AttValPoi.h

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//# AttValPoi.h: templated class for aliased AttributeValues
//# Copyright (C) 1996,1997,1999,2000,2001
//# 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 TRIALDISPLAY_ATTVALPOI_H
#define TRIALDISPLAY_ATTVALPOI_H

#include <casa/aips.h>
#include <display/Display/AttValBase.h>
#include <display/Display/AttVal.h>
#include <casa/Utilities/DataType.h>

namespace casa { //# NAMESPACE CASA - BEGIN

// <summary> 
// Templated class for storing a pointer to the value of an Attribute.
// </summary>

// <use visibility=local>
 
// <reviewed reviewer="" date="yyyy/mm/dd" tests="tAttribute" demos="">
// </reviewed>
 
// <prerequisite>
// <li> <linkto class="AttributeValue">AttributeValue</linkto>
// </prerequisite>

// <etymology> 
// "AttributeValuePoi" is a contraction of "Attribute Value" and
// "Pointer", and stores a pointer to the value of an Attribute.
// </etymology>

// <synopsis> 
// An AttributeValuePoi differs from a <linkto class="AttributeValue">
// AttributeValue</linkto> in that instead of using its own variable
// to store the actual value like AttributeValue does, it stores a
// pointer to the variable used in the constructor.  This means that
// the AttributeValuePoi is just an alias to this variable, and then
// the user can modify the value of an AttributeValuePoi without using
// its interface.  Alternatively, and perhaps more importantly, the
// Attribute interface can be used to modify members of a class.
// </synopsis>

// <example>
// A simple example will help illustrate the utility of the AttributeValuePoi
// class:
//
// <srcBlock>
// Int varInt = 1;
// AttributeValuePoi<Int> intAtt(&varInt, False);
// 
// Vector<Int> bla = intAtt.getValue();
// // bla(0) is 1;
//
// // This wil change also the AttributeValue:
// varInt = 2;
// bla = intAtt.getValue();
// // bla(0) is now 2
// 
// intAtt.setValue(5);
// // now also varInt == 5
//
// </srcBlock>
// </example>

// <motivation> 
// The motivation for this class is to be able to provide an Attribute
// interface for modifying private members of some classes.  For
// example, this interface is used to control the linear coordinate
// system of the <linkto class="WorldCanvas">WorldCanvas</linkto>.
// </motivation>

// <todo asof="2000/01/17">
// Nothing known.
// </todo>

template <class T> class AttributeValuePoi : public AttributeValue<T> {

 public:

  // Constructor for a pointer to a scalar.
  AttributeValuePoi(T* value, const Bool strict);

  // Constructor for a pointer to a <src>Vector</src>.
  AttributeValuePoi(Vector<T> *value, const Bool strict);
  
  // Copy constructor.
  AttributeValuePoi(const AttributeValuePoi<T> &other);

  // Destructor.
  virtual ~AttributeValuePoi();

  // Assignment operator.
  const AttributeValuePoi<T>& operator=(const AttributeValuePoi<T> &other);

  // Return a new copy of the AttributeValuePoi (virtual constructor).
  virtual AttributeValueBase *clone() const;

  // Add <src>other</src> to <src>*this</src>.  Needs to over-ride
  // base class definition because the pointers need to be 
  // dereferenced prior to addition.
  virtual void operator+=(const AttributeValueBase& other);

  // Change the value of the AttributeValue.
  // <group>
  virtual void setValue(const T &value);
  virtual void setValue(const Vector<T> &value);
  // </group>

  // Get the DataType of aliased variable.
  virtual DataType getPointerType() const;

  // Return class name
  virtual String className() const {return String("AttributeValuePoi");};


 private:

  // Update the variable that is aliased to the AttributeValuePoi.
  void updatePointerValue() const;
  
  // Pointer to the aliased variable. Only one is ever active depending
  // upon how the object was constructed.  The memory allocated to these pointers
  // does not belong to this object.  
  // <group>
  Vector<T>* itsVectorPointerPtr;
  T* itsScalarPointerPtr;
  // </group>
  
  // The pointer DataType 
  DataType itsPointerType;

  // Cast from base class
  const AttributeValuePoi<T>& myCast (const AttributeValueBase& other) const;

  // Default constructor
  AttributeValuePoi();

  //# Make parent members known.
public:
  using AttributeValue<T>::getType;
  using AttributeValue<T>::getValue;
};


} //# NAMESPACE CASA - END
#ifndef AIPS_NO_TEMPLATE_SRC
#include <display/Display/AttValPoi.tcc>
#endif //# AIPS_NO_TEMPLATE_SRC

#endif