From 423841e965ee72a474f176b16b79ce421549d5b9 Mon Sep 17 00:00:00 2001
From: ericLemanissier <ericLemanissier@users.noreply.github.com>
Date: Thu, 3 May 2018 08:08:41 +0200
Subject: [PATCH] fix requirement on not_null template

it should be comparable to nullptr, it does not have to be assignable
---
 include/gsl/pointers | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/gsl/pointers b/include/gsl/pointers
index ad15ce3..891dfc5 100644
--- a/include/gsl/pointers
+++ b/include/gsl/pointers
@@ -69,7 +69,7 @@ template <class T>
 class not_null
 {
 public:
-    static_assert(std::is_assignable<T&, std::nullptr_t>::value, "T cannot be assigned nullptr.");
+    static_assert(std::is_convertible<decltype(std::declval<T>() != nullptr), bool>::value, "T cannot be compared to nullptr.");
 
     template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
     constexpr explicit not_null(U&& u) : ptr_(std::forward<U>(u))