Guards
A match
guard can be added to filter the arm.
fn main() { let pair = (2, -2); // TODO ^ Try different values for `pair` println!("Tell me about {:?}", pair); match pair { (x, y) if x == y => println!("These are twins"), // The ^ `if condition` part is a guard (x, y) if x + y == 0 => println!("Antimatter, kaboom!"), (x, _) if x % 2 == 1 => println!("The first one is odd"), _ => println!("No correlation..."), } }
Note that the compiler does not check arbitrary expressions for whether all
possible conditions have been checked. Therefore, you must use the _
pattern
at the end.
fn main() { let number: u8 = 4; match number { i if i == 0 => println!("Zero"), i if i > 0 => println!("Greater than zero"), _ => println!("Fell through"), // This should not be possible to reach } }