From, Into traits

Posted on Sep 7, 2023

Let’s say we have a user-defined type Point defined as follows

struct Point {
    x: i32,
    y: i32,
}

and we want a String or &str of the form "(1,2)" to be converted into Point type. We need to implement the From trait on the Point type so that we can do something like

let p: Point = Point::from(String::from("(1,2)"));

let p: Point = Point::from("(1,2)");

The rust std library documentation says only to implement From since From<T> for U implies Into<U> for T which means by implementing the From trait on the Point type, we can make use of the standard library implementation of the Into trait. We can now also do

let p: Point = String::from("(1,2)").into();

let p: Point = "(1,2)".into();

Here is an implementation of the From trait on the Point type.

impl From<String> for Point {
    fn from(value: String) -> Self {
        let re = Regex::new(r#"\((\d+),(\d+)\)"#).unwrap();
        if let Some(caps) = re.captures(&value) {
            return Point {
                x: i32::from_str_radix(&caps[1], 10).unwrap(),
                y: i32::from_str_radix(&caps[2], 10).unwrap(),
            };
        }
        Point { x: 0, y: 0 }
    }
}

impl From<&str> for Point {
    fn from(value: &str) -> Self {
        let re = Regex::new(r#"\((\d+),(\d+)\)"#).unwrap();
        if let Some(caps) = re.captures(&value) {
            return Point {
                x: i32::from_str_radix(&caps[1], 10).unwrap(),
                y: i32::from_str_radix(&caps[2], 10).unwrap(),
            };
        }
        Point { x: 0, y: 0 }
    }
}

NOTE as per the documentation the From trait should not fail that is the reason i chose to return Point { x: 0, y: 0} at the end in case the regex does not capture.

Here is the link to the complete program on Rust Playground

References