diff --git a/sprout/complex.hpp b/sprout/complex.hpp
new file mode 100644
index 00000000..26df2016
--- /dev/null
+++ b/sprout/complex.hpp
@@ -0,0 +1,593 @@
+#ifndef SPROUT_COMPLEX_HPP
+#define SPROUT_COMPLEX_HPP
+
+#include <cmath>
+#include <sprout/config.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR T pi_div_two() {
+			return 1.5707963267948966192313216916397514L;
+		}
+	}	// namespace detail
+	template<typename T>
+	class complex;
+	template<typename T>
+	SPROUT_CONSTEXPR T norm(sprout::complex<T> const& x);
+	//
+	// complex
+	//
+	template<typename T>
+	class complex {
+	public:
+		typedef T value_type;
+	private:
+		T re_;
+		T im_;
+	public:
+		SPROUT_CONSTEXPR complex(T const& re = T(), T const& im = T())
+			: re_(re)
+			, im_(im)
+		{}
+		SPROUT_CONSTEXPR complex(complex const&) = default;
+		template<typename X>
+		SPROUT_CONSTEXPR complex(complex<X> const& other)
+			: re_(other.real())
+			, im_(other.imag())
+		{}
+		SPROUT_CONSTEXPR T real() const {
+			return re_;
+		}
+		void real(T re) {
+			re_ = re;
+		}
+		SPROUT_CONSTEXPR T imag() const{
+			return im_;
+		}
+		void imag(T im) {
+			im_ = im;
+		}
+		complex<T>& operator=(T const& rhs) {
+			re_ = rhs;
+			im_ = T();
+			return *this;
+		}
+		complex<T>& operator+=(T const& rhs) {
+			re_ += rhs;
+			return *this;
+		}
+		complex<T>& operator-=(T const& rhs) {
+			re_ -= rhs;
+			return *this;
+		}
+		complex<T>& operator*=(T const& rhs) {
+			re_ *= rhs;
+			im_ *= rhs;
+			return *this;
+		}
+		complex<T>& operator/=(T const& rhs) {
+			re_ /= rhs;
+			im_ /= rhs;
+			return *this;
+		}
+		complex& operator=(complex const&) = default;
+		template<typename X>
+		complex<T>& operator=(complex<X> const& rhs) {
+			re_ = rhs.real();
+			im_ = rhs.imag();
+			return *this;
+		}
+		template<typename X>
+		complex<T>& operator+=(complex<X> const& rhs) {
+			re_ += rhs.real();
+			im_ += rhs.imag();
+			return *this;
+		}
+		template<typename X>
+		complex<T>& operator-=(complex<X> const& rhs) {
+			re_ -= rhs.real();
+			im_ -= rhs.imag();
+			return *this;
+		}
+		template<typename X>
+		complex<T>& operator*=(complex<X> const& rhs) {
+			return *this = complex<T>(
+				re_ * rhs.real() - im_ * rhs.imag(),
+				re_ * rhs.imag() + im_ * rhs.imag()
+				);
+		}
+		template<typename X>
+		complex<T>& operator/=(complex<X> const& rhs) {
+			T n = sprout::norm(rhs);
+			return *this = complex<T>(
+				(re_ * rhs.real() + im_ * rhs.imag()) / n,
+				(im_ * rhs.real() - re_ * rhs.imag()) / n
+				);
+		}
+	};
+	// 26.4.6, operators:
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator+(sprout::complex<T> const& lhs, sprout::complex<T> const& rhs) {
+		return sprout::complex<T>(
+			lhs.real() + rhs.real(),
+			lhs.imag() + rhs.imag()
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator+(sprout::complex<T> const& lhs, T const& rhs) {
+		return sprout::complex<T>(
+			lhs.real() + rhs,
+			lhs.imag()
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator+(T const& lhs, sprout::complex<T> const& rhs) {
+		return sprout::complex<T>(
+			lhs + rhs.real(),
+			rhs.imag()
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator-(sprout::complex<T> const& lhs, sprout::complex<T> const& rhs) {
+		return sprout::complex<T>(
+			lhs.real() - rhs.real(),
+			lhs.imag() - rhs.imag()
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator-(sprout::complex<T> const& lhs, T const& rhs) {
+		return sprout::complex<T>(
+			lhs.real() - rhs,
+			lhs.imag()
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator-(T const& lhs, sprout::complex<T> const& rhs) {
+		return sprout::complex<T>(
+			lhs - rhs.real(),
+			-rhs.imag()
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator*(sprout::complex<T> const& lhs, sprout::complex<T> const& rhs) {
+		return sprout::complex<T>(
+			lhs.real() * rhs.real() - lhs.imag() * rhs.imag(),
+			lhs.real() * rhs.imag() + lhs.imag() * rhs.imag()
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator*(sprout::complex<T> const& lhs, T const& rhs) {
+		return sprout::complex<T>(
+			lhs.real() * rhs,
+			lhs.imag() * rhs
