Decodable

The Decodable protocol is used to easily decode JSON or similar data formats like XML. The required initializer is init(from: Decoder) which creates a new instance by decoding from the given decoder. The Decodable protocol is often used with the JSONDecoder class. Decodable should be used when there’s only a need to read data, when reading and writing are required the Codable protocol should be implemented.

Syntax

Create a structure to represent the data to decode, followed by Decodable using the standard syntax of a Swift protocol.

struct DataName: Decodable {
  // Properties that conform to Decodable
}

Example

In the example below, a User struct is defined and the Decodable protocol is used with JSONDecoder to convert stored JSON into a data object.

import Foundation
struct User: Decodable {
   var name: String
   var age: Int
   var location: String
 }

 let userJson = """
 {
   "name": "Charlotte Lucas",
   "age": 27,
   "location": "England"
 }
 """

 let userData = Data(userJson.utf8)

 let decoder = JSONDecoder()
 let user = try decoder.decode(User.self, from: userData)
 print(user.name)

This will result in the following output:

Charlotte Lucas