Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__ranges/single_view.h

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+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___RANGES_SINGLE_VIEW_H
+#define _LIBCPP___RANGES_SINGLE_VIEW_H
+
+#include <__concepts/constructible.h>
+#include <__config>
+#include <__ranges/copyable_box.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/view_interface.h>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_object.h>
+#include <__utility/forward.h>
+#include <__utility/in_place.h>
+#include <__utility/move.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace ranges {
+  template<copy_constructible _Tp>
+    requires is_object_v<_Tp>
+  class single_view : public view_interface<single_view<_Tp>> {
+    __copyable_box<_Tp> __value_;
+
+  public:
+    _LIBCPP_HIDE_FROM_ABI
+    single_view() requires default_initializable<_Tp> = default;
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr explicit single_view(const _Tp& __t) : __value_(in_place, __t) {}
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr explicit single_view(_Tp&& __t) : __value_(in_place, std::move(__t)) {}
+
+    template<class... _Args>
+      requires constructible_from<_Tp, _Args...>
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr explicit single_view(in_place_t, _Args&&... __args)
+      : __value_{in_place, std::forward<_Args>(__args)...} {}
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr _Tp* begin() noexcept { return data(); }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr const _Tp* begin() const noexcept { return data(); }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr _Tp* end() noexcept { return data() + 1; }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr const _Tp* end() const noexcept { return data() + 1; }
+
+    _LIBCPP_HIDE_FROM_ABI
+    static constexpr size_t size() noexcept { return 1; }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr _Tp* data() noexcept { return __value_.operator->(); }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr const _Tp* data() const noexcept { return __value_.operator->(); }
+  };
+
+template<class _Tp>
+single_view(_Tp) -> single_view<_Tp>;
+
+namespace views {
+namespace __single_view {
+
+struct __fn : __range_adaptor_closure<__fn> {
+  template<class _Range>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
+  constexpr auto operator()(_Range&& __range) const
+    noexcept(noexcept(single_view<decay_t<_Range&&>>(std::forward<_Range>(__range))))
+    -> decltype(      single_view<decay_t<_Range&&>>(std::forward<_Range>(__range)))
+    { return          single_view<decay_t<_Range&&>>(std::forward<_Range>(__range)); }
+};
+} // namespace __single_view
+
+inline namespace __cpo {
+  inline constexpr auto single = __single_view::__fn{};
+} // namespace __cpo
+
+} // namespace views
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___RANGES_SINGLE_VIEW_H