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[libc++] Simplify the implementation of std::get for pairs (#114984)

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This makes it clearer what the functions actually do. As a nice
side-effect it also avoids a function call. If the C++03 header split is
successful we could drop `__get_pair` entirely.
This commit is contained in:
Nikolas Klauser 2025-05-12 22:40:17 +02:00 committed by GitHub
parent 769c6a95ae
commit c8f2cdafd4
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GPG Key ID: B5690EEEBB952194
2 changed files with 112 additions and 67 deletions
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32
libcxx/include/__utility/pair.h
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@ -654,42 +654,42 @@ get(const pair<_T1, _T2>&& __p) _NOEXCEPT {
#if _LIBCPP_STD_VER >= 14
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1& get(pair<_T1, _T2>& __p) _NOEXCEPT {
return __get_pair<0>::get(__p);
return __p.first;
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1 const& get(pair<_T1, _T2> const& __p) _NOEXCEPT {
return __get_pair<0>::get(__p);
return __p.first;
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1&& get(pair<_T1, _T2>&& __p) _NOEXCEPT {
return __get_pair<0>::get(std::move(__p));
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 {
return __get_pair<0>::get(std::move(__p));
return std::forward<_T1 const&&>(__p.first);
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1& get(pair<_T2, _T1>& __p) _NOEXCEPT {
return __get_pair<1>::get(__p);
template <class _T2, class _T1>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T2& get(pair<_T1, _T2>& __p) _NOEXCEPT {
return __p.second;
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1 const& get(pair<_T2, _T1> const& __p) _NOEXCEPT {
return __get_pair<1>::get(__p);
template <class _T2, class _T1>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T2 const& get(pair<_T1, _T2> const& __p) _NOEXCEPT {
return __p.second;
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1&& get(pair<_T2, _T1>&& __p) _NOEXCEPT {
return __get_pair<1>::get(std::move(__p));
template <class _T2, class _T1>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T2&& get(pair<_T1, _T2>&& __p) _NOEXCEPT {
return std::forward<_T2&&>(__p.second);
}
template <class _T1, class _T2>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T1 const&& get(pair<_T2, _T1> const&& __p) _NOEXCEPT {
return __get_pair<1>::get(std::move(__p));
template <class _T2, class _T1>
inline _LIBCPP_HIDE_FROM_ABI constexpr _T2 const&& get(pair<_T1, _T2> const&& __p) _NOEXCEPT {
return std::forward<_T2 const&&>(__p.second);
}
#endif // _LIBCPP_STD_VER >= 14

147
libcxx/test/std/utilities/utility/pairs/pair.astuple/pairs.by.type.pass.cpp
View File

