diff --git a/sprout/adapt/boost/array.hpp b/sprout/adapt/boost/array.hpp
index 7b08fed3..9cbcb0cc 100644
--- a/sprout/adapt/boost/array.hpp
+++ b/sprout/adapt/boost/array.hpp
@@ -8,7 +8,7 @@
 #ifndef SPROUT_ADAPT_BOOST_ARRAY_HPP
 #define SPROUT_ADAPT_BOOST_ARRAY_HPP
 
-#include <array>
+#include <boost/array.hpp>
 #include <sprout/config.hpp>
 #include <sprout/container/boost/array.hpp>
 #include <sprout/functional/hash/boost/array.hpp>
diff --git a/sprout/container/at.hpp b/sprout/container/at.hpp
index bae01ffe..097ac0ba 100644
--- a/sprout/container/at.hpp
+++ b/sprout/container/at.hpp
@@ -26,12 +26,14 @@ namespace sprout {
 	//				otherwise, Container is not const
 	//					&& sprout::is_const_cast_convertible<const_reference, reference>
 	//					&& (callable sprout::as_const(cont).at(i)
+	//						|| callable sprout::as_const(cont)[i]
 	//						|| callable sprout::as_const(cont).begin()
 	//						|| ADL(without sprout) callable begin(sprout::as_const(cont))
 	//						)
 	//					-> const_cast<reference>(sprout::at(sprout::as_const(cont), i))
 	//				otherwise, callable cont.at(i) -> cont.at(i)
-	//				otherwise -> *sprout::next(sprout::begin(cont), i)
+	//				otherwise, callable cont[i] -> cont[sprout::range_index_check(cont, i)]
+	//				otherwise -> *sprout::next(sprout::begin(cont), sprout::range_index_check(cont, i))
 	//
 	template<typename Container>
 	inline SPROUT_CONSTEXPR typename sprout::container_traits<Container>::reference
diff --git a/sprout/container/boost/array.hpp b/sprout/container/boost/array.hpp
index 846fb1a2..888ce22f 100644
--- a/sprout/container/boost/array.hpp
+++ b/sprout/container/boost/array.hpp
@@ -14,6 +14,7 @@
 #include <type_traits>
 #include <sprout/workaround/std/cstddef.hpp>
 #include <sprout/container/traits.hpp>
+#include <sprout/container/range_index_check.hpp>
 #include <sprout/iterator/index_iterator.hpp>
 #include <sprout/utility/forward.hpp>
 #include <sprout/functional/transparent.hpp>
@@ -101,13 +102,21 @@ namespace sprout {
 			return cont.elems[N - 1];
 		}
 		static SPROUT_CONSTEXPR typename sprout::container_traits<boost::array<T, N> >::reference
-		range_at(boost::array<T, N>& cont, typename sprout::container_traits<boost::array<T, N> >::size_type i) {
+		range_subscript_at(boost::array<T, N>& cont, typename sprout::container_traits<boost::array<T, N> >::size_type i) {
 			return cont.elems[i];
 		}
 		static SPROUT_CONSTEXPR typename sprout::container_traits<boost::array<T, N> const>::reference
-		range_at(boost::array<T, N> const& cont, typename sprout::container_traits<boost::array<T, N> const>::size_type i) {
+		range_subscript_at(boost::array<T, N> const& cont, typename sprout::container_traits<boost::array<T, N> const>::size_type i) {
 			return cont.elems[i];
 		}
+		static SPROUT_CONSTEXPR typename sprout::container_traits<boost::array<T, N> >::reference
+		range_at(boost::array<T, N>& cont, typename sprout::container_traits<boost::array<T, N> >::size_type i) {
+			return cont.elems[sprout::range_index_check(cont, i)];
+		}
+		static SPROUT_CONSTEXPR typename sprout::container_traits<boost::array<T, N> const>::reference
+		range_at(boost::array<T, N> const& cont, typename sprout::container_traits<boost::array<T, N> const>::size_type i) {
+			return cont.elems[sprout::range_index_check(cont, i)];
+		}
 		// data access:
 		static SPROUT_CONSTEXPR typename sprout::container_traits<boost::array<T, N> >::pointer
 		range_data(boost::array<T, N>& cont) {
diff --git a/sprout/container/container_range_traits.hpp b/sprout/container/container_range_traits.hpp
index 21832901..30d03366 100644
--- a/sprout/container/container_range_traits.hpp
+++ b/sprout/container/container_range_traits.hpp
@@ -35,6 +35,7 @@ namespace sprout_adl {
 	sprout::not_found_via_adl range_empty(...);
 	sprout::not_found_via_adl range_front(...);
 	sprout::not_found_via_adl range_back(...);
+	sprout::not_found_via_adl range_subscript_at(...);
 	sprout::not_found_via_adl range_at(...);
 	sprout::not_found_via_adl range_nth(...);
 	sprout::not_found_via_adl range_index_of(...);
@@ -585,6 +586,89 @@ namespace sprout {
 			return *sprout::next(sprout::begin(cont), sprout::size(cont) - 1);
 		}
 
