diff --git a/libs/variant/test/variant.cpp b/libs/variant/test/variant.cpp
new file mode 100644
index 00000000..9deaeb4f
--- /dev/null
+++ b/libs/variant/test/variant.cpp
@@ -0,0 +1,213 @@
+#ifndef SPROUT_LIBS_VARIANT_TEST_VARIANT_CPP
+#define SPROUT_LIBS_VARIANT_TEST_VARIANT_CPP
+
+#include <sstream>
+#include <sprout/variant.hpp>
+#include <testspr/tools.hpp>
+
+namespace testspr {
+	static void variant_test() {
+		using namespace sprout;
+		{
+			SPROUT_STATIC_CONSTEXPR auto var1 = sprout::variant<int, double>(1.0);
+			SPROUT_STATIC_CONSTEXPR auto var2 = sprout::variant<int, double>();
+
+			// constructor
+			{
+				SPROUT_STATIC_CONSTEXPR auto var3 = sprout::variant<int, double>();
+				TESTSPR_BOTH_ASSERT(var3.which() == 0);
+				TESTSPR_BOTH_ASSERT(sprout::get<int>(var3) == 0);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto var3 = sprout::variant<int, double>(var1);
+				TESTSPR_BOTH_ASSERT(var3.which() == 1);
+				TESTSPR_BOTH_ASSERT(sprout::get<double>(var3) == 1.0);
+			}
+			{
+				SPROUT_STATIC_CONSTEXPR auto var3 = sprout::variant<int, double>(1.0);
+				TESTSPR_BOTH_ASSERT(var3.which() == 1);
+				TESTSPR_BOTH_ASSERT(sprout::get<double>(var3) == 1.0);
+			}
+
+			// swap
+			{
+				auto var3 = var1;
+				auto var4 = var2;
+				var3.swap(var4);
+				TESTSPR_ASSERT(var3.which() == 0);
+				TESTSPR_ASSERT(sprout::get<int>(var3) == 0);
+				TESTSPR_ASSERT(var4.which() == 1);
+				TESTSPR_ASSERT(sprout::get<double>(var4) == 1.0);
+			}
+			{
+				auto var3 = var1;
+				auto var4 = var2;
+				swap(var3, var4);
+				TESTSPR_ASSERT(var3.which() == 0);
+				TESTSPR_ASSERT(sprout::get<int>(var3) == 0);
+				TESTSPR_ASSERT(var4.which() == 1);
+				TESTSPR_ASSERT(sprout::get<double>(var4) == 1.0);
+			}
+
+			// operator=
+			{
+				auto var3 = var2;
+				var3 = sprout::variant<int, double>(1.0);
+				TESTSPR_ASSERT(var3.which() == 1);
+				TESTSPR_ASSERT(sprout::get<double>(var3) == 1.0);
+			}
+			{
+				auto var3 = var2;
+				var3 = 1.0;
+				TESTSPR_ASSERT(var3.which() == 1);
+				TESTSPR_ASSERT(sprout::get<double>(var3) == 1.0);
+			}
+
+			// which
+			TESTSPR_BOTH_ASSERT(var1.which() == 1);
+			TESTSPR_BOTH_ASSERT(var2.which() == 0);
+
+			// empty
+			TESTSPR_BOTH_ASSERT(!var1.empty());
+			TESTSPR_BOTH_ASSERT(!var2.empty());
+
+			// operator==
+			TESTSPR_BOTH_ASSERT(!(var1 == var2));
+			TESTSPR_BOTH_ASSERT((var1 == sprout::variant<int, double>(1.0)));
+
+			// operator!=
+			TESTSPR_BOTH_ASSERT(var1 != var2);
+			TESTSPR_BOTH_ASSERT(!(var1 != sprout::variant<int, double>(1.0)));
+
+			// operator<
+			TESTSPR_BOTH_ASSERT(!(var1 < var2));
+			TESTSPR_BOTH_ASSERT(!(var1 < sprout::variant<int, double>(0.0)));
+			TESTSPR_BOTH_ASSERT(!(var1 < sprout::variant<int, double>(1.0)));
+			TESTSPR_BOTH_ASSERT((var1 < sprout::variant<int, double>(2.0)));
