整理

include/boost/iterator/distance.hpp

@@ -0,0 +1,59 @@
+// 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 detail
+
+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());
+}
+
+} // namespace distance_adl_barrier
+
+using namespace distance_adl_barrier;
+
+} // namespace iterators
+
+using namespace iterators::distance_adl_barrier;
+
+} // namespace boost
+
+#endif