Is it possible to decode variable as nil if there's a type mismatch error

Question

So basically what I want is for anytime that the API returns a type different than what the model expects to make that property nil.

For example:

struct Person {
var name: String?
var someType: String?
}

If the API returns a number for the someType property instead of a string I want to just make its value nil

I know I can do that implementing the init(from decoder: Decoder) initializer but then I'd have to set that up for every property of every response which would take a long time. Is there a better and quicker way?

Answer 1

You can implement your own decodeIfPresent for Optional String and return nil if there is a type mismatch. This way you wont have to implement a custom initializer:

extension KeyedDecodingContainer {
    public func decodeIfPresent(_ type: String.Type, forKey key: KeyedDecodingContainer<K>.Key) throws -> String? {
        do {
            return try decode(String.self, forKey: key)
        } catch DecodingError.typeMismatch, DecodingError.keyNotFound {
            return nil
        }
    }
}

---

struct Person: Decodable {
    let name: String?
    let someType: String?
}

---

let json = #"{"name":"Steve","someType":1}"#
do {
    let person = try JSONDecoder().decode(Person.self, from: Data(json.utf8))
    person.name      // "Steve"
    person.someType  // nil
} catch {
    print(error)
}

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