From 9d13cb14c3cf6b59bd16071929f25ac5516a4d24 Mon Sep 17 00:00:00 2001
From: Eric Niebler <eniebler@boost.org>
Date: Fri, 9 Dec 2016 20:19:50 -0800
Subject: [PATCH] Fixes to typedef's for span::const_iterator.

* Don't const-qualify span::const_iterator's value_type
Fixes Microsoft/GSL#434
---
 gsl/span | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/gsl/span b/gsl/span
index 6d6992d..aec826a 100644
--- a/gsl/span
+++ b/gsl/span
@@ -140,15 +140,15 @@ namespace details
     template <class Span, bool IsConst>
     class span_iterator
     {
+        using element_type_ = typename Span::element_type;
     public:
         using iterator_category = std::random_access_iterator_tag;
-        using value_type =
-            std::conditional_t<IsConst, std::add_const_t<typename Span::element_type>,
-                               typename Span::element_type>;
+        using value_type = std::remove_const_t<element_type_>;
         using difference_type = typename Span::index_type;
 
-        using pointer = std::add_pointer_t<value_type>;
-        using reference = std::add_lvalue_reference_t<value_type>;
+        using reference =
+            std::conditional_t<IsConst, const element_type_, element_type_> &;
+        using pointer = std::add_pointer_t<reference>;
 
         constexpr span_iterator() noexcept : span_iterator(nullptr, 0) {}