How write parseJSON universal function? Swift - json

Question

I have different structs as my dataModels.
when i want to parse data with JsonDecoder().decode i need set a .Type.self in .decoder(SomeType.self , from: data)
I want write a support function which can return right Type respectively.
something like this
But I don't know how...
func check<T>(string: String) -> T
if string == "something" {
return Something.type
}
func parseJSON(from data: Data , with address: String)-> Codable? {
let type = check(string: address)
let decoder = JSONDecoder()
do {
let decodedData = try decoder.decode(type.self, from: data)
return decodedData
} catch let error {
print(error)
return nil
}
}
WHEN I WRITE THE code below, Everything works fine. But I always have to write parseJSON func with little difference over and over again
func fetch(from adress: String) {
guard let url = URL(string: adress) else {print("can't get URL from current urlAdress"); return}
let json = makeHttpBody(from: adress)
let jsonData = try? JSONSerialization.data(withJSONObject: json)
var request = URLRequest(url: url , cachePolicy: .useProtocolCachePolicy)
request.httpMethod = K.post
request.setValue(K.contentType, forHTTPHeaderField:K.applicationJson)
request.timeoutInterval = Double.infinity
request.httpBody = jsonData
let session = URLSession(configuration: .default)
let task = session.dataTask(with: request) { (data, responce, error) in
if error != nil {
print(error!.localizedDescription)
}
if let safeData = data {
if adress == K.balanceUrl {
if let parsedData = self.parseJsonBalance(from: safeData) {
self.delegate?.didUpdateData(with: self, with: parsedData)
}
} else if adress == K.projectsUrl {
if let parsedData = self.parseJsonProject(from: safeData) {
self.delegate?.didUpdateData(with: self, with: parsedData)
}
}
}
}
task.resume()
}
func makeHttpBody(from StringData: String) -> [String: Any] {
switch StringData {
case K.balanceUrl:
return K.authorization
case K.projectsUrl:
return K.projects
default:
return ["none" : "none"]
}
}

Answer 1

Your approach cannot work, you have to use a generic type constrained to Decodable. Checking for strings at runtime is not a good practice.
This is a reduced version of your code, the error is handed over to the caller
func parseJSON<T : Decodable>(from data: Data) throws -> T {
return try JSONDecoder().decode(T.self, from: data)
}
Then you can write (the return type must be annotated)
let result : [Foo] = try parseJSON(from: data)
Or if you want to specify the type in the function
func parseJSON<T : Decodable>(from data: Data, type : T.Type) throws -> T {
return try JSONDecoder().decode(T.self, from: data)
}
let result = try parseJSON(from: data, type: [Foo].self)