Generics Type 'T' does not conform to protocol 'Encodable'

Question

I am trying to use generics in swift to intrepret http response. All The Json responses have the same signature at the top :

{
"request": "foo",
"result": "[{},{}....]
}

So I am using this :

public struct HttpResponse<DATA: Codable>  {
    public let request: Bool?
    public let result: DATA?

    enum CodingKeys: String, CodingKey {
        case request= "request"
        case result = "result"

     }   ..

In My Network layer:

final class Network<T: Decodable> {
 func getItems(_ path: String) -> Observable<HttpResponse<[T]>> {
    let absolutePath = "\(endPoint)/\(path)"
    return RxAlamofire
        .data(.get, absolutePath)
        .debug()
        .observeOn(scheduler)
        .map({ data -> [T] in
            return try JSONDecoder().decode([T].self, from: data)
        })
}

I get this error in Observable<PlutusResponse<[T]>>

Generics Type 'T' does not conform to protocol 'Encodable'

How to correctly use this?

Stephan Schlecht Stephan Schlecht · Accepted Answer · 2018-11-17T20:59:03

There is a mismatch:

It should be HttpResponse<DATA: Decodable> instead of HttpResponse<DATA: Codable>, see definition Network<T: Decodable>.

Codable declares conformance to both Decodable and Encodable protocols, see the definition of Codable:

public typealias Codable = Decodable & Encodable

So your HttpResponse expects a generic that conforms to both Decodable and Encodable protocol. But in the definition of Network a generic that conforms only to Decodable is used. Therefore as soon as the compiler checks the method signature of getItems, it complains that 'T' does not conform to protocol 'Encodable'.

Generics Type 'T' does not conform to protocol 'Encodable'

1 Answers