[libcxx-commits] [libcxx] [libc++] Make __can_dynamic_cast a variable template (PR #202297)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/202297

This makes the code a bit easier to read and avoids a class template instatiation.


>From 6b5dfacf39816a55f2b6356963b43cd842ccbd0a Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Mon, 8 Jun 2026 11:06:20 +0200
Subject: [PATCH] [libc++] Make __can_dynamic_cast a variable template

---
 libcxx/include/__exception/nested_exception.h | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/libcxx/include/__exception/nested_exception.h b/libcxx/include/__exception/nested_exception.h
index f8abe7db50de7..8b33911efd4c6 100644
--- a/libcxx/include/__exception/nested_exception.h
+++ b/libcxx/include/__exception/nested_exception.h
@@ -14,7 +14,6 @@
 #include <__memory/addressof.h>
 #include <__type_traits/decay.h>
 #include <__type_traits/enable_if.h>
-#include <__type_traits/integral_constant.h>
 #include <__type_traits/is_base_of.h>
 #include <__type_traits/is_class.h>
 #include <__type_traits/is_constructible.h>
@@ -82,18 +81,17 @@ template <class _Tp>
 }
 
 template <class _From, class _To>
-struct __can_dynamic_cast
-    : _BoolConstant< is_polymorphic<_From>::value &&
-                     (!is_base_of<_To, _From>::value || is_convertible<const _From*, const _To*>::value)> {};
+inline const bool __can_dynamic_cast_v =
+    is_polymorphic<_From>::value && (!is_base_of<_To, _From>::value || is_convertible<const _From*, const _To*>::value);
 
-template <class _Ep, __enable_if_t< __can_dynamic_cast<_Ep, nested_exception>::value, int> = 0>
+template <class _Ep, __enable_if_t<__can_dynamic_cast_v<_Ep, nested_exception>, int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI void rethrow_if_nested(const _Ep& __e) {
   const nested_exception* __nep = dynamic_cast<const nested_exception*>(std::addressof(__e));
   if (__nep)
     __nep->rethrow_nested();
 }
 
-template <class _Ep, __enable_if_t<!__can_dynamic_cast<_Ep, nested_exception>::value, int> = 0>
+template <class _Ep, __enable_if_t<!__can_dynamic_cast_v<_Ep, nested_exception>, int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI void rethrow_if_nested(const _Ep&) {}
 
 _LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS