[WIP] Copy-make with readonly Position struct

src/Lynx.Benchmark/LocalVariableIn_vs_NoIn_Benchmark.cs

@@ -24,7 +24,7 @@ public int LocalVariableAndIn(string fen)
         var moves = new List<Move>(50_000);
 
         for (int i = 0; i < 1000; ++i)
-            moves.AddRange(Sort_LocalVariableAndIn(MoveGenerator.GenerateAllMoves(position), position));
+            moves.AddRange(Sort_LocalVariableAndIn(position.GenerateAllMoves(), position));
 
         return Sort_LocalVariableAndIn(moves, position)[0];
     }
@@ -37,7 +37,7 @@ public int NoIn(string fen)
         var position = new Position(fen);
 
         for (int i = 0; i < 1000; ++i)
-            moves.AddRange(Sort_NoIn(MoveGenerator.GenerateAllMoves(position), position));
+            moves.AddRange(Sort_NoIn(position.GenerateAllMoves(), position));
 
         return Sort_NoIn(moves, position)[0];
     }

src/Lynx.Benchmark/ParseGame_Benchmark.cs

@@ -509,7 +509,7 @@ internal OriginalGame(string fen, string[] movesUCIString) : this(fen)
         {
             foreach (var moveString in movesUCIString)
             {
-                var moveList = MoveGenerator.GenerateAllMoves(CurrentPosition);
+                var moveList = CurrentPosition.GenerateAllMoves();
 
                 if (!MoveExtensions.TryParseFromUCIString(moveString, moveList, out var parsedMove))
                 {
@@ -574,7 +574,7 @@ public ImprovedGame(ReadOnlySpan<char> fen)
 
             PositionHashHistory = new(1024) { CurrentPosition.UniqueIdentifier };
             HalfMovesWithoutCaptureOrPawnMove = parsedFen.HalfMoveClock;
-            _gameInitialPosition = new Position(CurrentPosition);
+            _gameInitialPosition = new Position(in CurrentPosition);
 #if DEBUG
             MoveHistory = new(1024);
 #endif
@@ -590,7 +590,7 @@ internal ImprovedGame(string fen, ReadOnlySpan<char> rawMoves, Span<Range> range
                     break;
                 }
                 var moveString = rawMoves[range];
-                var moveList = MoveGenerator.GenerateAllMoves(CurrentPosition);
+                var moveList = CurrentPosition.GenerateAllMoves();
 
                 if (!MoveExtensions.TryParseFromUCIString(moveString, moveList, out var parsedMove))
                 {
@@ -601,7 +601,7 @@ internal ImprovedGame(string fen, ReadOnlySpan<char> rawMoves, Span<Range> range
                 MakeMove(parsedMove.Value);
             }
 
-            _gameInitialPosition = new Position(CurrentPosition);
+            _gameInitialPosition = new Position(in CurrentPosition);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -655,7 +655,7 @@ public ImprovedGame2(ReadOnlySpan<char> fen)
 
             PositionHashHistory = new(1024) { CurrentPosition.UniqueIdentifier };
             HalfMovesWithoutCaptureOrPawnMove = parsedFen.HalfMoveClock;
-            _gameInitialPosition = new Position(CurrentPosition);
+            _gameInitialPosition = new Position(in CurrentPosition);
 #if DEBUG
             MoveHistory = new(1024);
 #endif
@@ -670,7 +670,7 @@ public ImprovedGame2(ReadOnlySpan<char> fen, ReadOnlySpan<char> rawMoves, Span<R
                     break;
                 }
                 var moveString = rawMoves[rangeSpan[i]];
-                var moveList = MoveGenerator.GenerateAllMoves(CurrentPosition, movePool);
+                var moveList = CurrentPosition.GenerateAllMoves(movePool);
 
                 if (!MoveExtensions.TryParseFromUCIString(moveString, moveList, out var parsedMove))
                 {
@@ -681,7 +681,7 @@ public ImprovedGame2(ReadOnlySpan<char> fen, ReadOnlySpan<char> rawMoves, Span<R
                 MakeMove(parsedMove.Value);
             }
 
