Merge pull request #781 from tlyu/advanced-errs

feature: advanced errors

2 files changed, 95 insertions, 35 deletions

diff --git a/exercises/conversions/from_str.rs b/exercises/conversions/from_str.rs
index 93a5299..ece0b3c 100644
--- a/exercises/conversions/from_str.rs
+++ b/exercises/conversions/from_str.rs
@@ -1,16 +1,31 @@
-// This does practically the same thing that TryFrom<&str> does.
+// from_str.rs
+// This is similar to from_into.rs, but this time we'll implement `FromStr`
+// and return errors instead of falling back to a default value.
 // Additionally, upon implementing FromStr, you can use the `parse` method
 // on strings to generate an object of the implementor type.
 // You can read more about it at https://doc.rust-lang.org/std/str/trait.FromStr.html
-use std::error;
+use std::num::ParseIntError;
 use std::str::FromStr;
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq)]
 struct Person {
     name: String,
     age: usize,
 }
 
+// We will use this error type for the `FromStr` implementation.
+#[derive(Debug, PartialEq)]
+enum ParsePersonError {
+    // Empty input string
+    Empty,
+    // Incorrect number of fields
+    BadLen,
+    // Empty name field
+    NoName,
+    // Wrapped error from parse::<usize>()
+    ParseInt(ParseIntError),
+}
+
 // I AM NOT DONE
 
 // Steps:
@@ -24,7 +39,7 @@ struct Person {
 // If everything goes well, then return a Result of a Person object
 
 impl FromStr for Person {
-    type Err = Box<dyn error::Error>;
+    type Err = ParsePersonError;
     fn from_str(s: &str) -> Result<Person, Self::Err> {
     }
 }
@@ -40,7 +55,7 @@ mod tests {
 
     #[test]
     fn empty_input() {
-        assert!("".parse::<Person>().is_err());
+        assert_eq!("".parse::<Person>(), Err(ParsePersonError::Empty));
     }
     #[test]
     fn good_input() {
@@ -52,41 +67,56 @@ mod tests {
     }
     #[test]
     fn missing_age() {
-        assert!("John,".parse::<Person>().is_err());
+        assert!(matches!(
+            "John,".parse::<Person>(),
+            Err(ParsePersonError::ParseInt(_))
+        ));
     }
 
     #[test]
     fn invalid_age() {
-        assert!("John,twenty".parse::<Person>().is_err());
+        assert!(matches!(
+            "John,twenty".parse::<Person>(),
+            Err(ParsePersonError::ParseInt(_))
+        ));
     }
 
     #[test]
     fn missing_comma_and_age() {
-        assert!("John".parse::<Person>().is_err());
+        assert_eq!("John".parse::<Person>(), Err(ParsePersonError::BadLen));
     }
 
     #[test]
     fn missing_name() {
-        assert!(",1".parse::<Person>().is_err());
+        assert_eq!(",1".parse::<Person>(), Err(ParsePersonError::NoName));
     }
 
     #[test]
     fn missing_name_and_age() {
-        assert!(",".parse::<Person>().is_err());
+        assert!(matches!(
+            ",".parse::<Person>(),
+            Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
+        ));
     }
 
     #[test]
     fn missing_name_and_invalid_age() {
-        assert!(",one".parse::<Person>().is_err());
+        assert!(matches!(
+            ",one".parse::<Person>(),
+            Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
+        ));
     }
 
     #[test]
     fn trailing_comma() {
-        assert!("John,32,".parse::<Person>().is_err());
+        assert_eq!("John,32,".parse::<Person>(), Err(ParsePersonError::BadLen));
     }
 
     #[test]
     fn trailing_comma_and_some_string() {
-        assert!("John,32,man".parse::<Person>().is_err());
+        assert_eq!(
+            "John,32,man".parse::<Person>(),
+            Err(ParsePersonError::BadLen)
+        );
     }
 }
diff --git a/exercises/conversions/try_from_into.rs b/exercises/conversions/try_from_into.rs
index c0b5d98..b8ec445 100644
--- a/exercises/conversions/try_from_into.rs
+++ b/exercises/conversions/try_from_into.rs
@@ -1,9 +1,9 @@
+// try_from_into.rs
 // TryFrom is a simple and safe type conversion that may fail in a controlled way under some circumstances.
 // Basically, this is the same as From. The main difference is that this should return a Result type
 // instead of the target type itself.
 // You can read more about it at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
 use std::convert::{TryFrom, TryInto};
-use std::error;
 
 #[derive(Debug, PartialEq)]
 struct Color {
@@ -12,12 +12,21 @@ struct Color {
     blue: u8,
 }
 
+// We will use this error type for these `TryFrom` conversions.
+#[derive(Debug, PartialEq)]
+enum IntoColorError {
+    // Incorrect length of slice
+    BadLen,
+    // Integer conversion error
+    IntConversion,
+}
+
 // I AM NOT DONE
 
 // Your task is to complete this implementation
 // and return an Ok result of inner type Color.
 // You need to create an implementation for a tuple of three integers,
-// an array of three integers and a slice of integers.
+// an array of three integers, and a slice of integers.
 //
 // Note that the implementation for tuple and array will be checked at compile time,
 // but the slice implementation needs to check the slice length!
@@ -25,20 +34,23 @@ struct Color {
 
