[libcxx-commits] [libcxx] [libc++][tuple][utility] P2968R2 Make `std::ignore` a first-class object (PR #97401)
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libcxx-commits at lists.llvm.org
Fri Jul 5 04:41:34 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Hristo Hristov (H-G-Hristov)
<details>
<summary>Changes</summary>
Implements as DR11: https://wg21.link/P2968R2
References:
- https://eel.is/c++draft/tuple.general
- https://eel.is/c++draft/tuple.syn
- https://eel.is/c++draft/tuple.creation
- https://github.com/cplusplus/draft/milestone/31
- https://github.com/cplusplus/papers/issues/1640
- https://cplusplus.github.io/LWG/issue2933
- https://cplusplus.github.io/LWG/issue3978
---
Full diff: https://github.com/llvm/llvm-project/pull/97401.diff
7 Files Affected:
- (modified) libcxx/docs/ReleaseNotes/19.rst (+1)
- (modified) libcxx/include/CMakeLists.txt (+1)
- (added) libcxx/include/__tuple/ignore.h (+35)
- (modified) libcxx/include/module.modulemap (+1)
- (modified) libcxx/include/tuple (+7-17)
- (modified) libcxx/include/utility (+4)
- (modified) libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp (+42-32)
``````````diff
diff --git a/libcxx/docs/ReleaseNotes/19.rst b/libcxx/docs/ReleaseNotes/19.rst
index d30021b7eb2347..5c3737d79876e4 100644
--- a/libcxx/docs/ReleaseNotes/19.rst
+++ b/libcxx/docs/ReleaseNotes/19.rst
@@ -46,6 +46,7 @@ Implemented Papers
- P2872R3 - Remove ``wstring_convert`` From C++26
- P3142R0 - Printing Blank Lines with ``println`` (as DR against C++23)
- P2944R3 - Comparisons for ``reference_wrapper`` (comparison operators for ``reference_wrapper`` only)
+- P2968R2 - Make ``std::ignore`` a first-class object (as DR against C++11)
- P2302R4 - ``std::ranges::contains``
- P1659R3 - ``std::ranges::starts_with`` and ``std::ranges::ends_with``
- P3029R1 - Better ``mdspan``'s CTAD
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 8d0ffd6ed725bd..07dd25604a9c76 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -710,6 +710,7 @@ set(files
__thread/timed_backoff_policy.h
__tree
__tuple/find_index.h
+ __tuple/ignore.h
__tuple/make_tuple_types.h
__tuple/sfinae_helpers.h
__tuple/tuple_element.h
diff --git a/libcxx/include/__tuple/ignore.h b/libcxx/include/__tuple/ignore.h
new file mode 100644
index 00000000000000..a00fc7e7d5b85e
--- /dev/null
+++ b/libcxx/include/__tuple/ignore.h
@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___TUPLE_IGNORE_H
+#define _LIBCPP___TUPLE_IGNORE_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+#ifndef _LIBCPP_CXX03_LANG
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+struct __ignore_type {
+ template <class _Tp>
+ _LIBCPP_HIDE_FROM_ABI constexpr const __ignore_type& operator=(const _Tp&) const noexcept {
+ return *this;
+ }
+};
+
+inline constexpr __ignore_type ignore;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_CXX03_LANG
+
+#endif // _LIBCPP___TUPLE_IGNORE_H
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
index 9ffccf66ff0948..4ad506781c489a 100644
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -1840,6 +1840,7 @@ module std_private_thread_thread [system] {
module std_private_thread_timed_backoff_policy [system] { header "__thread/timed_backoff_policy.h" }
module std_private_tuple_find_index [system] { header "__tuple/find_index.h" }
+module std_private_tuple_ignore [system] { header "__tuple/ignore.h" }
module std_private_tuple_make_tuple_types [system] { header "__tuple/make_tuple_types.h" }
module std_private_tuple_tuple_like_no_subrange [system] {
header "__tuple/tuple_like_no_subrange.h"
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index 26652ffe81e9f0..d2f6e19ede68df 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -132,7 +132,12 @@ tuple(allocator_arg_t, Alloc, pair<T1, T2>) -> tuple<T1, T2>; // since C++
template <class Alloc, class ...T>
tuple(allocator_arg_t, Alloc, tuple<T...>) -> tuple<T...>; // since C++17
-inline constexpr unspecified ignore;
++struct ignore-type { // exposition only
++ constexpr const ignore-type&
++ operator=(const auto &) const noexcept
++ { return *this; }
++};
+inline constexpr ignore-type ignore;