+		template<typename T>
+		struct has_mem_subscript_test {
+		public:
+			template<
+				typename U = T,
+				typename = typename sprout::identity<decltype(std::declval<U>()[std::declval<typename sprout::container_traits<U>::size_type>()])>::type
+			>
+			static sprout::true_type test(int);
+			static sprout::false_type test(...);
+		};
+#if defined(_MSC_VER) && (_MSC_VER > 1900)
+		template<typename T, typename Base_ = typename sprout::identity<decltype(sprout::detail::has_mem_subscript_test<T>::test(0))>::type>
+		struct has_mem_subscript
+			: public Base_
+		{};
+#else
+		template<typename T>
+		struct has_mem_subscript
+			: public sprout::identity<decltype(sprout::detail::has_mem_subscript_test<T>::test(0))>::type
+		{};
+#endif
+
+		template<typename T>
+		struct is_substitutable_const_subscript_at
+			: public sprout::bool_constant<
+				sprout::is_const_cast_convertible<
+					typename sprout::container_traits<T const>::reference,
+					typename sprout::container_traits<T>::reference
+				>::value
+				&& (
+					sprout::detail::has_mem_subscript<T const>::value
+					|| sprout::detail::has_mem_begin<T const>::value
+					|| sprout::detail::has_adl_begin_without_sprout<T const&>::value
+					)
+			>
+		{};
+
+		template<typename Container>
+		inline SPROUT_CONSTEXPR typename std::enable_if<
+			sprout::detail::is_substitutable_const_subscript_at<Container>::value,
+			typename sprout::container_traits<Container>::reference
+		>::type
+		range_subscript_at_impl(Container& cont, typename sprout::container_traits<Container>::size_type i) {
+			typedef typename sprout::container_traits<Container>::reference type;
+			return const_cast<type>(sprout::subscript_at(sprout::as_const(cont), i));
+		}
+		template<typename Container>
+		inline SPROUT_CONSTEXPR typename std::enable_if<
+			!sprout::detail::is_substitutable_const_subscript_at<Container>::value
+				&& sprout::detail::has_mem_subscript<Container>::value
+				,
+			typename sprout::container_traits<Container>::reference
+		>::type
+		range_subscript_at_impl(Container& cont, typename sprout::container_traits<Container>::size_type i) {
+			return cont[i];
+		}
+		template<typename Container>
+		inline SPROUT_CONSTEXPR typename std::enable_if<
+			!sprout::detail::is_substitutable_const_subscript_at<Container>::value
+				&& !sprout::detail::has_mem_subscript<Container>::value
+				,
+			typename sprout::container_traits<Container>::reference
+		>::type
+		range_subscript_at_impl(Container& cont, typename sprout::container_traits<Container>::size_type i) {
+			return *sprout::next(sprout::begin(cont), i);
+		}
+		template<typename Container>
+		inline SPROUT_CONSTEXPR typename std::enable_if<
+			sprout::detail::has_mem_subscript<Container const>::value,
+			typename sprout::container_traits<Container const>::reference
+		>::type
+		range_subscript_at_impl(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+			return cont[i];
