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113 lines
3 KiB
Rust
113 lines
3 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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// TODO: Complete this `From` implementation to be able to parse a `Person`
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// out of a string in the form of "Mark,20".
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// Note that you'll need to parse the age component into a `u8` with something
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// like `"4".parse::<u8>()`.
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//
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// Steps:
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// 1. Split the given string on the commas present in it.
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// 2. If the split operation returns less or more than 2 elements, return the
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// error `ParsePersonError::BadLen`.
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// 3. Use the first element from the split operation as the name.
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// 4. If the name is empty, return the error `ParsePersonError::NoName`.
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// 5. Parse the second element from the split operation into a `u8` as the age.
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// 6. If parsing the age fails, return the error `ParsePersonError::ParseInt`.
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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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}
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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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