DlHandle.h

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//# DlHandle.h: smart pointer for display library.
//# Copyright (C) 2010
//# Associated Universities, Inc. Washington DC, USA.
//#
//# 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; if not, write to the Free Software Foundation,
//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
//#
//# Correspondence concerning AIPS++ should be addressed as follows:
//#        Internet email: aips2-request@nrao.edu.
//#        Postal address: AIPS++ Project Office
//#                        National Radio Astronomy Observatory
//#                        520 Edgemont Road
//#                        Charlottesville, VA 22903-2475 USA
//#
//# $Id$

#ifndef DLHANDLE_H_
#define DLHANDLE_H_
#include <cstddef>

namespace casa { //# NAMESPACE CASA - BEGIN

        class DlTarget;

        class DlHandleBase {

        protected:
                DlHandleBase( ) { }
                DlHandleBase( const DlHandleBase & ) { }
                virtual void target_gone( ) const = 0;
                virtual bool null( ) const = 0;

                void throw_exception( const char * ) const;

                virtual ~DlHandleBase( ) { }
        private:
                friend class DlTarget;

                // Prevent heap allocation
                void * operator new   (size_t);
                void * operator new[] (size_t);
        };


        template <class T> class DlHandle : public DlHandleBase {
        public:
                DlHandle( ) : target_(0) { }
                DlHandle( T *tgt ) : target_(tgt) {
                        if ( target_ ) target_->reg(this);
                }
                DlHandle( const DlHandle<T> &other ) : DlHandleBase(other), target_(other.target_) {
                        if ( target_ ) target_->reg(this);
                }
                T *operator->( ) {
                        if ( ! target_ ) throw_exception( "null pointer in DlHandle" );
                        return target_;
                }
                const T *operator->( ) const {
                        if ( ! target_ ) throw_exception( "null pointer in DlHandle" );
                        return target_;
                }
                operator T*( ) {
                        if ( ! target_ ) throw_exception( "null pointer in DlHandle" );
                        return target_;
                }
                T &operator*( ) {
                        if ( ! target_ ) throw_exception( "null pointer in DlHandle" );
                        return *target_;
                }
                operator const T*( ) const {
                        if ( ! target_ ) throw_exception( "null pointer in DlHandle" );
                        return target_;
                }
                const T &operator*( ) const {
                        if ( ! target_ ) throw_exception( "null pointer in DlHandle" );
                        return *target_;
                }
                DlHandle<T> &operator=( const DlHandle<T> &other ) {
                        if ( target_ ) target_->unreg(this);
                        target_ = other.target_;
                        if ( target_ ) target_->reg(this);
                        return *this;
                }
                T *operator=( T *tgt ) {
                        if ( target_ ) target_->unreg(this);
                        target_ = tgt;
                        if ( target_ ) target_->reg(this);
                        return target_;
                }

                ~DlHandle( ) {
                        if ( target_ ) target_->unreg(this);
                }

                bool null( ) const {
                        return target_ == 0;
                }
                const T *ptr( ) const {
                        return target_;
                }

        protected:
                void target_gone( ) const {
                        ((DlHandle<T>*)this)->target_ = 0;
                }
                T *target_;
        };
}
#endif