text: /****************************************************************************
  **
  ** Copyright (C) 2016 The Qt Company Ltd.
  ** Contact: https://www.qt.io/licensing/
  **
  ** This file is part of the QtXmlPatterns module of the Qt Toolkit.
  **
  ** $QT_BEGIN_LICENSE:LGPL$
  ** Commercial License Usage
  ** Licensees holding valid commercial Qt licenses may use this file in
  ** accordance with the commercial license agreement provided with the
  ** Software or, alternatively, in accordance with the terms contained in
  ** a written agreement between you and The Qt Company. For licensing terms
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  ** information use the contact form at https://www.qt.io/contact-us.
  **
  ** GNU Lesser General Public License Usage
  ** Alternatively, this file may be used under the terms of the GNU Lesser
  ** General Public License version 3 as published by the Free Software
  ** Foundation and appearing in the file LICENSE.LGPL3 included in the
  ** packaging of this file. Please review the following information to
  ** ensure the GNU Lesser General Public License version 3 requirements
  ** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
  **
  ** GNU General Public License Usage
  ** Alternatively, this file may be used under the terms of the GNU
  ** General Public License version 2.0 or (at your option) the GNU General
  ** Public license version 3 or any later version approved by the KDE Free
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  ** information to ensure the GNU General Public License requirements will
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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_NoneType_H
  #define Patternist_NoneType_H
  
  #include <private/qatomictype_p.h>
  #include <private/qsequencetype_p.h>
  
  QT_BEGIN_NAMESPACE
  
  namespace QPatternist
  {
  
      /**
       * @short Represents the special <tt>none</tt> type.
       *
       * @ingroup Patternist_types
       * @see <a href="http://www.w3.org/TR/xquery-semantics/#sec_content_models">XQuery 1.0 and
       * XPath 2.0 Formal Semantics, 2.4.3 Content models</a>
       * @see <a href="http://www.w3.org/TR/xquery-semantics/#sec_fnerror">XQuery 1.0 and XPath 2.0
       * Formal Semantics, 7.2.9 The fn:error function</a>
       * @author Frans Englich <frans.englich@nokia.com>
       */
      class NoneType : public ItemType,
                       public SequenceType
      {
      public:
          typedef QExplicitlySharedDataPointer<NoneType> Ptr;
  
          bool itemMatches(const Item &item) const override;
          bool xdtTypeMatches(const ItemType::Ptr &other) const override;
  
          /**
           * @returns always "none". That is, no namespace prefix
           */
          QString displayName(const NamePool::Ptr &np) const override;
  
          /**
           * @note The semantical meaning of this type's item type can
           * surely be discussed. The function is provided due to
           * it being mandated by the SequenceType base class.
           *
           * @returns always 'this' since NoneType is also an ItemType
           */
          ItemType::Ptr itemType() const override;
  
          /**
           * @note The semantical meaning of this type's cardinality
           * can surely be discussed. The function is provided due to
           * it being mandated by the SequenceType base class.
           *
           * @returns always Cardinality::zeroOrMore()
           */
          Cardinality cardinality() const override;
  
          /**
           * @returns always @c false
           */
          bool isAtomicType() const override;
  
          /**
           * This can be thought to be a weird function for this type(none). There
           * is no atomized type for none, perhaps the best from a conceptual perspective
           * would be to return @c null.
           *
           * This function returns BuiltinTypes::xsAnyAtomicType because
           * the generic type checking code inserts an Atomizer in the AST
           * when an error() function(or other node which has type none) is part of
           * an operator expression(value/general comparison, arithmetics). The Atomizer
           * returns the atomizedType() of its child, and by here returning xsAnyAtomicType,
           * static operator lookup is postponed to runtime. Subsequently, expressions like error()
           * works properly with other XPath expressions.
           */
          ItemType::Ptr atomizedType() const override;
  
          /**
           * @returns always @c false
           */
          bool isNodeType() const override;
  
          /**
           * @returns always item()
           */
          ItemType::Ptr xdtSuperType() const override;
  
          /**
           * @returns always @p other. The none type can be thought as
           * disappearing when attempting to find the union of it and
           * another type.
           */
          const ItemType &operator|(const ItemType &other) const override;
  
      protected:
  
          friend class CommonSequenceTypes;
          NoneType();
      };
  }
  
  QT_END_NAMESPACE
  
  #endif
  