+		}
+		template<typename Container>
+		inline SPROUT_CONSTEXPR typename std::enable_if<
+			!sprout::detail::has_mem_subscript<Container const>::value,
+			typename sprout::container_traits<Container const>::reference
+		>::type
+		range_subscript_at_impl(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+			return *sprout::next(sprout::begin(cont), i);
+		}
+
 		template<typename T>
 		struct has_mem_at_test {
 		public:
@@ -616,6 +700,7 @@ namespace sprout {
 				>::value
 				&& (
 					sprout::detail::has_mem_at<T const>::value
+					|| sprout::detail::has_mem_subscript<T const>::value
 					|| sprout::detail::has_mem_begin<T const>::value
 					|| sprout::detail::has_adl_begin_without_sprout<T const&>::value
 					)
@@ -645,11 +730,23 @@ namespace sprout {
 		inline SPROUT_CONSTEXPR typename std::enable_if<
 			!sprout::detail::is_substitutable_const_at<Container>::value
 				&& !sprout::detail::has_mem_at<Container>::value
+				&& sprout::detail::has_mem_subscript<Container>::value
 				,
 			typename sprout::container_traits<Container>::reference
 		>::type
 		range_at_impl(Container& cont, typename sprout::container_traits<Container>::size_type i) {
-			return *sprout::next(sprout::begin(cont), i);
+			return cont[sprout::range_index_check(cont, i)];
+		}
+		template<typename Container>
+		inline SPROUT_CONSTEXPR typename std::enable_if<
+			!sprout::detail::is_substitutable_const_at<Container>::value
+				&& !sprout::detail::has_mem_at<Container>::value
+				&& !sprout::detail::has_mem_subscript<Container>::value
+				,
+			typename sprout::container_traits<Container>::reference
+		>::type
+		range_at_impl(Container& cont, typename sprout::container_traits<Container>::size_type i) {
+			return *sprout::next(sprout::begin(cont), sprout::range_index_check(cont, i));
 		}
 		template<typename Container>
 		inline SPROUT_CONSTEXPR typename std::enable_if<
@@ -661,11 +758,23 @@ namespace sprout {
 		}
 		template<typename Container>
 		inline SPROUT_CONSTEXPR typename std::enable_if<
-			!sprout::detail::has_mem_at<Container const>::value,
+			!sprout::detail::has_mem_at<Container const>::value
+				&& sprout::detail::has_mem_subscript<Container>::value
+				,
 			typename sprout::container_traits<Container const>::reference
 		>::type
 		range_at_impl(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
-			return *sprout::next(sprout::begin(cont), i);
+			return cont[sprout::range_index_check(cont, i)];
+		}
+		template<typename Container>
+		inline SPROUT_CONSTEXPR typename std::enable_if<
+			!sprout::detail::has_mem_at<Container const>::value
+				&& !sprout::detail::has_mem_subscript<Container>::value
+				,
+			typename sprout::container_traits<Container const>::reference
+		>::type
+		range_at_impl(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+			return *sprout::next(sprout::begin(cont), sprout::range_index_check(cont, i));
 		}
 
