qproperty.cpp

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// Copyright (C) 2020 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
// Qt-Security score:significant reason:default
 
#include "qproperty.h"
#include "qproperty_p.h"
 
#include <qscopedvaluerollback.h>
#include <QScopeGuard>
#include <QtCore/qalloc.h>
#include <QtCore/qloggingcategory.h>
#include <QtCore/private/qthread_p.h>
#include <QtCore/qmetaobject.h>
#include <QtCore/qmutex.h>
 
#include "qobject_p.h"
 
QT_BEGIN_NAMESPACE
 
Q_STATIC_LOGGING_CATEGORY(lcQPropertyBinding, "qt.qproperty.binding");
 
using namespace QtPrivate;
 
void QPropertyBindingPrivatePtr::destroyAndFreeMemory()
{
    QPropertyBindingPrivate::destroyAndFreeMemory(static_cast<QPropertyBindingPrivate *>(d));
}
 
void QPropertyBindingPrivatePtr::reset(QtPrivate::RefCounted *ptr) noexcept
{
    if (ptr != d) {
        if (ptr)
            ptr->addRef();
        auto *old = std::exchange(d, ptr);
        if (old && !old->deref())
            QPropertyBindingPrivate::destroyAndFreeMemory(static_cast<QPropertyBindingPrivate *>(d));
    }
}
 
 
void QPropertyBindingDataPointer::addObserver(QPropertyObserver *observer)
{
    if (auto *b = binding()) {
        observer->prev = &b->firstObserver.ptr;
        observer->next = b->firstObserver.ptr;
        if (observer->next)
            observer->next->prev = &observer->next;
        b->firstObserver.ptr = observer;
    } else {
        auto &d = ptr->d_ref();
        Q_ASSERT(!(d & QPropertyBindingData::BindingBit));
        auto firstObserver = reinterpret_cast<QPropertyObserver*>(d);
        observer->prev = reinterpret_cast<QPropertyObserver**>(&d);
        observer->next = firstObserver;
        if (observer->next)
            observer->next->prev = &observer->next;
        d = reinterpret_cast<quintptr>(observer);
    }
}
 
/*!
    \internal
 
    QPropertyDelayedNotifications is used to manage delayed notifications in grouped property updates.
    It acts as a pool allocator for QPropertyProxyBindingData, and has methods to manage delayed
    notifications.
 
    \sa beginPropertyUpdateGroup, endPropertyUpdateGroup
*/
struct QPropertyDelayedNotifications
{
    // we can't access the dynamic page size as we need a constant value
    // use 4096 as a sensible default
    static constexpr inline auto PageSize = 4096;
    int ref = 0;
    QPropertyDelayedNotifications *next = nullptr; // in case we have more than size dirty properties...
    qsizetype used = 0;
    // Size chosen to avoid allocating more than one page of memory, while still ensuring
    // that we can store many delayed properties without doing further allocations
    static constexpr qsizetype size = (PageSize - 3*sizeof(void *))/sizeof(QPropertyProxyBindingData);
    QPropertyProxyBindingData delayedProperties[size];
 
    /*!
        \internal
        This method is called when a property attempts to notify its observers while inside of a
        property update group. Instead of actually notifying, it replaces \a bindingData's d_ptr
        with a QPropertyProxyBindingData.
        \a bindingData and \a propertyData are the binding data and property data of the property
        whose notify call gets delayed.
        \sa QPropertyBindingData::notifyObservers
     */
    void addProperty(const QPropertyBindingData *bindingData, QUntypedPropertyData *propertyData) {
        if (bindingData->isNotificationDelayed())
            return;
        auto *data = this;
        while (data->used == size) {
            if (!data->next)
                // add a new page
                data->next = new QPropertyDelayedNotifications;
            data = data->next;
        }
        auto *delayed = data->delayedProperties + data->used;
        *delayed = QPropertyProxyBindingData { bindingData->d_ptr, bindingData, propertyData };
        ++data->used;
        // preserve the binding bit for faster access
        quintptr bindingBit = bindingData->d_ptr & QPropertyBindingData::BindingBit;
        bindingData->d_ptr = reinterpret_cast<quintptr>(delayed) | QPropertyBindingData::DelayedNotificationBit | bindingBit;
        Q_ASSERT(bindingData->d_ptr > 3);
        if (!bindingBit) {
            if (auto observer = reinterpret_cast<QPropertyObserver *>(delayed->d_ptr))
                observer->prev = reinterpret_cast<QPropertyObserver **>(&delayed->d_ptr);
        }
    }
 
    /*!
        \internal
        Called in Qt::endPropertyUpdateGroup. For the QPropertyProxyBindingData at position
        \a index, it
        \list
            \li restores the original binding data that was modified in addProperty and
            \li evaluates any bindings which depend on properties that were changed inside
                the group.
        \endlist
        Change notifications are sent later with notify (following the logic of separating
        binding updates and notifications used in non-deferred updates).
     */
     void evaluateBindings(PendingBindingObserverList &bindingObservers, qsizetype index, QBindingStatus *status) {
        auto *delayed = delayedProperties + index;
        auto *bindingData = delayed->originalBindingData;
        if (!bindingData)
            return;
 
        bindingData->d_ptr = delayed->d_ptr;
        Q_ASSERT(!(bindingData->d_ptr & QPropertyBindingData::DelayedNotificationBit));
        if (!bindingData->hasBinding()) {
            if (auto observer = reinterpret_cast<QPropertyObserver *>(bindingData->d_ptr))
                observer->prev = reinterpret_cast<QPropertyObserver **>(&bindingData->d_ptr);
        }
 
        QPropertyBindingDataPointer bindingDataPointer{bindingData};
        QPropertyObserverPointer observer = bindingDataPointer.firstObserver();
        if (observer)
            observer.evaluateBindings(bindingObservers, status);
    }
 
    /*!
        \internal
        Called in Qt::endPropertyUpdateGroup. For the QPropertyProxyBindingData at position
        \a i, it
        \list
            \li resets the proxy binding data and
            \li sends any pending notifications.
        \endlist
     */
    void notify(qsizetype index) {
        auto *delayed = delayedProperties + index;
        if (delayed->d_ptr  & QPropertyBindingData::BindingBit)
            return; // already handled
        if (!delayed->originalBindingData)
            return;
        delayed->originalBindingData = nullptr;
 
        QPropertyObserverPointer observer  { reinterpret_cast<QPropertyObserver *>(delayed->d_ptr & ~QPropertyBindingData::DelayedNotificationBit) };
        delayed->d_ptr = 0;
 
        if (observer)
            observer.notify(delayed->propertyData);
    }
};
 
/*
    The binding status needs some care: Conceptually, it is a thread-local. However, we cache it
    in QObjects via their QBindingStorage. Those QObjects might outlive the thread in which the
    binding status was initially created  (e.g. when their QThread is stopped).
    If they are not migrated to another (running) QThread, they would have a stale pointer if
    a plain thread local were used for the QBindingStatus.
 
    So instead of a normal thread_local, we use the following scheme:
    - On first access, the QBindingStatus gets allocated on the heap, and stored in QThreadData
    - It also gets cached in in a thread_local variable for faster access
    - The QThreadData takes care of deleting the QBindingStatus in its destructor
    - Moreover, if a QThread is restarted, the native thread's thread local gets initialized with
      the QBindingStatus of the QThreadData. Otherwise, we'd somehow need to update all objects
      whose affinity is pointing to that thread, which we can't easily do. Moreover, this avoids
      freeing and reallocating a QBindingStatus instance.
 
    Note that the lifetime is coupled to the QThreadData, which is kept alive by QObjects, even if
    the corresponding QThread is gone.
 
    The draw-back here is that even plain QProperty will cause the creation of QThreadData if used
    in a thread which doesn't already have it; however that should be rare in practice.
 */
 
 
Q_CONSTINIT thread_local QBindingStatus *tl_status = nullptr;
 
Q_NEVER_INLINE static void initBindingStatus()
{
    auto status = new QBindingStatus {};
    /* needs to happen before setting it on the thread-data, as
       setStatusAndClearList might need to actually update the objectt list, which would
       end up calling into bindingStatus again
    */
    tl_status = status;
    QThreadData *threadData = QThreadData::current();
    QThread *currentThread = threadData->thread;
    if (currentThread) {
        QThreadPrivate *threadPriv = static_cast<QThreadPrivate *>(QObjectPrivate::get(currentThread));
        QMutexLocker lock(&threadPriv->mutex);
        threadData->m_statusOrPendingObjects.setStatusAndClearList(status);
    } else {
        // if QThreadData is in the process of being created, we don't need to synchronize, as there's
        // no QThread to which another thread could move objects to
        threadData->m_statusOrPendingObjects.setStatusAndClearList(status);
    }
}
 
static QBindingStatus &bindingStatus()
{
    if (!tl_status)
        initBindingStatus();
    return *tl_status;
}
 
/*!
    \since 6.2
 
    \relates QProperty
 
    Marks the beginning of a property update group. Inside this group,
    changing a property does neither immediately update any dependent properties
    nor does it trigger change notifications.
    Those are instead deferred until the group is ended by a call to endPropertyUpdateGroup.
 
    Groups can be nested. In that case, the deferral ends only after the outermost group has been
    ended.
 
    \note Change notifications are only send after all property values affected by the group have
    been updated to their new values. This allows re-establishing a  class invariant if multiple
    properties need to be updated, preventing any external observer from noticing an inconsistent
    state.
 
    \sa Qt::endPropertyUpdateGroup, QScopedPropertyUpdateGroup
*/
void Qt::beginPropertyUpdateGroup()
{
    QPropertyDelayedNotifications *& groupUpdateData = bindingStatus().groupUpdateData;
    if (!groupUpdateData)
        groupUpdateData = new QPropertyDelayedNotifications;
    ++groupUpdateData->ref;
}
 
/*!
    \since 6.2
    \relates QProperty
 
    Ends a property update group. If the outermost group has been ended, and deferred
    binding evaluations and notifications happen now.
 
    \warning Calling endPropertyUpdateGroup without a preceding call to beginPropertyUpdateGroup
    results in undefined behavior.
 
    \sa Qt::beginPropertyUpdateGroup, QScopedPropertyUpdateGroup
*/
void Qt::endPropertyUpdateGroup()
{
    auto status = &bindingStatus();
    QPropertyDelayedNotifications *& groupUpdateData = status->groupUpdateData;
    auto *data = groupUpdateData;
    Q_ASSERT(data->ref);
    if (--data->ref)
        return;
    groupUpdateData = nullptr;
    // ensures that bindings are kept alive until endPropertyUpdateGroup concludes
    PendingBindingObserverList bindingObservers;
    // update all delayed properties
    auto start = data;
    while (data) {
        for (qsizetype i = 0; i < data->used; ++i)
            data->evaluateBindings(bindingObservers, i, status);
        data = data->next;
    }
    // notify all delayed notifications from binding evaluation
    for (const auto &bindingPtr: bindingObservers) {
        auto *binding = static_cast<QPropertyBindingPrivate *>(bindingPtr.get());
        binding->notifyNonRecursive();
    }
    // do the same for properties which only have observers
    data = start;
    while (data) {
        for (qsizetype i = 0; i < data->used; ++i)
            data->notify(i);
        delete std::exchange(data, data->next);
    }
}
 
/*!
    \since 6.6
    \class QScopedPropertyUpdateGroup
    \inmodule QtCore
    \ingroup tools
    \brief RAII class around Qt::beginPropertyUpdateGroup()/Qt::endPropertyUpdateGroup().
 