-            _gameInitialPosition = new Position(CurrentPosition);
+            _gameInitialPosition = new Position(in CurrentPosition);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]

src/Lynx.Benchmark/PositionIdGeneration_Benchmark.cs

@@ -62,18 +62,18 @@ public string Id(Position newPosition)
     public static IEnumerable<Position> Data =>
     [
         //Constants.EmptyBoardFEN,
-        Positions[0].ClonePositionAndMakeMove(MoveGenerator.GenerateAllMoves(Positions[0])[0]),
-        Positions[1].ClonePositionAndMakeMove(MoveGenerator.GenerateAllMoves(Positions[1])[0]),
-        Positions[2].ClonePositionAndMakeMove(MoveGenerator.GenerateAllMoves(Positions[2])[0]),
-        Positions[3].ClonePositionAndMakeMove(MoveGenerator.GenerateAllMoves(Positions[3])[0])
+        Positions[0].ClonePositionAndMakeMove(Positions[0].GenerateAllMoves()[0]),
+        Positions[1].ClonePositionAndMakeMove(Positions[1].GenerateAllMoves()[0]),
+        Positions[2].ClonePositionAndMakeMove(Positions[2].GenerateAllMoves()[0]),
+        Positions[3].ClonePositionAndMakeMove(Positions[3].GenerateAllMoves()[0])
     ];
 }
 
 internal static class PositionExtensions
 {
     public static Position ClonePositionAndMakeMove(this Position position, Move move)
     {
-        var newPosition = new Position(position);
+        var newPosition = new Position(in position);
         newPosition.MakeMove(move);
 
         return newPosition;

src/Lynx.Benchmark/TryParseFromUCIString_Benchmark.cs

@@ -211,7 +211,7 @@ public TryParseFromUCIString_Benchmark_Game(ReadOnlySpan<char> fen, ReadOnlySpan
                     break;
                 }
                 var moveString = rawMoves[rangeSpan[i]];
-                var moveList = MoveGenerator.GenerateAllMoves(CurrentPosition, movePool);
+                var moveList = CurrentPosition.GenerateAllMoves(movePool);
 
                 if (!MoveExtensions.TryParseFromUCIString(moveString, moveList, out var parsedMove))
                 {

src/Lynx.Dev/Program.cs

@@ -383,7 +383,7 @@ static void _22_Generate_Moves()
     position.Print();
 
     //position.OccupancyBitBoards[2] |= 0b11100111UL << 8 * 4;
-    var moves = MoveGenerator.GenerateAllMoves(position);
+    var moves = position.GenerateAllMoves();
 
     foreach (var move in moves)
     {
@@ -394,7 +394,7 @@ static void _22_Generate_Moves()
     position.PieceBitBoards[0].Print();
     position.PieceBitBoards[6].Print();
     position.Print();
-    moves = MoveGenerator.GenerateAllMoves(position);
+    moves = position.GenerateAllMoves();
 
     foreach (var move in moves)
     {
@@ -423,10 +423,10 @@ static void _26_Piece_Moves()
     var position = new Position(TrickyPosition);
     position.Print();
 
-    var moves = MoveGenerator.GenerateAllMoves(position).Where(m => m.Piece() == (int)Piece.N || m.Piece() == (int)Piece.n).ToList();
+    var moves = position.GenerateAllMoves().Where(m => m.Piece() == (int)Piece.N || m.Piece() == (int)Piece.n).ToList();
     moves.ForEach(m => Console.WriteLine(m));
 
