[libc++][NFC] Use __copy_cv to implement __apply_cv

[philnik777]

No description provided.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[github-actions]

✅ With the latest revision this PR passed the Python code formatter.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/86477.diff

1 Files Affected:

• (modified) libcxx/include/__type_traits/apply_cv.h (+5-45)

diff --git a/libcxx/include/__type_traits/apply_cv.h b/libcxx/include/__type_traits/apply_cv.h
index 7c6aabec8344b1..723af95b8d9280 100644
--- a/libcxx/include/__type_traits/apply_cv.h
+++ b/libcxx/include/__type_traits/apply_cv.h
@@ -10,9 +10,7 @@
 #define _LIBCPP___TYPE_TRAITS_APPLY_CV_H
 
 #include <__config>
-#include <__type_traits/is_const.h>
-#include <__type_traits/is_volatile.h>
-#include <__type_traits/remove_reference.h>
+#include <__type_traits/copy_cv.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -20,54 +18,16 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _Tp,
-          bool = is_const<__libcpp_remove_reference_t<_Tp> >::value,
-          bool = is_volatile<__libcpp_remove_reference_t<_Tp> >::value>
-struct __apply_cv_impl {
-  template <class _Up>
-  using __apply _LIBCPP_NODEBUG = _Up;
-};
-
 template <class _Tp>
-struct __apply_cv_impl<_Tp, true, false> {
-  template <class _Up>
-  using __apply _LIBCPP_NODEBUG = const _Up;
-};
-
-template <class _Tp>
-struct __apply_cv_impl<_Tp, false, true> {
-  template <class _Up>
-  using __apply _LIBCPP_NODEBUG = volatile _Up;
-};
-
-template <class _Tp>
-struct __apply_cv_impl<_Tp, true, true> {
-  template <class _Up>
-  using __apply _LIBCPP_NODEBUG = const volatile _Up;
-};
-
-template <class _Tp>
-struct __apply_cv_impl<_Tp&, false, false> {
-  template <class _Up>
-  using __apply _LIBCPP_NODEBUG = _Up&;
-};
-
-template <class _Tp>
-struct __apply_cv_impl<_Tp&, true, false> {
-  template <class _Up>
-  using __apply _LIBCPP_NODEBUG = const _Up&;
-};
-
-template <class _Tp>
-struct __apply_cv_impl<_Tp&, false, true> {
+struct __apply_cv_impl {
   template <class _Up>
-  using __apply _LIBCPP_NODEBUG = volatile _Up&;
+  using __apply _LIBCPP_NODEBUG = __copy_cv_t<_Tp, _Up>;
 };
 
 template <class _Tp>
-struct __apply_cv_impl<_Tp&, true, true> {
+struct __apply_cv_impl<_Tp&> {
   template <class _Up>
-  using __apply _LIBCPP_NODEBUG = const volatile _Up&;
+  using __apply _LIBCPP_NODEBUG = __copy_cv_t<_Tp, _Up>&;
 };
 
 template <class _Tp, class _Up>

[ldionne]

An improvement to __copy_cv_ref_t we could maybe do is

template <bool _Ref>
struct __copy_cv_ref_impl;

template <>
struct __copy_cv_ref_impl<true> {
  template <class _Tp>
  using __apply _LIBCPP_NODEBUG = _Tp&;
};

template <>
struct __copy_cv_ref_impl<false> {
  template <class _Tp>
  using __apply _LIBCPP_NODEBUG = _Tp;
};

template <class _Tp>
using __copy_cvref_t = typename __copy_cv_ref_impl<is_lvalue_reference_v<_Tp>>::template __apply<_Tp>;