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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
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::<u8>()
ParseInt(ParseIntError),
}
impl FromStr for Person {
type Err = ParsePersonError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
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::<Person>();
println!("{p:?}");
}
#[cfg(test)]
mod tests {
use super::*;
use ParsePersonError::*;
#[test]
fn empty_input() {
assert_eq!("".parse::<Person>(), Err(BadLen));
}
#[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);
}
#[test]
fn missing_age() {
assert!(matches!("John,".parse::<Person>(), Err(ParseInt(_))));
}
#[test]
fn invalid_age() {
assert!(matches!("John,twenty".parse::<Person>(), Err(ParseInt(_))));
}
#[test]
fn missing_comma_and_age() {
assert_eq!("John".parse::<Person>(), Err(BadLen));
}
#[test]
fn missing_name() {
assert_eq!(",1".parse::<Person>(), Err(NoName));
}
#[test]
fn missing_name_and_age() {
assert!(matches!(",".parse::<Person>(), Err(NoName | ParseInt(_))));
}
#[test]
fn missing_name_and_invalid_age() {
assert!(matches!(
",one".parse::<Person>(),
Err(NoName | ParseInt(_)),
));
}
#[test]
fn trailing_comma() {
assert_eq!("John,32,".parse::<Person>(), Err(BadLen));
}
#[test]
fn trailing_comma_and_some_string() {
assert_eq!("John,32,man".parse::<Person>(), Err(BadLen));
}
}
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