Overriding protected variable c++

Question

Suppose I have the following code:

class Board
{
  protected:
    std::vector<Piece*> pieces;
}

class ChessBoard : public Board
{
  protected:
    std::vector<ChessPiece*> pieces;

}

I am wanting the derived class to override the protected variable pieces with this new vector, however I am having difficulty with it, and it seems like this is bad practice.

Answer 1

There is no such thing as "overriding a variable", whether protected or otherwise.

In your example program, the class ChessBoard contains a member sub object pieces and a base sub object Board that contains the member Board::pieces. Thus, there are two vectors inside the object.

Object oriented programming is achieved through virtual functions. You haven't explained what you're trying to do (beyond something that cannot be done) so this is just a guess, but maybe you are looking for covariant return types:

class Board
{
    protected:
        virtual Piece&
        operator[](std::size_t index) = 0;

    public:
        virtual ~Board() = default;
};

class ChessBoard : public Board
{
    std::vector<ChessPiece> pieces;

    protected:
        virtual ChessPiece&
        operator[](std::size_t index) override;
};

Furthermore, if the sub classes have identical base and/or member function implementations except for the types, then you can avoid repetition by using a template.