 		template<typename T>
@@ -949,6 +1058,17 @@ namespace sprout_container_range_detail {
 		return sprout::detail::range_back_impl(cont);
 	}
 
+	template<typename Container>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<Container>::reference
+	range_subscript_at(Container& cont, typename sprout::container_traits<Container>::size_type i) {
+		return sprout::detail::range_subscript_at_impl(cont, i);
+	}
+	template<typename Container>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::reference
+	range_subscript_at(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+		return sprout::detail::range_subscript_at_impl(cont, i);
+	}
+
 	template<typename Container>
 	inline SPROUT_CONSTEXPR typename sprout::container_traits<Container>::reference
 	range_at(Container& cont, typename sprout::container_traits<Container>::size_type i) {
@@ -1066,6 +1186,18 @@ namespace sprout {
 				return range_back(cont);
 			}
 			static SPROUT_CONSTEXPR typename sprout::container_traits<Container>::reference
+			range_subscript_at(Container& cont, typename sprout::container_traits<Container>::size_type i) {
+				using sprout_container_range_detail::range_subscript_at;
+				using sprout_adl::range_subscript_at;
+				return range_subscript_at(cont, i);
+			}
+			static SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::reference
+			range_subscript_at(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+				using sprout_container_range_detail::range_subscript_at;
+				using sprout_adl::range_subscript_at;
+				return range_subscript_at(cont, i);
+			}
+			static SPROUT_CONSTEXPR typename sprout::container_traits<Container>::reference
 			range_at(Container& cont, typename sprout::container_traits<Container>::size_type i) {
 				using sprout_container_range_detail::range_at;
 				using sprout_adl::range_at;
@@ -1149,6 +1281,10 @@ namespace sprout {
 				return sprout::container_range_traits<Container>::range_back(cont);
 			}
 			static SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::reference
+			range_subscript_at(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+				return sprout::container_range_traits<Container>::range_subscript_at(cont, i);
+			}
+			static SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::reference
 			range_at(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
 				return sprout::container_range_traits<Container>::range_at(cont, i);
 			}
@@ -1231,6 +1367,14 @@ namespace sprout {
 			return arr[N - 1];
 		}
 		static SPROUT_CONSTEXPR typename sprout::container_traits<T[N]>::reference
+		range_subscript_at(T (& arr)[N], typename sprout::container_traits<T[N]>::size_type i) {
+			return arr[i];
+		}
+		static SPROUT_CONSTEXPR typename sprout::container_traits<T const[N]>::reference
+		range_subscript_at(T const (& arr)[N], typename sprout::container_traits<T const[N]>::size_type i) {
+			return arr[i];
+		}
+		static SPROUT_CONSTEXPR typename sprout::container_traits<T[N]>::reference
 		range_at(T (& arr)[N], typename sprout::container_traits<T[N]>::size_type i) {
 			return arr[i];
 		}
@@ -1301,6 +1445,10 @@ namespace sprout {
 			return sprout::container_range_traits<T[N]>::range_back(arr);
 		}
 		static SPROUT_CONSTEXPR typename sprout::container_traits<T const[N]>::reference
+		range_subscript_at(T const (& arr)[N], typename sprout::container_traits<T const[N]>::size_type i) {
+			return sprout::container_range_traits<T[N]>::range_subscript_at(arr, i);
+		}
+		static SPROUT_CONSTEXPR typename sprout::container_traits<T const[N]>::reference
 		range_at(T const (& arr)[N], typename sprout::container_traits<T const[N]>::size_type i) {
 			return sprout::container_range_traits<T[N]>::range_at(arr, i);
 		}
@@ -1325,8 +1473,11 @@ namespace sprout {
 #include <sprout/container/size.hpp>
 #include <sprout/container/front.hpp>
 #include <sprout/container/back.hpp>
+#include <sprout/container/subscript_at.hpp>
+#include <sprout/container/at.hpp>
 #include <sprout/container/nth.hpp>
 #include <sprout/container/index_of.hpp>
 #include <sprout/container/data.hpp>
+#include <sprout/container/range_index_check.hpp>
 
 #endif	// #ifndef SPROUT_CONTAINER_CONTAINER_RANGE_TRAITS_HPP
diff --git a/sprout/container/functions.hpp b/sprout/container/functions.hpp
index 8b1b024b..ffd956e3 100644
--- a/sprout/container/functions.hpp
+++ b/sprout/container/functions.hpp
@@ -14,6 +14,5 @@
 #include <sprout/container/construct_functions.hpp>
 #include <sprout/container/fitness_functions.hpp>
 #include <sprout/container/sub_functions.hpp>
-#include <sprout/container/shrink_to_fit.hpp>
 
 #endif	// #ifndef SPROUT_CONTAINER_FUNCTIONS_HPP
diff --git a/sprout/container/range_functions.hpp b/sprout/container/range_functions.hpp
index 72649623..1cf65d17 100644
--- a/sprout/container/range_functions.hpp
+++ b/sprout/container/range_functions.hpp
@@ -20,5 +20,7 @@
 #include <sprout/container/nth.hpp>
 #include <sprout/container/index_of.hpp>
 #include <sprout/container/data.hpp>
+#include <sprout/container/range_index_check.hpp>
+#include <sprout/container/shrink_to_fit.hpp>
 
