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[libc++] Add nodiscard attribute to std::make_unique/std::make_shared #153115

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[libc++] Add nodiscard attribute to std::make_unique/std::make_shared #153115

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935d246
added nodiscard attribute to std::make_unique()
lukasx999 Aug 12, 2025
30e0103
added nodiscard attribute to std::make_shared()
lukasx999 Aug 12, 2025
cf7c589
Merge branch 'main' into dev
lukasx999 Aug 12, 2025
2a26cb8
added nodiscard attribute to actual make_unique implementation
lukasx999 Aug 12, 2025
e13ed16
added nodiscard attribute to make_unique for C++17
lukasx999 Aug 12, 2025
b229542
added nodiscard for make_shared
lukasx999 Aug 12, 2025
1ae47c2
Merge remote-tracking branch 'origin/dev' into dev
lukasx999 Aug 12, 2025
cb4d239
removed _LIBCPP_NODISCARD_SINCE_CXX17 in favor of [[__nodiscard__]]
lukasx999 Aug 12, 2025
710f97c
removed nodiscard from memory synopsis
lukasx999 Aug 12, 2025
d793dae
removed _LIBCPP_NODISCARD_SINCE_CXX17 from make_shared
lukasx999 Aug 12, 2025
d6ac2b2
added tests for make_unique/make_shared nodiscard attribute
lukasx999 Aug 12, 2025
23356ef
using int instead of S for make_unique/make_shared nodiscard test
lukasx999 Aug 13, 2025
2e14fa1
removed version constraint for make_unique/make_shared nodiscard tests
lukasx999 Aug 13, 2025
b88cad5
added missing test cases
lukasx999 Aug 18, 2025
006a144
updated test description
lukasx999 Aug 18, 2025
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6 changes: 6 additions & 0 deletions libcxx/include/__config
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Original file line number Diff line number Diff line change
Expand Up @@ -789,6 +789,12 @@ typedef __char32_t char32_t;
# define _LIBCPP_CONSTEXPR_SINCE_CXX17
# endif

# if _LIBCPP_STD_VER >= 17
# define _LIBCPP_NODISCARD_SINCE_CXX17 [[nodiscard]]
# else
# define _LIBCPP_NODISCARD_SINCE_CXX17
# endif

# if _LIBCPP_STD_VER >= 20
# define _LIBCPP_CONSTEXPR_SINCE_CXX20 constexpr
# else
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16 changes: 8 additions & 8 deletions libcxx/include/__memory/shared_ptr.h
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Expand Up @@ -740,7 +740,7 @@ _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&&
}

template <class _Tp, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(_Args&&... __args) {
_LIBCPP_NODISCARD_SINCE_CXX17 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(_Args&&... __args) {
return std::allocate_shared<_Tp>(allocator<__remove_cv_t<_Tp> >(), std::forward<_Args>(__args)...);
}

Expand All @@ -754,7 +754,7 @@ _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc
}

template <class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
return std::allocate_shared_for_overwrite<_Tp>(allocator<__remove_cv_t<_Tp>>());
}

Expand Down Expand Up @@ -963,17 +963,17 @@ _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc
}

template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared() {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared() {
return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>());
}

template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(const remove_extent_t<_Tp>& __u) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(const remove_extent_t<_Tp>& __u) {
return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>(), __u);
}

template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
return std::__allocate_shared_bounded_array<_Tp>(allocator<__for_overwrite_tag>());
}

Expand All @@ -996,17 +996,17 @@ _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc
}

template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n) {
return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n);
}

template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n, const remove_extent_t<_Tp>& __u) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n, const remove_extent_t<_Tp>& __u) {
return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n, __u);
}

template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite(size_t __n) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite(size_t __n) {
return std::__allocate_shared_unbounded_array<_Tp>(allocator<__for_overwrite_tag>(), __n);
}

Expand Down
8 changes: 4 additions & 4 deletions libcxx/include/__memory/unique_ptr.h
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Original file line number Diff line number Diff line change
Expand Up @@ -755,12 +755,12 @@ operator<=>(const unique_ptr<_T1, _D1>& __x, nullptr_t) {
#if _LIBCPP_STD_VER >= 14

template <class _Tp, class... _Args, enable_if_t<!is_array<_Tp>::value, int> = 0>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unique_ptr<_Tp> make_unique(_Args&&... __args) {
_LIBCPP_NODISCARD_SINCE_CXX17 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unique_ptr<_Tp> make_unique(_Args&&... __args) {
return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...));
}

template <class _Tp, enable_if_t<__is_unbounded_array_v<_Tp>, int> = 0>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unique_ptr<_Tp> make_unique(size_t __n) {
_LIBCPP_NODISCARD_SINCE_CXX17 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unique_ptr<_Tp> make_unique(size_t __n) {
typedef __remove_extent_t<_Tp> _Up;
return unique_ptr<_Tp>(__private_constructor_tag(), new _Up[__n](), __n);
}
Expand All @@ -773,12 +773,12 @@ void make_unique(_Args&&...) = delete;
#if _LIBCPP_STD_VER >= 20

template <class _Tp, enable_if_t<!is_array_v<_Tp>, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unique_ptr<_Tp> make_unique_for_overwrite() {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unique_ptr<_Tp> make_unique_for_overwrite() {
return unique_ptr<_Tp>(new _Tp);
}

template <class _Tp, enable_if_t<is_unbounded_array_v<_Tp>, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unique_ptr<_Tp> make_unique_for_overwrite(size_t __n) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unique_ptr<_Tp> make_unique_for_overwrite(size_t __n) {
return unique_ptr<_Tp>(__private_constructor_tag(), new __remove_extent_t<_Tp>[__n], __n);
}