+			TESTSPR_BOTH_ASSERT(!(var1 < sprout::variant<int, double>(0)));
+			TESTSPR_BOTH_ASSERT(!(var1 < sprout::variant<int, double>(1)));
+			TESTSPR_BOTH_ASSERT(!(var1 < sprout::variant<int, double>(2)));
+
+			// operator>
+			TESTSPR_BOTH_ASSERT(var1 > var2);
+			TESTSPR_BOTH_ASSERT((var1 > sprout::variant<int, double>(0.0)));
+			TESTSPR_BOTH_ASSERT(!(var1 > sprout::variant<int, double>(1.0)));
+			TESTSPR_BOTH_ASSERT(!(var1 > sprout::variant<int, double>(2.0)));
+			TESTSPR_BOTH_ASSERT((var1 > sprout::variant<int, double>(0)));
+			TESTSPR_BOTH_ASSERT((var1 > sprout::variant<int, double>(1)));
+			TESTSPR_BOTH_ASSERT((var1 > sprout::variant<int, double>(2)));
+
+			// operator<=
+			TESTSPR_BOTH_ASSERT(!(var1 <= var2));
+			TESTSPR_BOTH_ASSERT(!(var1 <= sprout::variant<int, double>(0.0)));
+			TESTSPR_BOTH_ASSERT((var1 <= sprout::variant<int, double>(1.0)));
+			TESTSPR_BOTH_ASSERT((var1 <= sprout::variant<int, double>(2.0)));
+			TESTSPR_BOTH_ASSERT(!(var1 <= sprout::variant<int, double>(0)));
+			TESTSPR_BOTH_ASSERT(!(var1 <= sprout::variant<int, double>(1)));
+			TESTSPR_BOTH_ASSERT(!(var1 <= sprout::variant<int, double>(2)));
+
+			// operator>=
+			TESTSPR_BOTH_ASSERT(var1 >= var2);
+			TESTSPR_BOTH_ASSERT((var1 >= sprout::variant<int, double>(0.0)));
+			TESTSPR_BOTH_ASSERT((var1 >= sprout::variant<int, double>(1.0)));
+			TESTSPR_BOTH_ASSERT(!(var1 >= sprout::variant<int, double>(2.0)));
+			TESTSPR_BOTH_ASSERT((var1 >= sprout::variant<int, double>(0)));
+			TESTSPR_BOTH_ASSERT((var1 >= sprout::variant<int, double>(1)));
+			TESTSPR_BOTH_ASSERT((var1 >= sprout::variant<int, double>(2)));
+
+			// get_at
+			TESTSPR_BOTH_ASSERT(var1.get_at<1>() == 1.0);
+			TESTSPR_BOTH_ASSERT(var2.get_at<0>() == 0);
+			{
+				auto var3 = var1;
+				TESTSPR_ASSERT(var3.get_at<1>() == 1.0);
+			}
+			{
+				auto var3 = var2;
+				TESTSPR_ASSERT(var3.get_at<0>() == 0);
+			}
+
+			// get
+			TESTSPR_BOTH_ASSERT(sprout::get<double>(var1) == 1.0);
+			TESTSPR_BOTH_ASSERT(sprout::get<int>(var2) == 0);
+			{
+				auto var3 = var1;
+				TESTSPR_ASSERT(sprout::get<double>(var3) == 1.0);
+			}
+			{
+				auto var3 = var2;
+				TESTSPR_ASSERT(sprout::get<int>(var3) == 0);
+			}
+
+			// apply_visitor
+			TESTSPR_BOTH_ASSERT(var1.apply_visitor(testspr::x2_visitor<double>()) == 2.0);
+			TESTSPR_BOTH_ASSERT(var2.apply_visitor(testspr::x2_visitor<double>()) == 0.0);
+			{
+				auto var3 = var1;
+				TESTSPR_ASSERT(var3.apply_visitor(testspr::x2_assign_visitor<double>()) == 2.0);
+				TESTSPR_ASSERT(var3.which() == 1);
+				TESTSPR_ASSERT(sprout::get<double>(var3) == 2.0);
+			}
+			{
+				auto var3 = var2;
+				TESTSPR_ASSERT(var3.apply_visitor(testspr::x2_assign_visitor<double>()) == 0.0);
+				TESTSPR_ASSERT(var3.which() == 0);
+				TESTSPR_ASSERT(sprout::get<int>(var3) == 0);
+			}
+
