How do you assign an optional Swift property a decoded primitive with `NSCoder`?

[Austin_Conlon]

For an example like:

someOptionalDouble = aDecoder.decodeDouble(forKey: "SomeKey")

I'm not sure how to avoid a crash if the double was encoded as nil, while also avoiding Apple's console warning that decoding primitives as an object will become an error in the future.

I tried an approach

extension NSCoder {
    func decodeOptionalDouble(forKey key: String) -> Double? {
        guard self.containsValue(forKey: key) else { return nil }
        return self.decodeDouble(forKey: key)
    }
}

But encounter an error

Error: Error Domain=NSCocoaErrorDomain Code=4864 "*** -[NSKeyedUnarchiver decodeDoubleForKey:]: value for key (SomeKey) is not a 64-bit float" UserInfo={NSDebugDescription=*** -[NSKeyedUnarchiver decodeDoubleForKey:]: value for key (SomeKey) is not a 64-bit float}.

The optional double property is encoded with func encode(_ object: Any?, forKey key: String).

[wes1 (Wes)]

Outside NSCoder, on the decode side, there's a separate API, decodeIfPresent, for optionals - e.g.,

let container = try decoder.container(keyedBy: CodingKeys.self)
self.score = try container.decodeIfPresent(Int.self, forKey: .ckScore)