match patterns

Match against different patterns with match.

match patterns

match compares a value against patterns listed as arms; the first arm that fits runs. Patterns can be a literal value, several values with |, or a range with ..=:

fn harf_notu(p: u8) -> char {
    match p {
        90..=100 => 'A',
        70..=89 => 'B',
        50..=69 => 'C',
        _ => 'F',
    }
}

match is an expression; all arms must produce a value of the same type.

Multiple values and blocks

With |, several patterns join in one arm. If an arm's body is several lines, braces are used; the last expression is the arm's value:

let gun = 6;
let tur = match gun {
    1 | 2 | 3 | 4 | 5 => "iş",
    6 | 7 => {
        println!("tatil!");
        "hafta sonu"
    }
    _ => "geçersiz",
};

Exercise Letter grade

Write the function fn harf_notu(p: u8) -> char above with range patterns. Print the results for 95, 72 and 40 separated by spaces.

Show example solution

fn harf_notu(p: u8) -> char {
    match p {
        90..=100 => 'A',
        70..=89 => 'B',
        50..=69 => 'C',
        _ => 'F',
    }
}

fn main() {
    println!("{} {} {}", harf_notu(95), harf_notu(72), harf_notu(40));
}

Test yourself

What happens if the arms are written in the order <code>_ => 'F', 90..=100 => 'A'</code>?
- One is picked at random
- Every value becomes F; the compiler warns about an unreachable arm
- Compile error
- Order doesn't matter
Show answer

Every value becomes F; the compiler warns about an unreachable arm — Arms are tried from top to bottom; since _ fits everything, the later arms never run.

Range pattern

match p {
    90____100 => 'A',
    _ => 'F',
}

Show answer

match p {
    90..=100 => 'A',
    _ => 'F',
}

Score and harf_notu result

95

A
72

B
50

C
40

F

Next lesson: Value binding

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