make square frozen

RobO-Softwire · RobO-Softwire · commit b69391994455 · 2020-06-17T14:42:44.000+01:00
diff --git a/chessington/engine/data.py b/chessington/engine/data.py
@@ -16,7 +16,7 @@ def opponent(self):
         else: return Player.WHITE
 
 
-@dataclass
+@dataclass(frozen=True)
 class Square:
     row: int
     col: int