    This class calls Qt::beginPropertyUpdateGroup() in its constructor and
    Qt::endPropertyUpdateGroup() in its destructor, making sure the latter
    function is reliably called even in the presence of early returns or thrown
    exceptions.
 
    \note Qt::endPropertyUpdateGroup() may re-throw exceptions thrown by
    binding evaluations. This means your application may crash
    (\c{std::terminate()} called) if another exception is causing
    QScopedPropertyUpdateGroup's destructor to be called during stack
    unwinding. If you expect exceptions from binding evaluations, use manual
    Qt::endPropertyUpdateGroup() calls and \c{try}/\c{catch} blocks.
 
    \sa QProperty
*/
 
/*!
    \fn QScopedPropertyUpdateGroup::QScopedPropertyUpdateGroup()
 
    Calls Qt::beginPropertyUpdateGroup().
*/
 
/*!
    \fn QScopedPropertyUpdateGroup::~QScopedPropertyUpdateGroup()
 
    Calls Qt::endPropertyUpdateGroup().
*/
 
 
// check everything stored in QPropertyBindingPrivate's union is trivially destructible
// (though the compiler would also complain if that weren't the case)
static_assert(std::is_trivially_destructible_v<QPropertyBindingSourceLocation>);
static_assert(std::is_trivially_destructible_v<std::byte[sizeof(QPropertyBindingSourceLocation)]>);
 
QPropertyBindingPrivate::~QPropertyBindingPrivate()
{
    if (firstObserver)
        firstObserver.unlink();
    if (vtable->size)
        vtable->destroy(reinterpret_cast<std::byte *>(this)
                        + QPropertyBindingPrivate::getSizeEnsuringAlignment());
}
 
void QPropertyBindingPrivate::clearDependencyObservers() {
    for (size_t i = 0; i < qMin(dependencyObserverCount, inlineDependencyObservers.size()); ++i) {
        QPropertyObserverPointer p{&inlineDependencyObservers[i]};
        p.unlink_fast();
    }
    if (heapObservers)
        heapObservers->clear();
    dependencyObserverCount = 0;
}
 
QPropertyObserverPointer QPropertyBindingPrivate::allocateDependencyObserver_slow()
{
    ++dependencyObserverCount;
    if (!heapObservers)
        heapObservers.reset(new std::vector<QPropertyObserver>());
    return {&heapObservers->emplace_back()};
}
 
void QPropertyBindingPrivate::unlinkAndDeref()
{
    clearDependencyObservers();
    propertyDataPtr = nullptr;
    if (!deref())
        destroyAndFreeMemory(this);
}
 
bool QPropertyBindingPrivate::evaluateRecursive(PendingBindingObserverList &bindingObservers, QBindingStatus *status)
{
    if (!status)
        status = &bindingStatus();
    return evaluateRecursive_inline(bindingObservers, status);
}
 
void QPropertyBindingPrivate::notifyNonRecursive(const PendingBindingObserverList &bindingObservers)
{
    notifyNonRecursive();
    for (auto &&bindingPtr: bindingObservers) {
        auto *binding = static_cast<QPropertyBindingPrivate *>(bindingPtr.get());
        binding->notifyNonRecursive();
    }
}
 
QPropertyBindingPrivate::NotificationState QPropertyBindingPrivate::notifyNonRecursive()
{
    if (!pendingNotify)
        return Delayed;
    pendingNotify = false;
    Q_ASSERT(!updating);
    updating = true;
    if (firstObserver) {
        firstObserver.noSelfDependencies(this);
        firstObserver.notify(propertyDataPtr);
    }
    if (hasStaticObserver)
        staticObserverCallback(propertyDataPtr);
    updating = false;
    return Sent;
}
 
/*!
    \class QUntypedPropertyBinding
    \inmodule QtCore
    \since 6.0
    \ingroup tools
    \brief Represents a type-erased property binding.
 
    \sa QUntypedBindable
*/
 
/*!
  Constructs a null QUntypedPropertyBinding.
 
  \sa isNull()
*/
QUntypedPropertyBinding::QUntypedPropertyBinding() = default;
 
/*!
  \fn template<typename Functor> QUntypedPropertyBinding(
        QMetaType metaType, Functor &&f, const QPropertyBindingSourceLocation &location)
 
  \internal
*/
 
/*!
    \internal
 
    Constructs QUntypedPropertyBinding. Assumes that \a metaType, \a function and \a vtable match.
    Unless a specialization of \c BindingFunctionVTable is used, this function should never be called
    directly.
*/
QUntypedPropertyBinding::QUntypedPropertyBinding(QMetaType metaType, const BindingFunctionVTable *vtable, void *function,
                                                 const QPropertyBindingSourceLocation &location)
{
    std::byte *mem = new std::byte[QPropertyBindingPrivate::getSizeEnsuringAlignment() + vtable->size]();
    d = new(mem) QPropertyBindingPrivate(metaType, vtable, std::move(location));
    vtable->moveConstruct(mem + QPropertyBindingPrivate::getSizeEnsuringAlignment(), function);
}
 
/*!
    Move-constructs a QUntypedPropertyBinding from \a other.
 
    \a other is left in a null state.
    \sa isNull()
*/
QUntypedPropertyBinding::QUntypedPropertyBinding(QUntypedPropertyBinding &&other)
    : d(std::move(other.d))
{
}
 
/*!
    Copy-constructs a QUntypedPropertyBinding from \a other.
*/
QUntypedPropertyBinding::QUntypedPropertyBinding(const QUntypedPropertyBinding &other)
    : d(other.d)
{
}
/*!
    Copy-assigns \a other to this QUntypedPropertyBinding.
*/
QUntypedPropertyBinding &QUntypedPropertyBinding::operator=(const QUntypedPropertyBinding &other)
{
    d = other.d;
    return *this;
}
 
/*!
    Move-assigns \a other to this QUntypedPropertyBinding.
 
    \a other is left in a null state.
    \sa isNull
*/
QUntypedPropertyBinding &QUntypedPropertyBinding::operator=(QUntypedPropertyBinding &&other)
{
    d = std::move(other.d);
    return *this;
}
 
/*!
   \internal
*/
QUntypedPropertyBinding::QUntypedPropertyBinding(QPropertyBindingPrivate *priv)
    : d(priv)
{
}
 
/*!
  Destroys the QUntypedPropertyBinding.
*/
QUntypedPropertyBinding::~QUntypedPropertyBinding()
{
}
 
/*!
    Returns \c true if the \c QUntypedPropertyBinding is null.
    This is only true for default-constructed and moved-from instances.
 
    \sa isNull()
*/
bool QUntypedPropertyBinding::isNull() const
{
    return !d;
}
 
/*!
    Returns the error state of the binding.
 
    \sa QPropertyBindingError
*/
QPropertyBindingError QUntypedPropertyBinding::error() const
{
    if (!d)
        return QPropertyBindingError();
    return static_cast<QPropertyBindingPrivate *>(d.get())->bindingError();
}
 
/*!
    Returns the meta-type of the binding.
    If the QUntypedPropertyBinding is null, an invalid QMetaType is returned.
*/
QMetaType QUntypedPropertyBinding::valueMetaType() const
{
    if (!d)
        return QMetaType();
    return static_cast<QPropertyBindingPrivate *>(d.get())->valueMetaType();
}
 
QPropertyBindingData::~QPropertyBindingData()
{
    QPropertyBindingDataPointer d{this};
    if (isNotificationDelayed())
        proxyData()->originalBindingData = nullptr;
    for (auto observer = d.firstObserver(); observer;) {
        auto next = observer.nextObserver();
        observer.unlink();
        observer = next;
    }
    if (auto binding = d.binding())
        binding->unlinkAndDeref();
}
 
QUntypedPropertyBinding QPropertyBindingData::setBinding(const QUntypedPropertyBinding &binding,
                                                  QUntypedPropertyData *propertyDataPtr,
                                                  QPropertyObserverCallback staticObserverCallback,
                                                  QtPrivate::QPropertyBindingWrapper guardCallback)
{
    QPropertyBindingPrivatePtr oldBinding;
    QPropertyBindingPrivatePtr newBinding = binding.d;
 
    QPropertyBindingDataPointer d{this};
    QPropertyObserverPointer observer;
 
    auto &data = d_ref();
    if (auto *existingBinding = d.binding()) {
        if (existingBinding == newBinding.data())
            return QUntypedPropertyBinding(static_cast<QPropertyBindingPrivate *>(oldBinding.data()));
        if (existingBinding->isUpdating()) {
            existingBinding->setError({QPropertyBindingError::BindingLoop, QStringLiteral("Binding set during binding evaluation!")});
            return QUntypedPropertyBinding(static_cast<QPropertyBindingPrivate *>(oldBinding.data()));
        }
        oldBinding = QPropertyBindingPrivatePtr(existingBinding);
        observer = static_cast<QPropertyBindingPrivate *>(oldBinding.data())->takeObservers();
        static_cast<QPropertyBindingPrivate *>(oldBinding.data())->unlinkAndDeref();
        data = 0;
    } else {
        observer = d.firstObserver();
    }
 
    if (newBinding) {
        newBinding.data()->addRef();
        data = reinterpret_cast<quintptr>(newBinding.data());
        data |= BindingBit;
        auto newBindingRaw = static_cast<QPropertyBindingPrivate *>(newBinding.data());
        newBindingRaw->setProperty(propertyDataPtr);
        if (observer)
            newBindingRaw->prependObserver(observer);
        newBindingRaw->setStaticObserver(staticObserverCallback, guardCallback);
 
        PendingBindingObserverList bindingObservers;
        newBindingRaw->evaluateRecursive(bindingObservers);
        newBindingRaw->notifyNonRecursive(bindingObservers);
    } else if (observer) {
        d.setObservers(observer.ptr);
    } else {
        data = 0;
    }
 
    if (oldBinding)
        static_cast<QPropertyBindingPrivate *>(oldBinding.data())->detachFromProperty();
 
    return QUntypedPropertyBinding(static_cast<QPropertyBindingPrivate *>(oldBinding.data()));
}
 
QPropertyBindingData::QPropertyBindingData(QPropertyBindingData &&other) : d_ptr(std::exchange(other.d_ptr, 0))
{
    QPropertyBindingDataPointer::fixupAfterMove(this);
}
 
BindingEvaluationState::BindingEvaluationState(QPropertyBindingPrivate *binding, QBindingStatus *status)
    : binding(binding)
{
    Q_ASSERT(status);
    QBindingStatus *s = status;
    // store a pointer to the currentBindingEvaluationState to avoid a TLS lookup in
    // the destructor (as these come with a non zero cost)
    currentState = &s->currentlyEvaluatingBinding;
    previousState = *currentState;
    *currentState = this;
    binding->clearDependencyObservers();
}
 
CompatPropertySafePoint::CompatPropertySafePoint(QBindingStatus *status, QUntypedPropertyData *property)
    : property(property)
{
    // store a pointer to the currentBindingEvaluationState to avoid a TLS lookup in
    // the destructor (as these come with a non zero cost)
    currentState = &status->currentCompatProperty;
    previousState = *currentState;
    *currentState = this;
 
    currentlyEvaluatingBindingList = &bindingStatus().currentlyEvaluatingBinding;
    bindingState = *currentlyEvaluatingBindingList;
    *currentlyEvaluatingBindingList = nullptr;
}
 
