Tour of Go 2.0

Type switches

Need to branch on multiple types? A type switch lets you do several type assertions in one clean construct.

switch v := i.(type) {
case T:
	// here v has type T
case S:
	// here v has type S
default:
	// no match; here v has the same type as i
}

The syntax is like a type assertion — i.(type) — except you use the keyword type instead of a specific type name. In each case branch, v is automatically typed correctly.

Try it: do(true) hits the default case. Add a case bool: branch and see what happens.

main.go ▶ Run in Playground 
package main

import "fmt"

func do(i interface{}) {
	switch v := i.(type) {
	case int:
		fmt.Printf("Twice %v is %v\n", v, v*2)
	case string:
		fmt.Printf("%q is %v bytes long\n", v, len(v))
	default:
		fmt.Printf("I don't know about type %T!\n", v)
	}
}

func main() {
	do(21)
	do("hello")
	do(true)
}