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/****************************************************************************
**
** Copyright (C) 2021 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the QtXmlPatterns module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:COMM$
**
** 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 https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** $QT_END_LICENSE$
**
**
**
**
**
**
**
**
**
**
**
**
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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_EvaluationCache_H
#define Patternist_EvaluationCache_H
#include <private/qcachingiterator_p.h>
#include <private/qcommonsequencetypes_p.h>
#include <private/qnodebuilder_p.h>
#include <private/qoperandsiterator_p.h>
#include <private/qsinglecontainer_p.h>
#include <private/qvariabledeclaration_p.h>
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 <frans.englich@nokia.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_tpl_p.h"
}
QT_END_NAMESPACE
#endif
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