I’m only learning Swift and iOS dev but a fair amount of people recommended me to take a deeper look into Kickstarter for iOS app: https://github.com/kickstarter/ios-oss
2 of the guys that worked on that app are doing video series about functional programming now where they talk a lot about the ideas in the app, https://www.pointfree.co
It's got some interesting usage of custom Swift operators to create almost diagrammatic code, like here: https://github.com/kickstarter/ios-oss/blob/master/Kickstart...
And it's the first iOS codebase I've seen that puts test files right next to the files that define the things being tested. It's all there together.Tons of other goodies to find.