template <class... T> tuple<V...> make_tuple(T&&...); // constexpr in C++14
template <class... T> tuple<ATypes...> forward_as_tuple(T&&...) noexcept; // constexpr in C++14
@@ -215,6 +220,7 @@ template <class... Types>
#include <__memory/allocator_arg_t.h>
#include <__memory/uses_allocator.h>
#include <__tuple/find_index.h>
+#include <__tuple/ignore.h>
#include <__tuple/make_tuple_types.h>
#include <__tuple/sfinae_helpers.h>
#include <__tuple/tuple_element.h>
@@ -1112,22 +1118,6 @@ inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 tuple<_Tp&...> tie(_T
return tuple<_Tp&...>(__t...);
}
-template <class _Up>
-struct __ignore_t {
- template <class _Tp>
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const __ignore_t& operator=(_Tp&&) const {
- return *this;
- }
-};
-
-# if _LIBCPP_STD_VER >= 17
-inline constexpr __ignore_t<unsigned char> ignore = __ignore_t<unsigned char>();
-# else
-namespace {
-constexpr __ignore_t<unsigned char> ignore = __ignore_t<unsigned char>();
-} // namespace
-# endif
-
template <class... _Tp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 tuple<typename __unwrap_ref_decay<_Tp>::type...>
make_tuple(_Tp&&... __t) {
diff --git a/libcxx/include/utility b/libcxx/include/utility
index 90713da621c5da..f2f0052df27552 100644
--- a/libcxx/include/utility
+++ b/libcxx/include/utility
@@ -274,6 +274,10 @@ template <class T>
#include <compare>
#include <initializer_list>
+// [tuple.creation]
+
+#include <__tuple/ignore.h>
+
// [tuple.helper]
#include <__tuple/tuple_element.h>
#include <__tuple/tuple_size.h>
diff --git a/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp
index 769c55e10fc438..49f3249a4e413a 100644
--- a/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp
+++ b/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp
@@ -6,51 +6,61 @@
//
//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++03
+
// <tuple>
-// constexpr unspecified ignore;
-
-// UNSUPPORTED: c++03
+// inline constexpr ignore-type ignore;
#include <cassert>
+#include <cstdint>
#include <tuple>
#include <type_traits>
#include "test_macros.h"
-constexpr bool test_ignore_constexpr()
-{
-#if TEST_STD_VER > 11
- { // Test that std::ignore provides constexpr converting assignment.
- auto& res = (std::ignore = 42);
- assert(&res == &std::ignore);
- }
- { // Test that std::ignore provides constexpr copy/move constructors
- auto copy = std::ignore;
- auto moved = std::move(copy);
- ((void)moved);
- }
- { // Test that std::ignore provides constexpr copy/move assignment
- auto copy = std::ignore;
- copy = std::ignore;
- auto moved = std::ignore;
- moved = std::move(copy);
- }
+static_assert(std::is_trivial<decltype(std::ignore)>::value, "");
+
+#if TEST_STD_VER >= 17
+[[nodiscard]] constexpr int test_nodiscard() { return 8294; }
#endif
- return true;
+
+constexpr bool test() {
+#if TEST_STD_VER >= 17
+ { std::ignore = test_nodiscard(); }
+#endif
+
+ return true;
}
int main(int, char**) {
- {
- constexpr auto& ignore_v = std::ignore;
- ((void)ignore_v);
- }
- {
- static_assert(test_ignore_constexpr(), "");
- }
- {
- LIBCPP_STATIC_ASSERT(std::is_trivial<decltype(std::ignore)>::value, "");
- }
+ test();
+ static_assert(test(), "");
+
+ { [[maybe_unused]] constexpr auto& ignore_v = std::ignore; }
+ { // Test that std::ignore provides constexpr converting assignment.
+ constexpr auto& res = (std::ignore = 42);
+ static_assert(noexcept(res = (std::ignore = 42)), "Must be noexcept");
+ assert(&res == &std::ignore);
+ }
+ { // Test bit-field binding.
+ struct S {
+ unsigned int bf : 3;
+ };
+ constexpr S s{0b010};
+ constexpr auto& res = (std::ignore = s.bf);
+ assert(&res == &std::ignore);
+ }
+ { // Test that std::ignore provides constexpr copy/move constructors
+ constexpr auto copy = std::ignore;
+ [[maybe_unused]] constexpr auto moved = std::move(copy);
+ }
+ { // Test that std::ignore provides constexpr copy/move assignment
+ constexpr auto copy = std::ignore;
+ copy = std::ignore;
+ constexpr auto moved = std::ignore;
+ moved = std::move(copy);
+ }
return 0;
}
``````````
</details>
https://github.com/llvm/llvm-project/pull/97401
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