[iterators][segment iterator] fix for boost trac ticket #11346

Problem: segment iterator does not work with point iterators that return
a value instead of a reference when dereferenced.
Fix: check the if the reference type of the point iterator is indeed a
reference or not and use a pointing_segment or a segment as the value type
of the segment iterator, respectively.

include/boost/geometry/iterators/detail/segment_iterator/value_type.hpp

@@ -1,6 +1,6 @@
 // Boost.Geometry (aka GGL, Generic Geometry Library)
 
-// Copyright (c) 2014, Oracle and/or its affiliates.
+// Copyright (c) 2014-2015, Oracle and/or its affiliates.
 
 // Contributed and/or modified by Menelaos Karavelas, on behalf of Oracle
 
@@ -10,7 +10,14 @@
 #ifndef BOOST_GEOMETRY_ITERATORS_DETAIL_SEGMENT_ITERATOR_VALUE_TYPE_HPP
 #define BOOST_GEOMETRY_ITERATORS_DETAIL_SEGMENT_ITERATOR_VALUE_TYPE_HPP
 
-#include <boost/geometry/iterators/detail/point_iterator/value_type.hpp>
+#include <iterator>
+
+#include <boost/mpl/if.hpp>
+#include <boost/type_traits/is_reference.hpp>
+
+#include <boost/geometry/iterators/point_iterator.hpp>
+#include <boost/geometry/util/bare_type.hpp>
+#include <boost/geometry/geometries/segment.hpp>
 #include <boost/geometry/geometries/pointing_segment.hpp>
 
 
@@ -24,15 +31,36 @@ namespace detail { namespace segment_iterator
 template <typename Geometry>
 struct value_type
 {
+    typedef typename std::iterator_traits
+        <
+            geometry::point_iterator<Geometry>
+        >::reference point_iterator_reference_type;
+
     typedef typename detail::point_iterator::value_type
         <
             Geometry
         >::type point_iterator_value_type;
 
-    typedef geometry::model::pointing_segment
+    // If the reference type of the point iterator is not really a
+    // reference, then dereferencing a point iterator would create
+    // a temporary object.
+    // In this case using a pointing_segment to represent the
+    // dereferenced value of the segment iterator cannot be used, as
+    // it would store pointers to temporary objects. Instead we use a
+    // segment, which does a full copy of the temporary objects
+    // returned by the point iterator.
+    typedef typename boost::mpl::if_
         <
-            point_iterator_value_type
-        > type;
+            boost::is_reference<point_iterator_reference_type>,
+            geometry::model::pointing_segment<point_iterator_value_type>,
+            geometry::model::segment
+                <
+                    typename geometry::util::bare_type
+                        <
+                            point_iterator_value_type
+                        >::type
+                >
+        >::type type;
 };
 
 }} // namespace detail::segment_iterator