QPropertyBindingPrivate *QPropertyBindingPrivate::currentlyEvaluatingBinding()
{
    auto currentState = bindingStatus().currentlyEvaluatingBinding ;
    return currentState ? currentState->binding : nullptr;
}
 
// ### Unused, kept for BC with 6.0
void QPropertyBindingData::evaluateIfDirty(const QUntypedPropertyData *) const
{
}
 
void QPropertyBindingData::removeBinding_helper()
{
    QPropertyBindingDataPointer d{this};
 
    auto *existingBinding = d.binding();
    Q_ASSERT(existingBinding);
    if (existingBinding->isSticky()) {
        return;
    }
 
    auto observer = existingBinding->takeObservers();
    d_ref() = 0;
    if (observer)
        d.setObservers(observer.ptr);
    existingBinding->unlinkAndDeref();
}
 
void QPropertyBindingData::registerWithCurrentlyEvaluatingBinding() const
{
    auto currentState = bindingStatus().currentlyEvaluatingBinding;
    if (!currentState)
        return;
    registerWithCurrentlyEvaluatingBinding_helper(currentState);
}
 
 
void QPropertyBindingData::registerWithCurrentlyEvaluatingBinding_helper(BindingEvaluationState *currentState) const
{
    QPropertyBindingDataPointer d{this};
 
    if (currentState->alreadyCaptureProperties.contains(this))
        return;
    else
        currentState->alreadyCaptureProperties.push_back(this);
 
    QPropertyObserverPointer dependencyObserver = currentState->binding->allocateDependencyObserver();
    Q_ASSERT(QPropertyObserver::ObserverNotifiesBinding == 0);
    dependencyObserver.setBindingToNotify_unsafe(currentState->binding);
    d.addObserver(dependencyObserver.ptr);
}
 
void QPropertyBindingData::notifyObservers(QUntypedPropertyData *propertyDataPtr) const
{
    notifyObservers(propertyDataPtr, nullptr);
}
 
void QPropertyBindingData::notifyObservers(QUntypedPropertyData *propertyDataPtr, QBindingStorage *storage) const
{
    if (isNotificationDelayed())
        return;
    QPropertyBindingDataPointer d{this};
 
    PendingBindingObserverList bindingObservers;
    if (QPropertyObserverPointer observer = d.firstObserver()) {
        if (notifyObserver_helper(propertyDataPtr, storage, observer, bindingObservers) == Evaluated) {
            /* evaluateBindings() can trash the observers. We need to re-fetch here.
             "this" might also no longer be valid in case we have a QObjectBindableProperty
             and consequently d isn't either (this happens when binding evaluation has
             caused the binding storage to resize.
             If storage is nullptr, then there is no dynamically resizable storage,
             and we cannot run into the issue.
            */
            if (storage)
                d = QPropertyBindingDataPointer {storage->bindingData(propertyDataPtr)};
            if (QPropertyObserverPointer observer = d.firstObserver())
                observer.notify(propertyDataPtr);
            for (auto &&bindingPtr: bindingObservers) {
                auto *binding = static_cast<QPropertyBindingPrivate *>(bindingPtr.get());
                binding->notifyNonRecursive();
            }
        }
    }
}
 
QPropertyBindingData::NotificationResult QPropertyBindingData::notifyObserver_helper
(
            QUntypedPropertyData *propertyDataPtr, QBindingStorage *storage,
            QPropertyObserverPointer observer,
            PendingBindingObserverList &bindingObservers) const
{
#ifdef QT_HAS_FAST_CURRENT_THREAD_ID
    QBindingStatus *status = storage ? storage->bindingStatus : nullptr;
    if (!status || status->threadId != QThread::currentThreadId())
        status = &bindingStatus();
#else
    Q_UNUSED(storage);
    QBindingStatus *status = &bindingStatus();
#endif
    if (QPropertyDelayedNotifications *delay = status->groupUpdateData) {
        delay->addProperty(this, propertyDataPtr);
        return Delayed;
    }
 
    observer.evaluateBindings(bindingObservers, status);
    return Evaluated;
}
 
 
QPropertyObserver::QPropertyObserver(ChangeHandler changeHandler)
{
    QPropertyObserverPointer d{this};
    d.setChangeHandler(changeHandler);
}
 
#if QT_DEPRECATED_SINCE(6, 6)
QPropertyObserver::QPropertyObserver(QUntypedPropertyData *data)
{
    QT_WARNING_PUSH QT_WARNING_DISABLE_DEPRECATED
    aliasData = data;
    next.setTag(ObserverIsAlias);
    QT_WARNING_POP
}
#endif
 
/*! \internal
*/
void QPropertyObserver::setSource(const QPropertyBindingData &property)
{
    QPropertyObserverPointer d{this};
    QPropertyBindingDataPointer propPrivate{&property};
    d.observeProperty(propPrivate);
}
 
QPropertyObserver::~QPropertyObserver()
{
    QPropertyObserverPointer d{this};
    d.unlink();
}
 
QPropertyObserver::QPropertyObserver(QPropertyObserver &&other) noexcept
{
    binding = std::exchange(other.binding, {});
    next = std::exchange(other.next, {});
    prev = std::exchange(other.prev, {});
    if (next)
        next->prev = &next;
    if (prev)
        prev.setPointer(this);
}
 
QPropertyObserver &QPropertyObserver::operator=(QPropertyObserver &&other) noexcept
{
    if (this == &other)
        return *this;
 
    QPropertyObserverPointer d{this};
    d.unlink();
    binding = nullptr;
 
    binding = std::exchange(other.binding, {});
    next = std::exchange(other.next, {});
    prev = std::exchange(other.prev, {});
    if (next)
        next->prev = &next;
    if (prev)
        prev.setPointer(this);
 
    return *this;
}
 
/*!
    \fn QPropertyObserverPointer::unlink()
    \internal
    Unlinks
 */
 
 
/*!
    \fn QPropertyObserverPointer::unlink_fast()
    \internal
    Like unlink, but does not handle ObserverIsAlias.
    Must only be called in places where we know that we are not dealing
    with such an observer.
 */
 
void QPropertyObserverPointer::setChangeHandler(QPropertyObserver::ChangeHandler changeHandler)
{
    Q_ASSERT(ptr->next.tag() != QPropertyObserver::ObserverIsPlaceholder);
    ptr->changeHandler = changeHandler;
    ptr->next.setTag(QPropertyObserver::ObserverNotifiesChangeHandler);
}
 
/*!
    \internal
    The same as setBindingToNotify, but assumes that the tag is already correct.
 */
void QPropertyObserverPointer::setBindingToNotify_unsafe(QPropertyBindingPrivate *binding)
{
    Q_ASSERT(ptr->next.tag() == QPropertyObserver::ObserverNotifiesBinding);
    ptr->binding = binding;
}
 
/*!
 \class QPropertyObserverNodeProtector
 \internal
 QPropertyObserverNodeProtector is a RAII wrapper which takes care of the internal switching logic
 for QPropertyObserverPointer::notify (described ibidem)
*/
 
/*!
  \fn QPropertyObserverNodeProtector::notify(QUntypedPropertyData *propertyDataPtr)
  \internal
  \a propertyDataPtr is a pointer to the observed property's property data
*/
 
#ifndef QT_NO_DEBUG
void QPropertyObserverPointer::noSelfDependencies(QPropertyBindingPrivate *binding)
{
    auto observer = const_cast<QPropertyObserver*>(ptr);
    // See also comment in notify()
    while (observer) {
        if (QPropertyObserver::ObserverTag(observer->next.tag()) == QPropertyObserver::ObserverNotifiesBinding)
            if (observer->binding == binding) {
                qCritical("Property depends on itself!");
                break;
            }
 
        observer = observer->next.data();
    }
 
}
#endif
 
void QPropertyObserverPointer::evaluateBindings(PendingBindingObserverList &bindingObservers, QBindingStatus *status)
{
    Q_ASSERT(status);
    auto observer = const_cast<QPropertyObserver*>(ptr);
    // See also comment in notify()
    while (observer) {
        QPropertyObserver *next = observer->next.data();
 
        if (QPropertyObserver::ObserverTag(observer->next.tag()) == QPropertyObserver::ObserverNotifiesBinding) {
            auto bindingToEvaluate = observer->binding;
            QPropertyObserverNodeProtector protector(observer);
            // binding must not be gone after evaluateRecursive_inline
            QPropertyBindingPrivatePtr currentBinding(observer->binding);
            const bool evalStatus = bindingToEvaluate->evaluateRecursive_inline(bindingObservers, status);
            if (evalStatus)
                bindingObservers.push_back(std::move(currentBinding));
            next = protector.next();
        }
 
        observer = next;
    }
}
 
void QPropertyObserverPointer::observeProperty(QPropertyBindingDataPointer property)
{
    if (ptr->prev)
        unlink();
    property.addObserver(ptr);
}
 
/*!
    \class QPropertyBindingError
    \inmodule QtCore
    \ingroup tools
    \since 6.0
 
    QPropertyBindingError is used by \l{The Property System}{the property
    system} to report errors that occurred when a binding was evaluated. Use \l
    type()  to query which error occurred, and \l
    description() to extract an error message which might contain
    more details.
    If there is no error, QPropertyBindingError has type
    \c QPropertyBindingError::NoError and \c hasError() returns false.
 
    \code
    extern QProperty<int> prop;
 
    QPropertyBindingError error = prop.binding().error();
    if (error.hasError())
         qDebug() << error.description();
    \endcode
*/
 
/*!
    \enum QPropertyBindingError::Type
 
    This enum specifies which error occurred.
 
    \value NoError
        No error occurred while evaluating the binding.
    \value BindingLoop
        Binding evaluation was stopped because a property depended on its own
        value.
    \value EvaluationError
        Binding evaluation was stopped for any other reason than a binding loop.
        For example, this value is used in the QML engine when an exception occurs
        while a binding is evaluated.
    \value UnknownError
        A generic error type used when neither of the other values is suitable.
        Calling \l description() might provide details.
*/
 
/*!
    Default constructs QPropertyBindingError.
    hasError() will return false, type will return \c NoError and
    \l description() will return an empty string.
*/
QPropertyBindingError::QPropertyBindingError()
{
}
 
/*!
    Constructs a QPropertyBindingError of type \a type with \a description as its
    description.
*/
QPropertyBindingError::QPropertyBindingError(Type type, const QString &description)
{
    if (type != NoError) {
        d = new QPropertyBindingErrorPrivate;
        d->type = type;
        d->description = description;
    }
}
 
/*!
    Copy-constructs QPropertyBindingError from \a other.
*/
QPropertyBindingError::QPropertyBindingError(const QPropertyBindingError &other)
    : d(other.d)
{
}
 
/*!
    Copies \a other to this QPropertyBindingError.
*/
QPropertyBindingError &QPropertyBindingError::operator=(const QPropertyBindingError &other)
{
    d = other.d;
    return *this;
}
 
/*!
    Move-constructs QPropertyBindingError from \a other.
    \a other will be left in its default state.
*/
QPropertyBindingError::QPropertyBindingError(QPropertyBindingError &&other)
    : d(std::move(other.d))
{
}
 
/*!
    Move-assigns \a other to this QPropertyBindingError.
    \a other will be left in its default state.
*/
QPropertyBindingError &QPropertyBindingError::operator=(QPropertyBindingError &&other)
{
    d = std::move(other.d);
    return *this;
}
 
/*!
    Destroys the QPropertyBindingError.
*/
QPropertyBindingError::~QPropertyBindingError()
{
}
 
/*!
    Returns the type of the QPropertyBindingError.
 