 #endif	// #ifndef SPROUT_CONTAINER_RANGE_FUNCTIONS_HPP
diff --git a/sprout/container/range_functions_fwd.hpp b/sprout/container/range_functions_fwd.hpp
index 0df5b942..c0e99e9d 100644
--- a/sprout/container/range_functions_fwd.hpp
+++ b/sprout/container/range_functions_fwd.hpp
@@ -66,6 +66,16 @@ namespace sprout {
 	SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::reference
 	back(Container const& cont);
 
+	//
+	// subscript_at
+	//
+	template<typename Container>
+	SPROUT_CONSTEXPR typename sprout::container_traits<Container>::reference
+	subscript_at(Container& cont, typename sprout::container_traits<Container>::size_type i);
+	template<typename Container>
+	SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::reference
+	subscript_at(Container const& cont, typename sprout::container_traits<Container const>::size_type i);
+
 	//
 	// at
 	//
@@ -105,8 +115,21 @@ namespace sprout {
 	template<typename Container>
 	SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::pointer
 	data(Container const& cont);
-}	// namespace sprout
 
+	//
+	// range_index_check
+	//
+	template<typename Container>
+	SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::size_type
+	range_index_check(Container const& cont, typename sprout::container_traits<Container const>::size_type i);
+
+	//
+	// shrink_to_fit
+	//
+	template<typename Container>
+	SPROUT_CXX14_CONSTEXPR void
+	shrink_to_fit(Container&& cont);
+}	// namespace sprout
 
 #include <sprout/container/size.hpp>
 #include <sprout/container/empty.hpp>
diff --git a/sprout/container/range_index_check.hpp b/sprout/container/range_index_check.hpp
new file mode 100644
index 00000000..57908d87
--- /dev/null
+++ b/sprout/container/range_index_check.hpp
@@ -0,0 +1,31 @@
+/*=============================================================================
+  Copyright (c) 2011-2016 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_CONTAINER_RANGE_INDEX_CHECK_HPP
+#define SPROUT_CONTAINER_RANGE_INDEX_CHECK_HPP
+
+#include <stdexcept>
+#include <sprout/config.hpp>
+#include <sprout/container/range_functions_fwd.hpp>
+#include <sprout/container/container_traits.hpp>
+
+namespace sprout {
+	//
+	// range_index_check
+	//
+	template<typename Container>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::size_type
+	range_index_check(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+		return i >= sprout::size(cont) ? throw std::out_of_range("range_index_check: index out of range")
+			: i
+			;
+	}
+}	// namespace sprout
+
+#include <sprout/container/size.hpp>
+
+#endif	// #ifndef SPROUT_CONTAINER_RANGE_INDEX_CHECK_HPP
diff --git a/sprout/container/sscrisk/cel/array.hpp b/sprout/container/sscrisk/cel/array.hpp
index de52df87..6419a8f4 100644
--- a/sprout/container/sscrisk/cel/array.hpp
+++ b/sprout/container/sscrisk/cel/array.hpp
@@ -15,6 +15,7 @@
 #	include <sprout/workaround/std/cstddef.hpp>
 #	include <sprout/container/traits.hpp>
 #	include <sprout/iterator/index_iterator.hpp>
+#	include <sprout/detail/functional/const_subscript.hpp>
 #endif
 
 #if SPROUT_USE_INDEX_ITERATOR_IMPLEMENTATION
@@ -27,8 +28,8 @@ namespace sprout {
 		: public sprout::detail::container_traits_default<sscrisk::cel::array<T, N> >
 	{
 	public:
-		typedef sprout::index_iterator<sscrisk::cel::array<T, N>&, true> iterator;
-		typedef sprout::index_iterator<sscrisk::cel::array<T, N> const&, true> const_iterator;
+		typedef sprout::index_iterator<sscrisk::cel::array<T, N>&, true, sprout::detail::const_subscript<> > iterator;
+		typedef sprout::index_iterator<sscrisk::cel::array<T, N> const&, true, sprout::detail::const_subscript<> > const_iterator;
 	};
 
