Pattern Matching

The match keyword lets you match a value against one or more patterns. The comparisons are done from top to bottom and the first match wins.

The patterns can be simple values, similarly to switch in C and C++:

#[rustfmt::skip]
fn main() {
    let input = 'x';
    match input {
        'q'                       => println!("Quitting"),
        'a' | 's' | 'w' | 'd'     => println!("Moving around"),
        '0'..='9'                 => println!("Number input"),
        key if key.is_lowercase() => println!("Lowercase: {key}"),
        _                         => println!("Something else"),
    }
}

The _ pattern is a wildcard pattern which matches any value. The expressions must be irrefutable, meaning that it covers every possibility, so _ is often used as the final catch-all case.

Match can be used as an expression. Just like if, each match arm must have the same type. The type is the last expression of the block, if any. In the example above, the type is ().

A variable in the pattern (key in this example) will create a binding that can be used within the match arm.

A match guard causes the arm to match only if the condition is true.