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// 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),
}
}
}
#[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>());
}
}
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