`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.