| 1 | // Copyright (C) 2024 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 | |
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| 4 | #ifndef QMAYBE_P_H |
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| 5 | #define QMAYBE_P_H |
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| 6 | |
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| 7 | // |
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| 8 | // W A R N I N G |
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| 9 | // ------------- |
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| 10 | // |
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| 11 | // This file is not part of the Qt API. It exists purely as an |
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| 12 | // implementation detail. This header file may change from version to |
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| 13 | // version without notice, or even be removed. |
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| 14 | // |
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| 15 | // We mean it. |
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| 16 | // |
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| 17 | |
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| 18 | #include <QtCore/private/qglobal_p.h> |
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| 19 | #include <qstring.h> |
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| 20 | #include <optional> |
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| 21 | #include <utility> |
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| 22 | #include <memory> |
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| 23 | |
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| 24 | QT_BEGIN_NAMESPACE |
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| 25 | |
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| 26 | struct QUnexpect |
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| 27 | { |
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| 28 | }; |
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| 29 | |
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| 30 | static constexpr QUnexpect unexpect{}; |
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| 31 | |
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| 32 | template <typename Value, typename Error = QString> |
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| 33 | class QMaybe |
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| 34 | { |
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| 35 | public: |
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| 36 | QMaybe(const Value &v) |
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| 37 | { |
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| 38 | if constexpr (std::is_pointer_v<Value>) { |
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| 39 | if (!v) |
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| 40 | return; // nullptr is treated as nullopt (for raw pointer types only) |
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| 41 | } |
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| 42 | m_value = v; |
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| 43 | } |
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| 44 | |
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| 45 | QMaybe(Value &&v) |
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| 46 | { |
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| 47 | if constexpr (std::is_pointer_v<Value>) { |
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| 48 | if (!v) |
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| 49 | return; // nullptr is treated as nullopt (for raw pointer types only) |
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| 50 | } |
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| 51 | m_value = std::move(v); |
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| 52 | } |
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| 53 | |
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| 54 | QMaybe(const QMaybe &other) = default; |
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| 55 | |
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| 56 | QMaybe &operator=(const QMaybe &other) = default; |
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| 57 | |
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| 58 | QMaybe(const Error &error) : m_error(error) { } |
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| 59 | |
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| 60 | template <class... Args> |
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| 61 | QMaybe(QUnexpect, Args &&...args) : m_error{ std::forward<Args>(args)... } |
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| 62 | { |
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| 63 | static_assert(std::is_constructible_v<Error, Args &&...>, |
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| 64 | "Invalid arguments for creating an error type" ); |
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| 65 | } |
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| 66 | |
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| 67 | // NOTE: Returns false if holding a nullptr value, even if no error is set. |
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| 68 | // This is different from std::expected, where a nullptr is a valid value, not |
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| 69 | // an error. |
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| 70 | constexpr explicit operator bool() const noexcept { return m_value.has_value(); } |
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| 71 | |
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| 72 | constexpr Value &value() |
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| 73 | { |
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| 74 | Q_ASSERT(m_value.has_value()); |
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| 75 | return *m_value; |
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| 76 | } |
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| 77 | |
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| 78 | constexpr const Value &value() const |
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| 79 | { |
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| 80 | Q_ASSERT(m_value.has_value()); |
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| 81 | return *m_value; |
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| 82 | } |
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| 83 | |
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| 84 | constexpr Value *operator->() noexcept { return std::addressof(value()); } |
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| 85 | constexpr const Value *operator->() const noexcept { return std::addressof(value()); } |
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| 86 | |
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| 87 | constexpr Value &operator*() &noexcept { return value(); } |
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| 88 | constexpr const Value &operator*() const &noexcept { return value(); } |
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| 89 | |
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| 90 | constexpr const Error &error() const { return m_error; } |
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| 91 | |
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| 92 | private: |
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| 93 | std::optional<Value> m_value; |
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| 94 | Error m_error{}; |
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| 95 | }; |
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| 96 | |
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| 97 | QT_END_NAMESPACE |
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| 98 | |
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| 99 | #endif // QMAYBE_P_H |
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| 100 | |
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