Fallthrough statements

A “fallthrough” statement transfers control to the first statement of the next case clause in an expression “switch” statement. It may be used only as the final non-empty statement in such a clause.

FallthroughStmt = "fallthrough" .

Well that’s pretty straight forward.

for x := range 10 {
	switch {
	case x%2 == 0:
		fmt.Print("X")
		fallthrough
	case x%3 == 0:
		fmt.Print("x")
		fallthrough
	case x%5 == 0:
		fmt.Print("O")
	}
	fmt.Println()
}

In this ridiculous example, we get the following output:

XxO

XxO
xO
XxO
O
XxO

XxO
xO

The important thing to notice is that every line that contains (non-empty) output, the final case (which outputs O) is triggered.

The fallthrough unconditionally falls through to the next case. In other words, it doesn’t simply continue evaluating the options. If you want that, switch isn’t what you need—you need just a list of if conditions instead.

Quotes from The Go Programming Language Specification Language version go1.23 (June 13, 2024)