Rx’s handling of `withLatestFrom` completions.

rx_with_latest_from_completion.swift

import RxSwift

// **Scenario one**: `withLatestFrom`’s argument finishes first.

let first = PublishSubject<Int>()
let second = PublishSubject<Int>()
let disposeBag = DisposeBag()

first
	.withLatestFrom(second)
	.debug()
	.subscribe()
	.disposed(by: disposeBag)

second.onCompleted()

// Outputs (trimmed):
//
// ```
// -> subscribed
// ``

// **Scenario two**: Upstream finishes first.

// …

first.onCompleted()

// Outputs (trimmed):
//
// ```
// -> subscribed
// -> Event completed
// -> isDisposed
// ```