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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_NoneType_H
53 #define Patternist_NoneType_H
55 #include <private/qatomictype_p.h>
56 #include <private/qsequencetype_p.h>
66 * @short Represents the special <tt>none</tt> type.
68 * @ingroup Patternist_types
69 * @see <a href="http://www.w3.org/TR/xquery-semantics/#sec_content_models">XQuery 1.0 and
70 * XPath 2.0 Formal Semantics, 2.4.3 Content models</a>
71 * @see <a href="http://www.w3.org/TR/xquery-semantics/#sec_fnerror">XQuery 1.0 and XPath 2.0
72 * Formal Semantics, 7.2.9 The fn:error function</a>
73 * @author Frans Englich <frans.englich@nokia.com>
75 class NoneType : public ItemType,
79 typedef QExplicitlySharedDataPointer<NoneType> Ptr;
81 virtual bool itemMatches(const Item &item) const;
82 virtual bool xdtTypeMatches(const ItemType::Ptr &other) const;
85 * @returns always "none". That is, no namespace prefix
87 virtual QString displayName(const NamePool::Ptr &np) const;
90 * @note The semantical meaning of this type's item type can
91 * surely be discussed. The function is provided due to
92 * it being mandated by the SequenceType base class.
94 * @returns always 'this' since NoneType is also an ItemType
96 virtual ItemType::Ptr itemType() const;
99 * @note The semantical meaning of this type's cardinality
100 * can surely be discussed. The function is provided due to
101 * it being mandated by the SequenceType base class.
103 * @returns always Cardinality::zeroOrMore()
105 virtual Cardinality cardinality() const;
108 * @returns always @c false
110 virtual bool isAtomicType() const;
113 * This can be thought to be a weird function for this type(none). There
114 * is no atomized type for none, perhaps the best from a conceptual perspective
115 * would be to return @c null.
117 * This function returns BuiltinTypes::xsAnyAtomicType because
118 * the generic type checking code inserts an Atomizer in the AST
119 * when an error() function(or other node which has type none) is part of
120 * an operator expression(value/general comparison, arithmetics). The Atomizer
121 * returns the atomizedType() of its child, and by here returning xsAnyAtomicType,
122 * static operator lookup is postponed to runtime. Subsequently, expressions like error()
123 * works properly with other XPath expressions.
125 virtual ItemType::Ptr atomizedType() const;
128 * @returns always @c false
130 virtual bool isNodeType() const;
133 * @returns always item()
135 virtual ItemType::Ptr xdtSuperType() const;
138 * @returns always @p other. The none type can be thought as
139 * disappearing when attempting to find the union of it and
142 virtual const ItemType &operator|(const ItemType &other) const;
146 friend class CommonSequenceTypes;