これでもだめ #CodePiece

CodePiece.swift

(0...3)
    .publisher
    .flatMap { i -> AnyPublisher<Int, Never> in
        
        Future<Int, Never> { promise in
            
            DispatchQueue.global().async {
                print("start", i, "----", Thread.current)
                sleep(UInt32([0, 2, 3, 5].randomElement()!))
                print("end", i)
                
                promise(.success(i * 2))
            }
        }
        .eraseToAnyPublisher()
    }
    .collect()
    .sink { (i) in
        print(i)
    }