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203 lines
6.4 KiB
Rust
203 lines
6.4 KiB
Rust
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// advanced_errs2.rs
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// This exercise demonstrates a few traits that are useful for custom error
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// types to implement, especially so that other code can consume the custom
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// error type more usefully.
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// Make this compile, and make the tests pass!
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// Execute `rustlings hint advanced_errs2` for hints.
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// Steps:
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// 1. Implement a missing trait so that `main()` will compile.
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// 2. Complete the partial implementation of `From` for
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// `ParseClimateError`.
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// 3. Handle the missing error cases in the `FromStr` implementation for
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// `Climate`.
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// 4. Complete the partial implementation of `Display` for
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// `ParseClimateError`.
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// I AM NOT DONE
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use std::error::Error;
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use std::fmt::{self, Display, Formatter};
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use std::num::{ParseFloatError, ParseIntError};
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use std::str::FromStr;
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// This is the custom error type that we will be using for the parser for
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// `Climate`.
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#[derive(Debug, PartialEq)]
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enum ParseClimateError {
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Empty,
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BadLen,
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NoCity,
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ParseInt(ParseIntError),
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ParseFloat(ParseFloatError),
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}
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// This `From` implementation allows the `?` operator to work on
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// `ParseIntError` values.
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impl From<ParseIntError> for ParseClimateError {
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fn from(e: ParseIntError) -> Self {
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Self::ParseInt(e)
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}
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}
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// This `From` implementation allows the `?` operator to work on
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// `ParseFloatError` values.
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impl From<ParseFloatError> for ParseClimateError {
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fn from(e: ParseFloatError) -> Self {
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// TODO: Complete this function
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}
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}
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// TODO: Implement a missing trait so that `main()` below will compile. It
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// is not necessary to implement any methods inside the missing trait.
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// The `Display` trait allows for other code to obtain the error formatted
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// as a user-visible string.
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impl Display for ParseClimateError {
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// TODO: Complete this function so that it produces the correct strings
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// for each error variant.
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fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
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// Imports the variants to make the following code more compact.
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use ParseClimateError::*;
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match self {
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NoCity => write!(f, "no city name"),
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ParseFloat(e) => write!(f, "error parsing temperature: {}", e),
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}
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}
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}
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#[derive(Debug, PartialEq)]
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struct Climate {
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city: String,
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year: u32,
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temp: f32,
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}
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// Parser for `Climate`.
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// 1. Split the input string into 3 fields: city, year, temp.
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// 2. Return an error if the string is empty or has the wrong number of
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// fields.
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// 3. Return an error if the city name is empty.
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// 4. Parse the year as a `u32` and return an error if that fails.
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// 5. Parse the temp as a `f32` and return an error if that fails.
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// 6. Return an `Ok` value containing the completed `Climate` value.
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impl FromStr for Climate {
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type Err = ParseClimateError;
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// TODO: Complete this function by making it handle the missing error
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// cases.
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fn from_str(s: &str) -> Result<Self, Self::Err> {
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let v: Vec<_> = s.split(',').collect();
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let (city, year, temp) = match &v[..] {
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[city, year, temp] => (city.to_string(), year, temp),
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_ => return Err(ParseClimateError::BadLen),
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};
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let year: u32 = year.parse()?;
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let temp: f32 = temp.parse()?;
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Ok(Climate { city, year, temp })
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}
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}
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// Don't change anything below this line (other than to enable ignored
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// tests).
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fn main() -> Result<(), Box<dyn Error>> {
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println!("{:?}", "Hong Kong,1999,25.7".parse::<Climate>()?);
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println!("{:?}", "".parse::<Climate>()?);
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Ok(())
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}
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#[cfg(test)]
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mod test {
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use super::*;
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#[test]
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fn test_empty() {
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let res = "".parse::<Climate>();
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assert_eq!(res, Err(ParseClimateError::Empty));
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assert_eq!(res.unwrap_err().to_string(), "empty input");
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}
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#[test]
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fn test_short() {
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let res = "Boston,1991".parse::<Climate>();
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assert_eq!(res, Err(ParseClimateError::BadLen));
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assert_eq!(res.unwrap_err().to_string(), "incorrect number of fields");
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}
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#[test]
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fn test_long() {
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let res = "Paris,1920,17.2,extra".parse::<Climate>();
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assert_eq!(res, Err(ParseClimateError::BadLen));
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assert_eq!(res.unwrap_err().to_string(), "incorrect number of fields");
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}
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#[test]
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fn test_no_city() {
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let res = ",1997,20.5".parse::<Climate>();
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assert_eq!(res, Err(ParseClimateError::NoCity));
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assert_eq!(res.unwrap_err().to_string(), "no city name");
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}
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#[test]
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fn test_parse_int_neg() {
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let res = "Barcelona,-25,22.3".parse::<Climate>();
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assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
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let err = res.unwrap_err();
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if let ParseClimateError::ParseInt(ref inner) = err {
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assert_eq!(
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err.to_string(),
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format!("error parsing year: {}", inner.to_string())
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);
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} else {
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unreachable!();
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};
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}
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#[test]
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fn test_parse_int_bad() {
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let res = "Beijing,foo,15.0".parse::<Climate>();
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assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
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let err = res.unwrap_err();
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if let ParseClimateError::ParseInt(ref inner) = err {
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assert_eq!(
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err.to_string(),
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format!("error parsing year: {}", inner.to_string())
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);
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} else {
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unreachable!();
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};
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}
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#[test]
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fn test_parse_float() {
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let res = "Manila,2001,bar".parse::<Climate>();
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assert!(matches!(res, Err(ParseClimateError::ParseFloat(_))));
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let err = res.unwrap_err();
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if let ParseClimateError::ParseFloat(ref inner) = err {
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assert_eq!(
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err.to_string(),
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format!("error parsing temperature: {}", inner.to_string())
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);
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} else {
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unreachable!();
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};
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}
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#[test]
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fn test_parse_good() {
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let res = "Munich,2015,23.1".parse::<Climate>();
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assert_eq!(
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res,
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Ok(Climate {
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city: "Munich".to_string(),
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year: 2015,
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temp: 23.1,
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})
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);
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}
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#[test]
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#[ignore]
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fn test_downcast() {
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let res = "São Paulo,-21,28.5".parse::<Climate>();
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assert!(matches!(res, Err(ParseClimateError::ParseInt(_))));
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let err = res.unwrap_err();
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let inner: Option<&(dyn Error + 'static)> = err.source();
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assert!(inner.is_some());
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assert!(inner.unwrap().is::<ParseIntError>());
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}
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}
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