Board::what_if use Result

src/board.rs

@@ -234,14 +234,14 @@ impl Board {
 
     /// Return a modified [`Board`] with the piece placed at a position
     /// Returns None if the move was invalid
-    pub fn what_if(&self, i: usize, j: usize, piece: Piece) -> Option<Self> {
+    pub fn what_if(&self, i: usize, j: usize, piece: Piece) -> Result<Self, &'static str> {
         // extract check here to avoid copy
         if self.get(i, j).is_some() {
-            return None;
+            return Err("position is occupied");
         }
 
         let mut self_copy = *self;
-        self_copy.place(i, j, piece).ok().map(|_| self_copy)
+        self_copy.place(i, j, piece).map(|_| self_copy)
     }
 
     /// Returns a bool which represents whether or not a move would propegate and be valid