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator*(T const& lhs, sprout::complex<T> const& rhs) {
+		return sprout::complex<T>(
+			lhs * rhs.real(),
+			lhs * rhs.imag()
+			);
+	}
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> divides_impl(
+			sprout::complex<T> const& lhs,
+			sprout::complex<T> const& rhs,
+			T const& n
+			)
+		{
+			return sprout::complex<T>(
+				(lhs.real() * rhs.real() + lhs.imag() * rhs.imag()) / n,
+				(lhs.imag() * rhs.real() - lhs.real() * rhs.imag()) / n
+				);
+		}
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> divides_impl(
+			T const& lhs,
+			sprout::complex<T> const& rhs,
+			T const& n
+			)
+		{
+			return sprout::complex<T>(
+				lhs * rhs.real() / n,
+				-lhs * rhs.imag() / n
+				);
+		}
+	}	// namespace detail
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator/(sprout::complex<T> const& lhs, sprout::complex<T> const& rhs) {
+		return sprout::detail::divides_impl(lhs, rhs, sprout::norm(rhs));
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator/(sprout::complex<T> const& lhs, T const& rhs) {
+		return sprout::complex<T>(
+			lhs.real() / rhs,
+			lhs.imag() / rhs
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator/(T const& lhs, sprout::complex<T> const& rhs) {
+		return sprout::detail::divides_impl(lhs, rhs, sprout::norm(rhs));
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator+(sprout::complex<T> const& x) {
+		return x;
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> operator-(sprout::complex<T> const& x) {
+		return sprout::complex<T>(-x.real(), -x.imag());
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR bool operator==(sprout::complex<T> const& lhs, sprout::complex<T> const& rhs) {
+		return lhs.real() == rhs.real() && lhs.imag() == rhs.imag();
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR bool operator==(sprout::complex<T> const& lhs, T const& rhs) {
+		return lhs.real() == rhs && lhs.imag() == T();
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR bool operator==(T const& lhs, sprout::complex<T> const& rhs) {
+		return lhs == rhs.real() && T() == rhs.imag();
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR bool operator!=(sprout::complex<T> const& lhs, sprout::complex<T> const& rhs) {
+		return !(lhs == rhs);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR bool operator!=(sprout::complex<T> const& lhs, T const& rhs) {
+		return !(lhs == rhs);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR bool operator!=(T const& lhs, sprout::complex<T> const& rhs) {
+		return !(lhs == rhs);
+	}
+	template<typename T, typename Char, typename Traits>
+	std::basic_istream<Char, Traits>& operator>>(std::basic_istream<Char, Traits>& lhs, sprout::complex<T>& rhs) {
+		T re, im;
+		Char ch;
+		lhs >> ch;
+		if (ch == '(') {
+			lhs >> re >> ch;
+			if (ch == ',') {
+				lhs >> im >> ch;
+				if (ch == ')') {
+					rhs = sprout::complex<T>(re, im);
+				} else {
+					lhs.setstate(std::ios_base::failbit);
+				}
+			} else if (ch == ')') {
+				rhs = re;
+			} else {
+				lhs.setstate(std::ios_base::failbit);
+			}
+		} else {
+			lhs.putback(ch);
+			lhs >> re;
+			rhs = re;
+		}
+		return lhs;
+	}
+	template<typename T, typename Char, typename Traits>
+	std::basic_ostream<Char, Traits>& operator<<(std::basic_ostream<Char, Traits>& lhs, sprout::complex<T> const& rhs) {
+		return lhs << '(' << rhs.real() << ',' << rhs.imag() << ')';
+	}
+	// 26.4.7, values:
+	template<typename T>
+	SPROUT_CONSTEXPR T real(sprout::complex<T> const& x) {
+		return x.real();
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR T imag(sprout::complex<T> const& x) {
+		return x.imag();
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR T abs(sprout::complex<T> const& x) {
+		using std::sqrt;
+		return sqrt(sprout::norm(x));
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR T arg(sprout::complex<T> const& x) {
+		using std::atan2;
+		return atan2(x.imag(), x.real());
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR T norm(sprout::complex<T> const& x) {
+		return x.real() * x.real() + x.imag() * x.imag();
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> conj(sprout::complex<T> const& x) {
