怎样用Polymorphy 2D-Array创建抽象类？

Question

I want to have a 2D array of pointers that contains abstract classes called Piece. So I made a pointer to a 2D array of Piece in a class called Board that have private field of board -Piece** _board.

I tried to use vector or wrap the board field with class but apperently something went wrong..

class Piece
{
public:
Piece(bool, string);
Piece(){};
bool isChass(bool, Board*);
virtual int move(int x_src, int y_src, int x_dst, int y_dst, Board*   board)=0;
virtual ~Piece();
bool get_isWhite();
string get_type();
Piece(Piece & other);
Piece& operator= (const Piece & other);
bool inRange(int, int);

protected:
bool _isWhite;
string _type;
};


class Board
{
public:
Board();
Board(const Board& other);
~Board();
Board& operator=(const Board &other);
Piece& getPiece(int i, int j){ return _board[i][j]; }
void game();
void deletePiece(int x, int y) { delete &_board[x][y]; }
void allocateBlankPiece(int x, int y) { _board[x][y] = *new Blank(); }

private:
Piece** _board;
bool _isWhiteTurn;


friend class Piece;
friend class Rock;
friend class Bishop;
friend class Queen;
friend class Knight;
friend class King;
friend class Pawn;
};

Answer 1

You can't use polymorphism for arrays.

An array contains contiguous elements of the same size. But polymorphic elements could be of different size, so that the compiler would not be able to generate code to properly indexing the elements.

You can eventually consider an array of pointers to polymorphic elements:

Piece*** _board;  // store pointers to polyorphic elements 

But it would be more practical and safer to use vectors:

vector<vector<Piece*>> _board;  // Vector of vector of poitners to polymorphic elements

You could also consider even safer smart pointers:

vector<vector<shared_ptr<Piece>>> _board;    // assuming that several boards or cells could share the same Piece.