[libcxx-commits] [libcxx] [libc++] Use _If for conditional_t (PR #96193)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/96193

This avoids different instantiations when the if and else types are different, resulting in reduced memory use by the compiler.


>From fd9a857ac89ccc122a7b80b63fb01ed29abcd82d Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Thu, 20 Jun 2024 16:03:28 +0200
Subject: [PATCH] [libc++] Use _If for conditional_t

---
 libcxx/include/__type_traits/conditional.h | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/libcxx/include/__type_traits/conditional.h b/libcxx/include/__type_traits/conditional.h
index 5b5445a837427..7d5849ee824e3 100644
--- a/libcxx/include/__type_traits/conditional.h
+++ b/libcxx/include/__type_traits/conditional.h
@@ -44,15 +44,14 @@ struct _LIBCPP_TEMPLATE_VIS conditional<false, _If, _Then> {
   using type _LIBCPP_NODEBUG = _Then;
 };
 
+template <bool _Bp, class _IfRes, class _ElseRes>
+using __conditional_t _LIBCPP_NODEBUG = _If<_Bp, _IfRes, _ElseRes>;
+
 #if _LIBCPP_STD_VER >= 14
 template <bool _Bp, class _IfRes, class _ElseRes>
-using conditional_t _LIBCPP_NODEBUG = typename conditional<_Bp, _IfRes, _ElseRes>::type;
+using conditional_t _LIBCPP_NODEBUG = __conditional_t<_Bp, _IfRes, _ElseRes>;
 #endif
 
-// Helper so we can use "conditional_t" in all language versions.
-template <bool _Bp, class _If, class _Then>
-using __conditional_t _LIBCPP_NODEBUG = typename conditional<_Bp, _If, _Then>::type;
-
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___TYPE_TRAITS_CONDITIONAL_H