142 lines
4.2 KiB
Rust
142 lines
4.2 KiB
Rust
// from_str.rs
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// This is similar to from_into.rs, but this time we'll implement `FromStr`
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// and return errors instead of falling back to a default value.
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// Additionally, upon implementing FromStr, you can use the `parse` method
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// on strings to generate an object of the implementor type.
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// You can read more about it at https://doc.rust-lang.org/std/str/trait.FromStr.html
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// Execute `rustlings hint from_str` or use the `hint` watch subcommand for a hint.
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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: usize,
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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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// Empty input string
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Empty,
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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::<usize>()
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ParseInt(ParseIntError),
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}
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// Steps:
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// 1. If the length of the provided string is 0, an error should be returned
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// 2. Split the given string on the commas present in it
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// 3. Only 2 elements should be returned from the split, otherwise return an error
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// 4. Extract the first element from the split operation and use it as the name
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// 5. Extract the other element from the split operation and parse it into a `usize` as the age
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// with something like `"4".parse::<usize>()`
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// 6. If while extracting the name and the age something goes wrong, an error should be returned
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// If everything goes well, then return a Result of a Person object
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//
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// As an aside: `Box<dyn Error>` implements `From<&'_ str>`. This means that if you want to return a
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// string error message, you can do so via just using return `Err("my error message".into())`.
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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<Person, Self::Err> {
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let vec: Vec<&str> = s.split(",").collect();
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let name = vec[0].trim();
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let age = vec[vec.len() - 1].parse::<usize>();
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if vec.len() == 2 && name.len() > 0 && age.is_ok() {
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Ok(Person { name: name.to_string(), age: age.unwrap() })
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} else {
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if s.trim().len() == 0 {
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Err(ParsePersonError::Empty)
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} else if vec.len() != 2 {
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Err(ParsePersonError::BadLen)
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} else if name.len() == 0 {
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Err(ParsePersonError::NoName)
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} else {
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Err(ParsePersonError::ParseInt(age.unwrap_err()))
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}
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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>().unwrap();
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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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#[test]
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fn empty_input() {
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assert_eq!("".parse::<Person>(), Err(ParsePersonError::Empty));
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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!(
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"John,".parse::<Person>(),
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Err(ParsePersonError::ParseInt(_))
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));
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}
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#[test]
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fn invalid_age() {
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assert!(matches!(
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"John,twenty".parse::<Person>(),
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Err(ParsePersonError::ParseInt(_))
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));
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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(ParsePersonError::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(ParsePersonError::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!(
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",".parse::<Person>(),
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Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
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));
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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(ParsePersonError::NoName | ParsePersonError::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(ParsePersonError::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!(
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"John,32,man".parse::<Person>(),
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Err(ParsePersonError::BadLen)
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);
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}
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}
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