Deep copying an array c# without serialization

Question

Basically I have the problem that my MinMax algorithm isn't really working as intended.

What I need is to make my array pieces be copied to newPieces so that pieces isn't changed when newPieces is.

Here is an extract of the MinMax algorithm:

private int MinMax(
    int depth, Piece[] pieces, bool blacksTurn, 
    List<Move> Moves, Game game, int alpha, Move nextMove) {

    Piece[] newPieces=new Piece[24];
    Moves=Game.possibleMoves(pieces, blacksTurn, false);
    if(depth==0||Moves.Count==0) {
        return Evaluation(ref pieces);
    }

    int value;

    if(blacksTurn==true) {
        foreach(Move i in Moves) {
            newPieces=DeepCopy.ObjectExtensions.Copy(pieces);
            game.MovePiece(newPieces, blacksTurn, i.Moving, i.Destination, true);
            game.DisplayBoard(pieces);
            value=minMax(depth-1, newPieces, !blacksTurn, Moves, game, alpha, nextMove);

            if(alpha>value) {
                alpha=value;
                nextMove=i;
            }

    // ...

Here is the Piece class.

[StructLayout(LayoutKind.Sequential)]
public class Piece
{

    public CellReference Location;
    public bool isBlack { get; set; }
    public bool isKing { get; set; }
    private int Value { get; set; }
    public bool taken { get; set; }

    public Piece()
    {

    }

    public Piece(int i, bool isBlack, bool isKing, int CellsEast, int CellsNorth, bool taken)
    {
        this.Value = i;
        Location.CellsEast = CellsEast;
        Location.CellsNorth = CellsNorth;
        this.isBlack = isBlack;
        this.isKing = isKing;
        this.taken = taken;
    }
}

Is Piece complex enough to warrant a class over a struct? Depending on what game this is, there is also the option of not copying the board at all but instead record information that will let you revert a move after it's been evaluated. — 500 - Internal Server Error
– 500 - Internal Server Error, Commented Mar 12, 2013 at 18:05
Is this question about a "more efficient deep copy" or is it about a "more efficient min-max"? — user166390
– user166390, Commented Mar 12, 2013 at 18:06
@DJKRAZE the OP asked specifically for a deep copy, MemberwiseClose is documented as performing a shallow copy — Peter Ritchie
– Peter Ritchie, Commented Mar 12, 2013 at 18:09
That's correct Peter..I over looked that I will remove my comment — MethodMan
– MethodMan, Commented Mar 12, 2013 at 18:10
@500 I tried changing it to a struct, everything seemed to break so I changed it back. Also how would you suggest going about recording all of the information? — Henry
– Henry, Commented Mar 12, 2013 at 19:08

Dustin Kingen · Accepted Answer · 2013-03-12 18:17:56Z

3

I would implement ~~ICloneable~~ ICloneable<T> on the Piece class.

public interface ICloneable<T>
{
    T Clone();
}

pieces.Select(p => p.Clone()).ToArray(); or just use a foreach loop.

edited Mar 12, 2013 at 18:17

answered Mar 12, 2013 at 18:12

Dustin Kingen

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4 Comments

Roman Starkov Over a year ago

I suggest implementing just the Clone method. There's no benefit to implementing the ICloneable interface, and you can't even have the "nice" return type, forcing it to be object.

Dustin Kingen Over a year ago

Or make an ICloneable<T>.

Henry Over a year ago

When I do this it says it cannot convert type object[] to Piece[].

Dustin Kingen Over a year ago

Implement ICloneable<T> on Piece or you'll need to cast it pieces.Select(p => (Piece)p.Clone()).ToArray().

Ken Kin · Accepted Answer · 2015-01-28 15:19:23Z

1

Add attribute as this to class/structure Piece:

using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential)]
public class Piece {

And the code is following

namespace DeepCopy {
    public static class ObjectExtensions {
        public static T[] Copy<T>(this T[] pieces) {
            return pieces.Select(x => {
                var handle=Marshal.AllocHGlobal(Marshal.SizeOf(typeof(T)));

                try {
                    Marshal.StructureToPtr(x, handle, false);
                    return (T)Marshal.PtrToStructure(handle, typeof(T));
                }
                finally {
                    Marshal.FreeHGlobal(handle);
                }
            }).ToArray();
        }
    }
}

I temporarily modify Piece.Value to be public for the test, and have tested with a test class

public static partial class TestClass {
    public static void TestDeepCopy(Piece[] pieces) {
        Piece[] newPieces=new Piece[24];

        newPieces=DeepCopy.ObjectExtensions.Copy(pieces);

        newPieces[0].isKing=true;
        newPieces[0].Value=3;

        newPieces[1].isKing=true;
        newPieces[1].taken=true;
        newPieces[1].Value=4;

        Console.WriteLine("=== newPieces ===");
        foreach(var x in newPieces)
            Console.WriteLine(
                "x.isKing={0}; x.isBlack={1}; x.Value={2}",
                x.isKing, x.isBlack, x.Value
                );

        Console.WriteLine();
        Console.WriteLine("=== pieces ===");
        foreach(var x in pieces)
            Console.WriteLine(
                "x.isKing={0}; x.isBlack={1}; x.Value={2}",
                x.isKing, x.isBlack, x.Value
                );
    }

    public static void StartTest() {
        var pieceA=new Piece(1, false, false, 1, 1, false);
        var pieceB=new Piece(2, true, false, 1, 1, false);
        var pieces=new[] { pieceA, pieceB };
        TestDeepCopy(pieces);
    }
}

and it works. To perform the test, call

TestClass.StartTest();

edited Jan 28, 2015 at 15:19

answered Mar 12, 2013 at 20:07

Ken Kin

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4 Comments

Henry Over a year ago

It's still not working... I am frankly at a loss, every single copy seems to have the same results and the whole thing still doesn't work.

Ken Kin Over a year ago

Wow ... what did you do? What's the problem before ..? I'd like to discover that

Henry Over a year ago

Well its screwed up again but this time at least I know where the problem lies. It's not the copying at all it is in fact somewhere buried in my move function. I should actually be able to find the problem in there though. So your work was perfectly fine, it's just me that screwed it up ;D.

Dustin Kingen Over a year ago

Might want to be more careful with the AllocHGlobal. If it blows up while copying then you've got a memory leak.

L-Four · Accepted Answer · 2013-03-12 18:20:04Z

0

I think this may help to solve your problem. It uses the ICloneable interface to make objects aware on how to clone themselves.

answered Mar 12, 2013 at 18:20

L-Four

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