errors4 solution

exercises/13_error_handling/errors4.rs

@@ -1,16 +1,16 @@
-#[derive(PartialEq, Debug)]
-struct PositiveNonzeroInteger(u64);
-
 #[derive(PartialEq, Debug)]
 enum CreationError {
     Negative,
     Zero,
 }
 
+#[derive(PartialEq, Debug)]
+struct PositiveNonzeroInteger(u64);
+
 impl PositiveNonzeroInteger {
-    fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> {
-        // Hmm... Why is this always returning an Ok value?
-        Ok(PositiveNonzeroInteger(value as u64))
+    fn new(value: i64) -> Result<Self, CreationError> {
+        // TODO: This function shouldn't always return an `Ok`.
+        Ok(Self(value as u64))
     }
 }
 
@@ -24,11 +24,14 @@ mod tests {
 
     #[test]
     fn test_creation() {
-        assert!(PositiveNonzeroInteger::new(10).is_ok());
         assert_eq!(
-            Err(CreationError::Negative),
-            PositiveNonzeroInteger::new(-10)
+            PositiveNonzeroInteger::new(10),
+            Ok(PositiveNonzeroInteger(10)),
         );
-        assert_eq!(Err(CreationError::Zero), PositiveNonzeroInteger::new(0));
+        assert_eq!(
+            PositiveNonzeroInteger::new(-10),
+            Err(CreationError::Negative),
+        );
+        assert_eq!(PositiveNonzeroInteger::new(0), Err(CreationError::Zero));
     }
 }