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[libc++][pair] Applied [[nodiscard]] (#171999)

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`[[nodiscard]]` should be applied to functions where discarding the
return value is most likely a correctness issue.

- https://libcxx.llvm.org/CodingGuidelines.html
- https://wg21.link/pairs
This commit is contained in:
Hristo Hristov
2025-12-15 04:42:48 +02:00
committed by GitHub
parent b6d940d9bc
commit 59fb3bc3e7
2 changed files with 70 additions and 14 deletions
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32
libcxx/include/__utility/pair.h
View File

@@ -539,8 +539,8 @@ swap(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y) noexcept(noexcept(__x
#endif
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<__unwrap_ref_decay_t<_T1>, __unwrap_ref_decay_t<_T2> >
make_pair(_T1&& __t1, _T2&& __t2) {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
pair<__unwrap_ref_decay_t<_T1>, __unwrap_ref_decay_t<_T2> > make_pair(_T1&& __t1, _T2&& __t2) {
return pair<__unwrap_ref_decay_t<_T1>, __unwrap_ref_decay_t<_T2> >(std::forward<_T1>(__t1), std::forward<_T2>(__t2));
}
@@ -612,67 +612,71 @@ struct __get_pair<1> {
};
template <size_t _Ip, class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 typename tuple_element<_Ip, pair<_T1, _T2> >::type&
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
typename tuple_element<_Ip, pair<_T1, _T2> >::type&
get(pair<_T1, _T2>& __p) _NOEXCEPT {
return __get_pair<_Ip>::get(__p);
}
template <size_t _Ip, class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const typename tuple_element<_Ip, pair<_T1, _T2> >::type&
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI
_LIBCPP_CONSTEXPR_SINCE_CXX14 const typename tuple_element<_Ip, pair<_T1, _T2> >::type&
get(const pair<_T1, _T2>& __p) _NOEXCEPT {
return __get_pair<_Ip>::get(__p);
}
template <size_t _Ip, class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
get(pair<_T1, _T2>&& __p) _NOEXCEPT {
return __get_pair<_Ip>::get(std::move(__p));
}
template <size_t _Ip, class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI
_LIBCPP_CONSTEXPR_SINCE_CXX14 const typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
get(const pair<_T1, _T2>&& __p) _NOEXCEPT {
return __get_pair<_Ip>::get(std::move(__p));
}
#if _LIBCPP_STD_VER >= 14
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1& get(pair<_T1, _T2>& __p) _NOEXCEPT {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr _T1& get(pair<_T1, _T2>& __p) _NOEXCEPT {
return __p.first;
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1 const& get(pair<_T1, _T2> const& __p) _NOEXCEPT {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr _T1 const& get(pair<_T1, _T2> const& __p) _NOEXCEPT {
return __p.first;
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1&& get(pair<_T1, _T2>&& __p) _NOEXCEPT {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr _T1&& get(pair<_T1, _T2>&& __p) _NOEXCEPT {
return std::forward<_T1&&>(__p.first);
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1 const&& get(pair<_T1, _T2> const&& __p) _NOEXCEPT {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr _T1 const&& get(pair<_T1, _T2> const&& __p) _NOEXCEPT {
return std::forward<_T1 const&&>(__p.first);
}
template <class _T2, class _T1>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T2& get(pair<_T1, _T2>& __p) _NOEXCEPT {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr _T2& get(pair<_T1, _T2>& __p) _NOEXCEPT {
return __p.second;
}
template <class _T2, class _T1>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T2 const& get(pair<_T1, _T2> const& __p) _NOEXCEPT {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr _T2 const& get(pair<_T1, _T2> const& __p) _NOEXCEPT {
return __p.second;
}
template <class _T2, class _T1>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T2&& get(pair<_T1, _T2>&& __p) _NOEXCEPT {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr _T2&& get(pair<_T1, _T2>&& __p) _NOEXCEPT {
return std::forward<_T2&&>(__p.second);
}
template <class _T2, class _T1>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T2 const&& get(pair<_T1, _T2> const&& __p) _NOEXCEPT {
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr _T2 const&& get(pair<_T1, _T2> const&& __p) _NOEXCEPT {
return std::forward<_T2 const&&>(__p.second);
}

52
libcxx/test/libcxx/utilities/utility/pairs/nodiscard.verify.cpp Normal file
View File

@@ -0,0 +1,52 @@
//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
// Check that functions are marked [[nodiscard]]
#include <utility>
#include <test_macros.h>
void test() {
struct First {};
struct Second {};
std::pair<First, Second> p;
const std::pair<First, Second> cp;
std::make_pair(94, 82); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
#if TEST_STD_VER >= 11
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(p);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(cp);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(std::move(p));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(std::move(cp));
#endif // TEST_STD_VER >= 11
#if TEST_STD_VER >= 14
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<First>(p);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<First>(cp);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<First>(std::move(p));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<First>(std::move(cp));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<Second>(p);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<Second>(cp);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<Second>(std::move(p));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<Second>(std::move(cp));
#endif // TEST_STD_VER >= 14
}