1// Copyright (C) 2024 The Qt Company Ltd.
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
3
4#ifndef QMAYBE_P_H
5#define QMAYBE_P_H
6
7//
8// W A R N I N G
9// -------------
10//
11// This file is not part of the Qt API. It exists purely as an
12// implementation detail. This header file may change from version to
13// version without notice, or even be removed.
14//
15// We mean it.
16//
17
18#include <QtCore/private/qglobal_p.h>
19#include <qstring.h>
20#include <optional>
21#include <utility>
22#include <memory>
23
24QT_BEGIN_NAMESPACE
25
26struct QUnexpect
27{
28};
29
30static constexpr QUnexpect unexpect{};
31
32template <typename Value, typename Error = QString>
33class QMaybe
34{
35public:
36 QMaybe(const Value &v)
37 {
38 if constexpr (std::is_pointer_v<Value>) {
39 if (!v)
40 return; // nullptr is treated as nullopt (for raw pointer types only)
41 }
42 m_value = v;
43 }
44
45 QMaybe(Value &&v)
46 {
47 if constexpr (std::is_pointer_v<Value>) {
48 if (!v)
49 return; // nullptr is treated as nullopt (for raw pointer types only)
50 }
51 m_value = std::move(v);
52 }
53
54 QMaybe(const QMaybe &other) = default;
55
56 QMaybe &operator=(const QMaybe &other) = default;
57
58 QMaybe(const Error &error) : m_error(error) { }
59
60 template <class... Args>
61 QMaybe(QUnexpect, Args &&...args) : m_error{ std::forward<Args>(args)... }
62 {
63 static_assert(std::is_constructible_v<Error, Args &&...>,
64 "Invalid arguments for creating an error type");
65 }
66
67 // NOTE: Returns false if holding a nullptr value, even if no error is set.
68 // This is different from std::expected, where a nullptr is a valid value, not
69 // an error.
70 constexpr explicit operator bool() const noexcept { return m_value.has_value(); }
71
72 constexpr Value &value()
73 {
74 Q_ASSERT(m_value.has_value());
75 return *m_value;
76 }
77
78 constexpr const Value &value() const
79 {
80 Q_ASSERT(m_value.has_value());
81 return *m_value;
82 }
83
84 constexpr Value *operator->() noexcept { return std::addressof(value()); }
85 constexpr const Value *operator->() const noexcept { return std::addressof(value()); }
86
87 constexpr Value &operator*() &noexcept { return value(); }
88 constexpr const Value &operator*() const &noexcept { return value(); }
89
90 constexpr const Error &error() const { return m_error; }
91
92private:
93 std::optional<Value> m_value;
94 Error m_error{};
95};
96
97QT_END_NAMESPACE
98
99#endif // QMAYBE_P_H
100

source code of qtmultimedia/src/multimedia/qmaybe_p.h