/usr/include/soprano/iterator.h is in libsoprano-dev 2.7.6+dfsg.1-2wheezy1.
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* This file is part of Soprano Project.
*
* Copyright (C) 2006 Daniele Galdi <daniele.galdi@gmail.com>
* Copyright (C) 2007 Sebastian Trueg <trueg@kde.org>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public License
* along with this library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301, USA.
*/
#ifndef SOPRANO_ITERATOR_H
#define SOPRANO_ITERATOR_H
#include <QtCore/QSharedDataPointer>
#include <QtCore/QList>
#include "iteratorbackend.h"
#include "error.h"
namespace Soprano {
/**
* \class Iterator iterator.h Soprano/Iterator
*
* \brief The basic %Soprano iterator class.
*
* Iterators in %Soprano are very easy to use through two methods
* next() and current(). Instead of the latter operator*() can also be used.
* Both can be called subsequetially to retrieve the current element
* until next() has been called again.
*
* \code
* Soprano::Iterator<X> it;
* while( it.next() ) {
* doSomething( *it );
* doSomethingElse( it.current() );
* }
* \endcode
*
* Many backends do lock the underlying Model during iteration. Thus,
* it is always a good idea to cache the results if they are to be used
* to modify the model to prevent a deadlock:
*
* \code
* Soprano::StatementIterator it = model->listStatements();
* QList<Statement> allStatements = it.allElements();
* Q_FOREACH( Soprano::Statement s, allStatements ) {
* modifyTheModel( model, s );
* }
* \endcode
*
* Iterators have to be closed.
* This can either be achieved by deleting the iterator, finishing it (next() does return \p false),
* or calling close(). Before that other operations on the Model may block.
*
* Iterators are not thread-safe. Two threads using the same iterator may result
* in undefined behaviour and even crashes. An iterator needs to be closed by the
* same thread that opened it (except if the iterator contains special code to handle such
* a situation.)
*
* \warning Be aware that iterators in Soprano are shared objects which means
* that copies of one iterator object work on the same data.
*
* \author Daniele Galdi <daniele.galdi@gmail.com><br>Sebastian Trueg <trueg@kde.org>
*/
template<typename T> class Iterator : public Error::ErrorCache
{
public:
/**
* Creates and empty, invalid iterator.
*/
Iterator();
/**
* Create a new Iterator instance that uses sti as backend.
* Iterator will take ownership of the backend.
*/
Iterator( IteratorBackend<T> *sti );
Iterator( const Iterator &sti );
virtual ~Iterator();
Iterator& operator=( const Iterator& );
/**
* Close the iterator and release any locks on the underlying Model.
*/
void close();
/**
* Advances to the next element in the iterator.
*\return true if another element can be read from the iterator,
* false if the end has been reached.
*/
bool next();
/**
* Get the element the iterator currently points to. Be aware that
* a valid current element is only available if next() returned \p true.
*
*\return the current element.
*/
T current() const;
/**
* Retrieve the current element in the iterator.
*
* This is equivalent to current().
*
* \return The element the iterator currently points to or
* an invalid one if next has never been called.
*/
T operator*() const;
/**
* \return \p true if the Iterator is valid, \p false otherwise. (An invalid iterator
* has no backend.)
*/
bool isValid() const;
/**
* Convenience method which extracts all elements (this does not include the
* elements that have already been read from the iterator) from the iterator
* and returns them in a list.
*
* Be aware that after calling this method the iterator will be invalid.
*
* \return A list of all elements that rest in the iterator.
*/
QList<T> allElements();
protected:
/**
* Set the backend to read the actual data from.
* A previous backend will be deleted if there are no other Iterator
* instances using it.
*/
void setBackend( IteratorBackend<T>* b );
IteratorBackend<T>* backend() const;
private:
class Private;
QSharedDataPointer<Private> d;
};
}
/** \cond iterator_implementation */
template<typename T> class Soprano::Iterator<T>::Private : public QSharedData
{
public:
Private()
: backend( 0 ) {
}
~Private() {
if( backend ) {
backend->close();
delete backend;
}
}
IteratorBackend<T>* backend;
};
template<typename T> Soprano::Iterator<T>::Iterator()
: Error::ErrorCache(),
d( new Private() )
{
}
template<typename T> Soprano::Iterator<T>::Iterator( IteratorBackend<T> *sti )
: Error::ErrorCache(),
d( new Private() )
{
d->backend = sti;
}
template<typename T> Soprano::Iterator<T>::Iterator( const Iterator<T> &other )
: Error::ErrorCache(),
d( other.d )
{
}
template<typename T> Soprano::Iterator<T>::~Iterator()
{
}
template<typename T> Soprano::Iterator<T>& Soprano::Iterator<T>::operator=( const Iterator<T>& other )
{
d = other.d;
return *this;
}
template<typename T> void Soprano::Iterator<T>::setBackend( IteratorBackend<T>* b )
{
if ( d->backend != b ) {
// now we want it to detach
d->backend = b;
}
}
template<typename T> Soprano::IteratorBackend<T>* Soprano::Iterator<T>::backend() const
{
return d->backend;
}
template<typename T> void Soprano::Iterator<T>::close()
{
// some evil hacking to avoid detachment of the shared data
if( isValid() ) {
const Private* cd = d.constData();
cd->backend->close();
setError( cd->backend->lastError() );
}
}
template<typename T> bool Soprano::Iterator<T>::next()
{
// some evil hacking to avoid detachment of the shared data
const Private* cd = d.constData();
if( isValid() ) {
bool hasNext = cd->backend->next();
setError( cd->backend->lastError() );
if( !hasNext ) {
cd->backend->close();
}
return hasNext;
}
else {
setError( QString::fromLatin1( "Invalid iterator." ) );
return false;
}
}
template<typename T> T Soprano::Iterator<T>::current() const
{
if( isValid() ){
T c = d->backend->current();
setError( d->backend->lastError() );
return c;
}
else {
setError( QString::fromLatin1( "Invalid iterator." ) );
return T();
}
}
template<typename T> T Soprano::Iterator<T>::operator*() const
{
return current();
}
template<typename T> bool Soprano::Iterator<T>::isValid() const
{
return d->backend != 0;
}
template<typename T> QList<T> Soprano::Iterator<T>::allElements()
{
QList<T> sl;
if( isValid() ) {
while ( next() ) {
sl.append( current() );
}
close();
}
return sl;
}
/** \endcond */
#endif
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