decode(type:decoder:)

Declaration

func decode<Item, Coder>(type: Item.Type, decoder: Coder) -> Publishers.Decode<Self, Item, Coder> where Item : Decodable, Coder : TopLevelDecoder, Self.Output == Coder.Input

Parameters

• type:

  The encoded data to decode into a struct that conforms to the Decodable protocol.

• decoder:

  A decoder that implements the Topleveldecoder protocol.

Return Value

A publisher that decodes a given type using a specified decoder and publishes the result.

Discussion

Use decode(type:decoder:) with a JSONDecoder (or a PropertyListDecoder for property lists) to decode data received from a URLSession.DataTaskPublisher or other data source using the Decodable protocol.

In this example, a PassthroughSubject publishes a JSON string. The JSON decoder parses the string, converting its fields according to the Decodable protocol implemented by Article, and successfully populating a new Article. The Publishers.Decode publisher then publishes the Article to the downstream. If a decoding operation fails, which happens in the case of missing or malformed data in the source JSON string, the stream terminates and passes the error to the downstream subscriber.

struct Article: Codable {
    let title: String
    let author: String
    let pubDate: Date
}

let dataProvider = PassthroughSubject<Data, Never>()
cancellable = dataProvider
    .decode(type: Article.self, decoder: JSONDecoder())
    .sink(receiveCompletion: { print ("Completion: \($0)")},
          receiveValue: { print ("value: \($0)") })

dataProvider.send(Data("{\"pubDate\":1574273638.575666, \"title\" : \"My First Article\", \"author\" : \"Gita Kumar\" }".utf8))

// Prints: ".sink() data received Article(title: "My First Article", author: "Gita Kumar", pubDate: 2050-11-20 18:13:58 +0000)"

See Also

Encoding and decoding

• encode(encoder:)