NEW: My new book Pro SwiftUI is out now – level up your SwiftUI skills today! >>

When to use default parameters for functions

Paul Hudson    @twostraws   

Updated for Xcode 14.2

Default parameters let us make functions easier to call by letting us provide common defaults for parameters. So, when we want to call that function using those default values we can just ignore the parameters entirely – as if they didn’t exist – and our function will just do the right thing. Of course, when we want something custom it’s there for us to change.

Swift developers use default parameters very commonly, because they let us focus on the important parts that do need to change regularly. This can really help simplify complex function, and make your code easier to write.

For example, imagine some route finding code such as this:

func findDirections(from: String, to: String, route: String = "fastest", avoidHighways: Bool = false) {
    // code here

That assumes that most of the time folks want to drive between two locations by the fastest route, without avoiding highways – sensible defaults that are likely to work most of the time, while giving us the scope to provide custom values when needed.

As a result, we can call that same function in any of three ways:

findDirections(from: "London", to: "Glasgow")
findDirections(from: "London", to: "Glasgow", route: "scenic")
findDirections(from: "London", to: "Glasgow", route: "scenic", avoidHighways: true)

Shorter, simpler code most of the time, but flexibility when we need it – perfect.

Hacking with Swift is sponsored by Play

SPONSORED Play is the first native iOS design tool created for designers and engineers. You can install Play for iOS and iPad today and sign up to check out the Beta of our macOS app with SwiftUI code export. We're also hiring engineers!

Click to learn more about Play!

Sponsor Hacking with Swift and reach the world's largest Swift community!

Buy Pro Swift Buy Pro SwiftUI Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.8/5

Unknown user

You are not logged in

Log in or create account

Link copied to your pasteboard.