CodableNilOnFail

Easy failable optional enum properties in Swift Codable.

Installation

You can add CodableNilOnFail to an Xcode project by adding it as a package dependency.

1. From the File menu, select Add Packages…
2. Enter https://github.com/sochalewski/CodableNilOnFail into the package repository URL text field.
3. Add the package to your app target.

Why?

Consider the following data model:

struct Car: Codable {
    enum Manufacturer: String, Codable {
        case toyota, volkswagen, ford, honda, generalMotors
    }
    
    var manufacturer: Manufacturer?
    var vin: String?
    var owner: String?
}

Everything works perfectly if the received JSON matches the available Manufacturer enum values, like this:

{
    "manufacturer": "toyota",
    "vin": "JT4RN67S0G0002845",
    "owner": null
}

But Car.manufacturer is optional, so it makes sense to have a valid model, even if the received manufacturer doesn’t match one of the currently supported ones:

{
    "manufacturer": "tesla",
    "vin": "5YJSA2DP8DFP22249",
    "owner": "Elon Musk"
}

Unfortunately decoding this with JSONDecoder results in getting nil for the whole Car instead of just Car.manufacturer.

This can be solved by custom init(from:) of the Decodable protocol, but that’s a lot of boilerplate, especially when you have dozens of enums in your models.

This is where CodableNilOnFail comes in!

Usage

Just add the @NilOnFail property wrapper to your optional RawRepresentable properties.

struct Car: Codable, Equatable {
    enum Manufacturer: String, Codable {
        case toyota, volkswagen, ford, honda, generalMotors
    }
    
    @NilOnFail var manufacturer: Manufacturer?
    var vin: String?
    var owner: String?
}

Author

Piotr Sochalewski, sochalewski.github.io