add iterator_traits: SFINAE-friendly version

sprout/iterator.hpp

@@ -9,6 +9,7 @@
 #define SPROUT_ITERATOR_HPP
 
 #include <sprout/config.hpp>
+#include <sprout/iterator/iterator_traits.hpp>
 #include <sprout/iterator/type_traits.hpp>
 #include <sprout/iterator/operation.hpp>
 #include <sprout/iterator/predefined.hpp>

sprout/iterator/iterator_traits.hpp

@@ -0,0 +1,50 @@
+/*=============================================================================
+  Copyright (c) 2011-2014 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_ITERATOR_ITERATOR_TRAITS_HPP
+#define SPROUT_ITERATOR_ITERATOR_TRAITS_HPP
+
+#include <iterator>
+#include <sprout/config.hpp>
+#include <sprout/utility/pack.hpp>
+#include <sprout/detail/nil_base.hpp>
+
+namespace sprout {
+	//
+	// iterator_traits
+	//
+	namespace detail {
+		template<typename Iterator, typename = void>
+		struct iterator_traits_impl
+			: public sprout::detail::nil_base
+		{};
+		template<typename Iterator>
+		struct iterator_traits_impl<
+			Iterator,
+			typename sprout::head_element<
+				void,
+				typename Iterator::difference_type,
+				typename Iterator::value_type,
+				typename Iterator::pointer,
+				typename Iterator::reference,
+				typename Iterator::iterator_category
+			>::type
+		>
+			: public std::iterator_traits<Iterator>
+		{};
+	}	// namespace detail
+	template<typename Iterator>
+	struct iterator_traits
+		: public sprout::detail::iterator_traits_impl<Iterator>
+	{};
+	template<typename T>
+	struct iterator_traits<T*>
+		: public std::iterator_traits<T*>
+	{};
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_ITERATOR_ITERATOR_TRAITS_HPP

sprout/iterator/type_traits/is_iterator.hpp

@@ -8,9 +8,9 @@
 #ifndef SPROUT_ITERATOR_TYPE_TRAITS_IS_ITERATOR_HPP
 #define SPROUT_ITERATOR_TYPE_TRAITS_IS_ITERATOR_HPP
 
-#include <iterator>
 #include <sprout/config.hpp>
 #include <sprout/type_traits/has_xxx.hpp>
+#include <sprout/iterator/iterator_traits.hpp>
 
 namespace sprout {
 	namespace detail {
@@ -25,7 +25,7 @@ namespace sprout {
 	//
 	template<typename T>
 	struct is_iterator
-		: public sprout::detail::has_iterator_category<std::iterator_traits<T> >
+		: public sprout::detail::has_iterator_category<sprout::iterator_traits<T> >
 	{};
 
 #if SPROUT_USE_VARIABLE_TEMPLATES