Update Exercises Directory Names to Reflect Order

exercises/23_conversions/from_str.rs

@@ -0,0 +1,133 @@
+// 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
+//
+// Execute `rustlings hint from_str` or use the `hint` watch subcommand for a
+// hint.
+
+use std::num::ParseIntError;
+use std::str::FromStr;
+
+#[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:
+// 1. If the length of the provided string is 0, an error should be returned
+// 2. Split the given string on the commas present in it
+// 3. Only 2 elements should be returned from the split, otherwise return an
+//    error
+// 4. Extract the first element from the split operation and use it as the name
+// 5. Extract the other element from the split operation and parse it into a
+//    `usize` as the age with something like `"4".parse::<usize>()`
+// 6. If while extracting the name and the age something goes wrong, an error
+//    should be returned
+// If everything goes well, then return a Result of a Person object
+//
+// As an aside: `Box<dyn Error>` implements `From<&'_ str>`. This means that if
+// you want to return a string error message, you can do so via just using
+// return `Err("my error message".into())`.
+
+impl FromStr for Person {
+    type Err = ParsePersonError;
+    fn from_str(s: &str) -> Result<Person, Self::Err> {
+    }
+}
+
+fn main() {
+    let p = "Mark,20".parse::<Person>().unwrap();
+    println!("{:?}", p);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn empty_input() {
+        assert_eq!("".parse::<Person>(), Err(ParsePersonError::Empty));
+    }
+    #[test]
+    fn good_input() {
+        let p = "John,32".parse::<Person>();
+        assert!(p.is_ok());
+        let p = p.unwrap();
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 32);
+    }
+    #[test]
+    fn missing_age() {
+        assert!(matches!(
+            "John,".parse::<Person>(),
+            Err(ParsePersonError::ParseInt(_))
+        ));
+    }
+
+    #[test]
+    fn invalid_age() {
+        assert!(matches!(
+            "John,twenty".parse::<Person>(),
+            Err(ParsePersonError::ParseInt(_))
+        ));
+    }
+
+    #[test]
+    fn missing_comma_and_age() {
+        assert_eq!("John".parse::<Person>(), Err(ParsePersonError::BadLen));
+    }
+
+    #[test]
+    fn missing_name() {
+        assert_eq!(",1".parse::<Person>(), Err(ParsePersonError::NoName));
+    }
+
+    #[test]
+    fn missing_name_and_age() {
+        assert!(matches!(
+            ",".parse::<Person>(),
+            Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
+        ));
+    }
+
+    #[test]
+    fn missing_name_and_invalid_age() {
+        assert!(matches!(
+            ",one".parse::<Person>(),
+            Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
+        ));
+    }
+
+    #[test]
+    fn trailing_comma() {
+        assert_eq!("John,32,".parse::<Person>(), Err(ParsePersonError::BadLen));
+    }
+
+    #[test]
+    fn trailing_comma_and_some_string() {
+        assert_eq!(
+            "John,32,man".parse::<Person>(),
+            Err(ParsePersonError::BadLen)
+        );
+    }
+}