mirror of
https://github.com/tomahawk-player/tomahawk.git
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153 lines
3.7 KiB
C++
153 lines
3.7 KiB
C++
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/****************************************************************************
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** Copyright (c) 2006 - 2011, the LibQxt project.
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** See the Qxt AUTHORS file for a list of authors and copyright holders.
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** All rights reserved.
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**
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** Redistribution and use in source and binary forms, with or without
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** modification, are permitted provided that the following conditions are met:
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** * Redistributions of source code must retain the above copyright
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** notice, this list of conditions and the following disclaimer.
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** * Redistributions in binary form must reproduce the above copyright
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** notice, this list of conditions and the following disclaimer in the
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** documentation and/or other materials provided with the distribution.
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** * Neither the name of the LibQxt project nor the
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** names of its contributors may be used to endorse or promote products
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** derived from this software without specific prior written permission.
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**
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** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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** ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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** WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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** DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
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** DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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** (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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** ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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** SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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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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\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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