Copy on Write in Swift

Swift developers often get the impression that there's a lot of magic going on under the hood. But in fact, Swift is built around composing different types together. You can have your cake and eat it too, or you can have your array and eat your dictionary too for example. And I feel like we can use the same design pattern here as well where if you want a custom API to access your data, for example, you might want it to be accessible both using an ID or an index and so on.