[core] Improve API of Shape and Color

Clean up type and method declarations by using better type spelling. Use more
standard method spelling for iterators. Implement some useful traits.

core/src/colors.rs

@@ -17,10 +17,14 @@ impl Color {
     /// Slice of all possible colors
     pub const ALL: [Color; Color::NUM] = [Color::White, Color::Black];
 
-    pub fn iter() -> impl Iterator<Item = &'static Color> {
+    pub fn iter() -> std::slice::Iter<'static, Color> {
         Color::ALL.iter()
     }
 
+    pub fn into_iter() -> std::array::IntoIter<Color, { Self::NUM }> {
+        Color::ALL.into_iter()
+    }
+
     /// The other color
     #[must_use]
     pub const fn other(&self) -> Color {

core/src/pieces.rs

@@ -1,7 +1,7 @@
 // Eryn Wells <eryn@erynwells.me>
 
 use crate::{errors::TryFromCharError, try_from_string, Color, Square};
-use std::{fmt, slice::Iter};
+use std::{array, fmt, slice};
 
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub enum Shape {
@@ -14,7 +14,11 @@ pub enum Shape {
 }
 
 impl Shape {
-    pub const ALL: [Shape; 6] = [
+    /// Number of piece shapes
+    pub const NUM: usize = 6;
+
+    /// A slice of all piece shapes
+    pub const ALL: [Shape; Self::NUM] = [
         Shape::Pawn,
         Shape::Knight,
         Shape::Bishop,
@@ -23,11 +27,16 @@ impl Shape {
         Shape::King,
     ];
 
-    pub fn iter() -> Iter<'static, Shape> {
+    pub fn iter() -> slice::Iter<'static, Self> {
         Shape::ALL.iter()
     }
 
-    pub fn promotable() -> Iter<'static, Shape> {
+    pub fn into_iter() -> array::IntoIter<Self, { Self::NUM }> {
+        Shape::ALL.into_iter()
+    }
+
+    /// An iterator over the shapes that a pawn can promote to
+    pub fn promotable() -> slice::Iter<'static, Shape> {
         const PROMOTABLE_SHAPES: [Shape; 4] =
             [Shape::Queen, Shape::Rook, Shape::Bishop, Shape::Knight];
 
@@ -64,15 +73,15 @@ impl TryFrom<char> for Shape {
 
 try_from_string!(Shape);
 
-impl Into<char> for &Shape {
-    fn into(self) -> char {
-        self.to_ascii()
+impl From<&Shape> for char {
+    fn from(shape: &Shape) -> char {
+        char::from(*shape)
     }
 }
 
-impl Into<char> for Shape {
-    fn into(self) -> char {
-        self.to_ascii()
+impl From<Shape> for char {
+    fn from(shape: Shape) -> char {
+        shape.to_ascii()
     }
 }
 
@@ -174,6 +183,18 @@ impl fmt::Display for Piece {
     }
 }
 
+impl From<PlacedPiece> for Piece {
+    fn from(value: PlacedPiece) -> Self {
+        value.piece
+    }
+}
+
+impl From<&PlacedPiece> for Piece {
+    fn from(value: &PlacedPiece) -> Self {
+        value.piece
+    }
+}
+
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub struct PlacedPiece {
     piece: Piece,
@@ -198,8 +219,8 @@ impl PlacedPiece {
     /// The [Piece] itself
     #[inline]
     #[must_use]
-    pub fn piece(&self) -> &Piece {
-        &self.piece
+    pub fn piece(&self) -> Piece {
+        self.piece
     }
 
     /// The square the piece is on