text: /****************************************************************************
  **
  ** Copyright (C) 2016 The Qt Company Ltd.
  ** Contact: https://www.qt.io/licensing/
  **
  ** This file is part of the documentation of the Qt Toolkit.
  **
  ** $QT_BEGIN_LICENSE:BSD$
  ** 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
  ** and conditions see https://www.qt.io/terms-conditions. For further
  ** information use the contact form at https://www.qt.io/contact-us.
  **
  ** BSD License Usage
  ** Alternatively, you may use this file under the terms of the BSD license
  ** as follows:
  **
  ** "Redistribution and use in source and binary forms, with or without
  ** modification, are permitted provided that the following conditions are
  ** met:
  **   * Redistributions of source code must retain the above copyright
  **     notice, this list of conditions and the following disclaimer.
  **   * Redistributions in binary form must reproduce the above copyright
  **     notice, this list of conditions and the following disclaimer in
  **     the documentation and/or other materials provided with the
  **     distribution.
  **   * Neither the name of The Qt Company Ltd nor the names of its
  **     contributors may be used to endorse or promote products derived
  **     from this software without specific prior written permission.
  **
  **
  ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
  **
  ** $QT_END_LICENSE$
  **
  ****************************************************************************/
  
  //! [0]
  struct MyStruct
  {
      int i;
      ...
  };
  
  Q_DECLARE_METATYPE(MyStruct)
  //! [0]
  
  
  //! [1]
  namespace MyNamespace
  {
      ...
  }
  
  Q_DECLARE_METATYPE(MyNamespace::MyStruct)
  //! [1]
  
  
  //! [2]
  MyStruct s;
  QVariant var;
  var.setValue(s); // copy s into the variant
  
  ...
  
  // retrieve the value
  MyStruct s2 = var.value<MyStruct>();
  //! [2]
  
  
  //! [3]
  int id = QMetaType::type("MyClass");
  if (id != QMetaType::UnknownType) {
      void *myClassPtr = QMetaType::create(id);
      ...
      QMetaType::destroy(id, myClassPtr);
      myClassPtr = 0;
  }
  //! [3]
  
  
  //! [4]
  qRegisterMetaType<MyClass>("MyClass");
  //! [4]
  
  
  //! [5]
  qRegisterMetaTypeStreamOperators<MyClass>("MyClass");
  //! [5]
  
  
  //! [6]
  QDataStream &operator<<(QDataStream &out, const MyClass &myObj);
  QDataStream &operator>>(QDataStream &in, MyClass &myObj);
  //! [6]
  
  
  //! [7]
  int id = qRegisterMetaType<MyStruct>();
  //! [7]
  
  
  //! [8]
  int id = qMetaTypeId<QString>();    // id is now QMetaType::QString
  id = qMetaTypeId<MyStruct>();       // compile error if MyStruct not declared
  //! [8]
  
  //! [9]
  typedef QString CustomString;
  qRegisterMetaType<CustomString>("CustomString");
  //! [9]
  
  //! [10]
  
  #include <deque>
  
  Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE(std::deque)
  
  void someFunc()
  {
      std::deque<QFile*> container;
      QVariant var = QVariant::fromValue(container);
      // ...
  }
  
  //! [10]
  
  //! [11]
  
  #include <unordered_list>
  
  Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE(std::unordered_map)
  
  void someFunc()
  {
      std::unordered_map<int, bool> container;
      QVariant var = QVariant::fromValue(container);
      // ...
  }
  
  //! [11]
  
  //! [12]
  QPointer<QFile> fp(new QFile);
  QVariant var = QVariant::fromValue(fp);
  // ...
  if (var.canConvert<QObject*>()) {
      QObject *sp = var.value<QObject*>();
      qDebug() << sp->metaObject()->className(); // Prints 'QFile'.
  }
  //! [12]
  
  //! [13]
  
  #include <memory>
  
  Q_DECLARE_SMART_POINTER_METATYPE(std::shared_ptr)
  
  void someFunc()
  {
      auto smart_ptr = std::make_shared<QFile>();
      QVariant var = QVariant::fromValue(smart_ptr);
      // ...
      if (var.canConvert<QObject*>()) {
          QObject *sp = var.value<QObject*>();
          qDebug() << sp->metaObject()->className(); // Prints 'QFile'.
      }
  }
  
  //! [13]
  