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Checkpoint 6

Paul Hudson    @twostraws   

Structs sit at the core of every SwiftUI app, so it’s really important you take some extra time to make sure you understand what they do and how they work.

To check your knowledge, here’s a small task for you: create a struct to store information about a car, including its model, number of seats, and current gear, then add a method to change gears up or down. Have a think about variables and access control: what data should be a variable rather than a constant, and what data should be exposed publicly? Should the gear-changing method validate its input somehow?

As always I’ll write some hints below, but first I’m going to leave some space so you don’t see the hints by accident. As always, it’s a really good idea to try this challenge yourself before looking at the hints – it’s the fastest way to identify parts you feel less confident with.

Hacking with Swift+ subscribers can get a complete video solution for this checkpoint here: Solution to Checkpoint 6. If you don’t already subscribe, you can start a free trial today.

Still here? Okay, here are some hints:

  • A car’s model and seat count aren’t going to change once produced, so they can be constant. But its current gear clearly does change, so make that a variable.
  • Changing gears up or down should ensure such a change is possible – there is no gear 0, for example, and it’s safe to assume a maximum of 10 gears should cover most if not all cars.
  • If you use private access control, you will probably also need to create your own initializer. (Is private the best choice here? Try it for yourself and see what you think!)
  • Remember to use the mutating keyword on methods that change properties!
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