File: qitemmappingiterator_p.h

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/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the QtXmlPatterns module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see http://www.qt.io/terms-conditions. For further
** information use the contact form at http://www.qt.io/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 or version 3 as published by the Free
** Software Foundation and appearing in the file LICENSE.LGPLv21 and
** LICENSE.LGPLv3 included in the packaging of this file. Please review the
** following information to ensure the GNU Lesser General Public License
** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** As a special exception, The Qt Company gives you certain additional
** rights. These rights are described in The Qt Company LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** 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
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** $QT_END_LICENSE$
**
****************************************************************************/

//
//  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_ItemMappingIterator_H
#define Patternist_ItemMappingIterator_H

#include "qabstractxmlforwarditerator_p.h"
#include "qdynamiccontext_p.h"

QT_BEGIN_HEADER

QT_BEGIN_NAMESPACE

namespace QPatternist
{
    /**
     * @short Proxies another QAbstractXmlForwardIterator, and for each item, returns the
     * Item returned from a mapping function.
     *
     * ItemMappingIterator is practical when the items in an QAbstractXmlForwardIterator needs to
     * be translated to another sequence, while still doing it in a pipe-lined
     * fashion.
     *
     * This is achieved by that ItemMappingIterator's constructor takes
     * an instance of a class, that must have the following member:
     *
     * @code
     * TResult::Ptr mapToItem(const TSource &item,
     *                        const Context &context) const
     * @endcode
     *
     * For each item in the QAbstractXmlForwardIterator ItemMappingIterator proxies, this function is
     * called and its return value becomes the return value of the ItemMappingIterator. If the
     * mapping function returns null, ItemMappingIterator maps the next item in the source sequence
     * such that a contiguous sequence of items is returned.
     *
     * Declaring the mapToItem() function as inline, can be a good way to improve performance.
     *
     * @see SequenceMappingIterator
     * @author Frans Englich <frans.englich@nokia.com>
     * @ingroup Patternist_iterators
     */
    template<typename TResult, typename TSource, typename TMapper, typename Context = DynamicContext::Ptr>
    class ItemMappingIterator : public QAbstractXmlForwardIterator<TResult>
    {
    public:
        /**
         * Constructs an ItemMappingIterator.
         *
         * @param mapper the object that has the mapToItem() sequence.
         * @param iterator the QAbstractXmlForwardIterator whose items should be mapped.
         * @param context the context that will be passed to the map function.
         * May be null.
         */
        ItemMappingIterator(const TMapper &mapper,
                            const typename QAbstractXmlForwardIterator<TSource>::Ptr &iterator,
                            const Context &context) : m_mapper(mapper)
                                                    , m_it(iterator)
                                                    , m_context(context)
                                                    , m_position(0)
        {
            Q_ASSERT(mapper);
            Q_ASSERT(iterator);
        }

        /**
         * @returns the next item in the sequence, or
         * @c null if the end have been reached.
         */
        virtual TResult next()
        {
            while (true)
            {
                const TSource &sourceItem = m_it->next();
                if (qIsForwardIteratorEnd(sourceItem))
                {
                    m_current = TResult();
                    m_position = -1;
                    return m_current;
                }
                else
                {
                    m_current = m_mapper->mapToItem(sourceItem, m_context);
                    if (qIsForwardIteratorEnd(m_current))
                    {
                        continue; /* The mapper returned null, so continue with the next in the source. */
                    }
                    else
                    {
                        ++m_position;
                        return m_current;
                    }
                }
            }
        }

        virtual TResult current() const
        {
            return m_current;
        }

        virtual xsInteger position() const
        {
            return m_position;
        }

        virtual typename QAbstractXmlForwardIterator<TResult>::Ptr copy() const
        {
            return typename QAbstractXmlForwardIterator<TResult>::Ptr
                (new ItemMappingIterator<TResult, TSource, TMapper, Context>(m_mapper, m_it->copy(), m_context));
        }

    private:
        const TMapper                                               m_mapper;
        const typename QAbstractXmlForwardIterator<TSource>::Ptr    m_it;
        const Context                                               m_context;
        TResult                                                     m_current;
        xsInteger                                                   m_position;
    };

    /**
     * @short An object generator for ItemMappingIterator.
     *
     * makeItemMappingIterator() is a convenience function for avoiding specifying
     * the full template instantiation for ItemMappingIterator. Conceptually, it
     * is identical to Qt's qMakePair().
     *
     * @relates ItemMappingIterator
     */
    template<typename TResult, typename TSource, typename TMapper, typename Context>
    static inline
    typename QAbstractXmlForwardIterator<TResult>::Ptr
    makeItemMappingIterator(const TMapper &mapper,
                            const QExplicitlySharedDataPointer<QAbstractXmlForwardIterator<TSource> > &source,
                            const Context &context)
    {
        return typename QAbstractXmlForwardIterator<TResult>::Ptr
            (new ItemMappingIterator<TResult, TSource, TMapper, Context>(mapper, source, context));
    }
}

QT_END_NAMESPACE

QT_END_HEADER

#endif