error handling for position

src/position.rs

@@ -1,11 +1,13 @@
+use std::error::Error;
+
 #[derive(Debug, Eq, PartialEq)]
 pub struct Position {
     pub x: u8,
     pub y: u8,
 }
 
-impl From<String> for Position {
-    fn from(string: String) -> Position {
+impl Position {
+    pub(crate) fn from(string: String) -> Result<Position, &'static dyn Error> {
         // e.g. "2,5"
         let xy: Vec<&str> = string.split(',').collect();
         let x = xy[0].parse().unwrap();
@@ -16,7 +18,7 @@ impl From<String> for Position {
 
         let y = xy[1].parse().unwrap();
 
-        Position { x, y }
+        Ok(Position { x, y })
     }
 }
 
@@ -29,7 +31,7 @@ impl ToString for Position {
 
 #[test]
 fn test_position_from_string() {
-    assert_eq!(Position::from("4,12".to_string()), Position { x: 4, y: 12 });
+    assert_eq!(Position::from("4,12".to_string()).unwrap(), Position { x: 4, y: 12 });
 }
 
 #[test]