diff --git a/exercises/23_conversions/from_str.rs b/exercises/23_conversions/from_str.rs index 58270f02..1b3f553e 100644 --- a/exercises/23_conversions/from_str.rs +++ b/exercises/23_conversions/from_str.rs @@ -1,7 +1,8 @@ -// 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 +// This is similar to the previous `from_into` exercise. 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 in the documentation: // https://doc.rust-lang.org/std/str/trait.FromStr.html use std::num::ParseIntError; @@ -10,43 +11,42 @@ use std::str::FromStr; #[derive(Debug, PartialEq)] struct Person { name: String, - age: usize, + age: u8, } // 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::() + // Wrapped error from parse::() ParseInt(ParseIntError), } +// TODO: Complete this `From` implementation to be able to parse a `Person` +// out of a string in the form of "Mark,20". +// Note that you'll need to parse the age component into a `u8` with something +// like `"4".parse::()`. +// // 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::()` -// 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 - +// 1. Split the given string on the commas present in it. +// 2. If the split operation returns less or more than 2 elements, return the +// error `ParsePersonError::BadLen`. +// 3. Use the first element from the split operation as the name. +// 4. If the name is empty, return the error `ParsePersonError::NoName`. +// 5. Parse the second element from the split operation into a `u8` as the age. +// 6. If parsing the age fails, return the error `ParsePersonError::ParseInt`. impl FromStr for Person { type Err = ParsePersonError; - fn from_str(s: &str) -> Result { - } + + fn from_str(s: &str) -> Result {} } fn main() { - let p = "Mark,20".parse::().unwrap(); - println!("{:?}", p); + let p = "Mark,20".parse::(); + println!("{p:?}"); } #[cfg(test)] @@ -55,8 +55,9 @@ mod tests { #[test] fn empty_input() { - assert_eq!("".parse::(), Err(ParsePersonError::Empty)); + assert_eq!("".parse::(), Err(ParsePersonError::BadLen)); } + #[test] fn good_input() { let p = "John,32".parse::(); @@ -65,11 +66,12 @@ mod tests { assert_eq!(p.name, "John"); assert_eq!(p.age, 32); } + #[test] fn missing_age() { assert!(matches!( "John,".parse::(), - Err(ParsePersonError::ParseInt(_)) + Err(ParsePersonError::ParseInt(_)), )); } @@ -77,7 +79,7 @@ mod tests { fn invalid_age() { assert!(matches!( "John,twenty".parse::(), - Err(ParsePersonError::ParseInt(_)) + Err(ParsePersonError::ParseInt(_)), )); } @@ -95,7 +97,7 @@ mod tests { fn missing_name_and_age() { assert!(matches!( ",".parse::(), - Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_)) + Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_)), )); } @@ -103,7 +105,7 @@ mod tests { fn missing_name_and_invalid_age() { assert!(matches!( ",one".parse::(), - Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_)) + Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_)), )); } @@ -116,7 +118,7 @@ mod tests { fn trailing_comma_and_some_string() { assert_eq!( "John,32,man".parse::(), - Err(ParsePersonError::BadLen) + Err(ParsePersonError::BadLen), ); } } diff --git a/rustlings-macros/info.toml b/rustlings-macros/info.toml index b848e0ef..4ef1a0a3 100644 --- a/rustlings-macros/info.toml +++ b/rustlings-macros/info.toml @@ -1183,13 +1183,11 @@ hint = """ The implementation of `FromStr` should return an `Ok` with a `Person` object, or an `Err` with an error if the string is not valid. -This is almost like the `from_into` exercise, but returning errors instead -of falling back to a default value. +This is almost like the previous `from_into` exercise, but returning errors +instead of falling back to a default value. -Look at the test cases to see which error variants to return. - -Another hint: You can use the `map_err` method of `Result` with a function -or a closure to wrap the error from `parse::`. +Another hint: You can use the `map_err` method of `Result` with a function or a +closure to wrap the error from `parse::`. Yet another hint: If you would like to propagate errors by using the `?` operator in your solution, you might want to look at diff --git a/solutions/23_conversions/from_str.rs b/solutions/23_conversions/from_str.rs index 4e181989..301150b9 100644 --- a/solutions/23_conversions/from_str.rs +++ b/solutions/23_conversions/from_str.rs @@ -1 +1,128 @@ -// Solutions will be available before the stable release. Thank you for testing the beta version 🥰 +// This is similar to the previous `from_into` exercise. 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 in the documentation: +// https://doc.rust-lang.org/std/str/trait.FromStr.html + +use std::num::ParseIntError; +use std::str::FromStr; + +#[derive(Debug, PartialEq)] +struct Person { + name: String, + age: u8, +} + +// We will use this error type for the `FromStr` implementation. +#[derive(Debug, PartialEq)] +enum ParsePersonError { + // Incorrect number of fields + BadLen, + // Empty name field + NoName, + // Wrapped error from parse::() + ParseInt(ParseIntError), +} + +impl FromStr for Person { + type Err = ParsePersonError; + + fn from_str(s: &str) -> Result { + let mut split = s.split(','); + let (Some(name), Some(age), None) = (split.next(), split.next(), split.next()) else { + // ^^^^ there should be no third element + return Err(ParsePersonError::BadLen); + }; + + if name.is_empty() { + return Err(ParsePersonError::NoName); + } + + let age = age.parse().map_err(ParsePersonError::ParseInt)?; + + Ok(Self { + name: name.into(), + age, + }) + } +} + +fn main() { + let p = "Mark,20".parse::(); + println!("{p:?}"); +} + +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn empty_input() { + assert_eq!("".parse::(), Err(ParsePersonError::BadLen)); + } + + #[test] + fn good_input() { + let p = "John,32".parse::(); + 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::(), + Err(ParsePersonError::ParseInt(_)), + )); + } + + #[test] + fn invalid_age() { + assert!(matches!( + "John,twenty".parse::(), + Err(ParsePersonError::ParseInt(_)), + )); + } + + #[test] + fn missing_comma_and_age() { + assert_eq!("John".parse::(), Err(ParsePersonError::BadLen)); + } + + #[test] + fn missing_name() { + assert_eq!(",1".parse::(), Err(ParsePersonError::NoName)); + } + + #[test] + fn missing_name_and_age() { + assert!(matches!( + ",".parse::(), + Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_)), + )); + } + + #[test] + fn missing_name_and_invalid_age() { + assert!(matches!( + ",one".parse::(), + Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_)), + )); + } + + #[test] + fn trailing_comma() { + assert_eq!("John,32,".parse::(), Err(ParsePersonError::BadLen)); + } + + #[test] + fn trailing_comma_and_some_string() { + assert_eq!( + "John,32,man".parse::(), + Err(ParsePersonError::BadLen), + ); + } +}