Help for designing a chess game

Question

I am a C++ programmer trying to learn designing, as a start I am trying to get a hang of designing by giving myself a task to make a OO design for a game of chess.This is not a homework q just trying to develop some skills. Here is the summary of what i have in my mind till now: A "Piece" class which will hold the current position of the piece on the board. specialized classes "Camel" "Horse" "Queen" "Knight" "Pawn" & "Elephant" which will be derived from the "Piece" class. Each of these classes will hold 2 members, "no of places allowed to move" & "rule of moving" and get methods to retrieve the same.

A base "Player" Class which will be extended by classes "BlackPiecePlayer" & "WhitePiecePlayer". Each of these classes will hold another class instance called "PieceManager" The "PieceManager" class will be the one which will determine the logic of moving around the pieces on the Board.

A "ChessBoard" class which will hold the mapping of all the pieces on the board and have access to set of rules with which pieces can be moved. It will provide interfaces to authenticate a move calculated by "PieceManager" and then make the move while updating its own mappings.

Heres a generic flow that i can visualize. A class "WhitePiecePlayer" is asked to make a move, it will ask its own "WhitePieceManager" to make a move. The "WhitePieceManager" will access the positions of pieces on board by using interfaces of "Board" class. Then it will use its internal logic to calculate a move for an piece.Each piece stores its position so it calculates position for that piece. Then authenticates the move is possible by calling a method of the Board class and then makes the move by using Board class interface..and so on..

Sorry for the long story, I am just trying to develop a feel for the design and this is what i have in mind right now, Do you think its good for a start or any suggestions on how to make it better(if it is correct)

Answer 1

Hi ani,

A few comments

1) The most important thing in a chess prgoram is the algorithm to choose a move. Usually it is an alpha-beta pruning algorithm. In order for this algorithm to be efficient, the way that pieces in the board are represented is very important. You can read that in this implementation issues section of wikipedia. I'd read that for the basis of board-piece representation. There is a lot of discussion in internet, and open engines like Crazy or Fruit. I doubt that they use OO, though - I do not know if there is any Object Oriented engine in the wild.

2) What are the camel, elephant, etc? What kind of chess are you trying to represent? I am not familiar with that, sorry. Is elephant the rook and camel the bishop?

3) What is the utility of having two different classes, WhitePlayer and BlackPlayer? In which way would they be different from Player? Shouldn't you have two different instances of a Player class, called white and black?

Good luck with your project. I hope you learn a lot from it! :)

Answer 2

A few suggestions

• Your hierarchy of piece related classes seems reasonable (though using the proper names for the pieces Knight, Rook, and Bishop would probably be preferable to Horse, Camel, and Elephant).
• I would not store the number of squares a piece is allowed to move. You would want to encode that in the "rule of movement" method if only because that can change depending on the situation. A pawn can move two squares on its initial move and then one square in subsequent moves. A king can only move one square unless it is castling.
• Your piece classes will need to have some sort of method to get a list of all a piece's valid moves in order to provide those to the engine that is going to choose a move.
• You don't need BlackPiecePlayer and WhitePiecePlayer classes. You just need to instantiate two different instances of the Player class and ensure that there is a "color" attribute.
• A ChessBoard class is a good idea and will need to represent the positions of the pieces but it should not implement logic evaluating moves. That is something for the move engine to do.

As Javier discusses, building a chess program is likely going to involve quite a bit of effort on the design of an efficient algorithm for choosing a move. Assuming that your intention is to apply OO concepts and not to delve into the discussions about how to build a chess engine (which will often sacrifice OO purity for better performance), and assuming that you want to build something that can play well enough to be interesting, you may want to consider implementing antichess rather than regular chess. From an OO standpoint, it is essentially an identical problem, but the end result is something that plays reasonably well without investing hundreds of hours in mastering chess algorithms. That's a much more enjoyable outcome than a chess program that plays terribly.