[libc++] Simplify the implementation of std::get for pairs #114984
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libcxx/include/__utility/pair.h
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| 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&&>(std::move(__p).first); |
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Would it be better to just use static_cast (ditto below)?
Suggested change
| return std::forward<_T1&&>(std::move(__p).first); | |
| return static_cast<_T1&&>(__p.first); |
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Why do you think that a static_cast would be better?
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IMO given it's necessary spell out the resulted reference type anyway, it would be clearer to just use a cast.
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@llvm/pr-subscribers-libcxx Author: Nikolas Klauser (philnik777) ChangesThis 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 Full diff: https://github.com/llvm/llvm-project/pull/114984.diff 2 Files Affected:
diff --git a/libcxx/include/__utility/pair.h b/libcxx/include/__utility/pair.h
index f9d0f4e4723113..17631277691108 100644
--- a/libcxx/include/__utility/pair.h
+++ b/libcxx/include/__utility/pair.h
@@ -633,42 +633,42 @@ 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);
+ 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);
+ 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));
+ return std::forward<_T1&&>(__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));
+ return std::forward<_T1 const&&>(__p.second);
}
#endif // _LIBCPP_STD_VER >= 14
diff --git a/libcxx/test/std/utilities/utility/pairs/pair.astuple/get_ref.pass.cpp b/libcxx/test/std/utilities/utility/pairs/pair.astuple/get_ref.pass.cpp
new file mode 100644
index 00000000000000..4343361930959c
--- /dev/null
+++ b/libcxx/test/std/utilities/utility/pairs/pair.astuple/get_ref.pass.cpp
@@ -0,0 +1,68 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11
+
+// <utility>
+
+// template <class T1, class T2> struct pair
+
+// template<size_t I, class T1, class T2>
+// typename tuple_element<I, std::pair<T1, T2> >::type&&
+// get(pair<T1, T2>&&);
+
+#include <cassert>
+#include <utility>
+
+#include "test_macros.h"
+
+TEST_CONSTEXPR_CXX14 bool test() {
+ 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);
+ }
+
+ return true;
+}
+
+int main() {
+ test();
+#if TEST_STD_VER >= 14
+ static_assert(test(), "");
+#endif
+}
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ldionne
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Nov 12, 2024
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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ldionne
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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_pairentirely.