-    moves = [.. MoveGenerator.GenerateAllMoves(position)];
+    moves = [.. position.GenerateAllMoves()];
     Console.WriteLine($"Expected 48, found: {moves.Count}");
     foreach (var move in moves)
     {
@@ -482,16 +482,16 @@ static void PrintMoveList(IEnumerable<Move> moves)
 static void _29_Move_List()
 {
     var position = new Position(TrickyPosition);
-    var moves = MoveGenerator.GenerateAllMoves(position);
+    var moves = position.GenerateAllMoves();
     PrintMoveList(moves);
 
     position = new Position(TrickyPositionReversed);
-    moves = MoveGenerator.GenerateAllMoves(position);
+    moves = position.GenerateAllMoves();
     PrintMoveList(moves);
 
     position = new Position(KillerPosition);
     position.Print();
-    moves = MoveGenerator.GenerateAllMoves(position);
+    moves = position.GenerateAllMoves();
     PrintMoveList(moves);
 }
 
@@ -511,13 +511,13 @@ static void _32_Make_Move()
     //CastlingRightsTest(game);
     //CastlingRightsTest(reversedGame);
 
-    PrintMoveList(MoveGenerator.GenerateAllMoves(gameWithPromotion.CurrentPosition));
+    PrintMoveList(gameWithPromotion.CurrentPosition.GenerateAllMoves());
 
     GeneralMoveTest(gameWithPromotion);
 
     static void GeneralMoveTest(Game game)
     {
-        foreach (var move in MoveGenerator.GenerateAllMoves(game.CurrentPosition))
+        foreach (var move in game.CurrentPosition.GenerateAllMoves())
         {
             game.CurrentPosition.Print();
 
@@ -537,7 +537,7 @@ static void GeneralMoveTest(Game game)
 
     static void CastlingRightsTest(Game game)
     {
-        foreach (var move in MoveGenerator.GenerateAllMoves(game.CurrentPosition))
+        foreach (var move in game.CurrentPosition.GenerateAllMoves())
         {
             if (move.Piece() == (int)Piece.R || (move.Piece() == (int)Piece.r)
              || move.Piece() == (int)Piece.K || (move.Piece() == (int)Piece.k))
@@ -561,7 +561,7 @@ static void _42_Perft()
 
     for (int depth = 0; depth < 7; ++depth)
     {
-        Perft.RunPerft(pos, depth, Console.WriteLine);
+        pos.RunPerft(depth, Console.WriteLine);
     }
 }
 
@@ -583,7 +583,7 @@ static void _49_Rudimetary_Evaluation()
 
     //foreach (var move in MoveGenerator.GenerateAllMoves(position))
     //{
-    //    var newBlackPosition = new Position(position, move);
+    //    var newBlackPosition = new Position(in position, move);
     //    if (newBlackPosition.IsValid())
     //    {
     //        var newWhitePosition = new Position(newBlackPosition, newBlackPosition.AllPossibleMoves()[0]);
@@ -698,7 +698,7 @@ static void _54_ScoreMove()
 
     var engine = new Engine(Channel.CreateBounded<object>(new BoundedChannelOptions(100) { SingleReader = true, SingleWriter = false }));
     engine.SetGame(new(position.FEN()));
-    foreach (var move in MoveGenerator.GenerateAllMoves(position, capturesOnly: true))
+    foreach (var move in position.GenerateAllMoves(capturesOnly: true))
     {
         Console.WriteLine($"{move} {engine.ScoreMove(move, default, default)}");
     }
@@ -707,7 +707,7 @@ static void _54_ScoreMove()
     position.Print();
 
     engine.SetGame(new(position.FEN()));
-    foreach (var move in MoveGenerator.GenerateAllMoves(position, capturesOnly: true))
+    foreach (var move in position.GenerateAllMoves(capturesOnly: true))
     {
         Console.WriteLine($"{move} {engine.ScoreMove(move, default, default)}");
     }
@@ -718,7 +718,7 @@ static void ZobristTable()
     var pos = new Position(KillerPosition);
     var zobristTable = InitializeZobristTable();
     var hash = CalculatePositionHash(zobristTable, pos);
-    var updatedHash = UpdatePositionHash(zobristTable, hash, MoveGenerator.GenerateAllMoves(pos)[0]);
+    var updatedHash = UpdatePositionHash(zobristTable, hash, pos.GenerateAllMoves()[0]);
 
