#include <string>
#include <iostream>
using namespace std;

class Animal {
 public:
  Animal() : m_isAlive(true) {};
  Animal(bool isAlive) : m_isAlive(isAlive) {};
  bool IsAlive() const { return m_isAlive; };
  void Died() { m_isAlive = false; }
  virtual string Eats() = 0;
 private:
  bool m_isAlive;
};

class Lion : public Animal {
 public:
  Lion() : Animal() {};
  Lion(bool isAlive) : Animal(isAlive) {};
  virtual string Eats() { return "meat"; }
};

class Lamb : public Animal {
 public:
  Lamb() : Animal() {};
  Lamb(bool isAlive) : Animal(isAlive) {}
  virtual string Eats() { return "grass"; }
};

class Shark : public Animal {
 public:
  Shark() : Animal() {};
  Shark(bool isAlive) : Animal(isAlive) {};
  virtual string Eats() { return "people"; }
};

class CageOccupiedEx {
 public:
  CageOccupiedEx() : m_message("The cage is occupied!") {}
  string what() { return m_message; }
 private:
  string m_message;
};

template <class T> 
class Cage {
 public:
  Cage() :  m_occupied(false) {};
  void Enter(T & animal);
  T Leave();
 private:
  T m_animal;
  bool m_occupied;
};

template <class T>
void Cage<T>::Enter(T & animal) {

  if (m_occupied)
    throw CageOccupiedEx();

  m_animal = animal;
  m_occupied = true;
}

template <class T>
T Cage<T>::Leave() {
  T tmpAnimal = m_animal;
  m_animal = "";
  m_occupied = false;
  return tmpAnimal;
}
   

int main() {
  Lion leo;
  Lion simba;
  Lamb lambert;
  Shark leon;

  Cage<Lion> lionCage;
  Cage<Lamb> lambCage;

  cout << "Leo is entering his cage" << endl;

  try {
    lionCage.Enter(leo);
  }
  catch (CageOccupiedEx &e) {
    cout << "Error: " << e.what() << endl;
  }
    
  cout << "Lambert is entering his cage" << endl;

  try {
      lambCage.Enter(lambert);
  }
  catch (CageOccupiedEx &e) {
    cout << "Error: " << e.what() << endl;
  }
  
  cout << "Simba is entering his cage" << endl;

  try {
    lionCage.Enter(simba);
  }
  catch (CageOccupiedEx &e) {
    cout << "Error: " << e.what() << endl;
  }
  
  return 0;
}