SwiftUI view depending on abstract

[kelvinlauKL]

Checklist

• [x] I've looked at the contribution guidelines.

Description

Been doing some experimentation on having SwiftUI views to depend on an abstract model. The model could then be injected and have mock representations for testing.

Pros to this approach

• Ability to control surface area of Bindable properties
• Extracts some responsibility away from SwiftUI view
• SwiftUI view can now depend on an abstract type rather than concrete

Cons

• Binding<Value> requires a backing property; You will need a separate variable to hold the state of the Binding:

var _email = ""
var email: Binding<String> { return .init(getValue: {  self._email }, setValue: { self._email = $0 }) }

• Unable to harness the power of property wrappers
• Compiler complains if you try to use a struct type that exposes a Binding (binding requires a way to mutate some backing property, which violates the value semantics of the struct)

Asking for opinions on whether this is a good idea or not. Relevant thread with some opinions from Joe Groff: https://forums.swift.org/t/state-messing-with-initializer-flow/25276/8

[RCacheaux]

I really like this. I think we can build on it and iterate on it. This gave me an idea for how to combine MVVM, use cases, and a bit of Redux for a really nice clean architecture. Go ahead and merge this in and I'll raise some PRs branching off.