//: C10:CuriousSingleton.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Separates a class from its Singleton-ness (almost).
#include <iostream>
using namespace std;

template<class T> class Singleton {
  Singleton(const Singleton&);
  Singleton& operator=(const Singleton&);
protected:
  Singleton() {}
  virtual ~Singleton() {}
public:
  static T& instance() {
    static T theInstance;
    return theInstance;
  }
};

// A sample class to be made into a Singleton
class MyClass : public Singleton<MyClass> {
  int x;
protected:
  friend class Singleton<MyClass>;
  MyClass() { x = 0; }
public:
  void setValue(int n) { x = n; }
  int getValue() const { return x; }
};

int main() {
  MyClass& m = MyClass::instance();
  cout << m.getValue() << endl;
  m.setValue(1);
  cout << m.getValue() << endl;
} ///:~