+		return sprout::complex<T>(x.real(), -x.imag());
+	}
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> proj_impl(sprout::complex<T> const& x, T const& den) {
+			return sprout::complex<T>(
+				T(2) * x.real() / den,
+				T(2) * x.imag() / den
+				);
+		}
+	}	// detail
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> proj(sprout::complex<T> const& x) {
+		return sprout::detail::proj_impl(
+			x,
+			sprout::norm(x) + T(1)
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> polar(T const& rho, T const& theta = 0) {
+		using std::cos;
+		using std::sin;
+		return sprout::complex<T>(rho * cos(theta), rho * sin(theta));
+	}
+	// 26.4.8, transcendentals:
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> acos(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> asin(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> atan(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> acosh(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> asinh(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> atanh(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> cos(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> cosh(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> exp(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> log(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> log10(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> pow(sprout::complex<T> const& x, T const& y);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> pow(sprout::complex<T> const& x, sprout::complex<T> const& y);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> pow(T const& x, sprout::complex<T> const& y);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> sin(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> sinh(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> sqrt(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> tan(sprout::complex<T> const& x);
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> tanh(sprout::complex<T> const& x);
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> acos_impl(sprout::complex<T> const& t) {
+			return sprout::complex<T>(sprout::detail::pi_div_two<T>() - t.real(), -t.imag());
+		}
+	}	// namespace detail
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> acos(sprout::complex<T> const& x) {
+		return sprout::detail::acos_impl(sprout::asin(x));
+	}
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> asin_impl(sprout::complex<T> const& t) {
+			return sprout::complex<T>(t.imag(), -t.real());
+		}
+	}	// namespace detail
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> asin(sprout::complex<T> const& x) {
+		return sprout::detail::asin_impl(sprout::asinh(sprout::complex<T>(-x.imag(), x.real())));
+	}
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> atan_impl_1(
+			sprout::complex<T> const& x,
+			T const& r2,
+			T const& z,
+			T const& num,
+			T const& den
+			)
+		{
+			using std::atan2;
+			using std::log;
+			return sprout::complex<T>(
+				T(0.5) * atan2(T(2) * x.real(), z),
+				T(0.25) * log((r2 + num * num) / (r2 + den * den))
+				);
+		}
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> atan_impl(
+			sprout::complex<T> const& x,
+			T const& r2
+			)
+		{
+			return sprout::detail::atan_impl_1(
+				x,
+				r2,
+				T(1) - r2 - x.imag() * x.imag(),
+				x.imag() + T(1),
+				x.imag() - T(1)
+				);
+		}
+	}	// namespace detail
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> atan(sprout::complex<T> const& x) {
+		return sprout::detail::atan_impl(x, x.real() * x.real());
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> acosh(sprout::complex<T> const& x) {
+		return T(2) * sprout::log(sprout::sqrt(T(0.5) * (x + T(1))) + sprout::sqrt(T(0.5) * (x - T(1))));
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> asinh(sprout::complex<T> const& x) {
+		return sprout::log(
+			sprout::sqrt(
+				sprout::complex<T>(
+					(x.real() - x.imag()) * (x.real() + x.imag()) + T(1),
+					T(2) * x.real() * x.imag()
+					)
+				)
+				+ x
+			);
+	}
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> atanh_impl_1(
+			sprout::complex<T> const& x,
