hmm

src/board.rs

@@ -146,8 +146,16 @@ impl Board {
 
         let mut chains: Vec<Vec<(usize, usize)>> = Vec::with_capacity(8);
 
-        chains.extend(i_chain.map(|range| range.map(|i| (i, j)).collect()));
-        chains.extend(j_chain.map(|range| range.map(|j| (i, j)).collect()));
+        chains.extend(
+            i_chain
+                .map(|range| range.map(move |i| (i, j)))
+                .map(Iterator::collect),
+        );
+        chains.extend(
+            j_chain
+                .map(|range| range.map(move |j| (i, j)))
+                .map(Iterator::collect),
+        );
 
         // handle diagonals
         chains.extend(diag(i, j, 0, 0, BOARD_SIZE - 1, BOARD_SIZE - 1).map(Iterator::collect));