I'm using JSON Placeholder post api to make a HTTP POST request using Generics and Result Type in Swift. Here is my codable struct for request and response. For this API both response and request are same.
enum AddPostModel{
struct AddPostRequest: Codable{
let title: String
let body: String
let userId: String
let id: String
}
struct AddPostResponse: Codable{
let title: String
let body: String
let userId: String
let id: String
}
}
Here is my POST request code using URLSession async/await, generics and result type.
func sendPostRequest<T: Codable>(url: String,responseType: T.Type,params: T) async -> Result<T,Error>{
do{
let session = URLSession(configuration: .default)
guard let url = URL(string: url) else{return .failure(HTTPError.invalidUrl) }
var request = URLRequest(url: url)
request.httpMethod = HTTPMethods.POST.method
let jsonData = try JSONEncoder().encode(params)
request.httpBody = jsonData
let (data,response) = try await session.data(for: request)
guard let urlResponse = response as? HTTPURLResponse , (200...299).contains(urlResponse.statusCode)
else{ return .failure(HTTPError.failedResponse)}
let jsonResponse = try JSONDecoder().decode(responseType.self, from: data)
return .success(jsonResponse)
}
catch{
return .failure(error)
}
}
Here I call the Post method
func addPost(params: AddPostModel.AddPostRequest) async -> Result<AddPostModel.AddPostResponse,Error>{
return await service.sendPostRequest(url: Constant.BASE_URL + "/" + HomeEndPoints.posts.path, responseType: AddPostModel.AddPostResponse.self, params: params)
}
When I try to build I get the following error in the params parameter of the sendPostRequest method
Cannot convert value of type
AddPostModel.AddPostRequest
to expected argument typeAddPostModel.AddPostResponse
You're using the same generic T
for both request and response, that's impossible. Generic parameter mean a placeholder type with optional constraints that will be replaced at compile time, and they can't be two different types in the same context. Declaring another generic type like U
for request parameters will fix this.
func sendPostRequest<T: Codable, U: Codable>(url: String, responseType: T.Type, params: U) async -> Result<T, Error> {
...
}