// AbsPtr.hpp

#ifndef AbsPtr_H
#define AbsPtr_H

// Abstract base for a pointer class.
// The template class Ptr meets the interface of but does not inherit
// from AbsPtr to minimize its size and maximize its speed.
//
// Concrete subclasses implement the method pointer.
//
// Exception PtrInvalidPointer is thrown if user attempts dereference
// or member selection with a null pointer.

#include "ptr/PtrException.h"

template<class T>
class AbsPtr {

public:

  // Destructor.
  ~AbsPtr() { }

  // Return the pointer to the object.
  // Return 0 if the pointer is not valid.
  virtual T* pointer() const =0;

  // dereference
  T& operator*() const {
    T* ptr = pointer();
    if ( ! ptr ) throw PtrInvalidPointer();
    return *ptr;
  }

  // class member selection
  T* operator->() const {
    T* ptr = pointer();
    if ( ! ptr ) throw PtrInvalidPointer();
    return ptr;
  }

  // Conversion to void*.
  // This enables comparisons (==, <, ...) and output stream.
  operator const void*() const {
    return pointer();
  }

};

#endif