From be3037dbc8b2137af0d49642f558803ae4806cc7 Mon Sep 17 00:00:00 2001
From: Nils Wentzell <nwentzell@flatironinstitute.org>
Date: Tue, 1 Feb 2022 16:23:51 -0500
Subject: [PATCH] Add comment to itertools::distance implementation

---
 c++/itertools/itertools.hpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/c++/itertools/itertools.hpp b/c++/itertools/itertools.hpp
index 997764b..4786279 100644
--- a/c++/itertools/itertools.hpp
+++ b/c++/itertools/itertools.hpp
@@ -67,6 +67,7 @@ namespace itertools {
   template <typename Iter, typename EndIter>
   inline typename std::iterator_traits<Iter>::difference_type distance(Iter first, EndIter last) {
     if constexpr (std::is_same_v<typename std::iterator_traits<Iter>::iterator_category, std::random_access_iterator_tag>) {
+      // Difference should be defined also for the the case that last is a sentinel
       return last - first;
     } else {
       typename std::iterator_traits<Iter>::difference_type r(0);