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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_CastAs_H
51 #define Patternist_CastAs_H
52 
53 #include <private/qsinglecontainer_p.h>
54 #include <private/qcastingplatform_p.h>
55 
56 QT_BEGIN_NAMESPACE
57 
58 namespace QPatternist
59 {
60     /**
61      * @short Implements XPath 2.0's <tt>cast as</tt> expression.
62      *
63      * Implements the casting expression, such as <tt>'3' cast as xs:integer</tt>. This class also
64      * implements constructor functions, which are created in the ConstructorFunctionsFactory.
65      *
66      * CastAs uses CastingPlatform for carrying out the actual casting.
67      *
68      * @see <a href="http://www.w3.org/TR/xpath-functions/#casting">XQuery 1.0
69      * and XPath 2.0 Functions and Operators, 7 Casting</a>
70      * @see <a href="http://www.w3.org/TR/xpath20/#id-cast">XML Path Language
71      * (XPath) 2.0, 3.10.2 Cast</a>
72      * @author Frans Englich <frans.englich@nokia.com>
73      * @ingroup Patternist_expressions
74      */
75     class CastAs : public SingleContainer,
76                    public CastingPlatform<CastAs, true /* issueError */>
77     {
78     public:
79 
80         /**
81          * @todo Wrong/old documentation
82          *
83          * Creates a cast expression for the type @p name via the schema type
84          * factory @p factory. This function is used by parser when creating
85          * 'cast to' expressions, and the ConstructorFunctionsFactory, when creating
86          * constructor functions.
87          *
88          * @param targetType the type which the CastAs should cast to
89          * @param source the operand to evaluate and then cast from
90          */
91         CastAs(const Expression::Ptr &source,
92                const SequenceType::Ptr &targetType);
93 
94         virtual Item evaluateSingleton(const DynamicContext::Ptr &) const;
95 
96         virtual SequenceType::List expectedOperandTypes() const;
97 
98         /**
99          * @returns a SequenceType where the ItemType is this CastAs's
100          * target type, as per targetType(), and the Cardinality is inferred from the
101          * source operand to reflect whether this CastAs always will evaluate to
102          * exactly-one or zero-or-one values.
103          */
104         virtual SequenceType::Ptr staticType() const;
105 
106         /**
107          * Overridden in order to check that casting to an abstract type
108          * is not attempted.
109          */
110         virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context,
111                                           const SequenceType::Ptr &reqType);
112 
113         /**
114          * If the target type is the same as the source type, it is rewritten
115          * to the operand.
116          */
117         virtual Expression::Ptr compress(const StaticContext::Ptr &context);
118         virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const;
119 
targetType()120         inline ItemType::Ptr targetType() const
121         {
122             return m_targetType->itemType();
123         }
124 
targetSequenceType()125         inline SequenceType::Ptr targetSequenceType() const
126         {
127             return m_targetType;
128         }
129 
130     private:
131         /**
132          * Performs casting to @c xs:QName. This case is special, and is always done at compile time.
133          */
134         Expression::Ptr castToQName(const StaticContext::Ptr &context) const;
135 
136         const SequenceType::Ptr m_targetType;
137     };
138 }
139 
140 QT_END_NAMESPACE
141 
142 #endif
143