diff --git a/bitboard/src/bitboard.rs b/bitboard/src/bitboard.rs
index fa91c16..6bc3f38 100644
--- a/bitboard/src/bitboard.rs
+++ b/bitboard/src/bitboard.rs
@@ -22,18 +22,18 @@ impl BitBoard {
         BitBoard(0)
     }
 
-    pub fn new(bits: u64) -> BitBoard {
+    pub const fn new(bits: u64) -> BitBoard {
         BitBoard(bits)
     }
 
-    pub fn rank(rank: usize) -> BitBoard {
-        assert!(rank < 8);
-        RANKS[rank]
+    pub fn rank(rank: &u8) -> BitBoard {
+        debug_assert!(*rank < 8);
+        RANKS[*rank as usize]
     }
 
-    pub fn file(file: usize) -> BitBoard {
-        assert!(file < 8);
-        FILES[file]
+    pub fn file(file: &u8) -> BitBoard {
+        debug_assert!(*file < 8);
+        FILES[*file as usize]
     }
 
     pub fn ray(sq: Square, dir: Direction) -> BitBoard {
@@ -56,6 +56,10 @@ impl BitBoard {
 }
 
 impl BitBoard {
+    pub fn as_bits(&self) -> &u64 {
+        &self.0
+    }
+
     pub fn is_empty(&self) -> bool {
         self.0 == 0
     }
@@ -255,21 +259,22 @@ mod tests {
     use chessfriend_core::Square;
 
     #[test]
+    #[ignore]
     fn display_and_debug() {
-        let bb = BitBoard::file(0) | BitBoard::file(3) | BitBoard::rank(7) | BitBoard::rank(4);
+        let bb = BitBoard::file(&0) | BitBoard::file(&3) | BitBoard::rank(&7) | BitBoard::rank(&4);
         println!("{}", &bb);
     }
 
     #[test]
     fn rank() {
-        assert_eq!(BitBoard::rank(0).0, 0xFF, "Rank 1");
-        assert_eq!(BitBoard::rank(1).0, 0xFF00, "Rank 2");
-        assert_eq!(BitBoard::rank(2).0, 0xFF0000, "Rank 3");
-        assert_eq!(BitBoard::rank(3).0, 0xFF000000, "Rank 4");
-        assert_eq!(BitBoard::rank(4).0, 0xFF00000000, "Rank 5");
-        assert_eq!(BitBoard::rank(5).0, 0xFF0000000000, "Rank 6");
-        assert_eq!(BitBoard::rank(6).0, 0xFF000000000000, "Rank 7");
-        assert_eq!(BitBoard::rank(7).0, 0xFF00000000000000, "Rank 8");
+        assert_eq!(BitBoard::rank(&0).0, 0xFF, "Rank 1");
+        assert_eq!(BitBoard::rank(&1).0, 0xFF00, "Rank 2");
+        assert_eq!(BitBoard::rank(&2).0, 0xFF0000, "Rank 3");
+        assert_eq!(BitBoard::rank(&3).0, 0xFF000000, "Rank 4");
+        assert_eq!(BitBoard::rank(&4).0, 0xFF00000000, "Rank 5");
+        assert_eq!(BitBoard::rank(&5).0, 0xFF0000000000, "Rank 6");
+        assert_eq!(BitBoard::rank(&6).0, 0xFF000000000000, "Rank 7");
+        assert_eq!(BitBoard::rank(&7).0, 0xFF00000000000000, "Rank 8");
     }
 
     #[test]