// 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,
}

#[derive(Debug, PartialEq)]
enum ParsePersonError {
    Empty,
    BadLen,
    NoName,
    ParseInt(ParseIntError),
}

impl FromStr for Person {
    type Err = ParsePersonError;
    fn from_str(s: &str) -> Result<Person, Self::Err> {
        // 1. 检查输入字符串是否为空
        if s.is_empty() {
            return Err(ParsePersonError::Empty);
        }

        // 2. 按逗号分割字符串并收集结果
        let parts: Vec<&str> = s.split(',').collect();

        // 3. 检查分割后的部分数量是否为2
        if parts.len() != 2 {
            return Err(ParsePersonError::BadLen);
        }

        // 4. 提取姓名并检查是否为空
        let name = parts[0].trim();
        if name.is_empty() {
            return Err(ParsePersonError::NoName);
        }

        // 5. 解析年龄并处理可能的错误
        let age = parts[1].trim().parse().map_err(ParsePersonError::ParseInt)?;

        // 6. 成功解析，返回Person实例
        Ok(Person {
            name: name.to_string(),
            age,
        })
    }
}

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)
        );
    }
}

Author: unix-dot

exercises/conversions/from_str.rs

@@ -18,40 +18,44 @@ struct Person {
     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> {
+        // 1. 检查输入字符串是否为空
+        if s.is_empty() {
+            return Err(ParsePersonError::Empty);
+        }
+
+        // 2. 按逗号分割字符串并收集结果
+        let parts: Vec<&str> = s.split(',').collect();
+
+        // 3. 检查分割后的部分数量是否为2
+        if parts.len() != 2 {
+            return Err(ParsePersonError::BadLen);
+        }
+
+        // 4. 提取姓名并检查是否为空
+        let name = parts[0].trim();
+        if name.is_empty() {
+            return Err(ParsePersonError::NoName);
+        }
+
+        // 5. 解析年龄并处理可能的错误
+        let age = parts[1].trim().parse().map_err(ParsePersonError::ParseInt)?;
+
+        // 6. 成功解析，返回Person实例
+        Ok(Person {
+            name: name.to_string(),
+            age,
+        })
     }
 }