[PATCH] libstdc++: Use basic_string_view for std::bitset deduced types

[Jonathan Wakely]

This change was part of by P2697R1 (Interfacing bitset with string_view)
and should be slightly cheaper to instantiate.

libstdc++-v3/ChangeLog:

        * include/std/bitset (__bitset::__string) [__cpp_lib_bitset]:
        Change alias to refer to basic_string_view instead.
---

Tested x86_64-linux.

 libstdc++-v3/include/std/bitset | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
index 61756350cc9c..92f11f19807a 100644
--- a/libstdc++-v3/include/std/bitset
+++ b/libstdc++-v3/include/std/bitset
@@ -720,7 +720,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
   namespace __bitset
   {
-#if _GLIBCXX_HOSTED
+#ifdef __cpp_lib_bitset // ...construct from string_view
+    template<typename _CharT>
+      using __string = std::basic_string_view<_CharT>;
+#elif _GLIBCXX_HOSTED
     template<typename _CharT>
       using __string = std::basic_string<_CharT>;
 #else
-- 
2.50.1