//: C08:Mutable.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// The "mutable" keyword

class Z {
  int i;
  mutable int j;
public:
  Z();
  void f() const;
};

Z::Z() { i = j = 0; }

void Z::f() const {
//! i++; // Error -- const member function
    j++; // OK: mutable
}

int main() {
  const Z zz;
  zz.f(); // Actually changes it!
} ///:~