できた #CodePiece

CodePiece.swift

extension Sequence {
    
    func traverse<T>(_ transform: @escaping (Element) -> AnyPublisher<T, Never>) -> AnyPublisher<[T], Never> {
        
        var index = 0
        
        return self
            .publisher
            .flatMap { i -> AnyPublisher<(Int, T), Never> in
                
                defer { index += 1 }
                let index = index
                
                return Future<(Int, T), Never> { promise in
                    
                    DispatchQueue.global().async {
                        
                        let se = DispatchSemaphore(value: 1)
                        
                        DispatchQueue(label: "AAAA").async {
                        
                        _ = transform(i)
                            .sink { t in
                                
                                promise(.success((index, t)))
                                se.signal()
                            }
                        }
                        
                        se.wait()
                    }
                }
                .eraseToAnyPublisher()
            }
            .collect()
            .map { $0.sorted { $0.0 < $1.0 } }
            .map { $0.map { $0.1 } }
            .eraseToAnyPublisher()
    }
}