    \sa QPropertyBindingError::Type
*/
QPropertyBindingError::Type QPropertyBindingError::type() const
{
    if (!d)
        return QPropertyBindingError::NoError;
    return d->type;
}
 
/*!
    Returns a descriptive error message for the QPropertyBindingError if
    it has been set.
*/
QString QPropertyBindingError::description() const
{
    if (!d)
        return QString();
    return d->description;
}
 
/*!
  \class QPropertyData
  \inmodule QtCore
  \brief The QPropertyData class is a helper class for properties with automatic property bindings.
  \since 6.0
 
  \ingroup tools
 
  QPropertyData is a template class where the template parameter \a T specifies
  the type of the property value being stored.
 
  QPropertyData<T> is a common base class for classes that can hold properties with automatic
  data bindings. It mainly wraps the stored data, and offers low level access to that data.
 
  The low level access to the data provided by this class bypasses the binding mechanism, and should be
  used with care, as updates to the values will not get propagated to any bindings that depend on this
  property.
 
  You should usually call value() and setValue() on QProperty<T> or QObjectBindableProperty<T>, not use
  the low level mechanisms provided in this class.
*/
 
/*! \fn template <typename T> QPropertyData<T>::parameter_type QPropertyData<T>::valueBypassingBindings() const
 
    Returns the data stored in this property.
 
    \note As this will bypass any binding evaluation it might return an outdated value if a
    binding is set on this property. Using this method will also not register the property
    access with any currently executing binding.
*/
 
/*! \fn template <typename T> void QPropertyData<T>::setValueBypassingBindings(parameter_type v)
 
    Sets the data value stored in this property to \a v.
 
    \note Using this method will bypass any potential binding registered for this property.
*/
 
/*! \fn template <typename T> void QPropertyData<T>::setValueBypassingBindings(rvalue_ref v)
    \overload
 
    Sets the data value stored in this property to \a v.
 
    \note Using this method will bypass any potential binding registered for this property.
*/
 
/*!
  \class QUntypedBindable
  \inmodule QtCore
  \brief QUntypedBindable is a uniform interface over bindable properties like \c QProperty<T>
         and \c QObjectBindableProperty of any type \c T.
  \since 6.0
 
  \ingroup tools
 
  QUntypedBindable is a fully type-erased generic interface to wrap bindable properties.
  You can use it to interact with properties without knowing their type nor caring what
  kind of bindable property they are (e.g. QProperty or QObjectBindableProperty).
  For most use cases, using QBindable<T> (which is generic over the property implementation
  but has a fixed type) should be preferred.
*/
 
/*!
  \fn QUntypedBindable::QUntypedBindable()
 
  Default-constructs a QUntypedBindable. It is in an invalid state.
  \sa isValid()
*/
 
/*!
   \fn template<typename Property> QUntypedBindable::QUntypedBindable(Property *property)
 
   Constructs a QUntypedBindable from the property \a property. If Property is const,
   the QUntypedBindable will be read only. If \a property is null, the QUntypedBindable
   will be invalid.
 
   \sa isValid(), isReadOnly()
*/
 
/*!
   \fn bool QUntypedBindable::isValid() const
 
   Returns true if the QUntypedBindable is valid. Methods called on an invalid
   QUntypedBindable generally have no effect, unless otherwise noted.
*/
 
/*!
   \fn bool QUntypedBindable::isReadOnly() const
   \since 6.1
 
   Returns true if the QUntypedBindable is read-only.
*/
 
/*!
   \fn bool QUntypedBindable::isBindable() const
   \internal
 
   Returns true if the underlying property's binding can be queried
   with binding() and, if not read-only, changed with setBinding.
   Only QObjectComputedProperty currently leads to this method returning
   false.
 
   \sa isReadOnly()
*/
 
/*!
  \fn QUntypedPropertyBinding QUntypedBindable::makeBinding(const QPropertyBindingSourceLocation &location) const
 
  Creates a binding returning the underlying properties' value, using a specified source \a location.
*/
 
/*!
  \fn void QUntypedBindable::observe(QPropertyObserver *observer)
  \internal
 
  Installs the observer on the underlying property.
*/
 
/*!
  \fn template<typename Functor> QPropertyChangeHandler<Functor> QUntypedBindable::onValueChanged(Functor f) const
 
  Installs \a f as a change handler. Whenever the underlying property changes, \a f will be called, as
  long as the returned \c QPropertyChangeHandler and the property are kept alive.
  On each value change, the handler is either called immediately, or deferred, depending on the context.
 
  \sa QProperty::onValueChanged(), subscribe()
*/
 
/*!
    \fn template<typename Functor> QPropertyChangeHandler<Functor> QUntypedBindable::subscribe(Functor f) const
 
    Behaves like a call to \a f followed by \c onValueChanged(f),
 
    \sa onValueChanged()
*/
 
/*!
  \fn template<typename Functor> QPropertyNotifier QUntypedBindable::addNotifier(Functor f)
 
  Installs \a f as a change handler. Whenever the underlying property changes, \a f will be called, as
  long as the returned \c QPropertyNotifier and the property are kept alive.
 
  This method is in some cases easier to use than onValueChanged(), as the returned object is not a template.
  It can therefore more easily be stored, e.g. as a member in a class.
 
  \sa onValueChanged(), subscribe()
*/
 
/*!
  \fn QUntypedPropertyBinding QUntypedBindable::binding() const
 
  Returns the underlying property's binding if there is any, or a default
  constructed QUntypedPropertyBinding otherwise.
 
  \sa hasBinding()
*/
 
/*!
  \fn QUntypedPropertyBinding QUntypedBindable::takeBinding()
 
  Removes the currently set binding from the property and returns it.
  Returns a default-constructed QUntypedPropertyBinding if no binding is set.
 
  \since 6.1
*/
 
/*!
  \fn bool QUntypedBindable::setBinding(const QUntypedPropertyBinding &binding)
 
  Sets the underlying property's binding to \a binding. This does not have any effect
  if the QUntypedBindable is read-only, null or if \a binding's type does match the
  underlying property's type.
 
  \return \c true when the binding was successfully set.
 
  \sa QUntypedPropertyBinding::valueMetaType()
*/
 
/*!
  \fn bool QUntypedBindable::hasBinding() const
 
  Returns \c true if the underlying property has a binding.
*/
 
/*!
  \fn QMetaType QUntypedBindable::metaType() const
  \since 6.2
 
  Returns the metatype of the property from which the QUntypedBindable was created.
  If the bindable is invalid, an invalid metatype will be returned.
 
  \sa isValid(), QUntypedPropertyBinding::valueMetaType()
*/
 
/*!
  \class QBindable
  \inmodule QtCore
  \brief QBindable is a wrapper class around binding-enabled properties. It allows type-safe
         operations while abstracting the differences between the various property classes away.
  \inherits QUntypedBindable
 
   \ingroup tools
 
   QBindable is a template class where the template parameter \a T specifies
   the type of the property value.
 
   QBindable<T> helps to integrate Qt's traditional Q_PROPERTY with
   \l {Qt Bindable Properties}{binding-enabled} properties.
   If a property is backed by a QProperty, QObjectBindableProperty or QObjectComputedProperty,
   you can add \c BINDABLE bindablePropertyName to the Q_PROPERTY
   declaration, where bindablePropertyName is a function returning an instance of QBindable
   constructed from the QProperty. The returned QBindable allows users of the property to set
   and query bindings of the property, without having to know the exact kind of binding-enabled
   property used.
 
   \snippet code/src_corelib_kernel_qproperty.cpp 0
   \snippet code/src_corelib_kernel_qproperty.cpp 3
 
   \sa QMetaProperty::isBindable, QProperty, QObjectBindableProperty,
       QObjectComputedProperty, {Qt Bindable Properties}
*/
 
/*!
   \fn template<typename T> QBindable<T>::QBindable(QObject *obj, const char *property)
   \since 6.5
 
   Constructs a QBindable for the \l Q_PROPERTY \a property on \a obj. The property must
   have a notify signal but does not need to have \c BINDABLE in its \c Q_PROPERTY
   definition, so even binding unaware \c {Q_PROPERTY}s can be bound or used in binding
   expressions. You must use \c QBindable::value() in binding expressions instead of the
   normal property \c READ function (or \c MEMBER) to enable dependency tracking if the
   property is not \c BINDABLE. When binding using a lambda, you may prefer to capture the
   QBindable by value to avoid the cost of calling this constructor in the binding
   expression.
   This constructor should not be used to implement \c BINDABLE for a Q_PROPERTY, as the
   resulting Q_PROPERTY will not support dependency tracking. To make a property that is
   usable directly without reading through a QBindable use \l QProperty or
   \l QObjectBindableProperty.
 
   \code
   QProperty<QString> displayText;
   QDateTimeEdit *dateTimeEdit = findDateTimeEdit();
   QBindable<QDateTime> dateTimeBindable(dateTimeEdit, "dateTime");
   displayText.setBinding([dateTimeBindable](){ return dateTimeBindable.value().toString(); });
   \endcode
 
   \sa QProperty, QObjectBindableProperty, {Qt Bindable Properties}
*/
 
/*!
   \fn template<typename T> QBindable<T>::QBindable(QObject *obj, const QMetaProperty &property)
   \since 6.5
 
   See \l QBindable::QBindable(QObject *obj, const char *property)
*/
 
/*!
  \fn template<typename T> QPropertyBinding<T> QBindable<T>::makeBinding(const QPropertyBindingSourceLocation &location) const
 
  Constructs a binding evaluating to the underlying property's value, using a specified source
  \a location.
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> QBindable<T>::binding() const
 
   Returns the currently set binding of the underlying property. If the property does not
   have a binding, the returned \c QPropertyBinding<T> will be invalid.
 
   \sa setBinding, hasBinding
   //! \sa QPropertyBinding::isValid()
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> QBindable<T>::takeBinding()
 
   Removes the currently set binding of the underlying property and returns it.
   If the property does not have a binding, the returned \c QPropertyBinding<T> will be invalid.
 
   \sa binding, setBinding, hasBinding
   //! \sa QPropertyBinding::isValid()
*/
 
 
/*!
  \fn template <typename T> void QBindable<T>::setBinding(const QPropertyBinding<T> &binding)
 
   Sets the underlying property's binding to \a binding. Does nothing if the QBindable is
   read-only or invalid.
 
   \sa binding, isReadOnly(), isValid()
   //! \sa QPropertyBinding::isValid()
*/
 
/*!
  \fn  template <typename T> template <typename Functor> QPropertyBinding<T> QBindable<T>::setBinding(Functor f);
  \overload
 
  Creates a \c QPropertyBinding<T> from \a f, and sets it as the underlying property's binding.
*/
 
/*!
  \fn template <typename T> T QBindable<T>::value() const
 
  Returns the underlying property's current value. If the QBindable is invalid,
  a default constructed \c T is returned.
 
  \sa isValid()
*/
 
/*!
  \fn template <typename T> void QBindable<T>::setValue(const T &value)
 
  Sets the underlying property's value to \a value. This removes any currenltly set
  binding from it. This function has no effect if the QBindable is read-only or invalid.
 
  \sa isValid(), isReadOnly(), setBinding()
*/
 
/*!
  \class QProperty
  \inmodule QtCore
  \brief The QProperty class is a template class that enables automatic property bindings.
  \since 6.0
  \compares equality
  \compareswith equality T
  \endcompareswith
 
  \ingroup tools
 
  QProperty is a template class where the template parameter \a T specifies
  the type of the property value.
 