     Console.WriteLine(updatedHash);
 }
@@ -1079,30 +1079,30 @@ static void TesSize(int size)
 
     transpositionTable.Clear();
 
-    //transpositionTable.RecordHash(position, depth: 3, maxDepth: 5, move: 1234, eval: +5, nodeType: NodeType.Alpha);
-    //var entry = transpositionTable.ProbeHash(position, maxDepth: 5, depth: 3, alpha: 1, beta: 2);
+    //transpositionTable.RecordHash(in position, depth: 3, maxDepth: 5, move: 1234, eval: +5, nodeType: NodeType.Alpha);
+    //var entry = transpositionTable.ProbeHash(in position, maxDepth: 5, depth: 3, alpha: 1, beta: 2);
 
-    transpositionTable.RecordHash(position, position.StaticEvaluation().Score, depth: 5, ply: 3, score: +19, nodeType: NodeType.Alpha, move: 1234);
-    var entry = transpositionTable.ProbeHash(position, ply: 3);
+    transpositionTable.RecordHash(in position, position.StaticEvaluation().Score, depth: 5, ply: 3, score: +19, nodeType: NodeType.Alpha, move: 1234);
+    var entry = transpositionTable.ProbeHash(in position, ply: 3);
     Console.WriteLine(entry); // Expected 20
 
-    transpositionTable.RecordHash(position, position.StaticEvaluation().Score, depth: 5, ply: 3, score: +21, nodeType: NodeType.Alpha, move: 1234);
-    entry = transpositionTable.ProbeHash(position, ply: 3);
+    transpositionTable.RecordHash(in position, position.StaticEvaluation().Score, depth: 5, ply: 3, score: +21, nodeType: NodeType.Alpha, move: 1234);
+    entry = transpositionTable.ProbeHash(in position, ply: 3);
     Console.WriteLine(entry); // Expected 12_345_678
 
-    transpositionTable.RecordHash(position, position.StaticEvaluation().Score, depth: 5, ply: 3, score: +29, nodeType: NodeType.Beta, move: 1234);
-    entry = transpositionTable.ProbeHash(position, ply: 3);
+    transpositionTable.RecordHash(in position, position.StaticEvaluation().Score, depth: 5, ply: 3, score: +29, nodeType: NodeType.Beta, move: 1234);
+    entry = transpositionTable.ProbeHash(in position, ply: 3);
     Console.WriteLine(entry); // Expected 12_345_678
 
-    transpositionTable.RecordHash(position, position.StaticEvaluation().Score, depth: 5, ply: 3, score: +31, nodeType: NodeType.Beta, move: 1234);
-    entry = transpositionTable.ProbeHash(position, ply: 3);
+    transpositionTable.RecordHash(in position, position.StaticEvaluation().Score, depth: 5, ply: 3, score: +31, nodeType: NodeType.Beta, move: 1234);
+    entry = transpositionTable.ProbeHash(in position, ply: 3);
     Console.WriteLine(entry); // Expected 30
 }
 
 static void UnmakeMove()
 {
     var pos = new Position("r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq");
-    var a = Perft.PerftRecursiveImpl(pos, 1, default);
+    var a = pos.PerftRecursiveImpl(1, default);
 
     TestMoveGen(Constants.InitialPositionFEN);
     TestMoveGen(Constants.TTPositionFEN);
@@ -1115,15 +1115,15 @@ static void TestMoveGen(string fen)
         var position = new Position(fen);
         Console.WriteLine($"**Position\t{position.FEN()}, Zobrist key {position.UniqueIdentifier}**");
 