+			T const& i2,
+			T const& z,
+			T const& num,
+			T const& den
+			)
+		{
+			using std::atan2;
+			using std::log;
+			return sprout::complex<T>(
+				T(0.25) * (log(i2 + num * num) - log(i2 + den * den)),
+				T(0.5) * atan2(T(2) * x.imag(), z)
+				);
+		}
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> atanh_impl(
+			sprout::complex<T> const& x,
+			T const& i2
+			)
+		{
+			return sprout::detail::atanh_impl_1(
+				x,
+				i2,
+				T(1) - i2 - x.real() * x.real(),
+				T(1) + x.imag(),
+				T(1) - x.imag()
+				);
+		}
+	}	// namespace detail
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> atanh(sprout::complex<T> const& x) {
+		return sprout::detail::atanh_impl(x, x.imag() * x.imag());
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> cos(sprout::complex<T> const& x) {
+		using std::cos;
+		using std::sin;
+		using std::cosh;
+		using std::sinh;
+		return sprout::complex<T>(
+			cos(x.real()) * cosh(x.imag()),
+			-(sin(x.real()) * sinh(x.imag()))
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> cosh(sprout::complex<T> const& x) {
+		using std::cos;
+		using std::sin;
+		using std::cosh;
+		using std::sinh;
+		return sprout::complex<T>(
+			cosh(x.real()) * cos(x.imag()),
+			sinh(x.real()) * sin(x.imag())
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> exp(sprout::complex<T> const& x) {
+		using std::exp;
+		return sprout::polar(exp(x.real()), x.imag());
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> log(sprout::complex<T> const& x) {
+		return sprout::complex<T>(sprout::log(sprout::abs(x)), sprout::arg(x));
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> log10(sprout::complex<T> const& x) {
+		using std::log;
+		return sprout::log(x) / log(T(10));
+	}
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> pow_impl(sprout::complex<T> const& t, T const& y) {
+			using std::exp;
+			return sprout::polar(exp(y * t.real()), y * t.imag());
+		}
+	}	// namespace detail
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> pow(sprout::complex<T> const& x, T const& y) {
+		using std::pow;
+		return x == T() ? T()
+			: x.imag() == T() && x.real() > T() ? pow(x.real(), y)
+			: sprout::detail::pow_impl(sprout::log(x), y)
+			;
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> pow(sprout::complex<T> const& x, sprout::complex<T> const& y) {
+		return x == T() ? T()
+			: sprout::exp(y * sprout::log(x))
+			;
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> pow(T const& x, sprout::complex<T> const& y) {
+		using std::log;
+		return x > T() ? sprout::polar(sprout::pow(x, y.real()), y.imag() * log(x))
+			: sprout::pow(sprout::complex<T>(x), y)
+			;
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> sin(sprout::complex<T> const& x) {
+		using std::cos;
+		using std::sin;
+		using std::cosh;
+		using std::sinh;
+		return sprout::complex<T>(
+			sin(x.real()) * cosh(x.imag()),
+			cos(x.real()) * sinh(x.imag())
+			);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> sinh(sprout::complex<T> const& x) {
+		using std::cos;
+		using std::sin;
+		using std::cosh;
+		using std::sinh;
+		return sprout::complex<T>(
+			sinh(x.real()) * cos(x.imag()),
+			cosh(x.real()) * sin(x.imag())
+			);
+	}
+	namespace detail {
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> sqrt_impl_1(sprout::complex<T> const& x, T const& t) {
+			return sprout::complex<T>(t, x.imag() < T() ? -t : t);
+		}
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> sqrt_impl_2_1(sprout::complex<T> const& x, T const& t, T const& u) {
+			using std::abs;
+			return x.real() > T() ? sprout::complex<T>(u, x.imag() / t)
+				: sprout::complex<T>(abs(x.imag()) / t, x.imag() < T() ? -u : u)
+				;
+		}
+		template<typename T>
+		SPROUT_CONSTEXPR sprout::complex<T> sqrt_impl_2(sprout::complex<T> const& x, T const& t) {
+			return sqrt_impl_2(x, t, t / 2);
+		}
+	}	// namespace detail
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> sqrt(sprout::complex<T> const& x) {
+		using std::sqrt;
+		using std::abs;
+		return x.real() == T() ? sprout::detail::sqrt_impl_1(x, sqrt(abs(x.imag()) / 2))
