From: Patrick Palka <ppalka@redhat.com>
Date: Fri, 18 Jun 2021 15:51:33 +0000 (-0400)
Subject: libstdc++: Implement LWG 3557 change to convertible_to
X-Git-Tag: releases/gcc-11.3.0~768
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3c2397242a051eaf1f9fc9797142ecf7b00256b8;p=thirdparty%2Fgcc.git

libstdc++: Implement LWG 3557 change to convertible_to

libstdc++-v3/ChangeLog:

	* include/std/concepts (convertible_to): Just use declval as per
	LWG 3557.

(cherry picked from commit 83faf7eacd2081a373afb6069fd923c2dc497271)
---

diff --git a/libstdc++-v3/include/std/concepts b/libstdc++-v3/include/std/concepts
index 4490f5344125..7f5421f1475e 100644
--- a/libstdc++-v3/include/std/concepts
+++ b/libstdc++-v3/include/std/concepts
@@ -70,9 +70,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   /// [concept.convertible], concept convertible_to
   template<typename _From, typename _To>
     concept convertible_to = is_convertible_v<_From, _To>
-      && requires(add_rvalue_reference_t<_From> (&__f)()) {
-	  static_cast<_To>(__f());
-      };
+      && requires { static_cast<_To>(std::declval<_From>()); };
 
   /// [concept.commonref], concept common_reference_with
   template<typename _Tp, typename _Up>