Advanced Pattern Matching

Match Guards

Add Conditions to Patterns

A match guard refines a pattern with a boolean condition after the shape already matches.

Program

Play the program to choose a score and see which guarded arm classifies it.

match_guards.rs 
fn main() {
    let score = ;
    let label = grade(score);
    println!("{score}:{label}");
}

fn grade(score: i32) -> &'static str {
    match score {
        n if n >= 90 => "excellent",
        n if n >= 60 => "pass",
        _ => "retry",
    }
}

fn main() {
    let score = ;
    let label = grade(score);
    println!("{score}:{label}");
}

fn grade(score: i32) -> &'static str {
    match score {
        n if n >= 90 => "excellent",
        n if n >= 60 => "pass",
        _ => "retry",
    }
}

fn main() {
    let score = ;
    let label = grade(score);
    println!("{score}:{label}");
}

fn grade(score: i32) -> &'static str {
    match score {
        n if n >= 90 => "excellent",
        n if n >= 60 => "pass",
        _ => "retry",
    }
}
guard `n if n >= 60` matches only when the value also passes the condition.
arm order The first matching guarded arm wins, so the excellent arm is checked before pass.
fallback `_` catches values that did not satisfy any earlier guard.