+			: sprout::detail::sqrt_impl_2(x, sqrt(2 * (sprout::abs(x) + abs(x.real()))))
+			;
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> tan(sprout::complex<T> const& x) {
+		return sprout::sin(x) / sprout::cos(x);
+	}
+	template<typename T>
+	SPROUT_CONSTEXPR sprout::complex<T> tanh(sprout::complex<T> const& x) {
+		return sprout::sinh(x) / sprout::cosh(x);
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_COMPLEX_HPP
diff --git a/sprout/string.hpp b/sprout/string.hpp
index e3f09f90..061fa3f5 100644
--- a/sprout/string.hpp
+++ b/sprout/string.hpp
@@ -901,7 +901,27 @@ namespace sprout {
 			sprout::make_array<typename std::decay<T>::type>(
 				sprout::forward<T>(t),
 				sprout::forward<Types>(args)...,
-				T()
+				typename std::decay<T>::type()
+				),
+			typename sprout::index_range<0, 1 + sizeof...(Types)>::type()
+			);
+	}
+
+	//
+	// make_string_as
+	//
+	template<typename T>
+	SPROUT_CONSTEXPR inline sprout::basic_string<typename std::decay<T>::type, 0>
+	make_string_as() {
+		return sprout::basic_string<typename std::decay<T>::type, 0>{};
+	}
+	template<typename T, typename... Types>
+	SPROUT_CONSTEXPR inline sprout::basic_string<typename std::decay<T>::type, sizeof...(Types)>
+	make_string_as(Types&&... args) {
+		return sprout::detail::make_string_impl(
+			sprout::make_array<typename std::decay<T>::type>(
+				sprout::forward<Types>(args)...,
+				typename std::decay<T>::type()
 				),
 			typename sprout::index_range<0, 1 + sizeof...(Types)>::type()
 			);
diff --git a/sprout/type.hpp b/sprout/type.hpp
index 34e2206a..ed428b39 100644
--- a/sprout/type.hpp
+++ b/sprout/type.hpp
@@ -4,6 +4,8 @@
 #include <sprout/config.hpp>
 #include <sprout/type/tuple.hpp>
 #include <sprout/type/type_tuple.hpp>
+#include <sprout/type/integral_array.hpp>
+#include <sprout/type/string.hpp>
 #include <sprout/type/rebind_types.hpp>
 #include <sprout/type/algorithm.hpp>
 #include <sprout/type/operation.hpp>
diff --git a/sprout/type/boost/mpl/string.hpp b/sprout/type/boost/mpl/string.hpp
index 977c87be..6a7b5cfc 100644
--- a/sprout/type/boost/mpl/string.hpp
+++ b/sprout/type/boost/mpl/string.hpp
@@ -6,9 +6,13 @@
 #include <boost/mpl/size.hpp>
 #include <boost/mpl/at.hpp>
 #include <boost/mpl/next_prior.hpp>
+#include <boost/mpl/push_back.hpp>
+#include <boost/mpl/push_front.hpp>
 #include <sprout/type/tuple.hpp>
 #include <sprout/type/iterator/next.hpp>
 #include <sprout/type/iterator/prev.hpp>
+#include <sprout/type/operation/push_back.hpp>
+#include <sprout/type/operation/push_front.hpp>
 
 namespace sprout {
 	namespace types {
@@ -49,6 +53,7 @@ namespace sprout {
 		struct next<boost::mpl::string_iterator<Sequence, I, J> >
 			: public boost::mpl::next<boost::mpl::string_iterator<Sequence, I, J> >
 		{};
+
 		//
 		// prev
 		//
@@ -56,6 +61,22 @@ namespace sprout {
 		struct prev<boost::mpl::string_iterator<Sequence, I, J> >
 			: public boost::mpl::prior<boost::mpl::string_iterator<Sequence, I, J> >
 		{};
+
+		//
+		// push_back
+		//
+		template<int... Values, typename T>
+		struct push_back<boost::mpl::string<Values...>, T>
+			: public boost::mpl::push_back<boost::mpl::string<Values...>, T>
+		{};
+
+		//
+		// push_front
+		//
+		template<int... Values, typename T>
+		struct push_front<boost::mpl::string<Values...>, T>
+			: public boost::mpl::push_back<boost::mpl::string<Values...>, T>
+		{};
 	}	// namespace types
 }	// namespace sprout
 
diff --git a/sprout/type/string/to_string.hpp b/sprout/type/string/to_string.hpp
index 85d961ef..f6949d11 100644
--- a/sprout/type/string/to_string.hpp
+++ b/sprout/type/string/to_string.hpp
@@ -18,10 +18,10 @@ namespace sprout {
 		//
 		// to_string
 		//
-		template<typename StringClass>
+		template<typename Proxy>
 		struct to_string {
 		private:
-			typedef decltype(StringClass()()) string_type;
+			typedef decltype(Proxy()()) string_type;
 			typedef sprout::fixed_container_traits<string_type> traits_type;
 		private:
 			template<typename IndexTuple>
@@ -31,12 +31,12 @@ namespace sprout {
 			public:
 				typedef sprout::types::basic_string<
 					typename traits_type::value_type,
-					(*sprout::next(sprout::begin(StringClass()()), Indexes))...
