Category : C Source Code
Archive   : NIH.ZIP
Filename : NIL.CXX

/* Nil.c -- implementation of the nil object

THIS SOFTWARE FITS THE DESCRIPTION IN THE U.S. COPYRIGHT ACT OF A
"UNITED STATES GOVERNMENT WORK". IT WAS WRITTEN AS A PART OF THE
AUTHOR'S OFFICIAL DUTIES AS A GOVERNMENT EMPLOYEE. THIS MEANS IT
CANNOT BE COPYRIGHTED. THIS SOFTWARE IS FREELY AVAILABLE TO THE
PUBLIC FOR USE WITHOUT A COPYRIGHT NOTICE, AND THERE ARE NO
RESTRICTIONS ON ITS USE, NOW OR SUBSEQUENTLY.

Author:
K. E. Gorlen
Bg. 12A, Rm. 2017
Computer Systems Laboratory
Division of Computer Research and Technology
National Institutes of Health
Bethesda, Maryland 20892
Phone: (301) 496-5363
uucp: uunet!ncifcrf.gov!nih-csl!keith
Internet: keith%[email protected]
September, 1985

Function:

Declarations and member functions for the nil object.

$Log: Nil.c,v $
* Revision 1.3 88/02/04 12:59:38 keith
* Make Class class_CLASSNAME const.
*
* Revision 1.2 88/01/16 23:39:55 keith
* Remove pre-RCS modification history
*
*/

#include "Object.hxx"

extern const Class class_Nil;

class Nil : public Object {
public:
Nil() {}
#ifdef OBJECTIO
Nil(fileDescTy&,Nil&) {}
Nil(istream&,Nil&) {}
#endif //OBJECTIO
virtual int compare(const Object&); // compare objects
virtual Object* copy(); // copy returns nil
virtual Object* deepCopy(); // copy returns nil
virtual unsigned hash(); // calculate object hash
virtual const Class* isA();
virtual bool isEqual(const Object&); // equality test
#ifdef OBJECTIO
virtual void printOn(ostream& strm);
#endif //OBJECTIO
virtual Object* shallowCopy(); // copy returns nil
#ifdef OBJECTIO
virtual void storer(ostream&); // shouldNotImplement
virtual void storer(fileDescTy&); // shouldNotImplement
#endif //OBJECTIO
};

#define THIS Nil
#define BASE Object
DEFINE_CLASS(Nil,Object,1,"$Header: Nil.c,v 1.3 88/02/04 12:59:38 keith Exp $",NULL,NULL);
static const Nil nil_object; // the nil object

/*
extern const Object* const nil = (Object*)&nil_object; // pointer to the nil object
*/

extern const Object* nil = (Object*)&nil_object; // pointer to the nil object

bool Nil::isEqual(const Object& ob) { return (&ob==nil); }

unsigned Nil::hash() { return 0; }

int Nil::compare(const Object& ob)
{
assertArgSpecies(ob,class_Nil,"compare");
return 0;
}

Object* Nil::copy() { return nil; }

Object* Nil::shallowCopy() { return nil; }

Object* Nil::deepCopy() { return nil; }

#ifdef OBJECTIO
void Nil::printOn(ostream& strm) { strm << "NIL"; }

void Nil::storer(ostream&)
/*
The Nil object is always implicitly stored as object number zero; all
references to nil are stored as @0.
*/
{
shouldNotImplement("storer");
}

void Nil::storer(fileDescTy&)
{
shouldNotImplement("storer");
}
#endif //OBJECTIO