[libcxx-commits] [libcxx] b63fe0d - [libc++][NFC] Reduce the memory footprint of __copy_cv a bit (#87718)

[via libcxx-commits]

Author: Nikolas Klauser
Date: 2024-04-11T17:55:25+02:00
New Revision: b63fe0d72e2df3b3c4b9fcb91aea07b2582be195

URL: https://github.com/llvm/llvm-project/commit/b63fe0d72e2df3b3c4b9fcb91aea07b2582be195
DIFF: https://github.com/llvm/llvm-project/commit/b63fe0d72e2df3b3c4b9fcb91aea07b2582be195.diff

LOG: [libc++][NFC] Reduce the memory footprint of __copy_cv a bit (#87718)

Instead of instantiating `__copy_cv` for every combination of `_From`
and `_To` this only instantiates `__copy_cv` for every `_From` type,
reducing the number of instantiations.

Added: 
    

Modified: 
    libcxx/include/__type_traits/copy_cv.h

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__type_traits/copy_cv.h b/libcxx/include/__type_traits/copy_cv.h
index b1c057ff778b1b..d482cb42bffed9 100644
--- a/libcxx/include/__type_traits/copy_cv.h
+++ b/libcxx/include/__type_traits/copy_cv.h
@@ -19,28 +19,32 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 // Let COPYCV(FROM, TO) be an alias for type TO with the addition of FROM's
 // top-level cv-qualifiers.
-template <class _From, class _To>
+template <class _From>
 struct __copy_cv {
-  using type = _To;
+  template <class _To>
+  using __apply = _To;
 };
 
-template <class _From, class _To>
-struct __copy_cv<const _From, _To> {
-  using type = const _To;
+template <class _From>
+struct __copy_cv<const _From> {
+  template <class _To>
+  using __apply = const _To;
 };
 
-template <class _From, class _To>
-struct __copy_cv<volatile _From, _To> {
-  using type = volatile _To;
+template <class _From>
+struct __copy_cv<volatile _From> {
+  template <class _To>
+  using __apply = volatile _To;
 };
 
-template <class _From, class _To>
-struct __copy_cv<const volatile _From, _To> {
-  using type = const volatile _To;
+template <class _From>
+struct __copy_cv<const volatile _From> {
+  template <class _To>
+  using __apply = const volatile _To;
 };
 
 template <class _From, class _To>
-using __copy_cv_t = typename __copy_cv<_From, _To>::type;
+using __copy_cv_t = typename __copy_cv<_From>::template __apply<_To>;
 
 _LIBCPP_END_NAMESPACE_STD