hoge

NK.cpp

#include <iostream>

using namespace std;

typedef enum {
   ATOMIC,
   NOT,
   AND,
   OR, 
   IMPLIES,
} PropType;

class Prop {
public:
   Prop() {}
   virtual PropType type();
};

class AtomicProp : private Prop {
   const char ch_;
public:
   AtomicProp(const char ch):ch_(ch){}
   PropType type() const {
      return ATOMIC;
   }   
   friend ostream &operator<<(ostream &stream, AtomicProp &p);
};
ostream& operator<<(ostream &stream, AtomicProp &p) {
   stream << p.ch_;
   return stream;
}

int main(void) {
   AtomicProp p('A');
   cout << p << endl;
   return 0;
}