+					(*sprout::next(sprout::begin(Proxy()()), Indexes))...
 				> type;
 			};
 		public:
 			typedef typename impl<
-				typename sprout::index_range<0, sprout::size(StringClass()())>::type
+				typename sprout::index_range<0, sprout::size(Proxy()())>::type
 			>::type type;
 		};
 		namespace detail {
@@ -63,7 +63,7 @@ namespace sprout {
 		// SPROUT_TYPES_STRING_TYPEDEF
 		//
 #		define SPROUT_TYPES_STRING_TYPEDEF(SOURCE, TYPE) \
-		struct SPROUT_PP_CAT(SPROUT_TYPES_STRING_TYPEDEF_IMPL_, __LINE__) { \
+		struct SPROUT_PP_CAT(SPROUT_TYPES_STRING_TYPEDEF_PROXY_, __LINE__) { \
 		private: \
 			typedef typename std::remove_reference<decltype(SOURCE)>::type src_type; \
 			typedef sprout::types::detail::string_typedef_impl<src_type, std::is_array<src_type>::value> impl_type; \
@@ -74,7 +74,7 @@ namespace sprout {
 				return impl_type()(SOURCE); \
 			} \
 		}; \
-		typedef typename sprout::types::to_string<SPROUT_PP_CAT(SPROUT_TYPES_STRING_TYPEDEF_IMPL_, __LINE__)>::type TYPE
+		typedef typename sprout::types::to_string<SPROUT_PP_CAT(SPROUT_TYPES_STRING_TYPEDEF_PROXY_, __LINE__)>::type TYPE
 	}	// namespace types
 }	// namespace sprout
 
diff --git a/sprout/type/string/to_string_constant.hpp b/sprout/type/string/to_string_constant.hpp
index ccbf3fca..b9961287 100644
--- a/sprout/type/string/to_string_constant.hpp
+++ b/sprout/type/string/to_string_constant.hpp
@@ -42,14 +42,9 @@ namespace sprout {
 				typename Sequence::value_type,
 				sprout::types::detail::str_length<Sequence>::value
 			> to_string_constant_impl(sprout::index_tuple<Indexes...>) {
-				typedef sprout::basic_string<
-					typename Sequence::value_type,
-					sprout::types::detail::str_length<Sequence>::value
-				> type;
-				return type{
-					{sprout::types::tuple_element<Indexes, Sequence>::type::value...},
-					sprout::types::detail::str_length<Sequence>::value
-					};
+				return sprout::make_string_as<typename Sequence::value_type>(
+					sprout::types::tuple_element<Indexes, Sequence>::type::value...
+					);
 			}
 		}	// namespace detail
 		template<typename Sequence>
diff --git a/sprout/weed.hpp b/sprout/weed.hpp
index a8fe356e..a0e185cf 100644
--- a/sprout/weed.hpp
+++ b/sprout/weed.hpp
@@ -1,6 +1,7 @@
 #ifndef SPROUT_WEED_HPP
 #define SPROUT_WEED_HPP
 
+#include <sprout/config.hpp>
 #include <sprout/weed/expr.hpp>
 #include <sprout/weed/operator.hpp>
 #include <sprout/weed/attr_cnv.hpp>