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Raphael Reiter
Raphael Reiter
6,820 Points

underscore in Swift 3 ?


Can someone please explain to me what is the signification of the underscore in Swift 3?


func move(_ direction: Direction)

1 Answer

David Papandrew
David Papandrew
8,386 Points

Hi Raphael,

See the code below and the comments. It should help illustrate. Try in Playgrounds so you can play around with it.

//Example 1: Single name parameter
//Function has a single name that works as external and internal name.

func sayHello(greeting: String) {

sayHello(greeting: "Hello")

//Example 2: External and internal named parameter
//Function has external name, yourGreeting and internal name, greeting

func sayHelloExternalName(yourGreeting greeting: String) {
    print(greeting) //we use internal name inside function

//We use external name outside the function
sayHelloExternalName(yourGreeting: "Hello")

//Example 3: Parameter with underscore
//Function has underscore for external name which means "no need to use an external name"

func sayHelloNoExternalName(_ greeting: String) {
    print(greeting) //internal name used

//Function just passes argument. No external name.
Raphael Reiter
Raphael Reiter
6,820 Points

ok. very clear. thanks :-)