+			// apply_visitor
+			TESTSPR_BOTH_ASSERT(sprout::apply_visitor(testspr::x2_visitor<double>(), var1) == 2.0);
+			TESTSPR_BOTH_ASSERT(sprout::apply_visitor(testspr::x2_visitor<double>(), var2) == 0.0);
+			{
+				auto var3 = var1;
+				TESTSPR_ASSERT(sprout::apply_visitor(testspr::x2_assign_visitor<double>(), var3) == 2.0);
+				TESTSPR_ASSERT(var3.which() == 1);
+				TESTSPR_ASSERT(sprout::get<double>(var3) == 2.0);
+			}
+			{
+				auto var3 = var2;
+				TESTSPR_ASSERT(sprout::apply_visitor(testspr::x2_assign_visitor<double>(), var3) == 0.0);
+				TESTSPR_ASSERT(var3.which() == 0);
+				TESTSPR_ASSERT(sprout::get<int>(var3) == 0);
+			}
+
+			// operator<<
+			{
+				std::ostringstream os;
+				os << var1;
+				TESTSPR_ASSERT(os.str() == "1");
+			}
+			{
+				std::ostringstream os;
+				os << var2;
+				TESTSPR_ASSERT(os.str() == "0");
+			}
+
+			// tuples::get
+			TESTSPR_BOTH_ASSERT(sprout::tuples::get<1>(var1) == 1.0);
+			TESTSPR_BOTH_ASSERT(sprout::tuples::get<0>(var2) == 0);
+			{
+				auto var3 = var1;
+				TESTSPR_ASSERT(sprout::tuples::get<1>(var3) == 1.0);
+			}
+			{
+				auto var3 = var2;
+				TESTSPR_ASSERT(sprout::tuples::get<0>(var3) == 0);
+			}
+
+			// tuple_size
+			TESTSPR_BOTH_ASSERT(sprout::tuples::tuple_size<decltype(var1)>::value == 2);
+
+			// tuple_element
+			TESTSPR_BOTH_ASSERT((std::is_same<sprout::tuples::tuple_element<0, decltype(var1)>::type, int const>::value));
+			TESTSPR_BOTH_ASSERT((std::is_same<sprout::tuples::tuple_element<1, decltype(var1)>::type, double const>::value));
+		}
+	}
+}	// namespace testspr
+
+#ifndef TESTSPR_CPP_INCLUDE
+#	define TESTSPR_TEST_FUNCTION testspr::variant_test
+#	include <testspr/include_main.hpp>
+#endif
+
+#endif	// #ifndef SPROUT_LIBS_VARIANT_TEST_VARIANT_CPP
diff --git a/sprout/variant/io.hpp b/sprout/variant/io.hpp
index 76c3f10c..7ff19c89 100644
--- a/sprout/variant/io.hpp
+++ b/sprout/variant/io.hpp
@@ -31,9 +31,9 @@ namespace sprout {
 	template<typename Elem, typename Traits, typename... Types>
 	inline std::basic_ostream<Elem, Traits>&
 	operator<<(std::basic_ostream<Elem, Traits>& lhs, sprout::variant<Types...> const& rhs) {
-	    sprout::detail::variant_output_visitor<std::basic_ostream<Elem, Traits> > visitor(lhs);
+		sprout::detail::variant_output_visitor<std::basic_ostream<Elem, Traits> > visitor(lhs);
 		rhs.apply_visitor(visitor);
-	    return lhs;
+		return lhs;
 	}
 }	// namespace sprout
 
diff --git a/sprout/variant/variant.hpp b/sprout/variant/variant.hpp
index 7f5a182a..37ed0530 100644
--- a/sprout/variant/variant.hpp
+++ b/sprout/variant/variant.hpp
@@ -16,9 +16,14 @@
 #include <sprout/type/algorithm/find_index.hpp>
 
 namespace sprout {
+	template<typename... Types>
+	class variant;
+
 	namespace detail {
 		template<typename... Types>
 		class variant_impl {
+			template<typename...>
