if let expressions

The if let expression lets you execute different code depending on whether a value matches a pattern:

fn main() {
    let arg = std::env::args().next();
    if let Some(value) = arg {
        println!("Program name: {value}");
    } else {
        println!("Missing name?");
    }
}

See pattern matching for more details on patterns in Rust.

  • Unlike match, if let does not have to cover all branches. This can make it more concise than match.

  • A common usage is handling Some values when working with Option.

  • Unlike match, if let does not support guard clauses for pattern matching.

  • Since 1.65, a similar let-else construct allows to do a destructuring assignment, or if it fails, execute a block which is required to abort normal control flow (with panic/return/break/continue):

    fn main() {
    println!("{:?}", second_word_to_upper("foo bar"));
}
 
fn second_word_to_upper(s: &str) -> Option<String> {
    let mut it = s.split(' ');
    let (Some(_), Some(item)) = (it.next(), it.next()) else {
        return None;
    };
    Some(item.to_uppercase())
}