  QProperty<T> is one of the classes implementing \l {Qt Bindable Properties}.
  It is a container that holds an instance of T. You can assign
  a value to it and you can read it via the value() function or the T conversion
  operator. You can also tie the property to an expression that computes the value
  dynamically, the binding expression. It is represented as a C++ lambda and
  can be used to express relationships between different properties in your
  application.
 
  \note For QML, it's important to expose the \l QProperty in \l Q_PROPERTY
  with the BINDABLE keyword. As a result, the QML engine uses
  it as the bindable interface to set up the property binding. In turn, the
  binding can then be interacted with C++ via the normal API:
  QProperty<T>::onValueChanged, QProperty::takeBinding and QBindable::hasBinding
  If the property is BINDABLE, the engine will use the change-tracking
  inherent to the C++ property system for getting notified about changes, and it
  won't rely on signals being emitted.
*/
 
/*!
  \fn template <typename T> QProperty<T>::QProperty()
 
  Constructs a property with a default constructed instance of T.
*/
 
/*!
  \fn template <typename T> explicit QProperty<T>::QProperty(const T &initialValue)
 
  Constructs a property with the provided \a initialValue.
*/
 
/*!
  \fn template <typename T> explicit QProperty<T>::QProperty(T &&initialValue)
 
  Move-Constructs a property with the provided \a initialValue.
*/
 
/*!
  \fn template <typename T> QProperty<T>::QProperty(QProperty<T> &&other)
 
  Move-constructs a QProperty instance, making it point at the same object that
  \a other was pointing to.
*/
 
/*!
  \fn template <typename T> QProperty<T>::QProperty(const QPropertyBinding<T> &binding)
 
  Constructs a property that is tied to the provided \a binding expression.
  The property's value is set to the result of evaluating the new binding.
  Whenever a dependency of the binding changes, the binding will be re-evaluated,
  and the property's value gets updated accordingly.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QProperty<T>::QProperty(Functor &&f)
 
  Constructs a property that is tied to the provided binding expression \a f.
  The property's value is set to the result of evaluating the new binding.
  Whenever a dependency of the binding changes, the binding will be re-evaluated,
  and the property's value gets updated accordingly.
  */
 
/*!
  \fn template <typename T> QProperty<T>::~QProperty()
 
  Destroys the property.
*/
 
/*!
  \fn template <typename T> T QProperty<T>::value() const
 
  Returns the value of the property. This may evaluate a binding expression that
  is tied to this property, before returning the value.
*/
 
/*!
  \fn template <typename T> void QProperty<T>::setValue(rvalue_ref newValue)
  \fn template <typename T> void QProperty<T>::setValue(parameter_type newValue)
 
  Assigns \a newValue to this property and removes the property's associated
  binding, if present.
*/
 
/*!
  \fn template <typename T> QProperty<T> &QProperty<T>::operator=(rvalue_ref newValue)
  \fn template <typename T> QProperty<T> &QProperty<T>::operator=(parameter_type newValue)
 
  Assigns \a newValue to this property and returns a reference to this QProperty.
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> QProperty<T>::setBinding(const QPropertyBinding<T> &newBinding)
 
  Associates the value of this property with the provided \a newBinding
  expression and returns the previously associated binding. The property's value
  is set to the result of evaluating the new binding. Whenever a dependency of
  the binding changes, the binding will be re-evaluated, and the property's
  value gets updated accordingly.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QPropertyBinding<T> QProperty<T>::setBinding(Functor f)
  \overload
  \since 6.0
 
  Associates the value of this property with the provided functor \a f and
  returns the previously associated binding. The property's value is set to the
  result of evaluating the new binding. Whenever a dependency of the binding
  changes, the binding will be re-evaluated, and the property's value gets
  updated accordingly.
 
  \sa {Formulating a Property Binding}
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> bool QProperty<T>::setBinding(const QUntypedPropertyBinding &newBinding)
  \overload
 
  Associates the value of this property with the provided \a newBinding
  expression. The property's value is set to the result of evaluating the new
  binding. Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
 
  Returns true if the type of this property is the same as the type the binding
  function returns; false otherwise.
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> QProperty<T>::binding() const
 
  Returns the binding expression that is associated with this property. A
  default constructed QPropertyBinding<T> will be returned if no such
  association exists.
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> QProperty<T>::takeBinding()
 
  Disassociates the binding expression from this property and returns it. After
  calling this function, the value of the property will only change if you
  assign a new value to it, or when a new binding is set.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QPropertyChangeHandler<T, Functor> QProperty<T>::onValueChanged(Functor f)
 
  Registers the given functor \a f as a callback that shall be called whenever
  the value of the property changes. On each value change, the handler
  is either called immediately, or deferred, depending on the context.
 
  The callback \a f is expected to be a type that has a plain call operator
  \c{()} without any parameters. This means that you can provide a C++ lambda
  expression, a std::function or even a custom struct with a call operator.
 
  The returned property change handler object keeps track of the registration.
  When it goes out of scope, the callback is de-registered.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QPropertyChangeHandler<T, Functor> QProperty<T>::subscribe(Functor f)
  \since 6.0
 
  Subscribes the given functor \a f as a callback that is called immediately and
  whenever the value of the property changes in the future. On each value
  change, the handler is either called immediately, or deferred, depending on
  the context.
 
  The callback \a f is expected to be a type that can be copied and has a plain
  call operator() without any parameters. This means that you can provide a C++
  lambda expression, a std::function or even a custom struct with a call
  operator.
 
  The returned property change handler object keeps track of the subscription.
  When it goes out of scope, the callback is unsubscribed.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QPropertyNotifier QProperty<T>::addNotifier(Functor f)
  \since 6.2
 
  Subscribes the given functor \a f as a callback that is called whenever
  the value of the property changes.
 
  The callback \a f is expected to be a type that has a plain call operator
  \c{()} without any parameters. This means that you can provide a C++ lambda
  expression, a std::function or even a custom struct with a call operator.
 
  The returned property change handler object keeps track of the subscription.
  When it goes out of scope, the callback is unsubscribed.
 
  This method is in some cases easier to use than onValueChanged(), as the
  returned object is not a template. It can therefore more easily be stored,
  e.g. as a member in a class.
 
  \sa onValueChanged(), subscribe()
*/
 
/*!
  \fn template <typename T> QtPrivate::QPropertyBindingData &QProperty<T>::bindingData() const
  \internal
*/
 
/*!
  \class QObjectBindableProperty
  \inmodule QtCore
  \brief The QObjectBindableProperty class is a template class that enables
         automatic property bindings for property data stored in QObject derived
         classes.
  \since 6.0
  \compares equality
  \compareswith equality T
  \endcompareswith
 
  \ingroup tools
 
  QObjectBindableProperty is a template class where the template parameter
  \a Class specifies the owning QObject-derived class, \a T specifies the
  property value type, \a Offset specifies the property's location within
  the class, and \a Signal optionally specifies the notify signal to emit
  when the property value changes.
 
  QObjectBindableProperty is a generic container that holds an
  instance of T and behaves mostly like \l QProperty.
  It is one of the classes implementing \l {Qt Bindable Properties}.
  Unlike QProperty, it stores its management data structure in
  the surrounding QObject.
  The extra template parameters are used to identify the surrounding
  class and a member function of that class acting as a change handler.
 
  You can use QObjectBindableProperty to add binding support to code that uses
  Q_PROPERTY. The getter and setter methods must be adapted carefully according
  to the rules described in \l {Bindable Property Getters and Setters}.
 
  In order to invoke the change signal on property changes, use
  QObjectBindableProperty and pass the change signal as a callback.
 
  A simple example is given in the following.
 
  \snippet code/src_corelib_kernel_qproperty.cpp 4
  \snippet code/src_corelib_kernel_qproperty.cpp 4_include_moc
 
 
  QObjectBindableProperty is usually not used directly, instead an instance of
  it is created by using the Q_OBJECT_BINDABLE_PROPERTY macro.
 
  Use the Q_OBJECT_BINDABLE_PROPERTY macro in the class declaration to declare
  the property as bindable.
 
  \snippet code/src_corelib_kernel_qproperty.cpp 0
 
  If you need to directly initialize the property with some non-default value,
  you can use the Q_OBJECT_BINDABLE_PROPERTY_WITH_ARGS macro. It accepts a
  value for the initialization as one of its parameters.
 
  \snippet code/src_corelib_kernel_qproperty.cpp 1
 
  Q_OBJECT_BINDABLE_PROPERTY_WITH_ARGS does not support multiple arguments
  directly. If your property requires multiple arguments for initialization,
  please explicitly call the specific constructor.
 
  \snippet code/src_corelib_kernel_qproperty.cpp 2
  \snippet code/src_corelib_kernel_qproperty.cpp 2_property_use
 
  The change handler can optionally accept one argument, of the same type as the
  property, in which case it is passed the new value of the property. Otherwise,
  it should take no arguments.
 
  If the property does not need a changed notification, you can leave out the
  "NOTIFY xChanged" in the Q_PROPERTY macro as well as the last argument
  of the Q_OBJECT_BINDABLE_PROPERTY and Q_OBJECT_BINDABLE_PROPERTY_WITH_ARGS
  macros.
 
  \sa Q_OBJECT_BINDABLE_PROPERTY, Q_OBJECT_BINDABLE_PROPERTY_WITH_ARGS,
  QProperty, QObjectComputedProperty, {Qt's Property System}, {Qt Bindable
  Properties}
*/
 
/*!
  \macro Q_OBJECT_BINDABLE_PROPERTY(containingClass, type, name, signal)
  \since 6.0
  \relates QObjectBindableProperty
  \brief Declares a \l QObjectBindableProperty inside \a containingClass of type
  \a type with name \a name. If the optional argument \a signal is given, this
  signal will be emitted when the property is marked dirty.
 
  \sa {Qt's Property System}, {Qt Bindable Properties}
*/
 
/*!
  \macro Q_OBJECT_BINDABLE_PROPERTY_WITH_ARGS(containingClass, type, name, initialvalue, signal)
  \since 6.0
  \relates QObjectBindableProperty
  \brief Declares a \l QObjectBindableProperty inside \a containingClass
  of type \a type with name \a name which is initialized to \a initialvalue.
  If the optional argument \a signal is given, this signal will be emitted when
  the property is marked dirty.
 
  \sa {Qt's Property System}, {Qt Bindable Properties}
*/
 
/*!
  \class QObjectCompatProperty
  \inmodule QtCore
  \brief The QObjectCompatProperty class is a template class to help port old
         properties to the bindable property system.
  \since 6.0
  \ingroup tools
  \internal
 
  QObjectCompatProperty is a generic container that holds an
  instance of \c T and behaves mostly like QProperty, just like
  QObjectBindableProperty. It's one of the Qt internal classes implementing
  \l {Qt Bindable Properties}. Like QObjectBindableProperty,
  QObjectCompatProperty stores its management data structure in the surrounding
  QObject. The last template parameter specifies a method (of the owning
  class) to be called when the property is changed through the binding.
  This is usually a setter.
 
  As explained in \l {Qt Bindable Properties}, getters and setters for bindable
  properties have to be almost trivial to be correct. However, in legacy code,
  there is often complex logic in the setter. QObjectCompatProperty is a helper
  to port these properties to the bindable property system.
 
