[libcxx-commits] [libcxx] [libc++] Simplify the implementation of pointer_traits a bit (PR #142260)
Nikolas Klauser via libcxx-commits
libcxx-commits at lists.llvm.org
Sat May 31 00:46:57 PDT 2025
https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/142260
None
>From 797de751993f79703341ff60eded272143f32a89 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Sat, 31 May 2025 09:46:39 +0200
Subject: [PATCH] [libc++] Simplify the implementation of pointer_traits a bit
---
libcxx/include/__memory/pointer_traits.h | 100 +++++++----------------
1 file changed, 29 insertions(+), 71 deletions(-)
diff --git a/libcxx/include/__memory/pointer_traits.h b/libcxx/include/__memory/pointer_traits.h
index 4ba50898fb37d..4413834fd0e5f 100644
--- a/libcxx/include/__memory/pointer_traits.h
+++ b/libcxx/include/__memory/pointer_traits.h
@@ -16,7 +16,9 @@
#include <__type_traits/conditional.h>
#include <__type_traits/conjunction.h>
#include <__type_traits/decay.h>
+#include <__type_traits/detected_or.h>
#include <__type_traits/enable_if.h>
+#include <__type_traits/nat.h>
#include <__type_traits/integral_constant.h>
#include <__type_traits/is_class.h>
#include <__type_traits/is_function.h>
@@ -34,67 +36,37 @@ _LIBCPP_PUSH_MACROS
_LIBCPP_BEGIN_NAMESPACE_STD
-// clang-format off
-#define _LIBCPP_CLASS_TRAITS_HAS_XXX(NAME, PROPERTY) \
- template <class _Tp, class = void> \
- struct NAME : false_type {}; \
- template <class _Tp> \
- struct NAME<_Tp, __void_t<typename _Tp::PROPERTY> > : true_type {}
-// clang-format on
-
-_LIBCPP_CLASS_TRAITS_HAS_XXX(__has_pointer, pointer);
-_LIBCPP_CLASS_TRAITS_HAS_XXX(__has_element_type, element_type);
-
-template <class _Ptr, bool = __has_element_type<_Ptr>::value>
-struct __pointer_traits_element_type {};
-
template <class _Ptr>
-struct __pointer_traits_element_type<_Ptr, true> {
- using type _LIBCPP_NODEBUG = typename _Ptr::element_type;
-};
-
-template <template <class, class...> class _Sp, class _Tp, class... _Args>
-struct __pointer_traits_element_type<_Sp<_Tp, _Args...>, true> {
- using type _LIBCPP_NODEBUG = typename _Sp<_Tp, _Args...>::element_type;
-};
+struct __pointer_traits_element_type_impl {};
template <template <class, class...> class _Sp, class _Tp, class... _Args>
-struct __pointer_traits_element_type<_Sp<_Tp, _Args...>, false> {
+struct __pointer_traits_element_type_impl<_Sp<_Tp, _Args...> > {
using type _LIBCPP_NODEBUG = _Tp;
};
-template <class _Tp, class = void>
-struct __has_difference_type : false_type {};
-
-template <class _Tp>
-struct __has_difference_type<_Tp, __void_t<typename _Tp::difference_type> > : true_type {};
-
-template <class _Ptr, bool = __has_difference_type<_Ptr>::value>
-struct __pointer_traits_difference_type {
- using type _LIBCPP_NODEBUG = ptrdiff_t;
-};
+template <class _Ptr, class = void>
+struct __pointer_traits_element_type : __pointer_traits_element_type_impl<_Ptr> {};
template <class _Ptr>
-struct __pointer_traits_difference_type<_Ptr, true> {
- using type _LIBCPP_NODEBUG = typename _Ptr::difference_type;
+struct __pointer_traits_element_type<_Ptr, __void_t<typename _Ptr::element_type>> {
+ using type _LIBCPP_NODEBUG = typename _Ptr::element_type;
};
template <class _Tp, class _Up>
-struct __has_rebind {
-private:
- template <class _Xp>
- static false_type __test(...);
- _LIBCPP_SUPPRESS_DEPRECATED_PUSH
- template <class _Xp>
- static true_type __test(typename _Xp::template rebind<_Up>* = 0);
- _LIBCPP_SUPPRESS_DEPRECATED_POP
+struct __pointer_traits_rebind_impl {
+ static_assert(false, "Cannot rebind pointer; did you forget to add a rebind member to your pointer?");
