c++ - 用“虚拟”类继承

Question

我目前正在尝试编写一个通用的 minmax 算法。我对 c++ 相当陌生，具有 c 和 arm asm 编程背景。对于 MinMax-Algorithm，我使用了一个称为 Negamax 的变体，这使得它更加紧凑：

#define move typename game<evaluationtype>::_move
#define gamestate typename game<evaluationtype>::_gamestate
#define player typename game<evaluationtype>::_player


template <typename gametype, typename evaluationtype>
std::pair<evaluationtype, move> Negamax(game <evaluationtype> Game, int depth, evaluationtype alpha, evaluationtype beta) {
    if (depth == 0)
        return std::make_pair(Game.evaluation(), move());
    else {
        move savebestmove;
        evaluationtype maxValue = alpha;
        std::list<move> allpossiblemoves = Game.getpossiblemoves();
        for (move Move : allpossiblemoves) {
            gamestate state = Game.makemove(Move);
            evaluationtype checkvalue = -((Negamax<gametype, evaluationtype>(Game, depth - 1, -beta, -maxValue)).first);
            Game.undomove(Move, state);
            if (checkvalue > maxValue) {
                maxValue = checkvalue;
                savebestmove = Move;
                if (maxValue >= beta)
                    break;
            }
        }
        return std::make_pair(maxValue, savebestmove);
    }
}
#undef move
#undef gamestate
#undef player

在代码中设置游戏基类所需的成员函数，如下所示：

    template <typename evaluationtype>
class game {
    enum class _player;
    class _move;
    class _gamestate;
private:
    _player playersturn;
public:
    game() = delete;
    virtual evaluationtype evaluation() const;
    virtual std::list<_move>&& getpossiblemoves() const;
    virtual _gamestate makemove(const _move&);
    virtual void undomove(const _move&, const _gamestate&);
};

现在我尝试用井字游戏实现派生类：

template <typename evaluationtype>
class TicTacToe : game<evaluationtype> {
private:
    enum class _player {
        none, cross, circle
    };
    class _move {
        unsigned x;
        unsigned y;
    };
    class _gamestate {
        std::array<std::array<_player, 3> ,3> field;
        _player turn = cross;
    };
    _gamestate currentfield;
public:
    TicTacToe(); 
    evaluationtype evaluation() const;
    std::list<_move>&& getpossiblemoves() const;
    _gamestate makemove(const _move&);
    void undomove(const _move&, const _gamestate&);
};

当前唯一具有定义的方法是一个空的构造函数。Visual Studio 没有向我显示任何错误，但是一旦我尝试创建 TicTacToe 的实例，我就会得到以下输出：

1>C:\AlphaBetaNegamax\TicTacToe.h(17,3): error C2079: 'TicTacToe<int>::_gamestate::field' uses undefined class 'std::array<std::array<TicTacToe<int>::_player,3>,3>'
1>C:\AlphaBetaNegamax\TicTacToe.h(20): message : see reference to class template instantiation 'TicTacToe<int>::_gamestate' being compiled
1>C:\AlphaBetaNegamax\Source.cpp(3): message : see reference to class template instantiation 'TicTacToe<int>' being compiled
1>C:\AlphaBetaNegamax\TicTacToe.h(24,21): error C2555: 'TicTacToe<int>::getpossiblemoves': overriding virtual function return type differs and is not covariant from 'game<evaluationtype>::getpossiblemoves'
1>        with
1>        [
1>            evaluationtype=int
1>        ]
1>C:\AlphaBetaNegamax\Negamax_and_Gamestructure.h(17): message : see declaration of 'game<evaluationtype>::getpossiblemoves'
1>        with
1>        [
1>            evaluationtype=int
1>        ]

我知道我在继承嵌套类部分的某个地方搞砸了，我不确定在哪里。那是我真的不应该做的事情，还是我对继承结构有问题？

标签： c++inheritanceinner-classesminimax