rustlings/exercises/advanced_errors/advanced_errs2.rs

// advanced_errs2.rs

// This exercise demonstrates a few traits that are useful for custom error
// types to implement, especially so that other code can consume the custom
// error type more usefully.

// Make this compile, and make the tests pass!
// Execute `rustlings hint advanced_errs2` for hints.

// Steps:
// 1. Implement a missing trait so that `main()` will compile.
// 2. Complete the partial implementation of `From` for
//    `ParseClimateError`.
// 3. Handle the missing error cases in the `FromStr` implementation for
//    `Climate`.
// 4. Complete the partial implementation of `Display` for
//    `ParseClimateError`.

// I AM NOT DONE

use std::error::Error;
use std::fmt::{self, Display, Formatter};
use std::num::{ParseFloatError, ParseIntError};
use std::str::FromStr;

// This is the custom error type that we will be using for the parser for
// `Climate`.
#[derive(Debug, PartialEq)]
enum ParseClimateError {
    Empty,
    BadLen,
    NoCity,
    ParseInt(ParseIntError),
    ParseFloat(ParseFloatError),
}

// This `From` implementation allows the `?` operator to work on
// `ParseIntError` values.
impl From<ParseIntError> for ParseClimateError {
    fn from(e: ParseIntError) -> Self {
        Self::ParseInt(e)
    }
}

// This `From` implementation allows the `?` operator to work on
// `ParseFloatError` values.
impl From<ParseFloatError> for ParseClimateError {
    fn from(e: ParseFloatError) -> Self {
        // TODO: Complete this function
    }
}

// TODO: Implement a missing trait so that `main()` below will compile. It
// is not necessary to implement any methods inside the missing trait.

// The `Display` trait allows for other code to obtain the error formatted
// as a user-visible string.
impl Display for ParseClimateError {
    // TODO: Complete this function so that it produces the correct strings
    // for each error variant.
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        // Imports the variants to make the following code more compact.
        use ParseClimateError::*;
        match self {
            NoCity => write!(f, "no city name"),
            ParseFloat(e) => write!(f, "error parsing temperature: {}", e),
            _ => write!(f, "unhandled error!"),
        }
    }
}

#[derive(Debug, PartialEq)]
struct Climate {
    city: String,
    year: u32,
    temp: f32,
}

// Parser for `Climate`.
// 1. Split the input string into 3 fields: city, year, temp.
// 2. Return an error if the string is empty or has the wrong number of
//    fields.
// 3. Return an error if the city name is empty.
// 4. Parse the year as a `u32` and return an error if that fails.
// 5. Parse the temp as a `f32` and return an error if that fails.
// 6. Return an `Ok` value containing the completed `Climate` value.
impl FromStr for Climate {
    type Err = ParseClimateError;
    // TODO: Complete this function by making it handle the missing error
    // cases.
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let v: Vec<_> = s.split(',').collect();
        let (city, year, temp) = match &v[..] {
            [city, year, temp] => (city.to_string(), year, temp),
            _ => return Err(ParseClimateError::BadLen),
        };
        let year: u32 = year.parse()?;
        let temp: f32 = temp.parse()?;
        Ok(Climate { city, year, temp })
    }
}

// Don't change anything below this line (other than to enable ignored
// tests).

fn main() -> Result<(), Box<dyn Error>> {
    println!("{:?}", "Hong Kong,1999,25.7".parse::<Climate>()?);
    println!("{:?}", "".parse::<Climate>()?);
    Ok(())
}

#[cfg(test)]
mod test {
    use super::*;
    #[test]
    fn test_empty() {
        let res = "".parse::<Climate>();
        assert_eq!(res, Err(ParseClimateError::Empty));
        assert_eq!(res.unwrap_err().to_string(), "empty input");
    }
    #[test]
    fn test_short() {
        let res = "Boston,1991".parse::<Climate>();
        assert_eq!(res, Err(ParseClimateError::BadLen));
        assert_eq!(res.unwrap_err().to_string(), "incorrect number of fields");
    }
    #[test]
    fn test_long() {
        let res = "Paris,1920,17.2,extra".parse::<Climate>();
        assert_eq!(res, Err(ParseClimateError::BadLen));
        assert_eq!(res.unwrap_err().to_string(), "incorrect number of fields");
    }
    #[test]
    fn test_no_city() {
        let res = ",1997,20.5".parse::<Climate>();
        assert_eq!(res, Err(ParseClimateError::NoCity));
        assert_eq!(res.unwrap_err().to_string(), "no city name");
    }
    #[test]
    fn test_parse_int_neg() {
        let res = "Barcelona,-25,22.3".parse::<Climate>();
        assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
        let err = res.unwrap_err();
        if let ParseClimateError::ParseInt(ref inner) = err {
            assert_eq!(
                err.to_string(),
                format!("error parsing year: {}", inner.to_string())
            );
        } else {
            unreachable!();
        };
    }
    #[test]
    fn test_parse_int_bad() {
        let res = "Beijing,foo,15.0".parse::<Climate>();
        assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
        let err = res.unwrap_err();
        if let ParseClimateError::ParseInt(ref inner) = err {
            assert_eq!(
                err.to_string(),
                format!("error parsing year: {}", inner.to_string())
            );
        } else {
            unreachable!();
        };
    }
    #[test]
    fn test_parse_float() {
        let res = "Manila,2001,bar".parse::<Climate>();
        assert!(matches!(res, Err(ParseClimateError::ParseFloat(_))));
        let err = res.unwrap_err();
        if let ParseClimateError::ParseFloat(ref inner) = err {
            assert_eq!(
                err.to_string(),
                format!("error parsing temperature: {}", inner.to_string())
            );
        } else {
            unreachable!();
        };
    }
    #[test]
    fn test_parse_good() {
        let res = "Munich,2015,23.1".parse::<Climate>();
        assert_eq!(
            res,
            Ok(Climate {
                city: "Munich".to_string(),
                year: 2015,
                temp: 23.1,
            })
        );
    }
    #[test]
    #[ignore]
    fn test_downcast() {
        let res = "São Paulo,-21,28.5".parse::<Climate>();
        assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
        let err = res.unwrap_err();
        let inner: Option<&(dyn Error + 'static)> = err.source();
        assert!(inner.is_some());
        assert!(inner.unwrap().is::<ParseIntError>());
    }
}