+};
-public:
- static const bool value = decltype(__test<_Tp>(0))::value;
+template <template <class, class...> class _Sp, class _Tp, class... _Args, class _Up>
+struct __pointer_traits_rebind_impl<_Sp<_Tp, _Args...>, _Up> {
+ using type _LIBCPP_NODEBUG = _Sp<_Up, _Args...>;
};
-template <class _Tp, class _Up, bool = __has_rebind<_Tp, _Up>::value>
-struct __pointer_traits_rebind {
+template <class _Tp, class _Up, class = void>
+struct __pointer_traits_rebind : __pointer_traits_rebind_impl<_Tp, _Up> {};
+
+template <class _Tp, class _Up>
+struct __pointer_traits_rebind<_Tp, _Up, __void_t<typename _Tp::template rebind<_Up> > > {
#ifndef _LIBCPP_CXX03_LANG
using type _LIBCPP_NODEBUG = typename _Tp::template rebind<_Up>;
#else
@@ -102,19 +74,8 @@ struct __pointer_traits_rebind {
#endif
};
-template <template <class, class...> class _Sp, class _Tp, class... _Args, class _Up>
-struct __pointer_traits_rebind<_Sp<_Tp, _Args...>, _Up, true> {
-#ifndef _LIBCPP_CXX03_LANG
- using type _LIBCPP_NODEBUG = typename _Sp<_Tp, _Args...>::template rebind<_Up>;
-#else
- using type _LIBCPP_NODEBUG = typename _Sp<_Tp, _Args...>::template rebind<_Up>::other;
-#endif
-};
-
-template <template <class, class...> class _Sp, class _Tp, class... _Args, class _Up>
-struct __pointer_traits_rebind<_Sp<_Tp, _Args...>, _Up, false> {
- typedef _Sp<_Up, _Args...> type;
-};
+template <class _Tp>
+using __difference_type_member = typename _Tp::difference_type;
template <class _Ptr, class = void>
struct __pointer_traits_impl {};
@@ -123,7 +84,7 @@ template <class _Ptr>
struct __pointer_traits_impl<_Ptr, __void_t<typename __pointer_traits_element_type<_Ptr>::type> > {
typedef _Ptr pointer;
typedef typename __pointer_traits_element_type<pointer>::type element_type;
- typedef typename __pointer_traits_difference_type<pointer>::type difference_type;
+ using difference_type = __detected_or_t<ptrdiff_t, __difference_type_member, pointer>;
#ifndef _LIBCPP_CXX03_LANG
template <class _Up>
@@ -135,9 +96,6 @@ struct __pointer_traits_impl<_Ptr, __void_t<typename __pointer_traits_element_ty
};
#endif // _LIBCPP_CXX03_LANG
-private:
- struct __nat {};
-
public:
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static pointer
pointer_to(__conditional_t<is_void<element_type>::value, __nat, element_type>& __r) {
@@ -164,9 +122,6 @@ struct pointer_traits<_Tp*> {
};
#endif
-private:
- struct __nat {};
-
public:
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static pointer
pointer_to(__conditional_t<is_void<element_type>::value, __nat, element_type>& __r) _NOEXCEPT {
@@ -257,20 +212,23 @@ template <class _Tp>
struct __pointer_of {};
template <class _Tp>
- requires(__has_pointer<_Tp>::value)
+concept __use_pointer_member = requires { typename _Tp::pointer; };
+
+template <__use_pointer_member _Tp>
struct __pointer_of<_Tp> {
using type _LIBCPP_NODEBUG = typename _Tp::pointer;
};
template <class _Tp>
- requires(!__has_pointer<_Tp>::value && __has_element_type<_Tp>::value)
+concept __use_element_type_member = !__use_pointer_member<_Tp> && requires { typename _Tp::element_type; };
+
+template <__use_element_type_member _Tp>
struct __pointer_of<_Tp> {
using type _LIBCPP_NODEBUG = typename _Tp::element_type*;
};
template <class _Tp>
- requires(!__has_pointer<_Tp>::value && !__has_element_type<_Tp>::value &&
- __has_element_type<pointer_traits<_Tp>>::value)
+ requires(!__use_element_type_member<_Tp>)
struct __pointer_of<_Tp> {
using type _LIBCPP_NODEBUG = typename pointer_traits<_Tp>::element_type*;
};
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