From abd6b70c72dc6426752ff41f09160b839e5c449e Mon Sep 17 00:00:00 2001 From: Taylor Yu Date: Fri, 25 Jun 2021 16:52:10 -0500 Subject: [PATCH] feat: add advanced_errs2 New exercise to demonstrate traits that make it easier for other code to consume our custom error types. --- exercises/advanced_errors/advanced_errs2.rs | 203 ++++++++++++++++++++ info.toml | 32 +++ 2 files changed, 235 insertions(+) create mode 100644 exercises/advanced_errors/advanced_errs2.rs diff --git a/exercises/advanced_errors/advanced_errs2.rs b/exercises/advanced_errors/advanced_errs2.rs new file mode 100644 index 0000000000..d9d44d06cb --- /dev/null +++ b/exercises/advanced_errors/advanced_errs2.rs @@ -0,0 +1,203 @@ +// 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 for ParseClimateError { + fn from(e: ParseIntError) -> Self { + Self::ParseInt(e) + } +} + +// This `From` implementation allows the `?` operator to work on +// `ParseFloatError` values. +impl From 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 { + 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> { + println!("{:?}", "Hong Kong,1999,25.7".parse::()?); + println!("{:?}", "".parse::()?); + Ok(()) +} + +#[cfg(test)] +mod test { + use super::*; + #[test] + fn test_empty() { + let res = "".parse::(); + assert_eq!(res, Err(ParseClimateError::Empty)); + assert_eq!(res.unwrap_err().to_string(), "empty input"); + } + #[test] + fn test_short() { + let res = "Boston,1991".parse::(); + 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::(); + 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::(); + 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::(); + 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::(); + 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::(); + 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::(); + 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::(); + 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::()); + } +} diff --git a/info.toml b/info.toml index 8e24b7db76..1b8c65d249 100644 --- a/info.toml +++ b/info.toml @@ -994,3 +994,35 @@ it to the error type of the return type of the surrounding function. Hint: You will need to write another implementation of `From` that has a different input type. """ + +[[exercises]] +name = "advanced_errs2" +path = "exercises/advanced_errors/advanced_errs2.rs" +mode = "test" +hint = """ +This exercise demonstrates a few traits that are useful for custom error +types to implement. These traits make it easier for other code to consume +the custom error type. + +Follow the steps in the comment near the top of the file. You will have to +supply a missing trait implementation, and complete a few incomplete ones. + +You may find these pages to be helpful references: +https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/define_error_type.html +https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/boxing_errors.html +https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/wrap_error.html + +Hint: What trait must our error type have for `main()` to return the return +type that it returns? + +Another hint: It's not necessary to implement any methods inside the missing +trait. (Some methods have default implementations that are supplied by the +trait.) + +Another hint: Consult the tests to determine which error variants (and which +error message text) to produce for certain error conditions. + +Challenge: There is one test that is marked `#[ignore]`. Can you supply the +missing code that will make it pass? You may want to consult the standard +library documentation for a certain trait for more hints. +"""