Optional Default Parameter in Swift

Question

I have a function with default parameters in swift.

func test(string: String = "", middleString: String = "", endString: String = "") -> Void {   // do stuff } 

I want to pass in variables that will be optional strings.

let string: String?  let middleString: String? let endString: String? 

How do I make it so that if the parameters are nil, use the default parameters. If not, then use the values within the optionals.

test(string, middleString: middleString, endString: endString)

Answer 1

You'll have to use Optional strings String? as your argument type, with default values of nil. Then, when you call your function, you can supply a string or leave that argument out.

func test(string: String? = nil, middleString: String? = nil, endString: String? = nil) -> Void {     let s = string ?? ""     let mS = middleString ?? ""     let eS = endString ?? ""     // do stuff with s, mS, and eS, which are all guaranteed to be Strings } 

Inside your function, you'll have to check each argument for nil and replace with a default value there. Using the ?? operator makes this easy.

You can then call your function by supplying all arguments, no arguments, or only the ones you want to include:

test(string: "foo", middleString: "bar", endString: "baz") test() test(string: "hello", endString: "world")