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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 "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 <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.cpp"

}

QT_END_NAMESPACE

QT_END_HEADER

#endif