rustlings/exercises/23_conversions/from_str.rs

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// 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
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use std::num::ParseIntError;
use std::str::FromStr;
#[derive(Debug, PartialEq)]
struct Person {
name: String,
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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,
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// Wrapped error from parse::<u8>()
ParseInt(ParseIntError),
}
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// TODO: Complete this `FromStr` implementation to be able to parse a `Person`
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// 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::<u8>()`.
//
// Steps:
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// 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;
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fn from_str(s: &str) -> Result<Self, Self::Err> {}
}
fn main() {
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let p = "Mark,20".parse::<Person>();
println!("{p:?}");
}
#[cfg(test)]
mod tests {
use super::*;
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use ParsePersonError::*;
#[test]
fn empty_input() {
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assert_eq!("".parse::<Person>(), Err(BadLen));
}
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#[test]
fn good_input() {
let p = "John,32".parse::<Person>();
assert!(p.is_ok());
let p = p.unwrap();
assert_eq!(p.name, "John");
assert_eq!(p.age, 32);
}
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#[test]
fn missing_age() {
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assert!(matches!("John,".parse::<Person>(), Err(ParseInt(_))));
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}
#[test]
fn invalid_age() {
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assert!(matches!("John,twenty".parse::<Person>(), Err(ParseInt(_))));
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}
#[test]
fn missing_comma_and_age() {
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assert_eq!("John".parse::<Person>(), Err(BadLen));
}
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#[test]
fn missing_name() {
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assert_eq!(",1".parse::<Person>(), Err(NoName));
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}
#[test]
fn missing_name_and_age() {
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assert!(matches!(",".parse::<Person>(), Err(NoName | ParseInt(_))));
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}
#[test]
fn missing_name_and_invalid_age() {
assert!(matches!(
",one".parse::<Person>(),
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Err(NoName | ParseInt(_)),
));
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}
#[test]
fn trailing_comma() {
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assert_eq!("John,32,".parse::<Person>(), Err(BadLen));
}
#[test]
fn trailing_comma_and_some_string() {
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assert_eq!("John,32,man".parse::<Person>(), Err(BadLen));
}
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}