Type Switches

A type switch makes it easy to do several type assertions in a series.

A type switch is similar to a regular switch statement, but the cases specify types instead of values.

func printNumericValue(num interface{}) {
	switch v := num.(type) {
	case int:
		fmt.Printf("%T\n", v)
	case string:
		fmt.Printf("%T\n", v)
	default:
		fmt.Printf("%T\n", v)
	}
}

func main() {
	printNumericValue(1)
	// prints "int"

	printNumericValue("1")
	// prints "string"

	printNumericValue(struct{}{})
	// prints "struct {}"
}

fmt.Printf("%T\n", v) prints the type of a variable.

Assignment

After submitting our last snippet of code for review, a more experienced gopher told us to use a type switch instead of successive assertions. Let's make that improvement!

Implement the getExpenseReport function using a type switch.

• If the expense is an email then it should return the email's toAddress and the cost of the email.
• If the expense is an sms then it should return the sms's toPhoneNumber and its cost.
• If the expense has any other underlying type, just return an empty string and 0.0 for the cost.