RecordField.h

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// # RecordField.h: Access to an individual field in a record
// # Copyright (C) 1995,1996,1997
// # 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: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef CASA_RECORDFIELD_H
#define CASA_RECORDFIELD_H
 
// # Includes
#include <casacore/casa/aips.h>
#include <casacore/casa/Containers/Record.h>
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// # Forward Declarations
class TableRecord;
class Table;
 
// <summary>
// Access to an individual field in a record.
// </summary>
 
// <use visibility=export>
// <reviewed reviewer="Mark Wieringa" date="1996/04/15" tests="tRecord">
// </reviewed>
 
// <prerequisite>
//   <li> <linkto class="RecordInterface">RecordInterface</linkto>.
// </prerequisite>
 
// <etymology>
// RecordFieldPtr indicates that an object of this type is
// pointing to a field in a record.
// </etymology>
 
// <synopsis>
// RecordFieldPtr allows access to the fields in a record object.
// A record object is an object of a class derived from
// <linkto class=RecordInterface>RecordInterface</linkto>.
// <src>RecordFieldPtr<T></src> objects can only be instantiated for types `T'
// which are valid fields of a record object (e.g. Int, float, String,
// Record, TableRecord). It can, however, NOT be instantiated for
// a Table field, because Table fields are accessed indirectly via a
// TableKeyword object. Table fields have to be accessed directly
// through the <linkto class=TableRecord>TableRecord</linkto> interface.
// <p>
// Internally, a RecordFieldPtr stores a Record pointer and
// field number. Therefore, if the order of fields in a Record is modified,
// or if the Record is restructured, a RecordFieldPtr is invalidated and should
// no longer be used.
// <p>
// The RecordFieldPtr is pointer-like in the sense that it points to an
// object that is physically inside of another object (the enclosing
// record object).
// Access to the value is obtained via the dereference operator
// (<src>operator*()</src>) to emphasize the pointer like nature of these
// classes.
// <br>
// An alternative way to get access to the values is using the
// functions define and get. Note that in
// <srcblock>
//    RecordFieldPtr<Array<Int> > field (record, fieldNumber);
//    Array<Int> value;
//    *field = value;
//    field.define (value);
// </srcblock>
// the assignment (in line 3) and define (in line 4) are not equivalent.
// The assignment uses the normal Array assignment, thus it takes the
// Array conformance rules into account (an assign is only possible when
// the new array value conforms the current array value or when the current
// array value is empty).
// On the other hand, define does not take the current array value into
// account. Thus an array value can always be redefined.
// <br>
// However, note that if the field is defined with a non-fixed shape in
// the record description, a value must always conform that shape (in
// case of assignment as well as in case of define).
// </synopsis>
 
// <example>
// See the example in the <linkto class="Record">Record</linkto> class.
// </example>
 
// <motivation>
// RecordFieldPtr provides a fast way to access the data in a record.
// </motivation>
 
template <class T>
class RecordFieldPtr {
 public:
  // This object does not point to any field, i.e.
  // <src>this->isAttached() == False;</src>
  RecordFieldPtr();
 
  // Attach this field pointer to the given field. If it does not exist
  // an exception is thrown.
  // <group>
  RecordFieldPtr(RecordInterface& record, Int whichField);
  RecordFieldPtr(RecordInterface& record, const RecordFieldId&);
  // </group>
 
  // Change our pointer to the supplied field. If it doesn't exist an
  // exception is thrown.
  // <group>
  void attachToRecord(RecordInterface& record, Int whichField);
  void attachToRecord(RecordInterface& record, const RecordFieldId&);
  // </group>
 
  // Point to no field in any Record.
  void detach();
 
  // Provide access to the field's value.
  // <note>
  // To be sure a const function is called, it is best to use get().
  // For a non-const object, a non-const function is called, even if
  // used as an rvalue.
  // </note>
  // <group>
  T& operator*();
  const T& operator*() const { return get(); }
  const T& get() const { return *get_typed_ptr(parent_p, fieldNumber_p); }
  // </group>
 
