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// The `From` trait is used for value-to-value conversions. If `From` is
// implemented, an implementation of `Into` is automatically provided.
// You can read more about it in the documentation:
// https://doc.rust-lang.org/std/convert/trait.From.html
#[derive(Debug)]
struct Person {
name: String,
age: u8,
}
// We implement the Default trait to use it as a fallback when the provided
// string is not convertible into a `Person` object.
impl Default for Person {
fn default() -> Self {
Self {
name: String::from("John"),
age: 30,
}
}
}
impl From<&str> for Person {
fn from(s: &str) -> Self {
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 Self::default();
};
if name.is_empty() {
return Self::default();
}
let Ok(age) = age.parse() else {
return Self::default();
};
Self {
name: name.into(),
age,
}
}
}
fn main() {
// Use the `from` function.
let p1 = Person::from("Mark,20");
println!("{p1:?}");
// Since `From` is implemented for Person, we are able to use `Into`.
let p2: Person = "Gerald,70".into();
println!("{p2:?}");
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_default() {
let dp = Person::default();
assert_eq!(dp.name, "John");
assert_eq!(dp.age, 30);
}
#[test]
fn test_bad_convert() {
let p = Person::from("");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_good_convert() {
let p = Person::from("Mark,20");
assert_eq!(p.name, "Mark");
assert_eq!(p.age, 20);
}
#[test]
fn test_bad_age() {
let p = Person::from("Mark,twenty");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_missing_comma_and_age() {
let p: Person = Person::from("Mark");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_missing_age() {
let p: Person = Person::from("Mark,");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_missing_name() {
let p: Person = Person::from(",1");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_missing_name_and_age() {
let p: Person = Person::from(",");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_missing_name_and_invalid_age() {
let p: Person = Person::from(",one");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_trailing_comma() {
let p: Person = Person::from("Mike,32,");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_trailing_comma_and_some_string() {
let p: Person = Person::from("Mike,32,dog");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
}
|
