Switch

Run’s switch is used for pattern matching. There is no fallthrough — only the matched branch executes.

package main

use "fmt"

fun describe(x: int) string {
    switch x {
        1 :: return "one",
        2 :: return "two",
        3 :: return "three",
        _ :: return "other",
    }
}

pub fun main() {
    fmt.println(describe(2))
    fmt.println(describe(99))
}

The _ pattern is a wildcard that matches anything. It is often used as a default case.

switch is also used for matching on sum types and error unions, which are covered in later chapters.