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| // This does practically the same thing that TryFrom<&str> does. | |
| // 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 at https://doc.rust-lang.org/std/str/trait.FromStr.html | |
| use std::str::FromStr; | |
| #[derive(Debug)] | |
| struct Person { | |
| name: String, | |
| age: usize, | |
| } | |
| // Steps: | |
| // 1. If the length of the provided string is 0, then return an error | |
| // 2. Split the given string on the commas present in it | |
| // 3. Extract the first element from the split operation and use it as the name | |
| // 4. If the name is empty, then return an error | |
| // 5. Extract the other element from the split operation and parse it into a `usize` as the age | |
| // with something like `"4".parse::<usize>()`. | |
| // If while parsing the age, something goes wrong, then return an error | |
| // Otherwise, then return a Result of a Person object | |
| impl FromStr for Person { | |
| type Err = String; | |
| fn from_str(s: &str) -> Result<Person, Self::Err> { | |
| let mut it = s.split(','); | |
| let name = it | |
| .next() | |
| .filter(|string| string.len() > 0) | |
| .map(|string| string.parse::<String>()); | |
| let age = it.next().map(|string| string.parse::<usize>()); | |
| match (name, age) { | |
| (Some(Ok(name)), Some(Ok(age))) => Ok(Person { name, age }), | |
| (_, _) => Err(format!("something else wrong")), | |
| } | |
| } | |
| } | |
| fn main() { | |
| let p = "Mark,20".parse::<Person>().unwrap(); | |
| println!("{:?}", p); | |
| } | |
| #[cfg(test)] | |
| mod tests { | |
| use super::*; | |
| #[test] | |
| fn empty_input() { | |
| assert!("".parse::<Person>().is_err()); | |
| } | |
| #[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] | |
| #[should_panic] | |
| fn missing_age() { | |
| "John,".parse::<Person>().unwrap(); | |
| } | |
| #[test] | |
| #[should_panic] | |
| fn invalid_age() { | |
| "John,twenty".parse::<Person>().unwrap(); | |
| } | |
| #[test] | |
| #[should_panic] | |
| fn missing_comma_and_age() { | |
| "John".parse::<Person>().unwrap(); | |
| } | |
| #[test] | |
| #[should_panic] | |
| fn missing_name() { | |
| ",1".parse::<Person>().unwrap(); | |
| } | |
| #[test] | |
| #[should_panic] | |
| fn missing_name_and_age() { | |
| ",".parse::<Person>().unwrap(); | |
| } | |
| #[test] | |
| #[should_panic] | |
| fn missing_name_and_invalid_age() { | |
| ",one".parse::<Person>().unwrap(); | |
| } | |
| } |
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