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[libc++] Remove [[nodiscard]] from map etc. operator[] (#172444)

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This was added in #169971 and related PRs. As commented there,
discarding the return value on operator[] for these types does not
typically indicate a bug since the operator can also be used to insert a
default value.
This commit is contained in:
Hans Wennborg 2025-12-16 12:58:04 +01:00 committed by GitHub
parent a96ce5f09c
commit c3ebcfe0f5
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
6 changed files with 14 additions and 14 deletions
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6
libcxx/include/__flat_map/flat_map.h
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@ -465,13 +465,13 @@ public:
}
// [flat.map.access], element access
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](const key_type& __x)
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](const key_type& __x)
requires is_constructible_v<mapped_type>
{
return try_emplace(__x).first->second;
}
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](key_type&& __x)
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](key_type&& __x)
requires is_constructible_v<mapped_type>
{
return try_emplace(std::move(__x)).first->second;
@ -480,7 +480,7 @@ public:
template <class _Kp>
requires(__is_compare_transparent && is_constructible_v<key_type, _Kp> && is_constructible_v<mapped_type> &&
!is_convertible_v<_Kp &&, const_iterator> && !is_convertible_v<_Kp &&, iterator>)
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](_Kp&& __x) {
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](_Kp&& __x) {
return try_emplace(std::forward<_Kp>(__x)).first->second;
}

4
libcxx/include/map
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@ -1092,9 +1092,9 @@ public:
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __tree_.size(); }
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT { return __tree_.max_size(); }
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](const key_type& __k);
_LIBCPP_HIDE_FROM_ABI mapped_type& operator[](const key_type& __k);
# ifndef _LIBCPP_CXX03_LANG
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](key_type&& __k);
_LIBCPP_HIDE_FROM_ABI mapped_type& operator[](key_type&& __k);
# endif
template <class _Arg,

4
libcxx/include/unordered_map
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@ -1262,9 +1262,9 @@ public:
}
# endif // _LIBCPP_STD_VER >= 20
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](const key_type& __k);
_LIBCPP_HIDE_FROM_ABI mapped_type& operator[](const key_type& __k);
# ifndef _LIBCPP_CXX03_LANG
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](key_type&& __k);
_LIBCPP_HIDE_FROM_ABI mapped_type& operator[](key_type&& __k);
# endif
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI mapped_type& at(const key_type& __k);

6
libcxx/test/libcxx/diagnostics/flat_map.nodiscard.verify.cpp
View File

@ -66,9 +66,9 @@ void test() {
TransparentKey<int> tkey;
std::flat_map<int, int> nfm;
nfm[key]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fm[std::move(key)]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fm[std::move(tkey)]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
nfm[key]; // no-warning
fm[std::move(key)]; // no-warning
fm[std::move(tkey)]; // no-warning
fm.at(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfm.at(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

4
libcxx/test/libcxx/diagnostics/map.nodiscard.verify.cpp
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@ -55,8 +55,8 @@ void test() {
int key = 0;
m[key]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
m[std::move(key)]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
m[key]; // no-warning
m[std::move(key)]; // no-warning
#if TEST_STD_VER >= 14
std::map<std::string, int, std::less<>> strMap;

4
libcxx/test/libcxx/diagnostics/unordered_map.nodiscard.verify.cpp
View File

@ -81,8 +81,8 @@ void test() {
ctm.equal_range(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
#endif
m[key]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
m[std::move(key)]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
m[key]; // no-warning
m[std::move(key)]; // no-warning
m.at(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cm.at(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}