#include <iostream>

class Bipedal {
public:
  virtual void lose_balance() = 0;
};

class Sentient {
public:
  virtual void ponder() = 0;
};

class Creature {
public:
  virtual void reproduce() = 0;
};

class Human: public Creature, public Bipedal, public Sentient {
public:
  void reproduce() { std::cout<<"Getting funky"; }
  void lose_balance() { std::cout<<"Falling over"; }
  void ponder() { std::cout<<"Thinking about "; }
};

int main()
{
  Human eggy;
  Creature& thingy = eggy;
  Bipedal& twoleggy = eggy;
  Sentient& thinky = eggy;

  eggy.ponder(); eggy.lose_balance(); std::cout<<std::endl;
  thingy.reproduce(); std::cout<<std::endl;
  twoleggy.lose_balance(); std::cout<<std::endl;
  thinky.ponder(); std::cout<<std::endl;

  std::cin.get();
}

#include <iostream>

class NullType {};

class Bipedal {
public:
  void do_legs() { std::cout<<"Falling over"; }
};

class Sentient {
public:
  void do_brain() { std::cout<<"Thinking about "; }
};

template <
  typename Legs = NullType,
  typename Brain = NullType,
  typename Body = NullType
>
class Creature {
  Legs _legs;
  Brain _brain;
  Body _body;
public:
  void ponder() { _brain.do_brain(); }
  void lose_balance() { _legs.do_legs(); }
};

int main()
{
  Creature<Bipedal, Sentient> eggy;

  eggy.ponder(); eggy.lose_balance(); std::cout<<std::endl;

  std::cin.get();
}