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authorLars Knoll <lars.knoll@nokia.com>2009-03-23 09:18:55 (GMT)
committerSimon Hausmann <simon.hausmann@nokia.com>2009-03-23 09:18:55 (GMT)
commite5fcad302d86d316390c6b0f62759a067313e8a9 (patch)
treec2afbf6f1066b6ce261f14341cf6d310e5595bc1 /src/xmlpatterns/expr/qevaluationcache_p.h
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Long live Qt 4.5!
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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