From 4d023b5bd4553cc3a6da19289563430480cc303d Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Fri, 6 Jul 2018 11:20:38 +0100
Subject: [PATCH] * include/std/variant (__accepted_index): Use void_t.

From-SVN: r262471
---
 libstdc++-v3/ChangeLog           | 4 ++++
 libstdc++-v3/include/std/variant | 6 +++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index f78d3043858..30fe76958f0 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,7 @@
+2018-07-06  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/std/variant (__accepted_index): Use void_t.
+
 2018-07-05  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/85831
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 63eafdd58e5..66d878142a4 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -710,7 +710,8 @@ namespace __variant
     };
 
   // Helper for variant(_Tp&&) and variant::operator=(_Tp&&).
-  // __accepted_index maps the arbitrary _Tp to an alternative type in _Variant.
+  // __accepted_index maps an arbitrary _Tp to an alternative type in _Variant
+  // (or to variant_npos).
   template<typename _Tp, typename _Variant, typename = void>
     struct __accepted_index
     { static constexpr size_t value = variant_npos; };
@@ -718,8 +719,7 @@ namespace __variant
   template<typename _Tp, typename... _Types>
     struct __accepted_index<
       _Tp, variant<_Types...>,
-      decltype(__overload_set<_Types...>::_S_fun(std::declval<_Tp>()),
-	       std::declval<void>())>
+      void_t<decltype(__overload_set<_Types...>::_S_fun(std::declval<_Tp>()))>>
     {
       static constexpr size_t value = sizeof...(_Types) - 1
 	- decltype(__overload_set<_Types...>::
-- 
2.30.2