concat(
+			lhs, lhs.size(),
+			rhs,
+			sprout::index_range<0, N + 1>::make()
+			);
 	}
 	template<typename T, std::size_t N, typename Traits>
-	inline SPROUT_CONSTEXPR typename sprout::fixed::result_of::push_front<sprout::basic_string<T, N, Traits>, T>::type operator+(
-		T const& lhs,
-		sprout::basic_string<T, N, Traits> const& rhs
-		)
-	{
-		return sprout::fixed::push_front(rhs, lhs);
+	inline SPROUT_CONSTEXPR sprout::basic_string<T, 1 + N, Traits>
+	operator+(T const& lhs, sprout::basic_string<T, N, Traits> const& rhs) {
+		return sprout::detail::string_concat(
+			lhs,
+			rhs, rhs.size(),
+			sprout::index_range<0, 1 + N>::make()
+			);
 	}
-	template<typename T, std::size_t N, typename Traits, std::size_t N2>
-	inline SPROUT_CONSTEXPR typename sprout::fixed::result_of::append_back<
-		sprout::basic_string<T, N, Traits>,
-		sprout::basic_string<T, N2 - 1, Traits>
-	>::type operator+(
-		sprout::basic_string<T, N, Traits> const& lhs,
-		T const (& rhs)[N2]
-		)
-	{
-		return sprout::fixed::append_back(lhs, sprout::to_string(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]) {
+		return sprout::detail::string_concat(
+			lhs, lhs.size(),
+			rhs, sprout::char_traits<T>::length(rhs),
+			sprout::index_range<0, N + (M - 1)>::make()
+			);
 	}
-	template<typename T, std::size_t N, typename Traits, std::size_t N2>
-	inline SPROUT_CONSTEXPR typename sprout::fixed::result_of::append_front<
-		sprout::basic_string<T, N, Traits>,
-		sprout::basic_string<T, N2 - 1, Traits>
-	>::type operator+(
-		T const (& lhs)[N2],
-		sprout::basic_string<T, N, Traits> const& rhs
-		)
-	{
-		return sprout::fixed::append_front(rhs, sprout::to_string(lhs));
+	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) {
+		return sprout::detail::string_concat(
+			lhs, sprout::char_traits<T>::length(lhs),
+			rhs, rhs.size(),
+			sprout::index_range<0, (M - 1) + N>::make()
+			);
 	}
-	template<typename T, std::size_t N, typename Traits, std::size_t N2>
-	inline SPROUT_CONSTEXPR typename sprout::fixed::result_of::append_back<
-		sprout::basic_string<T, N, Traits>,
-		sprout::basic_string<T, N2, Traits>
-	>::type operator+(
-		sprout::basic_string<T, N, Traits> const& lhs,
-		sprout::basic_string<T, N2, Traits> const& rhs
-		)
-	{
-		return sprout::fixed::append_back(lhs, 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) {
+		return sprout::detail::string_concat(
+			lhs, lhs.size(),
+			rhs, rhs.size(),
+			sprout::index_range<0, N1 + N2>::make()
+			);
 	}
 }	// namespace sprout