  With QObjectCompatProperty, the same rules as described in
  \l {Bindable Property Getters and Setters} hold for the getter.
  For the setter, the rules are different. It remains that every possible code
  path in the setter must write to the underlying QObjectCompatProperty,
  otherwise calling the setter might not remove a pre-existing binding, as
  it should. However, as QObjectCompatProperty will call the setter on every
  change, the setter is allowed to contain code like updating class internals
  or emitting signals. Every write to the QObjectCompatProperty has to
  be analyzed carefully to comply with the rules given in
  \l {Writing to a Bindable Property}.
 
  \section2 Properties with Virtual Setters
 
  Some of the pre-existing Qt classes (for example, \l QAbstractProxyModel)
  have properties with virtual setters. Special care must be taken when
  making such properties bindable.
 
  For the binding to work properly, the property must be correctly handled in
  all reimplemented methods of each derived class.
 
  Unless the derived class has access to the underlying property object, the
  base implementation \e must be called for the binding to work correctly.
 
  If the derived class can directly access the property instance, there is no
  need to explicitly call the base implementation, but the property's value
  \e must be correctly updated.
 
  Refer to \l {Bindable Properties with Virtual Setters and Getters} for more
  details.
 
  In both cases the expected behavior \e must be documented in the property's
  documentation, so that users can correctly override the setter.
 
  Properties for which these conditions cannot be met should not be made
  bindable.
 
  \sa Q_OBJECT_COMPAT_PROPERTY, QObjectBindableProperty, {Qt's Property System}, {Qt Bindable
  Properties}
*/
 
/*!
  \macro Q_OBJECT_COMPAT_PROPERTY(containingClass, type, name, callback)
  \since 6.0
  \relates QObjectCompatProperty
  \internal
  \brief Declares a \l QObjectCompatProperty inside \a containingClass
  of type \a type with name \a name. The argument \a callback specifies
  a setter function to be called when the property is changed through the binding.
 
  \sa QObjectBindableProperty, {Qt's Property System}, {Qt Bindable Properties}
*/
 
/*!
  \macro Q_OBJECT_COMPAT_PROPERTY_WITH_ARGS(containingClass, type, name, callback, value)
  \since 6.0
  \relates QObjectCompatProperty
  \internal
  \brief Declares a \l QObjectCompatProperty inside of \a containingClass
  of type \a type with name \a name. The argument \a callback specifies
  a setter function to be called when the property is changed through the binding.
  \a value specifies an initialization value.
*/
 
/*!
  \class QObjectComputedProperty
  \inmodule QtCore
  \brief The QObjectComputedProperty class is a template class to help port old
         properties to the bindable property system.
  \since 6.0
  \ingroup tools
 
  QObjectComputedProperty is a template class where the template parameter
  \a Class specifies the owning QObject-derived class, \a T specifies the
  computed property value type, \a Offset specifies the property's location
  within the class, and \a Getter specifies the member function that computes
  the property value.
 
  QObjectComputedProperty is a read-only property which is recomputed on each read.
  It does not store the computed value.
  It is one of the Qt internal classes implementing \l {Qt Bindable Properties}.
  QObjectComputedProperty is usually not used directly, instead an instance of it is created by
  using the Q_OBJECT_COMPUTED_PROPERTY macro.
 
  See the following example.
 
  \snippet code/src_corelib_kernel_qproperty.cpp 5
 
  The rules for getters in \l {Bindable Property Getters and Setters}
  also apply for QObjectComputedProperty. Especially, the getter
  should be trivial and only return the value of the QObjectComputedProperty object.
  The callback given to the QObjectComputedProperty should usually be a private
  method which is only called by the QObjectComputedProperty.
 
  No setter is required or allowed, as QObjectComputedProperty is read-only.
 
  To correctly participate in dependency handling, QObjectComputedProperty
  has to know when its value, the result of the callback given to it, might
  have changed. Whenever a bindable property used in the callback changes,
  this happens automatically. If the result of the callback might change
  because of a change in a value which is not a bindable property,
  it is the developer's responsibility to call \c notify
  on the QObjectComputedProperty object.
  This will inform dependent properties about the potential change.
 
  Note that calling \c notify might trigger change handlers in dependent
  properties, which might in turn use the object the QObjectComputedProperty
  is a member of. So \c notify must not be called when in a transitional
  or invalid state.
 
  QObjectComputedProperty is not suitable for use with a computation that depends
  on any input that might change without notice, such as the contents of a file.
 
  \sa Q_OBJECT_COMPUTED_PROPERTY, QProperty, QObjectBindableProperty,
      {Qt's Property System}, {Qt Bindable Properties}
*/
 
/*!
  \macro Q_OBJECT_COMPUTED_PROPERTY(containingClass, type, name, callback)
  \since 6.0
  \relates QObjectComputedProperty
  \brief Declares a \l QObjectComputedProperty inside \a containingClass
  of type \a type with name \a name. The argument \a callback specifies
  a GETTER function to be called when the property is evaluated.
 
  \sa QObjectBindableProperty, {Qt's Property System}, {Qt Bindable Properties}
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> QObjectBindableProperty<Class, T, offset, Callback>::QObjectBindableProperty()
 
  Constructs a property with a default constructed instance of T.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> explicit QObjectBindableProperty<Class, T, offset, Callback>::QObjectBindableProperty(const T &initialValue)
 
  Constructs a property with the provided \a initialValue.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> explicit QObjectBindableProperty<Class, T, offset, Callback>::QObjectBindableProperty(T &&initialValue)
 
  Move-Constructs a property with the provided \a initialValue.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> QObjectBindableProperty<Class, T, offset, Callback>::QObjectBindableProperty(Class *owner, const QPropertyBinding<T> &binding)
 
  Constructs a property that is tied to the provided \a binding expression.
  The property's value is set to the result of evaluating the new binding.
  Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
  When the property value changes, \a owner is notified via the Callback
  function.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> QObjectBindableProperty<Class, T, offset, Callback>::QObjectBindableProperty(Class *owner, QPropertyBinding<T> &&binding)
 
  Constructs a property that is tied to the provided \a binding expression.
  The property's value is set to the result of evaluating the new binding.
  Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
  When the property value changes, \a
  owner is notified via the Callback function.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> template <typename Functor> QObjectBindableProperty<Class, T, offset, Callback>::QObjectBindableProperty(Functor &&f)
 
  Constructs a property that is tied to the provided binding expression \a f.
  The property's value is set to the result of evaluating the new binding.
  Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> QObjectBindableProperty<Class, T, offset, Callback>::~QObjectBindableProperty()
 
  Destroys the property.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> T QObjectBindableProperty<Class, T, offset, Callback>::value() const
 
  Returns the value of the property. This may evaluate a binding expression that
  is tied to this property, before returning the value.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> void QObjectBindableProperty<Class, T, offset, Callback>::setValue(parameter_type newValue)
  \fn template <typename Class, typename T, auto offset, auto Callback> void QObjectBindableProperty<Class, T, offset, Callback>::setValue(rvalue_ref newValue)
 
  Assigns \a newValue to this property and removes the property's associated
  binding, if present. If the property value changes as a result, calls the
  Callback function on \a owner.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> void QObjectBindableProperty<Class, T, offset, Callback>::notify()
 
  Programmatically signals a change of the property. Any binding which depend on
  it will be notified, and if the property has a signal, it will be emitted.
 
  This can be useful in combination with setValueBypassingBindings to defer
  signalling the change until a class invariant has been restored.
 
  \note If this property has a binding (i.e. hasBinding() returns true), that
  binding is not reevaluated when notify() is called. Any binding depending on
  this property is still reevaluated as usual.
 
  \sa Qt::beginPropertyUpdateGroup(), setValueBypassingBindings()
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> QPropertyBinding<T> QObjectBindableProperty<Class, T, offset, Callback>::setBinding(const QPropertyBinding<T> &newBinding)
 
  Associates the value of this property with the provided \a newBinding
  expression and returns the previously associated binding.
  The property's value is set to the result of evaluating the new binding. Whenever a dependency of
  the binding changes, the binding will be re-evaluated,
  and the property's value gets updated accordingly.
 When the property value changes, the owner
  is notified via the Callback function.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> template <typename Functor> QPropertyBinding<T> QObjectBindableProperty<Class, T, offset, Callback>::setBinding(Functor f)
  \overload
 
  Associates the value of this property with the provided functor \a f and
  returns the previously associated binding. The property's value is set to the
  result of evaluating the new binding by invoking the call operator \c{()} of \a
  f. Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
  When the property value changes, the owner is notified via the Callback
  function.
 
  \sa {Formulating a Property Binding}
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> QPropertyBinding<T> bool QObjectBindableProperty<Class, T, offset, Callback>::setBinding(const QUntypedPropertyBinding &newBinding)
  \overload
 
  Associates the value of this property with the provided \a newBinding
  expression. The property's value is set to the result of evaluating the new
  binding. Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
 
  Returns \c true if the type of this property is the same as the type the
  binding function returns; \c false otherwise.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> bool QObjectBindableProperty<Class, T, offset, Callback>::hasBinding() const
 
  Returns true if the property is associated with a binding; false otherwise.
*/
 
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> QPropertyBinding<T> QObjectBindableProperty<Class, T, offset, Callback>::binding() const
 
  Returns the binding expression that is associated with this property. A
  default constructed QPropertyBinding<T> will be returned if no such
  association exists.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> QPropertyBinding<T> QObjectBindableProperty<Class, T, offset, Callback>::takeBinding()
 
  Disassociates the binding expression from this property and returns it. After
  calling this function, the value of the property will only change if you
  assign a new value to it, or when a new binding is set.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> template <typename Functor> QPropertyChangeHandler<T, Functor> QObjectBindableProperty<Class, T, offset, Callback>::onValueChanged(Functor f)
 
  Registers the given functor \a f as a callback that shall be called whenever
  the value of the property changes. On each value change, the handler is either
  called immediately, or deferred, depending on the context.
 
  The callback \a f is expected to be a type that has a plain call operator
  \c{()} without any parameters. This means that you can provide a C++ lambda
  expression, a std::function or even a custom struct with a call operator.
 
  The returned property change handler object keeps track of the registration.
  When it goes out of scope, the callback is de-registered.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> template <typename Functor> QPropertyChangeHandler<T, Functor> QObjectBindableProperty<Class, T, offset, Callback>::subscribe(Functor f)
 
  Subscribes the given functor \a f as a callback that is called immediately and
  whenever the value of the property changes in the future. On each value
  change, the handler is either called immediately, or deferred, depending on
  the context.
 
  The callback \a f is expected to be a type that has a plain call operator
  \c{()} without any parameters. This means that you can provide a C++ lambda
  expression, a std::function or even a custom struct with a call operator.
 
  The returned property change handler object keeps track of the subscription.
  When it goes out of scope, the callback is unsubscribed.
*/
 
/*!
  \fn template <typename Class, typename T, auto offset, auto Callback> template <typename Functor> QPropertyNotifier QObjectBindableProperty<Class, T, offset, Callback>::addNotifier(Functor f)
 
  Subscribes the given functor \a f as a callback that is called whenever the
  value of the property changes.
 
  The callback \a f is expected to be a type that has a plain call operator
  \c{()} without any parameters. This means that you can provide a C++ lambda
  expression, a std::function or even a custom struct with a call operator.
 
  The returned property change handler object keeps track of the subscription.
  When it goes out of scope, the callback is unsubscribed.
 
  This method is in some cases easier to use than onValueChanged(), as the
  returned object is not a template. It can therefore more easily be stored,
  e.g. as a member in a class.
 
