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118 lines
2.8 KiB
Rust
118 lines
2.8 KiB
Rust
// This is similar to the previous `from_into` exercise. But this time, we'll
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// implement `FromStr` and return errors instead of falling back to a default
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// value. Additionally, upon implementing `FromStr`, you can use the `parse`
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// method on strings to generate an object of the implementor type. You can read
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// more about it in the documentation:
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// https://doc.rust-lang.org/std/str/trait.FromStr.html
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use std::num::ParseIntError;
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use std::str::FromStr;
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#[derive(Debug, PartialEq)]
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struct Person {
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name: String,
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age: u8,
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}
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// We will use this error type for the `FromStr` implementation.
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#[derive(Debug, PartialEq)]
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enum ParsePersonError {
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// Incorrect number of fields
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BadLen,
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// Empty name field
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NoName,
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// Wrapped error from parse::<u8>()
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ParseInt(ParseIntError),
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}
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impl FromStr for Person {
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type Err = ParsePersonError;
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fn from_str(s: &str) -> Result<Self, Self::Err> {
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let mut split = s.split(',');
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let (Some(name), Some(age), None) = (split.next(), split.next(), split.next()) else {
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// ^^^^ there should be no third element
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return Err(ParsePersonError::BadLen);
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};
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if name.is_empty() {
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return Err(ParsePersonError::NoName);
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}
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let age = age.parse().map_err(ParsePersonError::ParseInt)?;
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Ok(Self {
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name: name.into(),
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age,
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})
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}
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}
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fn main() {
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let p = "Mark,20".parse::<Person>();
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println!("{p:?}");
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use ParsePersonError::*;
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#[test]
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fn empty_input() {
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assert_eq!("".parse::<Person>(), Err(BadLen));
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}
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#[test]
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fn good_input() {
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let p = "John,32".parse::<Person>();
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assert!(p.is_ok());
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let p = p.unwrap();
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assert_eq!(p.name, "John");
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assert_eq!(p.age, 32);
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}
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#[test]
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fn missing_age() {
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assert!(matches!("John,".parse::<Person>(), Err(ParseInt(_))));
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}
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#[test]
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fn invalid_age() {
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assert!(matches!("John,twenty".parse::<Person>(), Err(ParseInt(_))));
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}
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#[test]
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fn missing_comma_and_age() {
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assert_eq!("John".parse::<Person>(), Err(BadLen));
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}
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#[test]
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fn missing_name() {
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assert_eq!(",1".parse::<Person>(), Err(NoName));
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}
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#[test]
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fn missing_name_and_age() {
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assert!(matches!(",".parse::<Person>(), Err(NoName | ParseInt(_))));
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}
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#[test]
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fn missing_name_and_invalid_age() {
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assert!(matches!(
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",one".parse::<Person>(),
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Err(NoName | ParseInt(_)),
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));
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}
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#[test]
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fn trailing_comma() {
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assert_eq!("John,32,".parse::<Person>(), Err(BadLen));
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}
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#[test]
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fn trailing_comma_and_some_string() {
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assert_eq!("John,32,man".parse::<Person>(), Err(BadLen));
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}
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}
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