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

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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.
This commit is contained in:
Nikolas Klauser
2024-04-11 17:55:25 +02:00
committed by GitHub
parent 7ab7e7a55f
commit b63fe0d72e
1 changed files with 22 additions and 18 deletions
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40
libcxx/include/__type_traits/copy_cv.h
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@@ -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>
struct __copy_cv<const _From> {
template <class _To>
using __apply = const _To;
};
template <class _From>
struct __copy_cv<volatile _From> {
template <class _To>
using __apply = volatile _To;
};
template <class _From>
struct __copy_cv<const volatile _From> {
template <class _To>
using __apply = const volatile _To;
};
template <class _From, class _To>
struct __copy_cv<const _From, _To> {
using type = const _To;
};
template <class _From, class _To>
struct __copy_cv<volatile _From, _To> {
using type = volatile _To;
};
template <class _From, class _To>
struct __copy_cv<const volatile _From, _To> {
using type = 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