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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_UnaryExpression_H
#define Patternist_UnaryExpression_H
QT_BEGIN_HEADER
QT_BEGIN_NAMESPACE
#include "qarithmeticexpression_p.h"
namespace QPatternist
{
/**
* @short Implements XPath 2.0 unary expression, <tt>(-|+)ValueExpr</tt>.
*
* UnaryExpression is implemented by rewriting the expression <tt>operator [expr]</tt>
* to the ArithmeticExpression <tt>0 operator [expr]</tt>. For example, the expression
* <tt>+3</tt> becomes <tt>0 + 3</tt>, and <tt>-nodetest</tt> becomes <tt>0 - nodetest</tt>.
*
* On top of that expression ArithmeticExpression does the usual type
* checking conversion. The only thing this class do, is to overide
* evaluateSingleton() and calls Numeric::toNegated(). The reason this
* UnaryExpression is needed at all and that <tt>0 - [expr]</tt> is
* insufficent is that <tt>0 - xs:double(0)</tt> needs to return -0,
* instead of 0. I know no other difference.
*
* In most cases the constant propagation optimization rewrites UnaryExpression into
* a value, an instance of a sub-class of the Numeric class, wrapped with
* Literal.
*
* Beyond the mathematical implication the unary expression have, it also
* have the significant effect that it may invoke type promotion or that an expression
* may contain a type error. For example, the expression "+'a string'" contains a type error, since
* no unary operator is defined for @c xs:string. This is the reason why the '+' unary
* operator isn't ignored.
*
* @see <a href="http://www.w3.org/TR/xpath20/#id-arithmetic">XML Path Language
* (XPath) 2.0, 3.4 Arithmetic Expressions</a>
* @see <a href="http://www.w3.org/TR/xpath-functions/#func-numeric-unary-plus">XQuery 1.0 and XPath
* 2.0 Functions and Operators, 6.2.7 op:numeric-unary-plus</a>
* @see <a href="http://www.w3.org/TR/xpath-functions/#func-numeric-unary-minus">XQuery 1.0 and XPath
* 2.0 Functions and Operators, 6.2.8 op:numeric-unary-minus</a>
* @author Frans Englich <fenglich@trolltech.com>
* @ingroup Patternist_expressions
*/
class UnaryExpression : public ArithmeticExpression
{
public:
UnaryExpression(const AtomicMathematician::Operator op,
const Expression::Ptr &operand,
const StaticContext::Ptr &context);
virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const;
private:
Q_DISABLE_COPY(UnaryExpression)
};
}
QT_END_NAMESPACE
QT_END_HEADER
#endif
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