reduce(into: [:]) equivalent for Combine in Swift

Question

I've been struggling to find an equivalent for reduce(into:_:) in Combine.

enum GenericError : Error {
    case with(message: String)
}

class Constants {
    fileprivate static let scheme = "sampleScheme"
    fileprivate static let host = "com.sampleHost"
    fileprivate static let authPath = "/auth"
    static let authQuery = "key"
}

func parse(_ url: URL, queryPathsFilterByKey: [String]) throws -> [String: String] {
    guard url.scheme == Constants.scheme,
          url.host == Constants.host,
          url.path == Constants.authPath,
          let urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: true),
          let queryItems = urlComponents.queryItems else {
        
        throw GenericError.with(message: "Invalid deep link.")
    }
    
    // Create a [String:String] from [UrlQueryItems]
    let query = queryItems.reduce(into: [:]) { result, item in
        result[item.name] = item.value
    }

    let result = query.filter { queryPathsFilterByKey.contains($0.key) }

    guard !result.isEmpty else {
            throw GenericError.with(message: "Error parsing query Items (deep linking)")
    }

    return result
}

what operator replaces reduce(into:) in Combine?

Answer 1

Found a way to do this

func parse(_ url: URL, queryPaths: [String]) -> AnyPublisher<[String: String], GenericError> {
        guard url.scheme == Constants.scheme,
              url.host == Constants.host,
              url.path == Constants.authPath,
              let urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: true),
              let queryItems = urlComponents.queryItems else {

            return Fail(outputType: [String:String].self, failure: GenericError.with(message: "Invalid deep link"))
                .eraseToAnyPublisher()
        }
        
        return queryItems
            .publisher
            .reduce ([String:String]()) { dictionary, value in
                var dict = dictionary
                dict[value.name] = value.value
                return dict
            }
            .filter { $0.allSatisfy { queryPaths.contains($0.key) } }
            .flatMap { dictionary -> AnyPublisher<[String:String], GenericError> in
                if(dictionary.isEmpty)
                {
                    return Fail(outputType: [String:String].self, failure: GenericError.with(message: "Error parsing query Items (deep linking)"))
                        .eraseToAnyPublisher()
                } else {
                    return Just(dictionary)
                        .setFailureType(to: GenericError.self)
                        .eraseToAnyPublisher()
                }
            }
            .eraseToAnyPublisher()
    }

Not sure if this is the best way but worked.