rx-swift-late-init-behavior-relay.swift

import RxSwift
import RxCocoa

public final class LateInitBehaviorRelay<Element>: ObservableType {
    public typealias E = Element
    
    private let _relay: BehaviorRelay<Element?>
    
    public func accept(_ event: Element) {
        _relay.accept(event)
    }
    
    public var value: Element {
        guard let value = _relay.value else {
            fatalError("value is not initialized")
        }
        return value
    }
    
    public init() {
        _relay = BehaviorRelay<Element?>(value: nil)
    }
    
    public func subscribe<O: ObserverType>(_ observer: O) -> Disposable where O.E == E {
        return asObservable().subscribe(observer)
    }
    
    public func asObservable() -> Observable<Element> {
        return _relay.filter { $0 != nil }.map { $0! }
    }
}