if let expressions

If you want to match a value against a pattern, you can use if let:

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.

• if let can be more concise than match, e.g., when only one case is interesting. In contrast, match requires all branches to be covered.
  • For the similar use case consider demonstrating a newly stabilized let else feature.
• A common usage is handling Some values when working with Option.
• Unlike match, if let does not support guard clauses for pattern matching.