#ifndef __singletonmonitor_ah__
#define __singletonmonitor_ah__

#include <iostream>

// Generic singleton monitor aspect
//
// A class obeying the singleton pattern should guarantee that
// no more than a single object of this class will be ever created.
// This generic aspect checks the behavior: it counts the instances
// and emits an error message if more than one instance is created.

// singletonmonitor::Counter is a helper class used to count the number
// of objects created.
// The usage of a template class and its intantiation with JoinPoint::That
// ensures, that a new counter will be used for each singleton class,
// while constructor and copy-constructor of the same class will use
// the same counter.


namespace singletonmonitor {
  template<typename T> struct Counter {
    static int _val;
  };
  template<typename T> int Counter<T>::_val = 0;
}


aspect GenericSingletonMonitor {
  pointcut virtual singleton() = 0;

  advice construction (singleton()) : before() {
    typedef singletonmonitor::Counter<JoinPoint::That> InstanceCounter;

    InstanceCounter::_val++;
    if (InstanceCounter::_val > 1) {
    std::cerr << "Error: "
	      << "created "<< InstanceCounter::_val << " instances of "
	      << "singleton class by calling the constructor "
	      << JoinPoint::signature()
	      << std::endl;
    }
  };
};

#endif