mirror of
https://github.com/tomahawk-player/tomahawk.git
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147 lines
3.1 KiB
C++
147 lines
3.1 KiB
C++
/****************************************************************************
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**
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** Copyright (C) Qxt Foundation. Some rights reserved.
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**
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** This file is part of the QxtCore module of the Qxt library.
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**
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** This library is free software; you can redistribute it and/or modify it
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** under the terms of the Common Public License, version 1.0, as published
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** by IBM, and/or under the terms of the GNU Lesser General Public License,
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** version 2.1, as published by the Free Software Foundation.
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**
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** This file is provided "AS IS", without WARRANTIES OR CONDITIONS OF ANY
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** KIND, EITHER EXPRESS OR IMPLIED INCLUDING, WITHOUT LIMITATION, ANY
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** WARRANTIES OR CONDITIONS OF TITLE, NON-INFRINGEMENT, MERCHANTABILITY OR
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** FITNESS FOR A PARTICULAR PURPOSE.
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**
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** You should have received a copy of the CPL and the LGPL along with this
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** file. See the LICENSE file and the cpl1.0.txt/lgpl-2.1.txt files
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** included with the source distribution for more information.
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** If you did not receive a copy of the licenses, contact the Qxt Foundation.
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**
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** <http://libqxt.org> <foundation@libqxt.org>
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**
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****************************************************************************/
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/*!
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\class QxtNullable QxtNullable
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\inmodule QxtCore
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\brief distinct null value compatible with any data type.
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in general it's a templated abstraction to allow any data type to be
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expressed with a null value distinct from any real value. An example
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of such a use is for optional arguments.
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\n
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prepare a function for argument skipping:
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\code
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void somefunction( qxtNull(int,a) , qxtNull(int,b) )
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{
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if (!a.isNull())
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{
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int i = a.value();
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//do something with i
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}
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if (!b.isNull())
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{
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int x = b.value();
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//do something with x
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}
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}
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\endcode
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usage:
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\code
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somefunction(SKIP,1,2);
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somefunction(3,4);
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somefunction(3,SKIP,6);
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somefunction(1);
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\endcode
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*/
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#ifndef QXTNULLABLE_H
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#define QXTNULLABLE_H
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#include <qxtglobal.h>
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/*! \relates QxtNullable
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* defines a skipable argument with type \a t and variable name \a n
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*/
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#define qxtNull(t,n) QxtNullable<t> n = QxtNullable<t>()
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#include <qxtnull.h>
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template<typename T>
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class /*QXT_CORE_EXPORT*/ QxtNullable
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{
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public:
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QxtNullable(QxtNull);
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QxtNullable(const T& p);
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QxtNullable();
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///determinates if the Value is set to something meaningfull
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bool isNull() const;
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///delete Value
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void nullify();
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T& value() const;
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operator T() const;
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void operator=(const T& p);
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private:
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T* val;
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};
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template<typename T>
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QxtNullable<T>::QxtNullable(QxtNull)
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{
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val = 0;
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}
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template<typename T>
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QxtNullable<T>::QxtNullable(const T& p)
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{
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val = const_cast<T*>(&p);
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}
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template<typename T>
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QxtNullable<T>::QxtNullable()
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{
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val = 0;
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}
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template<typename T>
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QxtNullable<T>::operator T() const
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{
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return *val;
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}
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template<typename T>
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T& QxtNullable<T>::value() const
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{
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return *val;
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}
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template<typename T>
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bool QxtNullable<T>::isNull() const
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{
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return (val == 0);
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}
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template<typename T>
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void QxtNullable<T>::nullify()
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{
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val = 0;
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}
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template<typename T>
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void QxtNullable<T>::operator=(const T & p)
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{
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val = const_cast<T*>(&p);
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}
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#endif
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