Swift extensions are the smart way to add functionality to existing types, and you're going to meet them time and time again – and hopefully write quite a few of your own too. They aren't all-encompassing, because they don't let you add properties to a class whereas a full subclass would, but they are easy to use and easy to share so I'm sure you'll use them frequently.
In this project, you've also learned a little of how useful Swift playgrounds can be for prototyping code, because the immediate feedback you get makes it extremely easy to try things out and make quick adjustments.
You finished another project, and I'm glad Hacking with Swift helped you. Now I need your help. Please take just a moment out of your day to tell others about Hacking with Swift so they can benefit too.
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Paul Hudson is the creator of Hacking with Swift, the most comprehensive series of Swift books in the world. He's also the editor of Swift Developer News, the maintainer of the Swift Knowledge Base, and Mario Kart world champion. OK, so that last part isn't true. If you're curious you can learn more here.
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