How to deal with "not covariant" errors in paired hierarchies (C++)

Question

Suppose I want a class Team to have a virtual get_player member which is implemented by FootballTeam and RugbyTeam , and that these implementations return the covariant types FootballPlayer and RugbyPlayer .

Suppose I also want Player to have a virtual get_team member which is implemented by FootballPlayer and RugbyPlayer , and that these implementations return the covariant types FootballTeam and RugbyTeam .

Is it possible to implement this pattern? I've tried, but, when overriding the get_player member of Team , I'm getting the error: "Return type of virtual function 'get_player' is not covariant with the return type of the function it overrides".

I can't define the Player hierarchy first, because then I'd have the same problem but the other way around!

class Player;
class FootballPlayer;
class RugbyPlayer;

class Team {
  virtual Player &get_player() = 0;
};
class FootballTeam : public Team {
  FootballPlayer &get_player() override; // error here
};
class RugbyTeam : public Team {
  RugbyPlayer &get_player() override; // error here
};

class Player {
  virtual Team& get_team() = 0;
};
class FootballPlayer : public Player {
  FootballTeam& get_team() override;
};
class RugbyPlayer : public Player {
  RugbyTeam& get_team() override;
};

Answer 1

We, unfortunately, cannot forward declare classes WITH inheritance.

So you have to drop one covariant return type and break the circular dependency loop somewhere.