  // Store a value in the field using redefinition.
  // Define differs from assignment w.r.t. arrays.
  // For define a variable shaped array is deleted first with the
  // effect that array conformance rules are not applied for them.
  void define(const T& value);
 
  // Get the comment of this field.
  const String& comment() const;
 
  // Set the comment for this field.
  void setComment(const String& comment);
 
  // Return the fieldnumber of this field.
  Int fieldNumber() const { return fieldNumber_p; }
 
  // Return the name of the field.
  String name() const { return parent_p->name(fieldNumber_p); }
 
  // Is this field pointer attached to a valid record? Operations which
  // might cause it to become detached are:
  // <ol>
  //     <li> Destruction of the Record
  //     <li> Restructuring of the record.
  //     <li> Explicit call of the detach() member.
  // </ol>
  // # This inherited function is shown for documentation purposes.
  Bool isAttached() const { return parent_p; }
 
 private:
  static const T* get_typed_ptr(RecordInterface* record, Int fieldNumber);
 
  RecordInterface* parent_p;
  Int fieldNumber_p;
};
 
// <summary>
//  Read-Only access to an individual field from a Record.
// </summary>
 
// <use visibility=export>
// <reviewed reviewer="Mark Wieringa" date="1996/04/15" tests="tRecord">
// </reviewed>
 
// <prerequisite>
//   <li> <linkto class="RecordFieldPtr">RecordRecordFieldPtr</linkto>.
// </prerequisite>
//
// <synopsis>
// This class is entirely like <linkto class="RecordFieldPtr">
// RecordFieldPtr</linkto>, except that it only allows Read-Only
// access to fields in a Record. The documentation for that class should
// be consulted.
// <p>
// Note that RecordFieldPtr is not inherited from RORecordFieldPtr,
// because that would give problems with the function attachToRecord.
// It would allow RecordFieldPtr to attach to a const RecordInterface object.
// </synopsis>
 
template <class T>
class RORecordFieldPtr {
 public:
  RORecordFieldPtr() {}
  RORecordFieldPtr(const RecordInterface& record, Int whichField)
      : fieldPtr_p((RecordInterface&)record, whichField) {}
  RORecordFieldPtr(const RecordInterface& record, const RecordFieldId& id)
      : fieldPtr_p((RecordInterface&)record, id) {}
  RORecordFieldPtr(const RecordFieldPtr<T>& other) : fieldPtr_p(other) {}
  RORecordFieldPtr(const RORecordFieldPtr<T>& other) : fieldPtr_p(other.fieldPtr_p) {}
  RORecordFieldPtr<T>& operator=(const RORecordFieldPtr<T>& other) {
    fieldPtr_p = other.fieldPtr_p;
    return *this;
  }
 
  ~RORecordFieldPtr() {}
 
  void attachToRecord(const RecordInterface& record, Int whichField) {
    fieldPtr_p.attachToRecord((RecordInterface&)record, whichField);
  }
  void attachToRecord(const RecordInterface& record, const RecordFieldId& id) {
    fieldPtr_p.attachToRecord((RecordInterface&)record, id);
  }
 
  const T& operator*() const { return *fieldPtr_p; }
  const T& get() const { return fieldPtr_p.get(); }
 
  const String& comment() const { return fieldPtr_p.comment(); }
 
  Int fieldNumber() const { return fieldPtr_p.fieldNumber(); }
 
  void detach() { fieldPtr_p.detach(); }
  Bool isAttached() const { return fieldPtr_p.isAttached(); }
 
 private:
  RecordFieldPtr<T> fieldPtr_p;
};
 
}  // namespace casacore
 
#ifndef CASACORE_NO_AUTO_TEMPLATES
#include <casacore/casa/Containers/RecordField.tcc>
#endif  // # CASACORE_NO_AUTO_TEMPLATES
#endif