From ab6c53b8ac7a291f730d5d260ea2b0cc19eb674c Mon Sep 17 00:00:00 2001
From: Eric Niebler <eniebler@nvidia.com>
Date: Sat, 25 Jan 2025 01:36:08 +0000
Subject: [PATCH] add a `__call_result_t` template alias, implement
 `__is_callable_v` with it

---
 .../include/cuda/std/__type_traits/is_callable.h     | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/libcudacxx/include/cuda/std/__type_traits/is_callable.h b/libcudacxx/include/cuda/std/__type_traits/is_callable.h
index 2e433f65cf8..7e577cfc8a0 100644
--- a/libcudacxx/include/cuda/std/__type_traits/is_callable.h
+++ b/libcudacxx/include/cuda/std/__type_traits/is_callable.h
@@ -20,23 +20,21 @@
 #  pragma system_header
 #endif // no system header
 
-#include <cuda/std/__type_traits/integral_constant.h>
+#include <cuda/std/__type_traits/is_valid_expansion.h>
 #include <cuda/std/__utility/declval.h>
 
 _LIBCUDACXX_BEGIN_NAMESPACE_STD
 
-template <class _Func, class... _Args, class = decltype(_CUDA_VSTD::declval<_Func>()(_CUDA_VSTD::declval<_Args>()...))>
-_LIBCUDACXX_HIDE_FROM_ABI true_type __is_callable_helper(int);
-template <class...>
-_LIBCUDACXX_HIDE_FROM_ABI false_type __is_callable_helper(...);
+template <class _Func, class... _Args>
+using __call_result_t = decltype(_CUDA_VSTD::declval<_Func>()(_CUDA_VSTD::declval<_Args>()...));
 
 template <class _Func, class... _Args>
-struct __is_callable : decltype(__is_callable_helper<_Func, _Args...>(0))
+struct __is_callable : _IsValidExpansion<__call_result_t, _Func, _Args...>
 {};
 
 #ifndef _CCCL_NO_VARIABLE_TEMPLATES
 template <class _Func, class... _Args>
-_CCCL_INLINE_VAR constexpr bool __is_callable_v = decltype(__is_callable_helper<_Func, _Args...>(0))::value;
+_CCCL_INLINE_VAR constexpr bool __is_callable_v = _IsValidExpansion<__call_result_t, _Func, _Args...>::value;
 #endif // !_CCCL_NO_VARIABLE_TEMPLATES
 
 _LIBCUDACXX_END_NAMESPACE_STD