 // Tuple implementation
 impl TryFrom<(i16, i16, i16)> for Color {
-    type Error = Box<dyn error::Error>;
-    fn try_from(tuple: (i16, i16, i16)) -> Result<Self, Self::Error> {}
+    type Error = IntoColorError;
+    fn try_from(tuple: (i16, i16, i16)) -> Result<Self, Self::Error> {
+    }
 }
 
 // Array implementation
 impl TryFrom<[i16; 3]> for Color {
-    type Error = Box<dyn error::Error>;
-    fn try_from(arr: [i16; 3]) -> Result<Self, Self::Error> {}
+    type Error = IntoColorError;
+    fn try_from(arr: [i16; 3]) -> Result<Self, Self::Error> {
+    }
 }
 
 // Slice implementation
 impl TryFrom<&[i16]> for Color {
-    type Error = Box<dyn error::Error>;
-    fn try_from(slice: &[i16]) -> Result<Self, Self::Error> {}
+    type Error = IntoColorError;
+    fn try_from(slice: &[i16]) -> Result<Self, Self::Error> {
+    }
 }
 
 fn main() {
@@ -46,15 +58,15 @@ fn main() {
     let c1 = Color::try_from((183, 65, 14));
     println!("{:?}", c1);
 
-    // Since From is implemented for Color, we should be able to use Into
+    // Since TryFrom is implemented for Color, we should be able to use TryInto
     let c2: Result<Color, _> = [183, 65, 14].try_into();
     println!("{:?}", c2);
 
     let v = vec![183, 65, 14];
-    // With slice we should use `from` function
+    // With slice we should use `try_from` function
     let c3 = Color::try_from(&v[..]);
     println!("{:?}", c3);
-    // or take slice within round brackets and use Into
+    // or take slice within round brackets and use TryInto
     let c4: Result<Color, _> = (&v[..]).try_into();
     println!("{:?}", c4);
 }
@@ -65,15 +77,24 @@ mod tests {
 
     #[test]
     fn test_tuple_out_of_range_positive() {
-        assert!(Color::try_from((256, 1000, 10000)).is_err());
+        assert_eq!(
+            Color::try_from((256, 1000, 10000)),
+            Err(IntoColorError::IntConversion)
+        );
     }
     #[test]
     fn test_tuple_out_of_range_negative() {
-        assert!(Color::try_from((-1, -10, -256)).is_err());
+        assert_eq!(
+            Color::try_from((-1, -10, -256)),
+            Err(IntoColorError::IntConversion)
+        );
     }
     #[test]
     fn test_tuple_sum() {
-        assert!(Color::try_from((-1, 255, 255)).is_err());
+        assert_eq!(
+            Color::try_from((-1, 255, 255)),
+            Err(IntoColorError::IntConversion)
+        );
     }
     #[test]
     fn test_tuple_correct() {
@@ -91,17 +112,17 @@ mod tests {
     #[test]
     fn test_array_out_of_range_positive() {
         let c: Result<Color, _> = [1000, 10000, 256].try_into();
-        assert!(c.is_err());
+        assert_eq!(c, Err(IntoColorError::IntConversion));
     }
     #[test]
     fn test_array_out_of_range_negative() {
         let c: Result<Color, _> = [-10, -256, -1].try_into();
-        assert!(c.is_err());
+        assert_eq!(c, Err(IntoColorError::IntConversion));
     }
     #[test]
     fn test_array_sum() {
         let c: Result<Color, _> = [-1, 255, 255].try_into();
-        assert!(c.is_err());
+        assert_eq!(c, Err(IntoColorError::IntConversion));
     }
     #[test]
     fn test_array_correct() {
@@ -119,17 +140,26 @@ mod tests {
     #[test]
     fn test_slice_out_of_range_positive() {
         let arr = [10000, 256, 1000];
-        assert!(Color::try_from(&arr[..]).is_err());
+        assert_eq!(
+            Color::try_from(&arr[..]),
+            Err(IntoColorError::IntConversion)
+        );
     }
     #[test]
     fn test_slice_out_of_range_negative() {
         let arr = [-256, -1, -10];
-        assert!(Color::try_from(&arr[..]).is_err());
+        assert_eq!(
+            Color::try_from(&arr[..]),
+            Err(IntoColorError::IntConversion)
+        );
     }
     #[test]
     fn test_slice_sum() {
         let arr = [-1, 255, 255];
-        assert!(Color::try_from(&arr[..]).is_err());
+        assert_eq!(
+            Color::try_from(&arr[..]),
+            Err(IntoColorError::IntConversion)
+        );
     }
     #[test]
     fn test_slice_correct() {
@@ -148,11 +178,11 @@ mod tests {
     #[test]
     fn test_slice_excess_length() {
         let v = vec![0, 0, 0, 0];
-        assert!(Color::try_from(&v[..]).is_err());
+        assert_eq!(Color::try_from(&v[..]), Err(IntoColorError::BadLen));
     }
     #[test]
     fn test_slice_insufficient_length() {
         let v = vec![0, 0];
-        assert!(Color::try_from(&v[..]).is_err());
+        assert_eq!(Color::try_from(&v[..]), Err(IntoColorError::BadLen));
     }
 }