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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_ExternalVariableLoader_H

#define Patternist_ExternalVariableLoader_H

#include "qitem_p.h"

#include "qsequencetype_p.h"

#include "qxmlname.h"

QT_BEGIN_HEADER

QT_BEGIN_NAMESPACE

namespace QPatternist

{

    class DynamicContext;

    /**

     * @short Responsible for loading and declaring available external variables.

     *

     * An external variable in XQuery is a global variable that has been declared to receive

     * its value from the XQuery implementation, as opposed to an initializing expression. Here

     * is an example of a query with an external variable declaration, followed by a ordinary

     * global variable:

     *

     * <tt> declare variable $theName external;

     * declare variable $theName := "the value";

     * "And here's the query body(a string literal)"</tt>

     *

     * An external variable declaration can also specify a sequence type:

     *

     * <tt>declare variable $theName as xs:integer external;</tt>

     *

     * This class allows the user to supply the values to external variables. When

     * an external variable declaration occur in the query,

     * announceExternalVariable() is called.

     *

     * @ingroup Patternist_xdm

     * @author Frans Englich <frans.englich@nokia.com>

     */

    class Q_AUTOTEST_EXPORT ExternalVariableLoader : public QSharedData

    {

    public:

        typedef QExplicitlySharedDataPointer<ExternalVariableLoader> Ptr;

        inline ExternalVariableLoader() {}

        virtual ~ExternalVariableLoader();

        /**

         * Called when Patternist encounters an external variable in the query. It is guaranteed

         * to be called once for each external variable appearing in a query module.

         *

         * @param name the name of the variable. Quaranteed to never be @c null.

         * @param declaredType the type that the user declared the variable to be of. Whether

         * this type matches the actual value of the variable or not is irrelevant. Patternist

         * will do the necessary error handling based on the sequence type that is returned from

         * this function. If the user didn't declare a type, the type is <tt>item()*</tt>(zero or

         * more items). Quaranteed to never be @c null.

         * @returns the sequence type of the value this ExternalVariableLoader actually supplies. However,

         * if the ExternalVariableLoader knows it cannot supply a variable by this name, @c null should be

         * returned.

         */

        virtual SequenceType::Ptr announceExternalVariable(const QXmlName name,

                                                           const SequenceType::Ptr &declaredType);

        /**

         * This function is called at runtime when the external variable by name @p name needs

         * to be evaluated. It is not defined how many times this function will be called. It

         * depends on aspects such as how the query was optimized.

         *

         * @param name the name of the variable. Quaranteed to never be @c null.

         * @param context the DynamicContext.

         * @returns the value of the variable. Remember that this value must match the

         * sequence type returned from announceExternalVariable() for the same name.

         */

        virtual Item::Iterator::Ptr evaluateSequence(const QXmlName name,

                                                     const QExplicitlySharedDataPointer<DynamicContext> &context);

        virtual Item evaluateSingleton(const QXmlName name,

                                            const QExplicitlySharedDataPointer<DynamicContext> &context);

        virtual bool evaluateEBV(const QXmlName name,

                                 const QExplicitlySharedDataPointer<DynamicContext> &context);

    };

}

QT_END_NAMESPACE

QT_END_HEADER

#endif