diff --git a/sprout/tuple/fused.hpp b/sprout/tuple/fused.hpp
index 054de1ea..29fcb48c 100644
--- a/sprout/tuple/fused.hpp
+++ b/sprout/tuple/fused.hpp
@@ -1,6 +1,7 @@
 #ifndef SPROUT_TUPLE_FUSED_HPP
 #define SPROUT_TUPLE_FUSED_HPP
 
+#include <utility>
 #include <type_traits>
 #include <sprout/config.hpp>
 #include <sprout/index_tuple.hpp>
@@ -16,14 +17,32 @@ namespace sprout {
 		class fused {
 		public:
 			typedef F functor_type;
+		private:
+			template<typename Tuple, typename IndexTuple>
+			struct result_impl;
+			template<typename Tuple, sprout::index_t... Indexes>
+			struct result_impl<Tuple, sprout::index_tuple<Indexes...> > {
+			public:
+				typedef decltype(
+					std::declval<functor_type const&>()(
+						sprout::tuples::get<Indexes>(std::declval<Tuple>())...
+						)
+				) type;
+			};
+		public:
+			template<typename Tuple>
+			struct result
+				: public result_impl<
+					Tuple,
+					typename sprout::index_range<0, sprout::tuples::tuple_size<typename std::remove_reference<Tuple>::type>::value>::type
+				>
+			{};
 		private:
 			functor_type f_;
 		private:
-			template<typename Tuple, sprout::index_t... Indexes>
-			SPROUT_CONSTEXPR auto
-			call(Tuple&& t, sprout::index_tuple<Indexes...>) const
-				-> decltype(f_(sprout::tuples::get<Indexes>(sprout::forward<Tuple>(t))...))
-			{
+			template<typename Result, typename Tuple, sprout::index_t... Indexes>
+			SPROUT_CONSTEXPR Result
+			call(Tuple&& t, sprout::index_tuple<Indexes...>) const {
 				return f_(sprout::tuples::get<Indexes>(sprout::forward<Tuple>(t))...);
 			}
 		public:
@@ -36,16 +55,11 @@ namespace sprout {
 				return f_;
 			}
 			template<typename Tuple>
-			SPROUT_CONSTEXPR auto
-			operator()(Tuple&& t) const
-				-> decltype(this->call(
+			SPROUT_CONSTEXPR typename result<Tuple>::type
+			operator()(Tuple&& t) const {
+				return call<typename result<Tuple>::type>(
 					sprout::forward<Tuple>(t),
-					sprout::index_range<0, sprout::tuples::tuple_size<typename std::decay<Tuple>::type>::value>::make()
-					))
-			{
-				return call(
-					sprout::forward<Tuple>(t),
-					sprout::index_range<0, sprout::tuples::tuple_size<typename std::decay<Tuple>::type>::value>::make()
+					sprout::index_range<0, sprout::tuples::tuple_size<typename std::remove_reference<Tuple>::type>::value>::make()
 					);
 			}
 		};
diff --git a/sprout/type/iterator/index_iterator.hpp b/sprout/type/iterator/index_iterator.hpp
index ad6f3d7d..6f3bcacd 100644
--- a/sprout/type/iterator/index_iterator.hpp
+++ b/sprout/type/iterator/index_iterator.hpp
@@ -9,109 +9,9 @@
 
 namespace sprout {
 	namespace types {
-//		template<typename Tuple, std::ptrdiff_t Index>
-//		struct index_iterator;
-//
-//		namespace detail {
-//			//
-//			// index_iterator_impl
-//			//
-//			template<typename Tuple, std::ptrdiff_t Index, typename = void>
-//			struct index_iterator_impl;
-//			template<typename Tuple, std::ptrdiff_t Index>
-//			struct index_iterator_impl<
-//				Tuple,
-//				Index,
-//				typename std::enable_if<
-//					sprout::types::tuple_size<Tuple>::value == 0
-//					|| (Index < 0)
-//					|| (Index > sprout::types::tuple_size<Tuple>::value)
-//				>::type
-//			> {
-//			public:
-//				typedef sprout::types::void_ type;
-//				typedef sprout::types::void_ next;
-//				typedef sprout::types::void_ prev;
-//			public:
-//				template<std::ptrdiff_t Disatnce>
-//				struct advance {
-//				public:
-//					typedef sprout::types::index_iterator<Tuple, Index + Disatnce> type;
-//				};
-//			};
-//			template<typename Tuple, std::ptrdiff_t Index>
-//			struct index_iterator_impl<
-//				Tuple,
-//				Index,
-//				typename std::enable_if<
-//					sprout::types::tuple_size<Tuple>::value != 0
-//					&& Index == 0
-//				>::type
-//			> {
-//			public:
-//				typedef typename sprout::types::tuple_element<Index, Tuple>::type type;
-//				typedef sprout::types::index_iterator<Tuple, Index + 1> next;
-//				typedef sprout::types::void_ prev;
-//			public:
-//				template<std::ptrdiff_t Disatnce>
-//				struct advance {
-//				public:
-//					typedef sprout::types::index_iterator<Tuple, Index + Disatnce> type;
-//				};
-//			};
-//			template<typename Tuple, std::ptrdiff_t Index>
-//			struct index_iterator_impl<
-//				Tuple,
-//				Index,
-//				typename std::enable_if<
-//					sprout::types::tuple_size<Tuple>::value != 0
-//					&& Index == sprout::types::tuple_size<Tuple>::value
-//				>::type
-//			> {
-//			public:
-//				typedef sprout::types::void_ type;
-//				typedef sprout::types::void_ next;
-//				typedef sprout::types::index_iterator<Tuple, sprout::types::tuple_size<Tuple>::value - 1> prev;
-//			public:
-//				template<std::ptrdiff_t Disatnce>
-//				struct advance {
-//				public:
-//					typedef sprout::types::index_iterator<Tuple, Index + Disatnce> type;
-//				};
-//			};
-//			template<typename Tuple, std::ptrdiff_t Index>
-//			struct index_iterator_impl<
-//				Tuple,
-//				Index,
-//				typename std::enable_if<
-//					sprout::types::tuple_size<Tuple>::value != 0
-//					&& (Index > 0)
-//					&& (Index < sprout::types::tuple_size<Tuple>::value)
-//				>::type
-//			> {
-//			public:
-//				typedef typename sprout::types::tuple_element<Index, Tuple>::type type;
-//				typedef sprout::types::index_iterator<Tuple, Index + 1> next;
-//				typedef sprout::types::index_iterator<Tuple, Index - 1> prev;
-//			public:
-//				template<std::ptrdiff_t Disatnce>
-//				struct advance {
-//				public:
-//					typedef sprout::types::index_iterator<Tuple, Index + Disatnce> type;
-//				};
-//			};
-//		}	// namespace detail
 		//
 		// index_iterator
 		//
-//		template<typename Tuple, std::ptrdiff_t Index>
-//		struct index_iterator
-//			: public sprout::types::detail::index_iterator_impl<Tuple, Index>
-//			, public std::integral_constant<std::ptrdiff_t, Index>
-//		{
-//		public:
-//			typedef typename sprout::types::detail::index_iterator_impl<Tuple, Index>::type type;
-//		};
 		template<typename Tuple, std::ptrdiff_t Index>
 		struct index_iterator
 			: public std::integral_constant<std::ptrdiff_t, Index>