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NIL.CPP
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C/C++ Source or Header
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1993-04-27
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2KB
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39 lines
#include "object.h"
extern const Class class_Nil;
class Nil : public Object {
public:
Nil() {}
virtual int compare(const Object&) const; // compare objects
virtual Object* copy() const; // copy returns nil
virtual Object* deepCopy() const; // copy returns nil
virtual unsigned hash() const; // calculate object hash
virtual const Class* isA() const;
virtual bool isEqual(const Object&) const; // equality test
virtual void printOn(ostream& strm) const;
virtual Object* shallowCopy() const; // copy returns nil
};
#define THIS Nil
#define BASE Object
DEFINE_CLASS(Nil,Object);
static const Nil nil_object; // the nil object
extern const Object* const nil = (Object*)&nil_object; // pointer to the nil object
bool Nil::isEqual(const Object& ob) const { return (&ob==nil); }
unsigned Nil::hash() const { return 0; }
int Nil::compare(const Object& ob) const
{
assertArgSpecies(ob,class_Nil,"compare");
return 0;
}
Object* Nil::copy() const { return (Object*) nil; }
Object* Nil::shallowCopy() const { return (Object*) nil; }
Object* Nil::deepCopy() const { return (Object*) nil; }
void Nil::printOn(ostream& strm) const { strm << "NIL"; }