Add support for Swift Observation

[DandyLyons]

It looks like SwiftTUI is only able to support view models on macOS, since @ObservedObject is only available on macOS.

If we supported language level Swift Observation, then SwiftTUI should be able to support view models on any platform.

It looks like it should be feasible to implement using a strategy similar to that found in View+Observable.swift.

[DandyLyons]

I have a working prototype of this. I'll send a PR soon.

[sisoje]

SwiftUI is a declarative framework based on reactivity and not on observability.
SwiftUI is not object oriented but based on value semantics and composability.
View models are cargo-culted from UIKit which is an imperative object-oriented framework.
View models do not belong to SwiftUI.

[DandyLyons]

SwiftUI is a declarative framework based on reactivity and not on observability.

False. SwiftUI has had first class support for observability since its first release via ObservedObject, EnvironmentObject and so many other mechanisms. In fact, Apple believes so strongly in observability that they added language level support for observability via Swift Observation.

View models do not belong to SwiftUI.

Whether or not view models and observability "belongs" in SwiftUI is irrelevant. It is already here and has been from the beginning. It is also already in this SwiftTUI library. If you don't like observation, then don't use it.

[sisoje]

Yes, SwiftUI does support observability but just to support legacy code. It is not BASED on observability but on reactivity.
You are using Observation wrong. It was ment to provide class semantics for the MODELS. It was never introduced so you can abuse it by writing view-models