@ -8,43 +8,114 @@
// UNSUPPORTED: c++03, c++11
#include <utility>
#include <string>
#include <type_traits>
#include <cassert>
#include <complex>
#include <memory>
#include <cassert>
#include <type_traits>
#include <utility>
#include "test_macros.h"
int main(int, char**)
{
TEST_CONSTEXPR_CXX14 bool test() {
{ // Make sure that references work as expected
int i = 1;
int j = 2;
{
std::pair<int&, int&&> p(i, std::move(j));
assert(&std::get<int&>(p) == &i);
assert(&std::get<int&&>(p) == &j);
assert(&std::get<int&>(std::move(p)) == &i);
assert(std::get<int&&>(std::move(p)) == 2);
const std::pair<int&, int&&> cp(i, std::move(j));
assert(&std::get<int&>(cp) == &i);
assert(&std::get<int&&>(cp) == &j);
assert(&std::get<int&>(std::move(cp)) == &i);
assert(std::get<int&&>(std::move(cp)) == 2);
}
{
std::pair<int&&, int&> p(std::move(i), j);
assert(&std::get<int&>(p) == &j);
assert(&std::get<int&&>(p) == &i);
assert(&std::get<int&>(std::move(p)) == &j);
assert(std::get<int&&>(std::move(p)) == 1);
const std::pair<int&&, int&> cp(std::move(i), j);
assert(&std::get<int&>(cp) == &j);
assert(&std::get<int&&>(cp) == &i);
assert(&std::get<int&>(std::move(cp)) == &j);
assert(std::get<int&&>(std::move(cp)) == 1);
}
}
{
typedef std::complex<float> cf;
{
auto t1 = std::make_pair<int, cf> ( 42, { 1,2 } );
assert ( std::get<int>(t1) == 42 );
assert ( std::get<cf>(t1).real() == 1 );
assert ( std::get<cf>(t1).imag() == 2 );
}
auto t1 = std::make_pair<int, cf>(42, {1, 2});
assert(std::get<int>(t1) == 42);
assert(std::get<cf>(t1).real() == 1);
assert(std::get<cf>(t1).imag() == 2);
}
{
const std::pair<int, const int> p1 { 1, 2 };
const int &i1 = std::get<int>(p1);
const int &i2 = std::get<const int>(p1);
assert ( i1 == 1 );
assert ( i2 == 2 );
}
{
const std::pair<int, const int> p1{1, 2};
const int& i1 = std::get<int>(p1);
const int& i2 = std::get<const int>(p1);
assert(i1 == 1);
assert(i2 == 2);
}
{
{
int x = 42;
int const y = 43;
std::pair<int&, int const&> const p(x, y);
static_assert(std::is_same<int&, decltype(std::get<int&>(std::move(p)))>::value, "");
static_assert(noexcept(std::get<int&>(std::move(p))), "");
static_assert(std::is_same<int const&, decltype(std::get<int const&>(std::move(p)))>::value, "");
static_assert(noexcept(std::get<int const&>(std::move(p))), "");
}
{
int x = 42;
int const y = 43;
std::pair<int&&, int const&&> const p(std::move(x), std::move(y));
static_assert(std::is_same<int&&, decltype(std::get<int&&>(std::move(p)))>::value, "");
static_assert(noexcept(std::get<int&&>(std::move(p))), "");
static_assert(std::is_same<int const&&, decltype(std::get<int const&&>(std::move(p)))>::value, "");
static_assert(noexcept(std::get<int const&&>(std::move(p))), "");
}
{
constexpr const std::pair<int, const int> p{1, 2};
static_assert(std::get<int>(std::move(p)) == 1, "");
static_assert(std::get<const int>(std::move(p)) == 2, "");
}
return true;
}
int main(int, char**) {
test();
#if TEST_STD_VER >= 14
static_assert(test(), "");
#endif
// These tests use types which only work during constant evaluation in very recent standards
{
typedef std::unique_ptr<int> upint;
std::pair<upint, int> t(upint(new int(4)), 42);
upint p = std::get<upint>(std::move(t)); // get rvalue
assert(*p == 4);
assert(std::get<upint>(t) == nullptr); // has been moved from
}
}
{
{
typedef std::unique_ptr<int> upint;
const std::pair<upint, int> t(upint(new int(4)), 42);
static_assert(std::is_same<const upint&&, decltype(std::get<upint>(std::move(t)))>::value, "");
@ -52,37 +123,11 @@ int main(int, char**)
static_assert(std::is_same<const int&&, decltype(std::get<int>(std::move(t)))>::value, "");
static_assert(noexcept(std::get<int>(std::move(t))), "");
auto&& p = std::get<upint>(std::move(t)); // get const rvalue
auto&& i = std::get<int>(std::move(t)); // get const rvalue
auto&& i = std::get<int>(std::move(t)); // get const rvalue
assert(*p == 4);
assert(i == 42);
assert(std::get<upint>(t) != nullptr);
}
{
int x = 42;
int const y = 43;
std::pair<int&, int const&> const p(x, y);
static_assert(std::is_same<int&, decltype(std::get<int&>(std::move(p)))>::value, "");
static_assert(noexcept(std::get<int&>(std::move(p))), "");
static_assert(std::is_same<int const&, decltype(std::get<int const&>(std::move(p)))>::value, "");
static_assert(noexcept(std::get<int const&>(std::move(p))), "");
}
{
int x = 42;
int const y = 43;
std::pair<int&&, int const&&> const p(std::move(x), std::move(y));
static_assert(std::is_same<int&&, decltype(std::get<int&&>(std::move(p)))>::value, "");
static_assert(noexcept(std::get<int&&>(std::move(p))), "");
static_assert(std::is_same<int const&&, decltype(std::get<int const&&>(std::move(p)))>::value, "");
static_assert(noexcept(std::get<int const&&>(std::move(p))), "");
}
{
constexpr const std::pair<int, const int> p { 1, 2 };
static_assert(std::get<int>(std::move(p)) == 1, "");
static_assert(std::get<const int>(std::move(p)) == 2, "");
}
}
return 0;
}