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46 // This file is not part of the Qt API. It exists purely as an
47 // implementation detail. This header file may change from version to
48 // version without notice, or even be removed.
52 #ifndef Patternist_UnaryExpression_H
53 #define Patternist_UnaryExpression_H
59 #include <private/qarithmeticexpression_p.h>
64 * @short Implements XPath 2.0 unary expression, <tt>(-|+)ValueExpr</tt>.
66 * UnaryExpression is implemented by rewriting the expression <tt>operator [expr]</tt>
67 * to the ArithmeticExpression <tt>0 operator [expr]</tt>. For example, the expression
68 * <tt>+3</tt> becomes <tt>0 + 3</tt>, and <tt>-nodetest</tt> becomes <tt>0 - nodetest</tt>.
70 * On top of that expression ArithmeticExpression does the usual type
71 * checking conversion. The only thing this class do, is to overide
72 * evaluateSingleton() and calls Numeric::toNegated(). The reason this
73 * UnaryExpression is needed at all and that <tt>0 - [expr]</tt> is
74 * insufficent is that <tt>0 - xs:double(0)</tt> needs to return -0,
75 * instead of 0. I know no other difference.
77 * In most cases the constant propagation optimization rewrites UnaryExpression into
78 * a value, an instance of a sub-class of the Numeric class, wrapped with
81 * Beyond the mathematical implication the unary expression have, it also
82 * have the significant effect that it may invoke type promotion or that an expression
83 * may contain a type error. For example, the expression "+'a string'" contains a type error, since
84 * no unary operator is defined for @c xs:string. This is the reason why the '+' unary
85 * operator isn't ignored.
87 * @see <a href="http://www.w3.org/TR/xpath20/#id-arithmetic">XML Path Language
88 * (XPath) 2.0, 3.4 Arithmetic Expressions</a>
89 * @see <a href="http://www.w3.org/TR/xpath-functions/#func-numeric-unary-plus">XQuery 1.0 and XPath
90 * 2.0 Functions and Operators, 6.2.7 op:numeric-unary-plus</a>
91 * @see <a href="http://www.w3.org/TR/xpath-functions/#func-numeric-unary-minus">XQuery 1.0 and XPath
92 * 2.0 Functions and Operators, 6.2.8 op:numeric-unary-minus</a>
93 * @author Frans Englich <frans.englich@nokia.com>
94 * @ingroup Patternist_expressions
96 class UnaryExpression : public ArithmeticExpression
99 UnaryExpression(const AtomicMathematician::Operator op,
100 const Expression::Ptr &operand,
101 const StaticContext::Ptr &context);
103 virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const;
106 Q_DISABLE_COPY(UnaryExpression)