so48244892.rs

#[derive(Debug)]
struct EmailAddr(String);    // e.g. user@example.com
#[derive(Debug)]
struct Domain<'a>(&'a str);  // a slice onward from the @ symbol of the above

impl<'a> From<&'a EmailAddr> for Domain<'a> {
    fn from(value: &'a EmailAddr) -> Self {
        Self(&value.0[value.0.find('@').unwrap_or(0)..])
    }
}

fn main() {
    let email = EmailAddr("user@example.com".to_string());
    let domain = Domain::from(&email);
    println!("domain for {:?} is {:?}", email, domain);
}