 	//
diff --git a/sprout/container/std/array.hpp b/sprout/container/std/array.hpp
index 4e312940..911ee21b 100644
--- a/sprout/container/std/array.hpp
+++ b/sprout/container/std/array.hpp
@@ -18,27 +18,9 @@
 #include <sprout/utility/forward.hpp>
 #include <sprout/utility/as_const.hpp>
 #include <sprout/memory/addressof.hpp>
-#include <sprout/functional/transparent.hpp>
+#include <sprout/detail/functional/const_subscript.hpp>
 
 namespace sprout {
-	namespace detail {
-		template<typename T = void>
-		struct const_subscript;
-		template<>
-		struct const_subscript<void>
-			: public sprout::transparent<>
-		{
-		public:
-			template<typename T, typename U>
-			SPROUT_CONSTEXPR decltype(std::declval<T>()[std::declval<U>()])
-			operator()(T&& x, U&& y)
-			const SPROUT_NOEXCEPT_IF_EXPR(const_cast<decltype(std::declval<T>()[std::declval<U>()])>(sprout::as_const(std::declval<T>())[std::declval<U>()]))
-			{
-				return const_cast<decltype(std::declval<T>()[std::declval<U>()])>(sprout::as_const(x)[SPROUT_FORWARD(U, y)]);
-			}
-		};
-	}	// namespace detail
-
 	//
 	// container_traits
 	//
@@ -60,10 +42,6 @@ namespace sprout {
 	{
 	private:
 		typedef sprout::detail::container_range_traits_default<std::array<T, N> > base_type;
-	public:
-		using base_type::range_front;
-		using base_type::range_back;
-		using base_type::range_at;
 	public:
 		// iterators:
 		static SPROUT_CONSTEXPR typename sprout::container_traits<std::array<T, N> >::iterator
@@ -82,27 +60,7 @@ namespace sprout {
 		range_end(std::array<T, N> const& cont) {
 			return typename sprout::container_traits<std::array<T, N> const>::iterator(cont, cont.size());
 		}
-		// element access:
-		static SPROUT_CONSTEXPR typename sprout::container_traits<std::array<T, N> >::reference
-		range_front(std::array<T, N>& cont) {
-			typedef typename sprout::container_traits<std::array<T, N> >::reference type;
-			return const_cast<type>(base_type::range_front(sprout::as_const(cont)));
-		}
-		static SPROUT_CONSTEXPR typename sprout::container_traits<std::array<T, N> >::reference
-		range_back(std::array<T, N>& cont) {
-			typedef typename sprout::container_traits<std::array<T, N> >::reference type;
-			return const_cast<type>(base_type::range_back(sprout::as_const(cont)));
-		}
-		static SPROUT_CONSTEXPR typename sprout::container_traits<std::array<T, N> >::reference
-		range_at(std::array<T, N>& cont, typename sprout::container_traits<std::array<T, N> >::size_type i) {
-			typedef typename sprout::container_traits<std::array<T, N> >::reference type;
-			return const_cast<type>(base_type::range_at(sprout::as_const(cont), i));
-		}
 		// data access:
-		static SPROUT_CONSTEXPR typename sprout::container_traits<std::array<T, N> >::pointer
-		range_data(std::array<T, N>& cont) {
-			return sprout::addressof(range_front(cont));
-		}
 		static SPROUT_CONSTEXPR typename sprout::container_traits<std::array<T, N> const>::pointer
 		range_data(std::array<T, N> const& cont) {
 			return sprout::addressof(range_front(cont));
diff --git a/sprout/container/subscript_at.hpp b/sprout/container/subscript_at.hpp
new file mode 100644
index 00000000..4a35d9eb
--- /dev/null
+++ b/sprout/container/subscript_at.hpp
@@ -0,0 +1,74 @@
+/*=============================================================================
+  Copyright (c) 2011-2016 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_CONTAINER_SUBSCRIPT_AT_HPP
+#define SPROUT_CONTAINER_SUBSCRIPT_AT_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/workaround/std/cstddef.hpp>
+#include <sprout/container/traits_fwd.hpp>
+#include <sprout/container/container_traits.hpp>
+
+namespace sprout {
+	//
+	// subscript_at
+	//
+	//	effect:
+	//		sprout::container_range_traits<Container>::range_subscript_at(cont, i)
+	//		[default]
