source: trunk/src/xmlpatterns/expr/qunaryexpression_p.h@ 317

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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_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 <[email protected]>
     * @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