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39
40//
41// W A R N I N G
42// -------------
43//
44// This file is not part of the Qt API. It exists purely as an
45// implementation detail. This header file may change from version to
46// version without notice, or even be removed.
47//
48// We mean it.
49
50#ifndef Patternist_UnaryExpression_H
51#define Patternist_UnaryExpression_H
52
53QT_BEGIN_NAMESPACE
54
55#include <private/qarithmeticexpression_p.h>
56
57namespace QPatternist
58{
59 /**
60 * @short Implements XPath 2.0 unary expression, <tt>(-|+)ValueExpr</tt>.
61 *
62 * UnaryExpression is implemented by rewriting the expression <tt>operator [expr]</tt>
63 * to the ArithmeticExpression <tt>0 operator [expr]</tt>. For example, the expression
64 * <tt>+3</tt> becomes <tt>0 + 3</tt>, and <tt>-nodetest</tt> becomes <tt>0 - nodetest</tt>.
65 *
66 * On top of that expression ArithmeticExpression does the usual type
67 * checking conversion. The only thing this class do, is to overide
68 * evaluateSingleton() and calls Numeric::toNegated(). The reason this
69 * UnaryExpression is needed at all and that <tt>0 - [expr]</tt> is
70 * insufficent is that <tt>0 - xs:double(0)</tt> needs to return -0,
71 * instead of 0. I know no other difference.
72 *
73 * In most cases the constant propagation optimization rewrites UnaryExpression into
74 * a value, an instance of a sub-class of the Numeric class, wrapped with
75 * Literal.
76 *
77 * Beyond the mathematical implication the unary expression have, it also
78 * have the significant effect that it may invoke type promotion or that an expression
79 * may contain a type error. For example, the expression "+'a string'" contains a type error, since
80 * no unary operator is defined for @c xs:string. This is the reason why the '+' unary
81 * operator isn't ignored.
82 *
83 * @see <a href="http://www.w3.org/TR/xpath20/#id-arithmetic">XML Path Language
84 * (XPath) 2.0, 3.4 Arithmetic Expressions</a>
85 * @see <a href="http://www.w3.org/TR/xpath-functions/#func-numeric-unary-plus">XQuery 1.0 and XPath
86 * 2.0 Functions and Operators, 6.2.7 op:numeric-unary-plus</a>
87 * @see <a href="http://www.w3.org/TR/xpath-functions/#func-numeric-unary-minus">XQuery 1.0 and XPath
88 * 2.0 Functions and Operators, 6.2.8 op:numeric-unary-minus</a>
89 * @author Frans Englich <frans.englich@nokia.com>
90 * @ingroup Patternist_expressions
91 */
92 class UnaryExpression : public ArithmeticExpression
93 {
94 public:
95 UnaryExpression(const AtomicMathematician::Operator op,
96 const Expression::Ptr &operand,
97 const StaticContext::Ptr &context);
98
99 virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const;
100
101 private:
102 Q_DISABLE_COPY(UnaryExpression)
103 };
104}
105
106QT_END_NAMESPACE
107
108#endif
109

source code of qtxmlpatterns/src/xmlpatterns/expr/qunaryexpression_p.h