match

let foo = 3
match foo {
    3 => { check bar == 3 }
    4 => { check bar == 0 }
    _ => { check bar > 3 }
}

match checks an expression against a series of match arms containing unique constant literal expressions (that is, expressions made up of only individual literals), and executes the first one that matches. You can think about it conceptually like a series of if-else if statements checking for equality between the first expression and the constant in each match arm. Except in the case of a match, all possibilities must be checked for.

The _ token is a “default” match that matches anything. This also means _ should be the last match arm, as nothing will be matched afterwards.

A match expression must match exactly one arm in order for the match statement to be valid. Non-exhaustive matches will produce a compile error when all match arms have failed to match. Duplicate match arms will produce a compile error.

Note that unlike the match expression, the match statement requires the use of curly braces around the statements in each arm.