From 663a30f659aefb1d8464d08b8a2a4eddb32dc8b4 Mon Sep 17 00:00:00 2001
From: morinmorin <mimomorin@gmail.com>
Date: Thu, 29 Jun 2017 22:06:12 +0900
Subject: [PATCH] Implement BoostIteratorTraversalConcepts-aware
 boost::advance/distance

---
 include/boost/iterator/advance.hpp  | 85 +++++++++++++++++++++++++++++
 include/boost/iterator/distance.hpp | 65 ++++++++++++++++++++++
 2 files changed, 150 insertions(+)
 create mode 100644 include/boost/iterator/advance.hpp
 create mode 100644 include/boost/iterator/distance.hpp

diff --git a/include/boost/iterator/advance.hpp b/include/boost/iterator/advance.hpp
new file mode 100644
index 0000000..2698f2b
--- /dev/null
+++ b/include/boost/iterator/advance.hpp
@@ -0,0 +1,85 @@
+// Copyright (C) 2017 Michel Morin.
+//
+// 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 BOOST_ITERATOR_ADVANCE_HPP
+#define BOOST_ITERATOR_ADVANCE_HPP
+
+#include <boost/config.hpp>
+#include <boost/iterator/iterator_categories.hpp>
+#include <boost/iterator/iterator_traits.hpp>
+
+namespace boost {
+namespace iterators {
+
+    namespace detail {
+        template <typename InputIterator>
+        inline BOOST_CXX14_CONSTEXPR void
+        advance_impl(
+            InputIterator& it
+          , typename iterator_difference<InputIterator>::type n
+          , incrementable_traversal_tag
+        )
+        {
+            while (n > 0) {
+                ++it;
+                --n;
+            }
+        }
+
+        template <typename BidirectionalIterator>
+        inline BOOST_CXX14_CONSTEXPR void
+        advance_impl(
+            BidirectionalIterator& it
+          , typename iterator_difference<BidirectionalIterator>::type n
+          , bidirectional_traversal_tag
+        )
+        {
+            if (n >= 0) {
+                while (n > 0) {
+                    ++it;
+                    --n;
+                }
+            }
+            else {
+                while (n < 0) {
+                    --it;
+                    ++n;
+                }
+            }
+        }
+
+        template <typename RandomAccessIterator>
+        inline BOOST_CXX14_CONSTEXPR void
+        advance_impl(
+            RandomAccessIterator& it
+          , typename iterator_difference<RandomAccessIterator>::type n
+          , random_access_traversal_tag
+        )
+        {
+            it += n;
+        }
+    }
+
+    namespace advance_adl_barrier {
+        template <typename InputIterator>
+        inline BOOST_CXX14_CONSTEXPR void
+        advance(InputIterator& it, typename iterator_difference<InputIterator>::type n)
+        {
+            detail::advance_impl(
+                it, n, typename iterator_traversal<InputIterator>::type()
+            );
+        }
+    }
+
+    using namespace advance_adl_barrier;
+
+} // namespace iterators
+
+using iterators::advance;
+
+} // namespace boost
+
+#endif
diff --git a/include/boost/iterator/distance.hpp b/include/boost/iterator/distance.hpp
new file mode 100644
index 0000000..8cf3f15
--- /dev/null
+++ b/include/boost/iterator/distance.hpp
@@ -0,0 +1,65 @@
+// Copyright (C) 2017 Michel Morin.
+//
+// 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 BOOST_ITERATOR_DISTANCE_HPP
+#define BOOST_ITERATOR_DISTANCE_HPP
+
+#include <boost/config.hpp>
+#include <boost/iterator/iterator_categories.hpp>
+#include <boost/iterator/iterator_traits.hpp>
+
+namespace boost {
+namespace iterators {
+
+    namespace detail {
+        template <typename SinglePassIterator>
+        inline BOOST_CXX14_CONSTEXPR typename iterator_difference<SinglePassIterator>::type
+        distance_impl(
+            SinglePassIterator first
+          , SinglePassIterator last
+          , single_pass_traversal_tag
+        )
+        {
+            typename iterator_difference<SinglePassIterator>::type n = 0;
+            while (first != last) {
+                ++first;
+                ++n;
+            }
+            return n;
+        }
+
+        template <typename RandomAccessIterator>
+        inline BOOST_CXX14_CONSTEXPR typename iterator_difference<RandomAccessIterator>::type
+        distance_impl(
+            RandomAccessIterator first
+          , RandomAccessIterator last
+          , random_access_traversal_tag
+        )
+        {
+            return last - first;
+        }
+    }
+
+    namespace distance_adl_barrier {
+        template <typename SinglePassIterator>
+        inline BOOST_CXX14_CONSTEXPR typename iterator_difference<SinglePassIterator>::type
+        distance(SinglePassIterator first, SinglePassIterator last)
+        {
+            return detail::distance_impl(
+                first, last, typename iterator_traversal<SinglePassIterator>::type()
+            );
+        }
+    }
+
+    using namespace distance_adl_barrier;
+
+} // namespace iterators
+
+using iterators::distance;
+
+} // namespace boost
+
+#endif