Code snippets for https://alexdremov.me/ios-app-as-a-microservice-using-swiftui-in-modular-app/

LogInState.swift

class LogInState: ObservableObject {
    @Published var isLoggedIn: Bool
    
    init(isLoggedIn: Bool) {
        self.isLoggedIn = isLoggedIn
    }
    
    func loggedOut() {
        isLoggedIn = false
    }
    
    func loggedIn() {
        isLoggedIn = true
    }
}

MeViewModules.swift

struct MyView: View {
	@ObservedObject var logInState: LogInState

	var body: some View {
    	Text(logInState.isLoggedIn ? "Yes" : "No")
    }
}

...
let logInState = LogInState(isLoggedIn: true)
HomePageModule(logInState: logInState)
...
SettingsModule(logInState: logInState)

ModulesReadonly.swift

struct ReadOnlyModule: View {
    @ObservedObject
    @ObservableValue
    var logInState: Bool
    
    init(logInState: ObservableValue<Bool>) {
        self._logInState = .init(wrappedValue: logInState)
    }
    
    var body: some View {
        Text(logInState ? "Yes" : "No")
    }
}

struct ModifyModule: View {
    @ObservableProperty
    var logInState: Bool
    
    init(logInState: ObservableProperty<Bool>) {
        self._logInState = logInState
    }
    
    var body: some View {
        Button("toggle") {
            logInState = !logInState
        }
    }
}

struct MyView: View {
    @ObservableProperty
    var logInState: Bool
    
    init(logInState: ObservableProperty<Bool>) {
        self._logInState = logInState
    }
    
    var body: some View {
        VStack {
        	// projected read-only value (ObservableValue)
            ReadOnlyModule(logInState: $logInState)
            
            // ObservableProperty reference
            ModifyModule(logInState: _logInState)
        }
    }
}

MyViewObservable.swift

struct MyView: View {
    @ObservedObject
    @ObservableProperty
    var logInState: Bool
    
    init(logInState: ObservableProperty<Bool>) {
        self._logInState = .init(initialValue: logInState)
    }
    
    var body: some View {
        VStack {
            Text(logInState ? "Yes" : "No")
            Button("toggle") {
                logInState = !logInState
            }
        }
    }
}

ObservableProperty.swift

@dynamicMemberLookup
@propertyWrapper
public class ObservableProperty<Output>: ObservableObject {
    @Published private var storedValue: Output
    
    public var wrappedValue: Output {
        get {
            storedValue
        }
        set {
            storedValue = newValue
        }
    }
    
    public init(wrappedValue initialValue: Output) {
        self.storedValue = initialValue
    }
    
    public subscript<Result>(dynamicMember keyPath: WritableKeyPath<Output, Result>) -> Result {
        get {
            storedValue[keyPath: keyPath]
        }
        set {
            storedValue[keyPath: keyPath] = newValue
        }
    }
    
    public subscript<Result>(dynamicMember keyPath: KeyPath<Output, Result>) -> Result {
        storedValue[keyPath: keyPath]
    }
    
    public var publisher: AnyPublisher<Output, Never> {
        $storedValue.eraseToAnyPublisher()
    }
    
    public var projectedValue: ObservableValue<Output> {
        ObservableValue<Output>(
            initialValue: storedValue,
            publisher: publisher
        )
    }
}

ObservablePropertyAdditions.swift

public class ObservableProperty<Output>: ObservableObject {
	...
    public var publisher: AnyPublisher<Output, Never> {
        $storedValue.eraseToAnyPublisher()
    }
    
    public var projectedValue: ObservableValue<Output> {
        ObservableValue<Output>(
            initialValue: storedValue,
            publisher: publisher
        )
    }
	...
}

ObservablePropertyFirst.swift

import Foundation
import Combine

@dynamicMemberLookup
@propertyWrapper
public class ObservableProperty<Output>: ObservableObject {
    @Published private var storedValue: Output
    
    public var wrappedValue: Output {
        get {
            storedValue
        }
        set {
            storedValue = newValue
        }
    }
    
    public init(wrappedValue initialValue: Output) {
        self.storedValue = initialValue
    }
    
    public subscript<Result>(dynamicMember keyPath: WritableKeyPath<Output, Result>) -> Result {
        get {
            storedValue[keyPath: keyPath]
        }
        set {
            storedValue[keyPath: keyPath] = newValue
        }
    }
    
    public subscript<Result>(dynamicMember keyPath: KeyPath<Output, Result>) -> Result {
        storedValue[keyPath: keyPath]
    }
}

ObservableValue.swift

@dynamicMemberLookup
@propertyWrapper
public class ObservableValue<Output>: ObservableObject {
    @Published private var storedValue: Output
    private var cancellable: AnyCancellable?
    public var wrappedValue: Output {
        storedValue
    }
    
    public init(wrappedValue initialValue: Output) {
        fatalError("ObservableValue cannot be initialized with value. Use constant()")
    }
    
    init<Pub: Publisher<Output, Never>>(initialValue: Output, publisher: Pub) {
        storedValue = initialValue
        cancellable = publisher.sink { newValue in
            self.storedValue = newValue
        }
    }
    
    public subscript<Result>(dynamicMember keyPath: WritableKeyPath<Output, Result>) -> Result {
        get {
            storedValue[keyPath: keyPath]
        }
        set {
            storedValue[keyPath: keyPath] = newValue
        }
    }
    
    public subscript<Result>(dynamicMember keyPath: KeyPath<Output, Result>) -> Result {
        storedValue[keyPath: keyPath]
    }
    
    public static func constant(initialValue: Output) -> ObservableValue<Output> {
        .init(
            initialValue: initialValue,
            publisher: Empty()
        )
    }
    
    public var publisher: Published<Output>.Publisher {
        $storedValue
    }
}