From 2722fdcda359b5b084f4a014b24ca93086d86525 Mon Sep 17 00:00:00 2001
From: Andrey Semashev <andrey.semashev@gmail.com>
Date: Sun, 23 Jul 2017 20:29:25 +0300
Subject: [PATCH] Use std::iterator_traits to detect iterators, when possible.

This allows next/prior to detect user's iterators that do not
define iterator_category nested type but specialize
std::iterator_traits instead.
---
 include/boost/next_prior.hpp | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/boost/next_prior.hpp b/include/boost/next_prior.hpp
index bad46ed..178cf67 100644
--- a/include/boost/next_prior.hpp
+++ b/include/boost/next_prior.hpp
@@ -52,7 +52,16 @@ struct is_iterator
 };
 
 template< typename T >
-struct is_iterator< T, typename enable_if_has_type< typename T::iterator_category >::type >
+struct is_iterator<
+    T,
+    typename enable_if_has_type<
+#if !defined(BOOST_NO_CXX17_ITERATOR_TRAITS)
+        typename std::iterator_traits< T >::iterator_category
+#else
+        typename T::iterator_category
+#endif
+    >::type
+>
 {
     static BOOST_CONSTEXPR_OR_CONST bool value = true;
 };