From 3d32d5d833a9e0ece9d62aa205c817454a9ad117 Mon Sep 17 00:00:00 2001
From: Jonas Hoppe <162709928+czjhoppe@users.noreply.github.com>
Date: Fri, 30 Aug 2024 13:27:37 +0200
Subject: [PATCH] [msvc][fix] internal compiler error for requires expression.
 "simplify" with extra concept

---
 src/core/include/mp-units/ostream.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/core/include/mp-units/ostream.h b/src/core/include/mp-units/ostream.h
index e2464bd7..d9ba6e5d 100644
--- a/src/core/include/mp-units/ostream.h
+++ b/src/core/include/mp-units/ostream.h
@@ -89,9 +89,12 @@ std::basic_ostream<CharT, Traits>& to_stream(std::basic_ostream<CharT, Traits>&
 
 MP_UNITS_EXPORT_BEGIN
 
+template<typename OStream, typename T>
+concept is_mp_units_stream = requires (OStream os, T v) { detail::to_stream_impl(os, v); }; 
+
 template<typename CharT, typename Traits, typename T>
 std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const T& v)
-  requires requires { detail::to_stream_impl(os, v); }
+  requires is_mp_units_stream<std::basic_ostream<CharT, Traits>, T>
 {
   return detail::to_stream(os, v);
 }