Swift Codable init

Question

I would like to do some initialization logic after the Swift Coding/Encoding feature has finished decoding a JSON.

struct MyStruct: Codable {
    let id: Int 
           


        

Answer 1

Use a factory method that first uses init(from:) and then calls your custom initialization code

struct Foo: Decodable {
    let name: String
    let id: Int

    var x: String!

    private mutating func finalizeInit() {
        self.x = "\(name) \(id)"
    }

    static func createFromJSON(_ data: Data) -> Foo? {
        guard var f = try? JSONDecoder().decode(Foo.self, from: data) else { 
            return nil 
        }
        f.finalizeInit()
        return f
    }
}

let sampleData = """
    { "name": "foo", "id": 42 }
    """.data(using: .utf8)!
let f = Foo.createFromJSON(sampleData)