A property wrapper that creates subject-backed observers (RxSwift)

Example.swift

class ViewModel {

    init() {
        // accessing underlying subject:
        $buttonTapped
            .asObservable()
            ...
    }
    
    // look ma, no explicit subject property
    @SubjectBackedObserver(PublishSubject.init)
    var buttonTapped: AnyObserver<Void>
}

SubjectBackedObserver.swift

@propertyWrapper
struct SubjectBackedObserver<Subject: SubjectType>: ObservableConvertibleType {
    private let subject: Subject
    private let typeErasingObserver: AnyObserver<Subject.Observer.Element>

    init(_ factory: () -> Subject) {
        let subject = factory()
        typeErasingObserver = AnyObserver<Subject.Observer.Element> { event in
            let observer: Subject.Observer = subject.asObserver()
            observer.on(event)
        }
        self.subject = subject
    }

    func asObservable() -> Observable<Subject.Element> {
        subject.asObservable()
    }

    var projectedValue: Self {
        self
    }

    var wrappedValue: AnyObserver<Subject.Observer.Element> {
        typeErasingObserver
    }
}