abstract away more coordinates

src/repr/coords.rs

@@ -0,0 +1,63 @@
+use std::fmt::Display;
+
+use super::Board;
+use static_assertions::const_assert;
+
+// PERF! having `Coord` be of type `u8` (instead of usize) increases
+// performance by about 1-2% overall
+pub type CoordAxis = u8;
+
+pub type CoordPairInner = u8;
+
+const_assert!(CoordPairInner::MAX as usize >= Board::BOARD_AREA as usize);
+
+#[derive(PartialEq, Eq, Copy, Clone, Hash)]
+pub struct CoordPair(pub CoordPairInner);
+
+impl Display for CoordPair {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let (i, j) = (*self).into();
+        write!(f, "({}, {})", i, j)
+    }
+}
+
+impl std::fmt::Debug for CoordPair {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self)
+    }
+}
+
+/// Convert a row and column to an index in the board
+pub const fn get_index(row: CoordAxis, col: CoordAxis) -> CoordPair {
+    CoordPair(row * Board::BOARD_SIZE + col)
+}
+
+pub const fn from_index(index: CoordPair) -> (CoordAxis, CoordAxis) {
+    let row = index.0 % Board::BOARD_SIZE;
+    let col = (index.0 - row) / Board::BOARD_SIZE;
+    (col, row)
+}
+
+impl From<(CoordAxis, CoordAxis)> for CoordPair {
+    fn from(value: (CoordAxis, CoordAxis)) -> Self {
+        get_index(value.0, value.1)
+    }
+}
+
+impl From<CoordPair> for (CoordAxis, CoordAxis) {
+    fn from(val: CoordPair) -> Self {
+        from_index(val)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn into_outof() {
+        let a: CoordPair = (1, 3).into();
+        let back: (CoordAxis, CoordAxis) = a.into();
+        assert_eq!(back, (1, 3));
+    }
+}