+			friend class variant;
 		protected:
 			typedef sprout::tuples::tuple<Types...> tuple_type;
 			typedef sprout::types::type_tuple<typename std::decay<Types>::type...> uncvref_tuple_type;
@@ -45,6 +50,7 @@ namespace sprout {
 			{
 				static_assert(Index::value < sizeof...(Types), "variant<>: invalid operand");
 			}
+		public:
 			void swap(variant_impl& other)
 			SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(sprout::swap(tuple_, other.tuple_)))
 			{
@@ -154,7 +160,7 @@ namespace sprout {
 		{}
 		// modifiers
 		void swap(variant& other)
-		SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(impl_type::swap(other)))
+		SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(std::declval<impl_type&>().swap(other)))
 		{
 			impl_type::swap(other);
 		}
@@ -244,11 +250,11 @@ namespace sprout {
 		// visitation support
 		template<typename Visitor>
 		SPROUT_CONSTEXPR typename Visitor::result_type apply_visitor(Visitor&& visitor) const {
-			return visit(tuple_, sprout::forward<Visitor>(visitor), which_);
+			return visit<0>(tuple_, sprout::forward<Visitor>(visitor), which_);
 		}
 		template<typename Visitor>
 		typename Visitor::result_type apply_visitor(Visitor&& visitor) {
-			return visit(tuple_, sprout::forward<Visitor>(visitor), which_);
+			return visit<0>(tuple_, sprout::forward<Visitor>(visitor), which_);
 		}
 	};
 
diff --git a/testspr/sprout.cpp b/testspr/sprout.cpp
index ca5e9baa..1e4d839a 100644
--- a/testspr/sprout.cpp
+++ b/testspr/sprout.cpp
@@ -11,6 +11,7 @@
 #include "../libs/bitset/test/bitset.cpp"
 #include "../libs/tuple/test/tuple.cpp"
 #include "../libs/optional/test/optional.cpp"
+#include "../libs/variant/test/variant.cpp"
 #include "../libs/algorithm/test/algorithm.cpp"
 #include "../libs/random/test/random.cpp"
 
@@ -25,6 +26,7 @@ namespace testspr {
 		testspr::bitset_test();
 		testspr::tuple_test();
 		testspr::optional_test();
+		testspr::variant_test();
 		testspr::algorithm_test();
 		testspr::random_test();
 	}
diff --git a/testspr/tools.hpp b/testspr/tools.hpp
index 3670c92d..99b7365c 100644
--- a/testspr/tools.hpp
+++ b/testspr/tools.hpp
@@ -231,6 +231,29 @@ namespace testspr {
 		SPROUT_CONSTEXPR result operator()(T const& val) const { return result{val}; }
 	};
 
+	//
+	// x2_visitor
+	//
+	template<typename R = void>
+	class x2_visitor {
+	public:
+		typedef R result_type;
+	public:
+		template<typename T>
+		SPROUT_CONSTEXPR result_type operator()(T const& t) const { return static_cast<result_type>(t + t); }
+	};
+	//
+	// x2_assign_visitor
+	//
+	template<typename R = void>
+	class x2_assign_visitor {
+	public:
+		typedef R result_type;
+	public:
+		template<typename T>
+		SPROUT_CONSTEXPR result_type operator()(T& t) const { return static_cast<result_type>(t += t); }
+	};
+
 	//
 	// distance
 	//