116 lines
2.7 KiB
C++
116 lines
2.7 KiB
C++
/*
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----
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This file is part of SECONDO.
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Copyright (C) 2004, University in Hagen, Department of Computer Science,
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Database Systems for New Applications.
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SECONDO is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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SECONDO is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with SECONDO; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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----
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//characters [1] verbatim: [\verb|] [|]
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January 2008, V. Ferderer
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February 2008, M. Spiekermann. Minor modifications and documentation.
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1 Class StreamIterator
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The template class below can be used to iterate over input streams. It can be
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typically used in operator implementations which operate on streams. It
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encapsulates calls to the query processor. Since this is done very often in
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many operator implementations it is a helpful tool for code reduction.
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*/
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#ifndef SECONDO_STREAM_ITERATOR_H
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#define SECONDO_STREAM_ITERATOR_H
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#include "QueryProcessor.h"
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template< typename T >
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struct StreamIterator
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{
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/*
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2 Constructors
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The empty Constructor does nothing while the other ones request for the first
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element of a stream.
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*/
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StreamIterator() : valid_(false), element_(0), handle_(0)
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{}
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StreamIterator( void* arg ) : valid_(false), element_(0), handle_(arg)
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{
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request();
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}
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StreamIterator( Word& arg ) : valid_(false), element_(0), handle_(arg.addr)
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{
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request();
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}
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void init( Word& arg ) { handle_ = arg.addr; }
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bool valid() const { return valid_; }
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/*
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3 Overloaded Operators
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The current value of an iterator "it"[1] can be referenced by the prefix star
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operator and the next value can be requested by the postfix-"++" operation,
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e.g. "it++"; example code for a stream iteration:
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----
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StreamIterator<Tuple>( arg[0] );
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while( it.valid() ) {
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cout << *it << endl;
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it++;
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}
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----
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*/
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T* operator*() const
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{
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return element_;
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}
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StreamIterator& operator++()
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{
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request();
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return *this;
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}
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private:
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void request()
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{
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if ( handle_ )
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{
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element_ = static_cast< T* >( qp->Request( handle_ ).addr );
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valid_ = qp->Received( handle_ );
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}
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}
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bool valid_;
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T* element_;
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void* handle_;
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};
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#endif // SECONDO_STREAM_ITERATOR_H
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