  \sa onValueChanged(), subscribe()
*/
 
/*!
  \fn template <typename T> QtPrivate::QPropertyBase &QObjectBindableProperty<Class, T, offset, Callback>::propertyBase() const
  \internal
*/
 
/*!
  \class QPropertyChangeHandler
  \inmodule QtCore
  \brief The QPropertyChangeHandler class controls the lifecycle of change
  callback installed on a QProperty.
 
  \ingroup tools
 
  QPropertyChangeHandler is a template class where the template parameter
  \a Functor specifies the type of the callback function that is invoked
  when the property value changes.
 
  QPropertyChangeHandler<Functor> is created when registering a callback on a
  QProperty to listen to changes to the property's value, using
  QProperty::onValueChanged and QProperty::subscribe. As long as the change
  handler is alive, the callback remains installed.
 
  A handler instance can be transferred between C++ scopes using move semantics.
*/
 
/*!
  \class QPropertyNotifier
  \inmodule QtCore
  \brief The QPropertyNotifier class controls the lifecycle of change callback installed on a QProperty.
 
  \ingroup tools
  \since 6.2
 
  QPropertyNotifier is created when registering a callback on a QProperty to
  listen to changes to the property's value, using QProperty::addNotifier. As
  long as the change handler is alive, the callback remains installed.
 
  A handler instance can be transferred between C++ scopes using move semantics.
*/
 
/*!
  \class QPropertyAlias
  \inmodule QtCore
  \internal
 
  \brief The QPropertyAlias class is a safe alias for a QProperty with same
  template parameter.
 
  \ingroup tools
 
  QPropertyAlias<T> wraps a pointer to a QProperty<T> and automatically
  invalidates itself when the QProperty<T> is destroyed. It forwards all
  method invocations to the wrapped property. For example:
 
  \code
    QProperty<QString> *name = new QProperty<QString>("John");
    QProperty<int> age(41);
 
    QPropertyAlias<QString> nameAlias(name);
    QPropertyAlias<int> ageAlias(&age);
 
    QProperty<QString> fullname;
    fullname.setBinding([&]() { return nameAlias.value() + " age: " + QString::number(ageAlias.value()); });
 
    qDebug() << fullname.value(); // Prints "John age: 41"
 
    *name = "Emma"; // Marks binding expression as dirty
 
    qDebug() << fullname.value(); // Re-evaluates the binding expression and prints "Emma age: 41"
 
    // Birthday is coming up
    ageAlias.setValue(age.value() + 1); // Writes the age property through the alias
 
    qDebug() << fullname.value(); // Re-evaluates the binding expression and prints "Emma age: 42"
 
    delete name; // Leaves the alias in an invalid, but accessible state
    nameAlias.setValue("Eve"); // Ignored: nameAlias carries a default-constructed QString now
 
    ageAlias.setValue(92);
    qDebug() << fullname.value(); // Re-evaluates the binding expression and prints " age: 92"
  \endcode
*/
 
/*!
  \fn template <typename T> QPropertyAlias<T>::QPropertyAlias(QProperty<T> *property)
 
  Constructs a property alias for the given \a property.
*/
 
/*!
  \fn template <typename T> explicit QPropertyAlias<T>::QPropertyAlias(QPropertyAlias<T> *alias)
 
  Constructs a property alias for the property aliased by \a alias.
*/
 
/*!
  \fn template <typename T> T QPropertyAlias<T>::value() const
 
  Returns the value of the aliased property. This may evaluate a binding
  expression that is tied to the property, before returning the value.
*/
 
/*!
  \fn template <typename T> QPropertyAlias<T>::operator T() const
 
  Returns the value of the aliased property. This may evaluate a binding
  expression that is tied to the property, before returning the value.
*/
 
/*!
  \fn template <typename T> void QPropertyAlias<T>::setValue(const T &newValue)
 
  Assigns \a newValue to the aliased property and removes the property's
  associated binding, if present.
*/
 
/*!
  \fn template <typename T> QPropertyAlias<T> &QPropertyAlias<T>::operator=(const T &newValue)
 
  Assigns \a newValue to the aliased property and returns a reference to this
  QPropertyAlias.
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> QPropertyAlias<T>::setBinding(const QPropertyBinding<T> &newBinding)
 
  Associates the value of the aliased property with the provided \a newBinding
  expression and returns any previous binding the associated with the aliased
  property.The property's value is set to the result of evaluating the new
  binding. Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
 
  Returns any previous binding associated with the property, or a
  default-constructed QPropertyBinding<T>.
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> bool QPropertyAlias<T>::setBinding(const QUntypedPropertyBinding &newBinding)
  \overload
 
  Associates the value of the aliased property with the provided \a newBinding
  expression. The property's value is set to the result of evaluating the new
  binding. Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
 
  Returns true if the type of this property is the same as the type the binding
  function returns; false otherwise.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QPropertyBinding<T> QPropertyAlias<T>::setBinding(Functor f)
  \overload
 
  Associates the value of the aliased property with the provided functor \a f
  expression. The property's value is set to the result of evaluating the new
  binding. Whenever a dependency of the binding changes, the binding will be
  re-evaluated, and the property's value gets updated accordingly.
 
 
  Returns any previous binding associated with the property, or a
  default-constructed QPropertyBinding<T>.
 
  \sa {Formulating a Property Binding}
*/
 
/*!
  \fn template <typename T> bool QPropertyAlias<T>::hasBinding() const
 
  Returns true if the aliased property is associated with a binding; false
  otherwise.
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> QPropertyAlias<T>::binding() const
 
  Returns the binding expression that is associated with the aliased property. A
  default constructed QPropertyBinding<T> will be returned if no such
  association exists.
*/
 
/*!
  \fn template <typename T> QPropertyBinding<T> QPropertyAlias<T>::takeBinding()
 
  Disassociates the binding expression from the aliased property and returns it.
  After calling this function, the value of the property will only change if
  you assign a new value to it, or when a new binding is set.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QPropertyChangeHandler<T, Functor> QPropertyAlias<T>::onValueChanged(Functor f)
 
  Registers the given functor \a f as a callback that shall be called whenever
  the value of the aliased property changes. On each value change, the handler
  is either called immediately, or deferred, depending on the context.
 
  The callback \a f is expected to be a type that has a plain call operator
  \c{()} without any parameters. This means that you can provide a C++ lambda
  expression, a std::function or even a custom struct with a call operator.
 
  The returned property change handler object keeps track of the registration. When it
  goes out of scope, the callback is de-registered.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QPropertyChangeHandler<T, Functor> QPropertyAlias<T>::subscribe(Functor f)
 
  Subscribes the given functor \a f as a callback that is called immediately and
  whenever the value of the aliased property changes in the future. On each
  value change, the handler is either called immediately, or deferred, depending
  on the context.
 
  The callback \a f is expected to be a type that has a plain call operator
  \c{()} without any parameters. This means that you can provide a C++ lambda
  expression, a std::function or even a custom struct with a call operator.
 
  The returned property change handler object keeps track of the subscription.
  When it goes out of scope, the callback is unsubscribed.
*/
 
/*!
  \fn template <typename T> template <typename Functor> QPropertyNotifier QPropertyAlias<T>::addNotifier(Functor f)
 
  Subscribes the given functor \a f as a callback that is called whenever
  the value of the aliased property changes.
 
  The callback \a f is expected to be a type that has a plain call operator
  \c{()} without any parameters. This means that you can provide a C++ lambda
  expression, a std::function or even a custom struct with a call operator.
 
  The returned property change handler object keeps track of the subscription.
  When it goes out of scope, the callback is unsubscribed.
 
  This method is in some cases easier to use than onValueChanged(), as the
  returned object is not a template. It can therefore more easily be stored,
  e.g. as a member in a class.
 
  \sa onValueChanged(), subscribe()
*/
 
/*!
  \fn template <typename T> bool QPropertyAlias<T>::isValid() const
 
  Returns true if the aliased property still exists; false otherwise.
 
  If the aliased property doesn't exist, all other method calls are ignored.
*/
 
struct QBindingStorageData
{
    size_t size = 0;
    size_t used = 0;
    // Pair[] pairs;
};
 
struct QBindingStoragePrivate
{
    // This class basically implements a simple and fast hash map to store bindings for a QObject
    // The reason that we're not using QHash is that QPropertyBindingData can not be copied, only
    // moved. That doesn't work well together with an implicitly shared class.
    struct Pair
    {
        QUntypedPropertyData *data;
        QPropertyBindingData bindingData;
    };
    static_assert(alignof(Pair) == alignof(void *));
    static_assert(alignof(size_t) == alignof(void *));
 
    QBindingStorageData *&d;
 
    static inline Pair *pairs(QBindingStorageData *dd)
    {
        Q_ASSERT(dd);
        return reinterpret_cast<Pair *>(dd + 1);
    }
    void reallocate(size_t newSize)
    {
        Q_ASSERT(!d || newSize > d->size);
        size_t allocSize = sizeof(QBindingStorageData) + newSize*sizeof(Pair);
        void *nd = calloc(1, allocSize);
        QBindingStorageData *newData = new (nd) QBindingStorageData;
        newData->size = newSize;
        if (!d) {
            d = newData;
            return;
        }
        newData->used = d->used;
        Pair *p = pairs(d);
        for (size_t i = 0; i < d->size; ++i, ++p) {
            if (p->data) {
                Pair *pp = pairs(newData);
                Q_ASSERT(newData->size && (newData->size & (newData->size - 1)) == 0); // size is a power of two
                size_t index = qHash(p->data) & (newData->size - 1);
                while (pp[index].data) {
                    ++index;
                    if (index == newData->size)
                        index = 0;
                }
                new (pp + index) Pair{p->data, QPropertyBindingData(std::move(p->bindingData))};
            }
        }
        // data has been moved, no need to call destructors on old Pairs
        const size_t oldAllocSize = sizeof(QBindingStorageData) + d->size*sizeof(Pair);
        QtPrivate::sizedFree(d, oldAllocSize);
        d = newData;
    }
 
    QBindingStoragePrivate(QBindingStorageData *&_d) : d(_d) {}
 
    QPropertyBindingData *get(const QUntypedPropertyData *data)
    {
        Q_ASSERT(d);
        Q_ASSERT(d->size && (d->size & (d->size - 1)) == 0); // size is a power of two
        size_t index = qHash(data) & (d->size - 1);
        Pair *p = pairs(d);
        while (p[index].data) {
            if (p[index].data == data)
                return &p[index].bindingData;
            ++index;
            if (index == d->size)
                index = 0;
        }
        return nullptr;
    }
    QPropertyBindingData *get(QUntypedPropertyData *data, bool create)
    {
        if (!d) {
            if (!create)
                return nullptr;
            reallocate(8);
        }
        else if (d->used*2 >= d->size)
            reallocate(d->size*2);
        Q_ASSERT(d->size && (d->size & (d->size - 1)) == 0); // size is a power of two
        size_t index = qHash(data) & (d->size - 1);
        Pair *p = pairs(d);
        while (p[index].data) {
            if (p[index].data == data)
                return &p[index].bindingData;
            ++index;
            if (index == d->size)
                index = 0;
        }
        if (!create)
            return nullptr;
        ++d->used;
        new (p + index) Pair{data, QPropertyBindingData()};
        return &p[index].bindingData;
    }
 
    void destroy()
    {
        if (!d)
            return;
        Pair *p = pairs(d);
        for (size_t i = 0; i < d->size; ++i) {
            if (p->data)
                p->~Pair();
            ++p;
        }
        const size_t allocSize = sizeof(QBindingStorageData) + d->size*sizeof(Pair);
        QtPrivate::sizedFree(d, allocSize);
    }
};
 
