From 2f3aaa63b93aa9babf332462a92c2a5c0779e88c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Loriot?= <sebastien.loriot@cgal.org>
Date: Tue, 25 Jul 2017 08:19:03 +0200
Subject: [PATCH] make random accessor working even if the base container is
 not random access

---
 Polygon/include/CGAL/Polygon_2.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Polygon/include/CGAL/Polygon_2.h b/Polygon/include/CGAL/Polygon_2.h
index 7623916b0a5..abc2805a2fb 100644
--- a/Polygon/include/CGAL/Polygon_2.h
+++ b/Polygon/include/CGAL/Polygon_2.h
@@ -35,6 +35,7 @@
 #include <list>
 #include <iterator>
 
+#include <CGAL/algorithm.h>
 #include <CGAL/circulator.h>
 #include <CGAL/enum.h>
 
@@ -423,7 +424,7 @@ class Polygon_2 {
 
     /// Returns a (const) reference to the `i`-th vertex.
     const Point_2& vertex(std::size_t i) const
-      { return *(d_container.begin() + i); }
+      { return *(cpp11::next(d_container.begin(), i)); }
 
 
     /// Returns a (const) reference to the `i`-th vertex.
@@ -432,7 +433,7 @@ class Polygon_2 {
 
     /// Returns the `i`-th edge.
     Segment_2 edge(std::size_t i) const
-      { return *(edges_begin() + i); }
+      { return *(cpp11::next(edges_begin(), i)); }
 
     /// @}