[libc++] Avoid unnecessary instantiations for __copy_cvref_t #123718
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@llvm/pr-subscribers-libcxx Author: Nikolas Klauser (philnik777) ChangesThis changes the implementation of Full diff: https://github.com/llvm/llvm-project/pull/123718.diff 1 Files Affected:
diff --git a/libcxx/include/__type_traits/copy_cvref.h b/libcxx/include/__type_traits/copy_cvref.h
index 511d4e0776d609..158e5a5d78bb35 100644
--- a/libcxx/include/__type_traits/copy_cvref.h
+++ b/libcxx/include/__type_traits/copy_cvref.h
@@ -20,23 +20,26 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-template <class _From, class _To>
+template <class _From>
struct __copy_cvref {
- using type = __copy_cv_t<_From, _To>;
+ template <class _To>
+ using __apply _LIBCPP_NODEBUG = __copy_cv_t<_From, _To>;
};
-template <class _From, class _To>
-struct __copy_cvref<_From&, _To> {
- using type = __add_lvalue_reference_t<__copy_cv_t<_From, _To> >;
+template <class _From>
+struct __copy_cvref<_From&> {
+ template <class _To>
+ using __apply _LIBCPP_NODEBUG = __add_lvalue_reference_t<__copy_cv_t<_From, _To> >;
};
-template <class _From, class _To>
-struct __copy_cvref<_From&&, _To> {
- using type = __add_rvalue_reference_t<__copy_cv_t<_From, _To> >;
+template <class _From>
+struct __copy_cvref<_From&&> {
+ template <class _To>
+ using __apply _LIBCPP_NODEBUG = __add_rvalue_reference_t<__copy_cv_t<_From, _To> >;
};
template <class _From, class _To>
-using __copy_cvref_t _LIBCPP_NODEBUG = typename __copy_cvref<_From, _To>::type;
+using __copy_cvref_t _LIBCPP_NODEBUG = typename __copy_cvref<_From>::template __apply<_To>;
_LIBCPP_END_NAMESPACE_STD
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This changes the implementation of
__copy_cvref_tto only template the implementation class on the_Fromparameter, avoiding instantiations for every combination of_Fromand_To.