From 01eaf5bef131ff51274ca57f5ade2d10851aa00b Mon Sep 17 00:00:00 2001
From: Jordan Maples <jomaples@microsoft.com>
Date: Mon, 10 Aug 2020 16:45:47 -0700
Subject: [PATCH] macro version

---
 include/gsl/gsl_util | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index 89fb2ee..2e79605 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -32,6 +32,12 @@
 
 #endif            // _MSC_VER
 
+#if __has_cpp_attribute(nodiscard) >= 201603L
+#define GSL_NODISCARD [[nodiscard]]
+#else
+#define GSL_NODISCARD
+#endif
+
 namespace gsl
 {
 //
@@ -67,13 +73,13 @@ private:
 
 // finally() - convenience function to generate a final_action
 template <class F>
-final_action<F> finally(const F& f) noexcept
+GSL_NODISCARD final_action<F> finally(const F& f) noexcept
 {
     return final_action<F>(f);
 }
 
 template <class F>
-final_action<F> finally(F&& f) noexcept
+GSL_NODISCARD final_action<F> finally(F&& f) noexcept
 {
     return final_action<F>(std::forward<F>(f));
 }
@@ -98,16 +104,16 @@ constexpr
 T narrow(U u) noexcept(false)
 {
     constexpr const bool is_different_signedness = (std::is_signed<T>::value != std::is_signed<U>::value);
-    
+
     const T t = narrow_cast<T>(u);
-    
+
     if (static_cast<U>(t) != u
         || (is_different_signedness
             && ((t < T{}) != (u < U{}))))
     {
         throw narrowing_error{};
     }
-    
+
     return t;
 }