source: trunk/src/xmlpatterns/data/qitem_p.h@ 846

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** This file is part of the QtXmlPatterns module of the Qt Toolkit.
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//
//  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.

#ifndef Patternist_Item_H
#define Patternist_Item_H

#include <QtXmlPatterns/private/qcppcastinghelper_p.h>
#include <QtXmlPatterns/private/qitemtype_p.h>
#include <QtXmlPatterns/private/qsingletoniterator_p.h>
#include <QtXmlPatterns/QAbstractXmlNodeModel>

#include <QUrl>
#include <QVariant>

/**
 * @file
 * @short Due to strong interdependencies, this file contains the definitions for
 * the classes Item, QXmlNodeModelIndex, QAbstractXmlNodeModel and AtomicValue. The implementations are
 * in their respective source files.
 */

/**
 * @class QSharedData
 * @short Qt's base class for reference counting.
 */

QT_BEGIN_HEADER

QT_BEGIN_NAMESPACE

template<typename T> class QList;
template<typename T> class QVector;
template<typename T> class QAbstractXmlForwardIterator;

class QSourceLocation;
class QAbstractXmlReceiver;

namespace QPatternist
{
    class DynamicContext;
    class Item;
    class ItemType;
    class QObjectNodeModel;
    template<typename T> class EmptyIterator;
    template<typename T, typename ListType> class ListIterator;

    /**
     * @short Base class for all classes representing atomic values.
     *
     * Instantiating AtomicValues sub classes from a value of somekind,
     * for a certain type is done in three different ways:
     *
     * - The static factory fromLexical which available in most classes. This
     * function attempts to create a value from a QString that is considered
     * a lexical representation of the value. Thus, this function performs validation, takes
     * care of whitespace facets, and everything else related to instantiating a value from
     * a lexical representation.
     * - The static factory function fromValue. This function exists for
     * values where a C++ type exists which corresponds to the type's value space.
     * - By using instances available in CommonValues. This is the preferred method
     * since it uses existing singleton instances and thus saves memory. CommonValues
     * should be used whenever possible, it can be thought as a collection of constant values.
     *
     * For types that does not distinguish the value space and lexical space, such as <tt>xs:string</tt>,
     * only the fromValue() function exist, and fromLexical() is omitted.
     *
     * @ingroup Patternist_xdm
     * @author Frans Englich <[email protected]>
     */
    class AtomicValue : public QSharedData
                      , public CppCastingHelper<AtomicValue>
    {
    public:
        virtual ~AtomicValue();

        /**
         * A smart pointer wrapping AtomicValue instances.
         */
        typedef QExplicitlySharedDataPointer<AtomicValue> Ptr;

        /**
         * A list if smart pointers wrapping AtomicValue instances.
         */
        typedef QList<AtomicValue::Ptr> List;

        /**
         * Determines whether this atomic value has an error. This is used
         * for implementing casting.
         *
         * @returns always @c false
         */
        virtual bool hasError() const;

        /**
         * Always fails by issuing the type error ReportContext::FORG0006. Sub-classes
         * whose represented type do allow EBV to be extracted from, must thus
         * re-implement this function.
         */
        virtual bool evaluateEBV(const QExplicitlySharedDataPointer<DynamicContext> &context) const;

        virtual QString stringValue() const = 0;
        virtual ItemType::Ptr type() const = 0;

        /**
         * Converts @p value to a QVariant.
         */
        static QVariant toQt(const AtomicValue *const value);