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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information (qt-info@nokia.com)
**
** This file is part of the QtXmlPatterns module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the either Technology Preview License Agreement or the
** Beta Release License Agreement.
**
** 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 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain
** additional rights. These rights are described in the Nokia Qt LGPL
** Exception version 1.0, 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.
**
** If you are unsure which license is appropriate for your use, please
** contact the sales department at qt-sales@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/
//
// 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_EvaluationCache_H
#define Patternist_EvaluationCache_H
#include "qcachingiterator_p.h"
#include "qcommonsequencetypes_p.h"
#include "qnodebuilder_p.h"
#include "qoperandsiterator_p.h"
#include "qsinglecontainer_p.h"
#include "qvariabledeclaration_p.h"
QT_BEGIN_HEADER
QT_BEGIN_NAMESPACE
namespace QPatternist
{
/**
* @short Evaluates to the same result as its operand, but ensures the
* operand is evaluated once even if this Expression is evaluated several
* times.
*
* EvaluationCache does this in a pipelined way, by delivering items from
* its cache, which is stored in the DynamicContext. If the cache has less
* items than what the caller requests, EvaluationCache continues to
* deliver but this time from the source, which it also populates into the
* cache.
*
* EvaluationCache is used as an optimization in order to avoid running
* expensive code paths multiple times, but also is sometimes a necessity:
* for instance, when objects must be unique, such as potentially in the
* case of node identity.
*
* EvaluationCache is in particular used for variables, whose sole purpose
* is to store it once(at least conceptually) and then use it in multiple
* places.
*
* In some cases an EvaluationCache isn't necessary. For instance, when a
* variable is only referenced once. In those cases EvaluationCache removes
* itself as an optimization; implemented in compress().
*
* @author Frans Englich <fenglich@trolltech.com>
* @ingroup Patternist_expressions
*/
template<bool IsForGlobal>
class EvaluationCache : public SingleContainer
{
public:
EvaluationCache(const Expression::Ptr &operand,
const VariableDeclaration::Ptr &varDecl,
const VariableSlotID slot);
virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const;
virtual Item::Iterator::Ptr evaluateSequence(const DynamicContext::Ptr &context) const;
virtual Expression::Ptr compress(const StaticContext::Ptr &context);
virtual SequenceType::Ptr staticType() const;
/**
* The first operand must be exactly one @c xs:string.
*/
virtual SequenceType::List expectedOperandTypes() const;
virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const;
virtual Properties properties() const;
virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context,
const SequenceType::Ptr &reqType);
virtual const SourceLocationReflection *actualReflection() const;
inline VariableSlotID slot() const
{
return m_varSlot;
}
private:
static DynamicContext::Ptr topFocusContext(const DynamicContext::Ptr &context);
const VariableDeclaration::Ptr m_declaration;
/**
* This variable must not be called m_slot. If it so, a compiler bug on
* HP-UX-aCC-64 is triggered in the constructor initializor. See the
* preprocessor output.
*
* Note that this is the cache slot, and is disjoint to any variable's
* regular slot.
*/
const VariableSlotID m_varSlot;
};
#include "qevaluationcache.cpp"
}
QT_END_NAMESPACE
QT_END_HEADER
#endif
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