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** This file is part of the QtQml module of the Qt Toolkit.
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** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
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#ifndef QQMLABSTRACTEXPRESSION_P_H
#define QQMLABSTRACTEXPRESSION_P_H

//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API.  It exists purely as an
// implementation detail.  This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//

#include <private/qqmlcontext_p.h>
#include <private/qfieldlist_p.h>
#include <private/qflagpointer_p.h>

QT_BEGIN_NAMESPACE

class Q_QML_PRIVATE_EXPORT QQmlAbstractExpression
{
public:
    QQmlAbstractExpression();
    virtual ~QQmlAbstractExpression();

    bool isValid() const;

    QQmlContextData *context() const;
    void setContext(QQmlContextData *);

    virtual void refresh();

    class DeleteWatcher {
    public:
        inline DeleteWatcher(QQmlAbstractExpression *);
        inline ~DeleteWatcher();
        inline bool wasDeleted() const;
    private:
        friend class QQmlAbstractExpression;
        QQmlContextData *_c;
        QQmlAbstractExpression **_w;
        QQmlAbstractExpression *_s;
    };

private:
    friend class QQmlContext;
    friend class QQmlContextData;
    friend class QQmlContextPrivate;

    QBiPointer<QQmlContextData, DeleteWatcher> m_context;
    QQmlAbstractExpression **m_prevExpression;
    QQmlAbstractExpression  *m_nextExpression;
};

QQmlAbstractExpression::DeleteWatcher::DeleteWatcher(QQmlAbstractExpression *e)
: _c(0), _w(0), _s(e)
{
    if (e->m_context.isT1()) {
        _w = &_s;
        _c = e->m_context.asT1();
        e->m_context = this;
    } else {
        // Another watcher is already registered
        _w = &e->m_context.asT2()->_s;
    }
}

QQmlAbstractExpression::DeleteWatcher::~DeleteWatcher()
{
    Q_ASSERT(*_w == 0 || (*_w == _s && _s->m_context.isT2()));
    if (*_w && _s->m_context.asT2() == this)
        _s->m_context = _c;
}

bool QQmlAbstractExpression::DeleteWatcher::wasDeleted() const
{
    return *_w == 0;
}

QT_END_NAMESPACE

#endif // QQMLABSTRACTEXPRESSION_P_H