qprotobuflazymessagepointer.h

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// Copyright (C) 2020 Alexey Edelev <semlanik@gmail.com>

// Copyright (C) 2022 The Qt Company Ltd.

// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

#ifndef QPROTOBUFLAZYMESSAGEPOINTER_H

#define QPROTOBUFLAZYMESSAGEPOINTER_H

#include <QtProtobuf/qtprotobufexports.h>

#include <QtProtobuf/qprotobufmessage.h>

#include <QtProtobuf/qtprotobuftypes.h>

QT_BEGIN_NAMESPACE

namespace QtProtobufPrivate {

class QProtobufLazyMessagePointerBase

    Q_DISABLE_COPY(QProtobufLazyMessagePointerBase)

    mutable QProtobufMessage *m_ptr = nullptr;

protected:

    QProtobufLazyMessagePointerBase() noexcept = default;

    explicit QProtobufLazyMessagePointerBase(QProtobufMessage *ptr) noexcept : m_ptr(ptr) { }

    QProtobufLazyMessagePointerBase(QProtobufLazyMessagePointerBase &&other) noexcept

        : m_ptr(std::exchange(other.m_ptr, nullptr))

    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QProtobufLazyMessagePointerBase)

    QProtobufMessage *message() const noexcept { return m_ptr; }

    void setMessage(QProtobufMessage *msg) const noexcept{ m_ptr = msg; }

    ~QProtobufLazyMessagePointerBase() { QProtobufMessageDeleter()(m_ptr); }

    void swap(QProtobufLazyMessagePointerBase &other) noexcept { qt_ptr_swap(m_ptr, other.m_ptr); }

    explicit operator bool() const noexcept { return message() != nullptr; }

};

template <typename T, QtProtobuf::if_protobuf_message<T> = true>

class QProtobufLazyMessagePointer : private QProtobufLazyMessagePointerBase

    T *messageAsT() const { return static_cast<T *>(message()); }

public:

    QProtobufLazyMessagePointer() noexcept = default;

    explicit QProtobufLazyMessagePointer(T *p) noexcept { setMessage(p); }

    QProtobufLazyMessagePointer(const QProtobufLazyMessagePointer &other) noexcept = default;

    QProtobufLazyMessagePointer &

    operator=(const QProtobufLazyMessagePointer &other) noexcept = default;

    QProtobufLazyMessagePointer(QProtobufLazyMessagePointer &&other) noexcept = default;

    QProtobufLazyMessagePointer &operator=(QProtobufLazyMessagePointer &&other) noexcept = default;

    ~QProtobufLazyMessagePointer() = default; // We don't own anything + base is not virtual

    T &operator*() const { return *get(); }

    T *operator->() const { return get(); }

    T *get() const

        if (!*this)

            setMessage(new T);

        return messageAsT();

    void reset(T *p = nullptr) noexcept

        Q_ASSERT(!p || message() != p);

        QProtobufLazyMessagePointer(p).swap(*this);

    void swap(QProtobufLazyMessagePointer &other) noexcept

        QProtobufLazyMessagePointerBase::swap(other);

    using QProtobufLazyMessagePointerBase::operator bool;

private:

    friend bool operator==(const QProtobufLazyMessagePointer &lhs,

                           const QProtobufLazyMessagePointer &rhs) noexcept

        T *lhsPtr = lhs.messageAsT();

        T *rhsPtr = rhs.messageAsT();

        return (lhsPtr == nullptr && rhsPtr == nullptr)

            || (lhsPtr != nullptr && rhsPtr != nullptr && *lhsPtr == *rhsPtr);

    friend bool operator!=(const QProtobufLazyMessagePointer &lhs,

                           const QProtobufLazyMessagePointer &rhs) noexcept

        return !operator==(lhs, rhs);

};

} // namespace QtProtobufPrivate

QT_END_NAMESPACE

#endif // QPROTOBUFLAZYMESSAGEPOINTER_H