error handling for position

src/position.rs

@@ -1,4 +1,7 @@
 use std::error::Error;
+use std::fmt;
+use std::fmt::Formatter;
+use std::str::FromStr;
 
 #[derive(Debug, Eq, PartialEq)]
 pub struct Position {
@@ -6,9 +9,14 @@ pub struct Position {
     pub y: u8,
 }
 
-impl Position {
-    #[inline]
-    pub(crate) fn from(string: String) -> Result<Position, &'static dyn Error> {
+impl Error for Position {}
+
+impl FromStr for Position {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let string = s.to_string();
+
         // e.g. "2,5"
         let xy: Vec<&str> = string.split(',').collect();
         let x = xy[0].parse().expect("Bad x coordinate supplied for Position");
@@ -23,21 +31,22 @@ impl Position {
     }
 }
 
-impl ToString for Position {
+impl fmt::Display for Position {
     #[inline]
-    fn to_string(&self) -> String {
-        format!("{},{}", self.x, self.y)
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{},{}", self.x, self.y)
     }
 }
 
 #[cfg(test)]
 mod test {
     use crate::position::Position;
+    use std::str::FromStr;
 
     #[test]
-    fn test_position_from_string() {
+    fn test_position_from_str() {
         assert_eq!(
-            Position::from("4,12".to_string()).unwrap(),
+            Position::from_str(&"4,12").unwrap(),
             Position { x: 4, y: 12 }
         );
     }