5 switch statement patterns

Basic switch with default

A switch statement runs the first case equal to the condition expression.
The cases are evaluated from top to bottom, stopping when a case succeeds.
If no case matches and there is a default case,its statements are executed.

switch time.Now().Weekday() {case time.Saturday:fmt.Println("Today is Saturday.")case time.Sunday:fmt.Println("Today is Sunday.")default:fmt.Println("Today is a weekday.")}

Unlike C and Java, the case expressions do not need to be constants.

No condition

A switch without a condition is the same as switch true.

switch hour := time.Now().Hour(); {// missing expression means "true"case hour< 12:fmt.Println("Good morning!")case hour< 17:fmt.Println("Good afternoon!")default:fmt.Println("Good evening!")}

Case list

func WhiteSpace(c rune) bool {    switch c {case ' ', '\t', '\n', '\f', '\r':        return true    }    return false}

Fallthrough

Afallthrough statement transfers control to the next case.
It may be used only as the final statement in a clause.

switch 2 {case 1:fmt.Println("1")fallthroughcase 2:fmt.Println("2")fallthroughcase 3:fmt.Println("3")}

Exit with break

Abreak statement terminates execution of theinnermostfor,switch, orselect statement.

If you need to break out of a surrounding loop, not the switch, you can put alabelon the loop and break to that label. This example shows both uses.

Loop:for _, ch := range "a b\nc" {switch ch {case ' ':// skip spacebreakcase '\n':// break at newlinebreak Loopdefault:fmt.Printf("%c\n", ch)}}

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Execution order

First the switch expression is evaluated once.
Then case expressions are evaluated left-to-right and top-to-bottom:
- the first one that equals the switch expression triggers executionof the statements of the associated case,
- the other cases are skipped.

// Foo prints and returns n.func Foo(n int) int {fmt.Println(n)return n}func main() {switch Foo(2) {case Foo(1), Foo(2), Foo(3):fmt.Println("First case")fallthroughcase Foo(4):fmt.Println("Second case")}}