Default parameter values

One convenience in Swift is that you can specify default values for parameters, which allows you to omit the parameter when calling. Let's take the preceding example situation, where we are creating a contact app to hold information about our family and friends. Many of your family members are likely to have the same family name as you, so you can set your family name as the default value for that parameter so that you only need specify the family name if it is different from the default.

Let's enter the following code into a playground:

func fullName(givenName: String, middleName: String, familyName: String = "Moon") -> String { 
    return "\(givenName) \(middleName) \(familyName)" 
}

Defining a default value looks similar to assigning a value to the familyName: String = "Moon" parameter. When calling the function, the parameter with the default value does not have to be given:

let keith = fullName(givenName: "Keith", middleName: "David") 
let alissa = fullName(givenName: "Alissa", middleName: "May") 
let laura = fullName(givenName: "Laura", middleName: "May", familyName: "Jones") 
print(keith) // Keith David Moon 
print(alissa) // Alissa May Moon 
print(laura)  // Laura May Jones