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36 changes: 18 additions & 18 deletions libcxx/include/memory
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Original file line number Diff line number Diff line change
Expand Up @@ -566,15 +566,15 @@ class bad_weak_ptr
};

template<class T, class... Args>
constexpr unique_ptr<T> make_unique(Args&&... args); // C++14, constexpr since C++23
[[nodiscard]] constexpr unique_ptr<T> make_unique(Args&&... args); // C++14, constexpr since C++23
template<class T>
constexpr unique_ptr<T> make_unique(size_t n); // C++14, constexpr since C++23
[[nodiscard]] constexpr unique_ptr<T> make_unique(size_t n); // C++14, constexpr since C++23
template<class T, class... Args> unspecified make_unique(Args&&...) = delete; // C++14, T == U[N]

template<class T>
constexpr unique_ptr<T> make_unique_for_overwrite(); // T is not array, C++20, constexpr since C++23
[[nodiscard]] constexpr unique_ptr<T> make_unique_for_overwrite(); // T is not array, C++20, constexpr since C++23
template<class T>
constexpr unique_ptr<T> make_unique_for_overwrite(size_t n); // T is U[], C++20, constexpr since C++23
[[nodiscard]] constexpr unique_ptr<T> make_unique_for_overwrite(size_t n); // T is U[], C++20, constexpr since C++23
template<class T, class... Args>
unspecified make_unique_for_overwrite(Args&&...) = delete; // T is U[N], C++20

Expand Down Expand Up @@ -702,39 +702,39 @@ template<class E, class T, class Y>
template<class D, class T> D* get_deleter(shared_ptr<T> const& p) noexcept;

template<class T, class... Args>
shared_ptr<T> make_shared(Args&&... args); // T is not an array
[[nodiscard]] shared_ptr<T> make_shared(Args&&... args); // T is not an array
template<class T, class A, class... Args>
shared_ptr<T> allocate_shared(const A& a, Args&&... args); // T is not an array
[[nodiscard]] shared_ptr<T> allocate_shared(const A& a, Args&&... args); // T is not an array

template<class T>
shared_ptr<T> make_shared(size_t N); // T is U[] (since C++20)
[[nodiscard]] shared_ptr<T> make_shared(size_t N); // T is U[] (since C++20)
template<class T, class A>
shared_ptr<T> allocate_shared(const A& a, size_t N); // T is U[] (since C++20)
[[nodiscard]] shared_ptr<T> allocate_shared(const A& a, size_t N); // T is U[] (since C++20)

template<class T>
shared_ptr<T> make_shared(); // T is U[N] (since C++20)
[[nodiscard]] shared_ptr<T> make_shared(); // T is U[N] (since C++20)
template<class T, class A>
shared_ptr<T> allocate_shared(const A& a); // T is U[N] (since C++20)
[[nodiscard]] shared_ptr<T> allocate_shared(const A& a); // T is U[N] (since C++20)

template<class T>
shared_ptr<T> make_shared(size_t N, const remove_extent_t<T>& u); // T is U[] (since C++20)
[[nodiscard]] shared_ptr<T> make_shared(size_t N, const remove_extent_t<T>& u); // T is U[] (since C++20)
template<class T, class A>
shared_ptr<T> allocate_shared(const A& a, size_t N, const remove_extent_t<T>& u); // T is U[] (since C++20)
[[nodiscard]] shared_ptr<T> allocate_shared(const A& a, size_t N, const remove_extent_t<T>& u); // T is U[] (since C++20)

template<class T> shared_ptr<T>
make_shared(const remove_extent_t<T>& u); // T is U[N] (since C++20)
[[nodiscard]] make_shared(const remove_extent_t<T>& u); // T is U[N] (since C++20)
template<class T, class A>
shared_ptr<T> allocate_shared(const A& a, const remove_extent_t<T>& u); // T is U[N] (since C++20)
[[nodiscard]] shared_ptr<T> allocate_shared(const A& a, const remove_extent_t<T>& u); // T is U[N] (since C++20)

template<class T>
shared_ptr<T> make_shared_for_overwrite(); // T is not U[], C++20
[[nodiscard]] shared_ptr<T> make_shared_for_overwrite(); // T is not U[], C++20
template<class T, class A>
shared_ptr<T> allocate_shared_for_overwrite(const A& a); // T is not U[], C++20
[[nodiscard]] shared_ptr<T> allocate_shared_for_overwrite(const A& a); // T is not U[], C++20

template<class T>
shared_ptr<T> make_shared_for_overwrite(size_t N); // T is U[], C++20
[[nodiscard]] shared_ptr<T> make_shared_for_overwrite(size_t N); // T is U[], C++20
template<class T, class A>
shared_ptr<T> allocate_shared_for_overwrite(const A& a, size_t N); // T is U[], C++20
[[nodiscard]] shared_ptr<T> allocate_shared_for_overwrite(const A& a, size_t N); // T is U[], C++20

template<class T>
class weak_ptr
Expand Down