#include <iostream>
using namespace std;

//------------------------------------------------------------------------------
// An abstract base class.
//------------------------------------------------------------------------------
class AbstractBase {
public:
  AbstractBase() {}
  virtual void pureMethod() const = 0;
};

//------------------------------------------------------------------------------
// Derived class from AbstractBase.
//------------------------------------------------------------------------------
class DerivedClass: public AbstractBase {
public:
  DerivedClass(): AbstractBase() {}
  virtual void pureMethod() const {
    cout << "Derived instance at " << this << endl;
  }
};

//------------------------------------------------------------------------------
// A class which takes an instance of the abstract base class
//------------------------------------------------------------------------------
class UseAbstractType {
public:
  UseAbstractType(const AbstractBase& base): mBasePtr(&base) {}
  void callPureMethod() const {
    mBasePtr->pureMethod();
  }
private:
  const AbstractBase* mBasePtr;
};

//------------------------------------------------------------------------------
// A non-abstract (definite?) base.
//------------------------------------------------------------------------------
class DefiniteBase {
public:
  DefiniteBase() {}
  virtual void method() const {
    cout << "DefiniteBase instance at " << this << endl;
  }
};

//------------------------------------------------------------------------------
// Derived class from DefiniteBase.
//------------------------------------------------------------------------------
class AnotherDerivedClass: public DefiniteBase {
public:
  AnotherDerivedClass(): DefiniteBase() {}
  virtual void method() const {
    cout << "AnotherDerived instance at " << this << endl;
  }
};

//------------------------------------------------------------------------------
// A class which takes an instance of the definite base class
//------------------------------------------------------------------------------
class UseDefiniteType {
public:
  UseDefiniteType(const DefiniteBase& base): mBasePtr(&base) {}
  void callMethod() const {
    mBasePtr->method();
  }
private:
  const DefiniteBase* mBasePtr;
};