Add 'Piece' enum

src/board/mod.rs

@@ -13,6 +13,9 @@ pub use direction::*;
 pub mod file;
 pub use file::*;
 
+pub mod piece;
+pub use piece::*;
+
 pub mod rank;
 pub use rank::*;
 

src/board/piece.rs

@@ -0,0 +1,72 @@
+/// An enum representing the type of a piece.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum Piece {
+    King,
+    Queen,
+    Rook,
+    Bishop,
+    Knight,
+    Pawn,
+}
+
+impl Piece {
+    /// The number of [Piece] variants.
+    pub const NUM_VARIANTS: usize = 6;
+
+    const ALL: [Self; Self::NUM_VARIANTS] = [
+        Self::King,
+        Self::Queen,
+        Self::Rook,
+        Self::Bishop,
+        Self::Knight,
+        Self::Pawn,
+    ];
+
+    /// Iterate over all piece types.
+    pub fn iter() -> impl Iterator<Item = Self> {
+        Self::ALL.iter().cloned()
+    }
+
+    /// Convert from a piece index into a [Piece] type.
+    #[inline(always)]
+    pub fn from_index(index: usize) -> Self {
+        assert!(index < Self::NUM_VARIANTS);
+        // SAFETY: we know the value is in-bounds
+        unsafe { Self::from_index_unchecked(index) }
+    }
+
+    /// Convert from a piece index into a [Piece] type, no bounds checking.
+    ///
+    /// # Safety
+    ///
+    /// Should only be called with values that can be output by [Piece::index()].
+    #[inline(always)]
+    pub unsafe fn from_index_unchecked(index: usize) -> Self {
+        std::mem::transmute(index as u8)
+    }
+
+    /// Return the index of a given [Piece].
+    #[inline(always)]
+    pub fn index(self) -> usize {
+        self as usize
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn from_index() {
+        assert_eq!(Piece::from_index(0), Piece::King);
+        assert_eq!(Piece::from_index(1), Piece::Queen);
+        assert_eq!(Piece::from_index(5), Piece::Pawn);
+    }
+
+    #[test]
+    fn index() {
+        assert_eq!(Piece::King.index(), 0);
+        assert_eq!(Piece::Queen.index(), 1);
+        assert_eq!(Piece::Pawn.index(), 5);
+    }
+}