Ensure MoveTree.Node is sendable

Sources/ChessKit/MoveTree/MoveTree.swift

@@ -3,6 +3,8 @@
 //  ChessKit
 //
 
+import Foundation
+
 /// A tree-like data structure that represents the moves of a chess game.
 ///
 /// The tree maintains the move order including variations and
@@ -27,6 +29,10 @@ public struct MoveTree: Hashable, Sendable {
     Array(dictionary.keys)
   }
 
+  /// Lock to restrict modification of tree nodes
+  /// to ensure `Sendable` conformance for ``Node``.
+  private static let nodeLock = NSLock()
+
   /// Adds a move to the move tree.
   ///
   /// - parameter move: The move to add to the tree.
@@ -67,7 +73,9 @@ public struct MoveTree: Hashable, Sendable {
       }
     }
 
-    dictionary[newIndex] = newNode
+    Self.nodeLock.withLock {
+      dictionary[newIndex] = newNode
+    }
     newNode.index = newIndex
 
     if newIndex.variation == Index.mainVariation {
@@ -257,8 +265,10 @@ public struct MoveTree: Hashable, Sendable {
     assessment: Move.Assessment = .null,
     comment: String = ""
   ) -> Move? {
-    dictionary[index]?.move.assessment = assessment
-    dictionary[index]?.move.comment = comment
+    Self.nodeLock.withLock {
+      dictionary[index]?.move.assessment = assessment
+      dictionary[index]?.move.comment = comment
+    }
     return dictionary[index]?.move
   }
 
@@ -343,7 +353,7 @@ extension MoveTree: Equatable {
 extension MoveTree {
 
   /// Object that represents a node in the move tree.
-  final class Node: Hashable, @unchecked Sendable {
+  class Node: Hashable, @unchecked Sendable {
 
     /// The move for this node.
     var move: Move

Tests/ChessKitTests/MoveTreeTests.swift

@@ -27,6 +27,14 @@ final class MoveTreeTests: XCTestCase {
     XCTAssertEqual(moveTree[.minimum.next], e4)
   }
 
+  func testNodeHashValue() {
+    var moveTree = MoveTree()
+    let e4 = Move(san: "e4", position: .standard)
+    moveTree[.minimum.next] = e4
+    print(moveTree.dictionary[.minimum.next]?.hashValue)
+    XCTAssertNotNil(moveTree.dictionary[.minimum.next]?.hashValue)
+  }
+
   func testSameVariationComparability() {
     let wIndex = MoveTree.Index(number: 4, color: .white, variation: 2)
     XCTAssertLessThan(wIndex, wIndex.next)