| 1 | // Copyright (C) 2023 The Qt Company Ltd. |
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| 2 | // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only |
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| 3 | #ifndef Q23UTILITY_H |
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| 4 | #define Q23UTILITY_H |
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| 5 | |
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| 6 | #include <QtCore/qtconfigmacros.h> |
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| 7 | |
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| 8 | #include <utility> |
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| 9 | |
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| 10 | // |
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| 11 | // W A R N I N G |
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| 12 | // ------------- |
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| 13 | // |
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| 14 | // This file is not part of the Qt API. Types and functions defined in this |
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| 15 | // file can reliably be replaced by their std counterparts, once available. |
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| 16 | // You may use these definitions in your own code, but be aware that we |
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| 17 | // will remove them once Qt depends on the C++ version that supports |
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| 18 | // them in namespace std. There will be NO deprecation warning, the |
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| 19 | // definitions will JUST go away. |
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| 20 | // |
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| 21 | // If you can't agree to these terms, don't use these definitions! |
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| 22 | // |
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| 23 | // We mean it. |
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| 24 | // |
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| 25 | |
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| 26 | QT_BEGIN_NAMESPACE |
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| 27 | |
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| 28 | namespace q23 { |
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| 29 | // like std::forward_like |
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| 30 | #ifdef __cpp_lib_forward_like |
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| 31 | using std::forward_like; |
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| 32 | #else |
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| 33 | |
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| 34 | namespace _detail { |
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| 35 | |
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| 36 | // [forward]/6.1 COPY_CONST |
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| 37 | template <typename A, typename B> |
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| 38 | using copy_const_t = std::conditional_t< |
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| 39 | std::is_const_v<A>, const B, |
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| 40 | /* else */ B |
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| 41 | >; |
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| 42 | |
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| 43 | // [forward]/6.2 OVERRIDE_REF |
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| 44 | template <typename A, typename B> |
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| 45 | using override_ref_t = std::conditional_t< |
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| 46 | std::is_rvalue_reference_v<A>, std::remove_reference_t<B>&&, |
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| 47 | /* else */ B& |
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| 48 | >; |
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| 49 | |
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| 50 | // [forward]/6.3 "V" |
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| 51 | template <typename T, typename U> |
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| 52 | using forward_like_ret_t = override_ref_t< |
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| 53 | T&&, |
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| 54 | copy_const_t< |
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| 55 | std::remove_reference_t<T>, |
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| 56 | std::remove_reference_t<U> |
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| 57 | > |
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| 58 | >; |
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| 59 | |
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| 60 | } // namespace detail |
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| 61 | |
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| 62 | // http://eel.is/c++draft/forward#lib:forward_like |
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| 63 | template <class T, class U> |
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| 64 | [[nodiscard]] constexpr auto forward_like(U &&x) noexcept |
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| 65 | -> _detail::forward_like_ret_t<T, U> |
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| 66 | { |
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| 67 | using V = _detail::forward_like_ret_t<T, U>; |
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| 68 | return static_cast<V>(x); |
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| 69 | } |
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| 70 | #endif // __cpp_lib_forward_like |
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| 71 | } // namespace q23 |
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| 72 | |
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| 73 | QT_END_NAMESPACE |
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| 74 | |
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| 75 | #endif /* Q23UTILITY_H */ |
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| 76 | |
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