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q3deepcopy.cpp

/****************************************************************************
**
** Copyright (C) 1992-2007 Trolltech ASA. All rights reserved.
**
** This file is part of the Qt3Support module of the Qt Toolkit.
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** 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
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****************************************************************************/

#include "q3deepcopy.h"

/*!
    \class Q3DeepCopy qdeepcopy.h
    \brief The Q3DeepCopy class is a template class which ensures that
    implicitly shared and explicitly shared classes reference unique
    data.

    \reentrant

    \compat

    Normally, shared copies reference the same data to optimize memory
    use and for maximum speed. In the example below, \c s1, \c s2, \c
    s3, \c s4 and \c s5 share data.

    \code
    // all 5 strings share the same data
    QString s1 = "abcd";
    QString s2 = s1;
    QString s3 = s2;
    QString s4 = s3;
    QString s5 = s2;
    \endcode

    Q3DeepCopy can be used several ways to ensure that an object
    references unique, unshared data. In the example below, \c s1, \c
    s2 and \c s5 share data, while neither \c s3 nor \c s4 share data.
    \code
    // s1, s2 and s5 share the same data, neither s3 nor s4 are shared
    QString s1 = "abcd";
    QString s2 = s1;
    Q3DeepCopy<QString> s3 = s2;  // s3 is a deep copy of s2
    QString s4 = s3;             // s4 is a deep copy of s3
    QString s5 = s2;
    \endcode

    In the example below, \c s1, \c s2 and \c s5 share data, and \c s3
    and \c s4 share data.
    \code
    // s1, s2 and s5 share the same data, s3 and s4 share the same data
    QString s1 = "abcd";
    QString s2 = s1;
    QString s3 = Q3DeepCopy<QString>( s2 );  // s3 is a deep copy of s2
    QString s4 = s3;                        // s4 is a shallow copy of s3
    QString s5 = s2;
    \endcode

    Q3DeepCopy can also provide safety in multithreaded applications
    that use shared classes. In the example below, the variable \c
    global_string is used safely since the data contained in \c
    global_string is always a deep copy. This ensures that all threads
    get a unique copy of the data, and that any assignments to \c
    global_string will result in a deep copy.

    \code
    Q3DeepCopy<QString> global_string;  // global string data
    QMutex global_mutex;               // mutex to protext global_string

    ...

    void setGlobalString( const QString &str )
    {
      global_mutex.lock();
      global_string = str;           // global_string is a deep copy of str
      global_mutex.unlock();
    }

    ...

    void MyThread::run()
    {
      global_mutex.lock();
      QString str = global_string;          // str is a deep copy of global_string
      global_mutex.unlock();

      // process the string data
      ...

      // update global_string
      setGlobalString( str );
    }
    \endcode

    \warning It is the application developer's responsibility to
    protect the object shared across multiple threads.

    The examples above use QString, which is an implicitly shared
    class. The behavior of Q3DeepCopy is the same when using explicitly
    shared classes like QByteArray.

    Currently, Q3DeepCopy works with the following classes:
    \list
    \i QMemArray (including subclasses like QByteArray and QCString)
    \i QMap
    \i QString
    \i QValueList (including subclasses like QStringList and QValueStack)
    \i QValueVector
    \endlist

    \sa \link threads.html Thread Support in Qt \endlink
*/

/*!
    \fn Q3DeepCopy::Q3DeepCopy()

    Constructs an empty instance of type \e T.
*/

/*!
    \fn Q3DeepCopy::Q3DeepCopy( const T &t )

    Constructs a deep copy of \a t.
*/

/*!
    \fn Q3DeepCopy<T>& Q3DeepCopy::operator=( const T &t )

    Assigns a deep copy of \a t.
*/

/*!
    \fn Q3DeepCopy::operator T ()

    Returns a deep copy of the encapsulated data.
*/


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