Switch Statements

Switch statements in Go are much more powerful than in JavaScript/TypeScript, generally they have the following syntax:

switch.go

var x int = 1

switch x {
case 1:
    fmt.Println("x is 1")
case 2:
    fmt.Println("x is 2")
default:
    fmt.Println("x is neither 1 nor 2")
}

You can also declare a variable in the switch statement using the shorthand := syntax, this variable will be then scoped to the switch statement:

switch_short.go

switch x := 1; x {
case 1:
    fmt.Println("x is 1")
case 2:
    fmt.Println("x is 2")
default:
    fmt.Println("x is neither 1 nor 2")
}
// x is not accessible here

However there is a key difference in behavior:

Note

Go’s switch statements don’t fall through!

No fall-through

The above code is equivalent to the following JavaScript/TypeScript code:

switch.ts

switch (x) {
    case 1:
        console.log("x is 1");
        break;
    case 2:
        console.log("x is 2");
        break;
    default:
        console.log("x is neither 1 nor 2");
}

To have fall-through behavior in Go, you need to explicitely say so via the fallthrough statement:

switch_fallthrough.go

switch x {
case 1:
    fmt.Println("x is 1")
    fallthrough
case 2:
    fmt.Println("x is 2")
default:
    fmt.Println("x is neither 1 nor 2")
}

If x is 1, it will print:

x is 1
x is 2

Case Expressions

While JavaScript/TypeScript is fairly limited, only allowing for equality checks ===, Go’s switch statements can use a variety of expressions:

Boolean Expressions

switch_bool.go

switch {
case x > 0:
    fmt.Println("x is positive")
case x < 0:
    fmt.Println("x is negative")
default:
    fmt.Println("x is zero")
}

Note, the absence of a condition after switch! This is perfectly valid in Go.

Function Calls

You can evaluate function calls in switch statements:

switch_func.go

func isChild(age int) bool {
    return age >= 0 && age < 13
}

func isTeen(age int) bool {
    return age >= 13 && age < 18
}

func isAdult(age int) bool {
    return age >= 18
}

func main() {
    age := 15

    switch {
    case isChild(age):
        fmt.Println("You are a child")
    case isTeen(age):
        fmt.Println("You are a teenager")
    case isAdult(age):
        fmt.Println("You are an adult")
    default:
        fmt.Println("Invalid age")
    }
}

Type Switches

todo