[c++] Overloading unary operators (C++ only)

An overloaded unary operator may return any type. The following example overloads the ! operator:

#include <iostream>

using namespace std;

struct X { };

void operator!(X) {

  cout << "void operator!(X)" << endl;

}

struct Y {

  void operator!() {

    cout << "void Y::operator!()" << endl;

  }

};

struct Z { };

int main() {

  X ox; Y oy; Z oz;

  !ox;

  !oy;

//  !oz;

}

  !oy;

//  !oz;

}