-        var allMoves = MoveGenerator.GenerateAllMoves(position);
+        var allMoves = position.GenerateAllMoves();
 
         var oldZobristKey = position.UniqueIdentifier;
         foreach (var move in allMoves)
         {
             var epdMoveString = move.ToEPDString(position);
             Console.WriteLine($"Trying {epdMoveString} in\t{position.FEN()}");
 
-            var newPosition = new Position(position);
+            var newPosition = new Position(in position);
             newPosition.MakeMove(move);
             var savedState = position.MakeMove(move);
 

src/Lynx/Model/Game.cs

@@ -28,7 +28,7 @@ public sealed class Game : IDisposable
 
     public int HalfMovesWithoutCaptureOrPawnMove { get; set; }
 
-    public Position CurrentPosition { get; private set; }
+    public Position CurrentPosition { get; set; }
 
     public Position PositionBeforeLastSearch { get; private set; }
 
@@ -66,7 +66,7 @@ public Game(ReadOnlySpan<char> fen, ReadOnlySpan<char> rawMoves, Span<Range> ran
                 break;
             }
             var moveString = rawMoves[rangeSpan[i]];
-            var moveList = MoveGenerator.GenerateAllMoves(CurrentPosition, movePool);
+            var moveList = CurrentPosition.GenerateAllMoves(movePool);
 
             // TODO: consider creating moves on the fly
             if (!MoveExtensions.TryParseFromUCIString(moveString, moveList, out var parsedMove))
@@ -159,7 +159,7 @@ public bool Is50MovesRepetition()
             return false;
         }
 
-        return !CurrentPosition.IsInCheck() || MoveGenerator.CanGenerateAtLeastAValidMove(CurrentPosition);
+        return !CurrentPosition.IsInCheck() || CurrentPosition.CanGenerateAtLeastAValidMove();
     }
 
     /// <summary>
@@ -190,9 +190,10 @@ public static bool IsThreefoldRepetition(ReadOnlySpan<ulong> positionHashHistory
     public static bool Is50MovesRepetition(int halfMovesWithoutCaptureOrPawnMove) => halfMovesWithoutCaptureOrPawnMove >= 100;
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public GameState MakeMove(Move moveToPlay)
+    public Position MakeMove(Move moveToPlay)
     {
-        var gameState = CurrentPosition.MakeMove(moveToPlay);
+        var oldPosition = CurrentPosition;
+        CurrentPosition = new Position(CurrentPosition, moveToPlay);
 
         if (CurrentPosition.WasProduceByAValidMove())
         {
@@ -205,10 +206,10 @@ public GameState MakeMove(Move moveToPlay)
         else
         {
             _logger.Warn("Error trying to play {0}", moveToPlay.UCIString());
-            CurrentPosition.UnmakeMove(moveToPlay, gameState);
+            CurrentPosition = oldPosition;
         }
 
-        return gameState;
+        return oldPosition;
     }
 
     /// <summary>

src/Lynx/Model/Move.cs

@@ -393,16 +393,17 @@ private static string DisambiguateMove(Move move, Position position)
         var targetSquare = move.TargetSquare();
 
         Span<Move> moves = stackalloc Move[Constants.MaxNumberOfPossibleMovesInAPosition];
-        var pseudoLegalMoves = MoveGenerator.GenerateAllMoves(position, moves).ToArray();
+        var pseudoLegalMoves = position.GenerateAllMoves(moves).ToArray();
 
         var movesWithSameSimpleRepresentation = pseudoLegalMoves
             .Where(m => m != move && m.Piece() == piece && m.TargetSquare() == targetSquare)
             .Where(m =>
             {
                 // If any illegal moves exist with the same simple representation there's no need to disambiguate
-                var gameState = position.MakeMove(m);
+                var oldPosition = position;
+                position = new Position(in position, m);
                 var isLegal = position.WasProduceByAValidMove();
-                position.UnmakeMove(m, gameState);
+                position = oldPosition;
 
                 return isLegal;
             })