Codable variable in Codable Class

Question

Given this class:

class MyClass: Codable {
    var variable : Codable? = nil
}

I get error:

Type 'MyClass' does not conform to protocol 'Decodable'

Type 'MyClass' does not conform to protocol 'Encodable'

How can I have a generic variable that conforms to Codable as a property in a Codable class?

None of the answers have actually covered the reason for your error: it is because [Swift procotols don't conform to themselves](https://stackoverflow.com/questions/33112559/protocol-doesnt-conform-to-itself). — Dávid Pásztor, Jun 13 '18 at 15:04
I believe it has to do with Codable. [This code works](https://gist.github.com/hayek/b7bdd14e720e36ad5b38ba518d1adf73). I think the reason is Codable itself, check out Y.Bonafons answer. — amir, Jun 13 '18 at 19:19

score 4 · Accepted Answer · 2018-06-13T12:57:44.810

4

May be like this if i got your question correctly

class MyClass<T: Codable>: Codable {
    var variable : T? = nil
}

edited Jun 13 '18 at 12:57

answered Jun 13 '18 at 12:52

score 3 · Answer 2 · answered Jun 13 '18 at 13:09

If you try to implement your decoder you will have something like:

class MyClass: Codable {
    var variable: Codable?
    enum MyClassKeys: String, CodingKey {
        case variable = "variable"
    }
    required init(from decoder: Decoder) {
        let container = try! decoder.container(keyedBy: MyClassKeys.self)
        variable = try! container.decode(XXXX, forKey: .variable)
    }
}

But instead of XXXX, you should put a class type (for example String.self). What can you put here? Its not possible for the compiler to guess what you want. Instead of Codable type maybe you can put a class which conform to Codable protocol. So you can have something like this:

class MyClass: Codable {
    var variable: MyClass?
    enum MyClassKeys: String, CodingKey {
        case variable = "variable"
    }
    required init(from decoder: Decoder) {
        let container = try! decoder.container(keyedBy: MyClassKeys.self)
        variable = try! container.decode(MyClass.self, forKey: .variable)
    }
}

Thank you, your answer helped me understand why I am getting the error. — amir, Jun 13 '18 at 13:13

score 0 · Answer 3 · answered Jun 13 '18 at 12:40

0

You can't.

But as a workaround, you can create an enum conforming to Codable.

enum SubType: Codable {
    case foo
    case bar
}

answered Jun 13 '18 at 12:40

CZ54

5,488
1
24
39

Codable variable in Codable Class

3 Answers3