Check out ReactiveCocoa/Loop for a ReactiveSwift-based unidirectional data flow architecture that can integrate with SwiftUI. If you aren't adopting SwiftUI just yet, it can be used in conjunction with declarative UI frameworks like Bento or Carbon to provide you a SwiftUI-like developer experience.

Check out Pointfree's Compositional Architecture if you are building a SwiftUI + Combine application from scratch, and you aren't already familiar with the unidirectional data flow pattern.