/******************************************************************************** Copyright (C) 1992-2006 Trolltech ASA. All rights reserved.**** This file is part of the QtCore module of the Qt Toolkit.**** This file may be used under the terms of the GNU General Public** License version 2.0 as published by the Free Software Foundation** and appearing in the file LICENSE.GPL included in the packaging of** this file.  Please review the following information to ensure GNU** General Public Licensing requirements will be met:** http://www.trolltech.com/products/qt/opensource.html**** If you are unsure which license is appropriate for your use, please** review the following information:** http://www.trolltech.com/products/qt/licensing.html or contact the** sales department at sales@trolltech.com.**** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.******************************************************************************/#include <qshareddata.h>/*! \class QSharedData    \brief The QSharedData class is a base class for shared data objects.    \reentrant    \ingroup misc    QSharedData is designed to be used together with    QSharedDataPointer to implement custom \l{implicitly shared}    classes. It provides thread-safe reference counting.    See the QSharedDataPointer documentation for details.*//*! \fn QSharedData::QSharedData()    Constructs a QSharedData object with a reference count of 0.*//*! \fn QSharedData::QSharedData(const QSharedData &other)    Constructs a QSharedData object with a reference count of 0. (\a    other is ignored.)*//*! \class QSharedDataPointer    \brief The QSharedDataPointer class provides a pointer to a shared data object.    \reentrant    \ingroup misc    \mainclass    QSharedDataPointer\<T\> makes it easier to write your own    implicitly shared classes. It handles reference counting behind    the scenes in a thread-safe manner, ensuring that classes that use    it can be \l{reentrant}.    Implicit sharing is used throughout Qt to combine the memory and    speed efficiency of pointers with the ease of use of value types.    See the \l{Shared Classes} page for more information.    Let's suppose that you want to make an \c Employee class    implicitly shared. The procedure is:    \list    \o Define the \c Employee class with a single data member variable of       type QSharedDataPointer<\c{EmployeeData}>.    \o Define an \c EmployeeData class that derives from \l QSharedData       and that contains all the variables that you would normally       put in \c Employee.    \endlist    To show how this works in practice, we will review the entire    source code for an implicitly shared \c Employee class. Here's the    header file that defines the \c Employee class:    \include snippets/sharedemployee/employee.h    All accesses to the data in the setter and getter functions are    made through the QSharedDataPointer object \c d. For non-const    functions, operator->() automatically calls detach(), ensuring    that modifications to one \c Employee object don't affect other    \c Employee objects.    The \c EmployeeData type is a simple class that inherits QSharedData    and that provides a default constructor, a copy constructor,    and a destructor. Normally, this is all you need in the "data"    class.    Here's the implementation of the \c EmployeeData members:    \quotefromfile snippets/sharedemployee/employee.cpp    \skipto ::EmployeeData()    \printuntil /^\}/    \printline ::EmployeeData(const    \printuntil /^\}/    \printline ::~EmployeeData    \printuntil /^\}/    Let's now see how to implement the \c Employee constructors:    \printline ::Employee()    \printuntil }    In the default constructor, we create an object of type    \c EmployeeData and assign it to the \c d pointer using operator=().    Behind the scenes, QSharedDataPointer automatically increments or    decrements the reference count of the shared data object pointed    to by \c d, and deletes shared objects when the reference count    reaches 0.    \printline ::Employee(int    \printuntil }    In the constructor that takes an ID and an employee's name, we    also create an object of type \c EmployeeData and assign it to the    \c d pointer.    \printline ::setName    \printuntil /^\}/    When we use the \c d pointer from a non-const function, detach()    is automatically called to ensure that we work on our own copy    of the data.    \printline ::name    \printuntil /^\}/    When we use the \c d pointer in a const function, detach() is \e not    called.    Notice that there is no need to implement a copy constructor or    assignment operator in the \c Employee class. This is because the    C++ compiler provides default implementations that simply perform    member-by-member copy. Here, the only member is \c d, and its    operator=() simply increments a reference count (which is precisely    what we want).    \sa QSharedData*//*! \fn T &QSharedDataPointer::operator*()    Provides access to the shared object's members.    This function does a detach().*//*! \fn const T &QSharedDataPointer::operator*() const    \overload    This function does not call detach().*//*! \fn T *QSharedDataPointer::operator->()    Provides access to the shared object's members.    This function does a detach().*//*! \fn const T *QSharedDataPointer::operator->() const    \overload    This function does not call detach().*//*! \fn QSharedDataPointer::operator T *()    Returns a pointer to the shared object.    This function does a detach().    \sa data(), constData()*//*! \fn QSharedDataPointer::operator const T *() const    Returns a pointer to the shared object.    This function does not call detach().*//*! \fn T * QSharedDataPointer::data()    Returns a pointer to the shared object.    This function does a detach().    \sa constData()*//*! \fn const T * QSharedDataPointer::data() const    \overload    This function does not call detach().*//*! \fn const T * QSharedDataPointer::constData() const    Returns a const pointer to the shared object.    This function does not call detach().    \sa data()*//*! \fn bool QSharedDataPointer::operator==(const QSharedDataPointer<T> &other) const    Returns a true if the pointer to the shared object in \a other is equal to    to the pointer to the shared data in this else returns false.    This function does not call detach().*//*! \fn bool QSharedDataPointer::operator!=(const QSharedDataPointer<T> &other) const    Returns a true if the pointer to the shared object in \a other is not equal to    to the pointer to the shared data in this else returns false.    This function does not call detach().*//*! \fn QSharedDataPointer::QSharedDataPointer()    Constructs a QSharedDataPointer initialized with a null pointer.*//*! \fn QSharedDataPointer::~QSharedDataPointer()    Destroys the QSharedDataPointer.    This function automatically decrements the reference count of the    shared object and deletes the object if the reference count    reaches 0.*//*! \fn QSharedDataPointer::QSharedDataPointer(T *sharedData)    Constructs a QSharedDataPointer that points to \a sharedData.    This function automatically increments \a{sharedData}'s reference    count.*//*! \fn QSharedDataPointer::QSharedDataPointer(const QSharedDataPointer<T> &other)    Constructs a copy of \a other.    This function automatically increments the reference count of the    shared data object pointed to by \a{other}.*//*! \fn QSharedDataPointer<T> &QSharedDataPointer::operator=(const QSharedDataPointer<T> &other)    Assigns \a other to this pointer.    This function automatically increments the reference count of the    shared data object pointed to by \a{other}, and decrements the    reference count of the object previously pointed to by this    QSharedDataPointer. If the reference count reaches 0, the shared    data object is deleted.*//*! \fn QSharedDataPointer &QSharedDataPointer::operator=(T *sharedData)    \overload    Sets this QSharedDataPointer to point to \a sharedData.    This function automatically increments \a{sharedData}'s reference    count, and decrements the reference count of the object    previously pointed to by this QSharedDataPointer. If the    reference count reaches 0, the shared data object is deleted.*//*! \fn bool QSharedDataPointer::operator!() const    Returns true if this pointer is null; otherwise returns false.*//*! \fn void QSharedDataPointer::detach()    If the shared data's reference count is greater than 1, creates a    deep copy of the shared data.    This function is automatically called by QSharedDataPointer when    necessary. You should never need to call it yourself.*/