/*!
    \class QBindingStorage
    \internal
 
    QBindingStorage acts as a storage for property binding related data in QObject.
    Any property in a QObject can be made bindable by using the Q_OBJECT_BINDABLE_PROPERTY
    macro to declare it. A setter and a getter for the property and a declaration using
    Q_PROPERTY have to be made as usual.
    Binding related data will automatically be stored within the QBindingStorage
    inside the QObject.
*/
 
QBindingStorage::QBindingStorage()
{
    bindingStatus = &QT_PREPEND_NAMESPACE(bindingStatus)();
    Q_ASSERT(bindingStatus);
}
 
QBindingStorage::~QBindingStorage()
{
    QBindingStoragePrivate(d).destroy();
}
 
void QBindingStorage::reinitAfterThreadMove()
{
    bindingStatus = &QT_PREPEND_NAMESPACE(bindingStatus)();
    Q_ASSERT(bindingStatus);
}
 
void QBindingStorage::clear()
{
    QBindingStoragePrivate(d).destroy();
    d = nullptr;
    bindingStatus = nullptr;
}
 
void QBindingStorage::registerDependency_helper(const QUntypedPropertyData *data) const
{
    Q_ASSERT(bindingStatus);
    // Use ::bindingStatus to get the binding from TLS. This is required, so that reads from
    // another thread do not register as dependencies
    QtPrivate::BindingEvaluationState *currentBinding;
#ifdef QT_HAS_FAST_CURRENT_THREAD_ID
    const bool threadMatches = (QThread::currentThreadId() == bindingStatus->threadId);
    if (Q_LIKELY(threadMatches))
        currentBinding = bindingStatus->currentlyEvaluatingBinding;
    else
        currentBinding = QT_PREPEND_NAMESPACE(bindingStatus)().currentlyEvaluatingBinding;
#else
    currentBinding = QT_PREPEND_NAMESPACE(bindingStatus)().currentlyEvaluatingBinding;
#endif
    QUntypedPropertyData *dd = const_cast<QUntypedPropertyData *>(data);
    if (!currentBinding)
        return;
    auto storage = QBindingStoragePrivate(d).get(dd, true);
    if (!storage)
        return;
    storage->registerWithCurrentlyEvaluatingBinding(currentBinding);
}
 
 
QPropertyBindingData *QBindingStorage::bindingData_helper(const QUntypedPropertyData *data) const
{
    return QBindingStoragePrivate(d).get(data);
}
 
const QBindingStatus *QBindingStorage::status(QtPrivate::QBindingStatusAccessToken) const
{
    return bindingStatus;
}
 
QPropertyBindingData *QBindingStorage::bindingData_helper(QUntypedPropertyData *data, bool create)
{
    return QBindingStoragePrivate(d).get(data, create);
}
 
 
namespace QtPrivate {
 
 
void initBindingStatusThreadId()
{
    bindingStatus().threadId = QThread::currentThreadId();
}
 
BindingEvaluationState *suspendCurrentBindingStatus()
{
    auto ret = bindingStatus().currentlyEvaluatingBinding;
    bindingStatus().currentlyEvaluatingBinding = nullptr;
    return ret;
}
 
void restoreBindingStatus(BindingEvaluationState *status)
{
    bindingStatus().currentlyEvaluatingBinding = status;
}
 
/*!
    \internal
    This function can be used to detect whether we are currently
    evaluating a binding. This can e.g. be used to defer the allocation
    of extra data for a QPropertyBindingStorage in a getter.
    Note that this function accesses TLS storage, and is therefore soemwhat
    costly to call.
*/
bool isAnyBindingEvaluating()
{
    return bindingStatus().currentlyEvaluatingBinding != nullptr;
}
 
bool isPropertyInBindingWrapper(const QUntypedPropertyData *property)
{
    // Accessing bindingStatus is expensive because it's thread-local. Do it only once.
    if (const auto current = bindingStatus().currentCompatProperty)
        return current->property == property;
    return false;
}
 
namespace BindableWarnings {
 
void printUnsuitableBindableWarning(QAnyStringView prefix, BindableWarnings::Reason reason)
{
    switch (reason) {
    case QtPrivate::BindableWarnings::NonBindableInterface:
        qCWarning(lcQPropertyBinding).noquote() << prefix.toString()
                                                << "The QBindable does not allow interaction with the binding.";
        break;
    case QtPrivate::BindableWarnings::ReadOnlyInterface:
        qCWarning(lcQPropertyBinding).noquote() << prefix.toString()
                                                << "The QBindable is read-only.";
        break;
    default:
    case QtPrivate::BindableWarnings::InvalidInterface:
        qCWarning(lcQPropertyBinding).noquote() << prefix.toString()
                                                << "The QBindable is invalid.";
        break;
    }
}
 
void printMetaTypeMismatch(QMetaType actual, QMetaType expected)
{
    qCWarning(lcQPropertyBinding) << "setBinding: Could not set binding as the property expects it to be of type"
                                  << actual.name()
                                  << "but got" << expected.name() << "instead.";
}
 
void printSignalArgumentsWithCustomGetter()
{
    qCWarning(lcQPropertyBinding)
            << "Property has a custom getter and also a change signal with arguments."
            << "This requires the getter to be called to retrieve the argument,"
            << "possibly creating spurious binding dependencies";
}
 
} // namespace BindableWarnings end
 
/*!
    \internal
    Returns the binding statusof the current thread.
 */
QBindingStatus* getBindingStatus(QtPrivate::QBindingStatusAccessToken)
{
    return &QT_PREPEND_NAMESPACE(bindingStatus)();
}
void setBindingStatus(QBindingStatus *status, QBindingStatusAccessToken)
{
    Q_ASSERT(!tl_status);
    Q_ASSERT(status);
    tl_status = status;
}
 
namespace PropertyAdaptorSlotObjectHelpers {
void getter(const QUntypedPropertyData *d, void *value)
{
    auto adaptor = static_cast<const QtPrivate::QPropertyAdaptorSlotObject *>(d);
    adaptor->bindingData().registerWithCurrentlyEvaluatingBinding();
    auto mt = adaptor->metaProperty().metaType();
    mt.destruct(value);
    mt.construct(value, adaptor->metaProperty().read(adaptor->object()).data());
}
 
void setter(QUntypedPropertyData *d, const void *value)
{
    auto adaptor = static_cast<QtPrivate::QPropertyAdaptorSlotObject *>(d);
    adaptor->bindingData().removeBinding();
    adaptor->metaProperty().write(adaptor->object(),
                                  QVariant(adaptor->metaProperty().metaType(), value));
}
 
QUntypedPropertyBinding getBinding(const QUntypedPropertyData *d)
{
    auto adaptor = static_cast<const QtPrivate::QPropertyAdaptorSlotObject *>(d);
    return QUntypedPropertyBinding(adaptor->bindingData().binding());
}
 
bool bindingWrapper(QMetaType type, QUntypedPropertyData *d,
                    QtPrivate::QPropertyBindingFunction binding, QUntypedPropertyData *temp,
                    void *value)
{
    auto adaptor = static_cast<const QtPrivate::QPropertyAdaptorSlotObject *>(d);
    type.destruct(value);
    type.construct(value, adaptor->metaProperty().read(adaptor->object()).data());
    if (binding.vtable->call(type, temp, binding.functor)) {
        adaptor->metaProperty().write(adaptor->object(), QVariant(type, value));
        return true;
    }
    return false;
}
 
QUntypedPropertyBinding setBinding(QUntypedPropertyData *d, const QUntypedPropertyBinding &binding,
                                   QPropertyBindingWrapper wrapper)
{
    auto adaptor = static_cast<QPropertyAdaptorSlotObject *>(d);
    return adaptor->bindingData().setBinding(binding, d, nullptr, wrapper);
}
 
void setObserver(const QUntypedPropertyData *d, QPropertyObserver *observer)
{
    observer->setSource(static_cast<const QPropertyAdaptorSlotObject *>(d)->bindingData());
}
}
 
QPropertyAdaptorSlotObject::QPropertyAdaptorSlotObject(QObject *o, const QMetaProperty &p)
    : QSlotObjectBase(&impl), obj(o), metaProperty_(p)
{
}
 
#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
void QPropertyAdaptorSlotObject::impl(int which, QSlotObjectBase *this_, QObject *r, void **a,
                                      bool *ret)
#else
void QPropertyAdaptorSlotObject::impl(QSlotObjectBase *this_, QObject *r, void **a, int which,
                                      bool *ret)
#endif
{
    auto self = static_cast<QPropertyAdaptorSlotObject *>(this_);
    switch (which) {
    case Destroy:
        delete self;
        break;
    case Call:
        if (!self->bindingData_.hasBinding())
            self->bindingData_.notifyObservers(self);
        break;
    case Compare:
    case NumOperations:
        Q_UNUSED(r);
        Q_UNUSED(a);
        Q_UNUSED(ret);
        break;
    }
}
 
} // namespace QtPrivate end
 
QUntypedBindable::QUntypedBindable(QObject *obj, const QMetaProperty &metaProperty,
                                   const QtPrivate::QBindableInterface *i)
    : iface(i)
{
    if (!obj)
        return;
 
    if (!metaProperty.isValid()) {
        qCWarning(lcQPropertyBinding) << "QUntypedBindable: Property is not valid";
        return;
    }
 
    if (metaProperty.isBindable()) {
        *this = metaProperty.bindable(obj);
        return;
    }
 
    if (!metaProperty.hasNotifySignal()) {
        qCWarning(lcQPropertyBinding)
                << "QUntypedBindable: Property" << metaProperty.name() << "has no notify signal";
        return;
    }
 
    auto metatype = iface->metaType();
    if (metaProperty.metaType() != metatype) {
        qCWarning(lcQPropertyBinding) << "QUntypedBindable: Property" << metaProperty.name()
                                      << "of type" << metaProperty.metaType().name()
                                      << "does not match requested type" << metatype.name();
        return;
    }
 
    // Test for name pointer equality proves it's exactly the same property
    if (obj->metaObject()->property(metaProperty.propertyIndex()).name() != metaProperty.name()) {
        qCWarning(lcQPropertyBinding) << "QUntypedBindable: Property" << metaProperty.name()
                                      << "does not belong to this object";
        return;
    }
 
    // Get existing binding data if it exists
    auto adaptor = QObjectPrivate::get(obj)->getPropertyAdaptorSlotObject(metaProperty);
 
    if (!adaptor) {
        adaptor = new QPropertyAdaptorSlotObject(obj, metaProperty);
 
        auto c = QObjectPrivate::connect(obj, metaProperty.notifySignalIndex(), obj, adaptor,
                                         Qt::DirectConnection);
        Q_ASSERT(c);
    }
 
    data = adaptor;
}
 
QUntypedBindable::QUntypedBindable(QObject *obj, const char *property,
                                   const QtPrivate::QBindableInterface *i)
    : QUntypedBindable(
            obj,
            [=]() -> QMetaProperty {
                if (!obj)
                    return {};
                auto propertyIndex = obj->metaObject()->indexOfProperty(property);
                if (propertyIndex < 0) {
                    qCWarning(lcQPropertyBinding)
                            << "QUntypedBindable: No property named" << property;
                    return {};
                }
                return obj->metaObject()->property(propertyIndex);
            }(),
            i)
{
}
 
QT_END_NAMESPACE