I was dealing with a request that need to modify our app config structure, the modification was moving the EncodingOption parameter to the EditingOptions class from OutputOptions struct.

Hierarchy of the config

AppConfig {
profile: ProfileSetting
}

ProfileSetting {
editSetting:EditingOptions
outputSetting: OutputOptions
}

Previous data structure:

class EditingOptions: NSObject, Codable {
//..other parameters
}

struct OutputOptions: Codable {
var barcodeEncoding: EncodingOption = .utf8
//..other parameters
}

Modified data structure:

class EditSetting: NSObject, Codable {
var encodingOption: EncodingOption
//..other parameters
}

struct OutputSetting: Codable {
//..other parameters
}

The modified structure was not compatible with previous config file with the JSON error keyNotFound:

keyNotFound(CodingKeys(stringValue: "encodingOption", intValue: nil), 
Swift.DecodingError.Context(codingPath: [
CodingKeys(stringValue: "profileManage", intValue: nil), CodingKeys(stringValue: "deviceName",
 intValue: nil), CodingKeys(stringValue: "profiles", intValue: nil), 
_JSONKey(stringValue: "Index 0", intValue: 0), 
CodingKeys(stringValue: "outputOptions", intValue: nil)
],
 debugDescription: "No value associated with key CodingKeys(stringValue: "encodingOption", intValue: nil) ("encodingOption").", underlyingError: nil))

The solution from ChatGPT was add a init(from decoder: Decoder) method for ProfileSetting class:

required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

        //...other parameters
        
        if let editingOptions = try? container.decode(EditingOptions.self, forKey: .editingOptions) {
            self.editingOptions = editingOptions
        } else {
            self.editingOptions = EditingOptions()
        }
    }

The solution did resolved the keyNotFound error, however, I’m not sured that the solution was the RIGHT way to solve the issue.