errors6 solution

exercises/13_error_handling/errors6.rs

@@ -1,52 +1,51 @@
-// Using catch-all error types like `Box<dyn error::Error>` isn't recommended
-// for library code, where callers might want to make decisions based on the
-// error content, instead of printing it out or propagating it further. Here, we
-// define a custom error type to make it possible for callers to decide what to
-// do next when our function returns an error.
+// Using catch-all error types like `Box<dyn Error>` isn't recommended for
+// library code where callers might want to make decisions based on the error
+// content instead of printing it out or propagating it further. Here, we define
+// a custom error type to make it possible for callers to decide what to do next
+// when our function returns an error.
 
 use std::num::ParseIntError;
 
-// This is a custom error type that we will be using in `parse_pos_nonzero()`.
-#[derive(PartialEq, Debug)]
-enum ParsePosNonzeroError {
-    Creation(CreationError),
-    ParseInt(ParseIntError),
-}
-
-impl ParsePosNonzeroError {
-    fn from_creation(err: CreationError) -> ParsePosNonzeroError {
-        ParsePosNonzeroError::Creation(err)
-    }
-    // TODO: add another error conversion function here.
-    // fn from_parseint...
-}
-
-fn parse_pos_nonzero(s: &str) -> Result<PositiveNonzeroInteger, ParsePosNonzeroError> {
-    // TODO: change this to return an appropriate error instead of panicking
-    // when `parse()` returns an error.
-    let x: i64 = s.parse().unwrap();
-    PositiveNonzeroInteger::new(x).map_err(ParsePosNonzeroError::from_creation)
-}
-
-// Don't change anything below this line.
-
-#[derive(PartialEq, Debug)]
-struct PositiveNonzeroInteger(u64);
-
 #[derive(PartialEq, Debug)]
 enum CreationError {
     Negative,
     Zero,
 }
 
+// A custom error type that we will be using in `PositiveNonzeroInteger::parse`.
+#[derive(PartialEq, Debug)]
+enum ParsePosNonzeroError {
+    Creation(CreationError),
+    ParseInt(ParseIntError),
+}
+
+impl ParsePosNonzeroError {
+    fn from_creation(err: CreationError) -> Self {
+        Self::Creation(err)
+    }
+
+    // TODO: Add another error conversion function here.
+    // fn from_parseint(???) -> Self { ??? }
+}
+
+#[derive(PartialEq, Debug)]
+struct PositiveNonzeroInteger(u64);
+
 impl PositiveNonzeroInteger {
-    fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> {
+    fn new(value: i64) -> Result<Self, CreationError> {
         match value {
             x if x < 0 => Err(CreationError::Negative),
             x if x == 0 => Err(CreationError::Zero),
-            x => Ok(PositiveNonzeroInteger(x as u64)),
+            x => Ok(Self(x as u64)),
         }
     }
+
+    fn parse(s: &str) -> Result<Self, ParsePosNonzeroError> {
+        // TODO: change this to return an appropriate error instead of panicking
+        // when `parse()` returns an error.
+        let x: i64 = s.parse().unwrap();
+        Self::new(x).map_err(ParsePosNonzeroError::from_creation)
+    }
 }
 
 fn main() {
@@ -56,36 +55,36 @@ fn main() {
 #[cfg(test)]
 mod test {
     use super::*;
+    use std::num::IntErrorKind;
 
     #[test]
     fn test_parse_error() {
-        // We can't construct a ParseIntError, so we have to pattern match.
         assert!(matches!(
-            parse_pos_nonzero("not a number"),
-            Err(ParsePosNonzeroError::ParseInt(_))
+            PositiveNonzeroInteger::parse("not a number"),
+            Err(ParsePosNonzeroError::ParseInt(_)),
         ));
     }
 
     #[test]
     fn test_negative() {
         assert_eq!(
-            parse_pos_nonzero("-555"),
-            Err(ParsePosNonzeroError::Creation(CreationError::Negative))
+            PositiveNonzeroInteger::parse("-555"),
+            Err(ParsePosNonzeroError::Creation(CreationError::Negative)),
         );
     }
 
     #[test]
     fn test_zero() {
         assert_eq!(
-            parse_pos_nonzero("0"),
-            Err(ParsePosNonzeroError::Creation(CreationError::Zero))
+            PositiveNonzeroInteger::parse("0"),
+            Err(ParsePosNonzeroError::Creation(CreationError::Zero)),
         );
     }
 
     #[test]
     fn test_positive() {
-        let x = PositiveNonzeroInteger::new(42);
-        assert!(x.is_ok());
-        assert_eq!(parse_pos_nonzero("42"), Ok(x.unwrap()));
+        let x = PositiveNonzeroInteger::new(42).unwrap();
+        assert_eq!(x.0, 42);
+        assert_eq!(PositiveNonzeroInteger::parse("42"), Ok(x));
     }
 }