+	//			ADL callable range_subscript_at(cont, i) -> range_subscript_at(cont, i)
+	//			[default]
+	//				Container is T[N] -> cont[i]
+	//				otherwise, Container is not const
+	//					&& sprout::is_const_cast_convertible<const_reference, reference>
+	//					&& (callable sprout::as_const(cont)[i]
+	//						|| callable sprout::as_const(cont).begin()
+	//						|| ADL(without sprout) callable begin(sprout::as_const(cont))
+	//						)
+	//					-> const_cast<reference>(sprout::subscript_at(sprout::as_const(cont), i))
+	//				otherwise, callable cont[i] -> cont[i]
+	//				otherwise -> *sprout::next(sprout::begin(cont), i)
+	//
+	template<typename Container>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<Container>::reference
+	subscript_at(Container& cont, typename sprout::container_traits<Container>::size_type i) {
+		return sprout::container_range_traits<Container>::range_subscript_at(cont, i);
+	}
+	template<typename Container>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::reference
+	subscript_at(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+		return sprout::container_range_traits<Container const>::range_subscript_at(cont, i);
+	}
+	template<typename T, std::size_t N>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<T[N]>::reference
+	subscript_at(T (& arr)[N], typename sprout::container_traits<T[N]>::size_type i) {
+		return sprout::container_range_traits<T[N]>::range_subscript_at(arr, i);
+	}
+	template<typename T, std::size_t N>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<T const[N]>::reference
+	subscript_at(T const (& arr)[N], typename sprout::container_traits<T const[N]>::size_type i) {
+		return sprout::container_range_traits<T const[N]>::range_subscript_at(arr, i);
+	}
+
+	//
+	// csubscript_at
+	//
+	template<typename Container>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<Container const>::reference
+	csubscript_at(Container const& cont, typename sprout::container_traits<Container const>::size_type i) {
+		return sprout::subscript_at(cont, i);
+	}
+	template<typename T, std::size_t N>
+	inline SPROUT_CONSTEXPR typename sprout::container_traits<T const[N]>::reference
+	csubscript_at(T const (& arr)[N], typename sprout::container_traits<T const[N]>::size_type i) {
+		return sprout::subscript_at(arr, i);
+	}
+}	// namespace sprout
+
+#include <sprout/container/container_range_traits.hpp>
+
+#endif	// #ifndef SPROUT_CONTAINER_SUBSCRIPT_AT_HPP
diff --git a/sprout/detail/functional/const_subscript.hpp b/sprout/detail/functional/const_subscript.hpp
new file mode 100644
index 00000000..ee71dd95
--- /dev/null
+++ b/sprout/detail/functional/const_subscript.hpp
@@ -0,0 +1,37 @@
+/*=============================================================================
+  Copyright (c) 2011-2016 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_DETAIL_FUNCTIONAL_CONST_SUBSCRIPT_HPP
+#define SPROUT_DETAIL_FUNCTIONAL_CONST_SUBSCRIPT_HPP
+
+#include <utility>
+#include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
+#include <sprout/utility/as_const.hpp>
+#include <sprout/functional/transparent.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename T = void>
+		struct const_subscript;
+		template<>
+		struct const_subscript<void>
+			: public sprout::transparent<>
+		{
+		public:
+			template<typename T, typename U>
+			SPROUT_CONSTEXPR decltype(std::declval<T>()[std::declval<U>()])
+			operator()(T&& x, U&& y)
+			const SPROUT_NOEXCEPT_IF_EXPR(const_cast<decltype(std::declval<T>()[std::declval<U>()])>(sprout::as_const(std::declval<T>())[std::declval<U>()]))
+			{
+				return const_cast<decltype(std::declval<T>()[std::declval<U>()])>(sprout::as_const(x)[SPROUT_FORWARD(U, y)]);
+			}
+		};
+	}	// namespace detail
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_DETAIL_FUNCTIONAL_CONST_SUBSCRIPT_HPP