Checking if Optional<Int> is nil

Question

Help me understand this weird nil-check.

I have a variable of the type Int? and I need to switch on nil.

This makes sense:

buildFrameId is 3 and not equal to nil

This does not:

buildFrameId is nil and still not equal to nil

How do I check (single line statement) if buildFrameId is equal to nil?

You have a nested optional and ... == nil tests the outermost level. — Martin R
– Martin R, Commented Jun 27, 2024 at 11:58
You are right @MartinR. It's declared like this var buildFrameId: Int?? in order to achieve that a nil-value is JSON encoded to "buildFrameId": null. having only one optional-sign omits the property when JSON encoded. Any ideas on how to double unwrap or avoid the ?? — esbenr
– esbenr, Commented Jun 27, 2024 at 12:42
@RoyRodney Thanks for the link, My solution is exactly the first answer - if you check the comments, I also commented. There are many creative suggestions in that thread - all of them (besides the ??) are an eyesore. At least it should be possible to configure the JSONEncoder to do this. — esbenr
– esbenr, Commented Jun 27, 2024 at 14:54

esbenr · Accepted Answer · 2024-06-27 15:19:59Z

While @martin-r led me to the reason for this behaviour, I came up with a solution my self.

The "problem" is that I'm declaring the variable as nested optional:

var buildFrameId: Int??

This is needed in order for the JSONEncoder to actually encode the nil-property as null instead of omitting it.

The solution is to flatten the nested optional - then normal unwrapping works. I used the proposed solution from this article: https://brodigy.medium.com/nested-optionals-in-swift-design-mistake-by-apple-7240ea61edd

Here is the code for a flattening extension:

extension Optional {
    public func flatten<Result>() -> Result?
    where Wrapped == Result?
    {
        return self.flatMap { $0 }
    }
}

It still doesen't feel that well, but it's better than the proposed solutions in the link provided by @roy-rodney. Encode nil value as null with JSONEncoder

I don't know why someone down voted the question - I guess it would have been a bit more helpful with a comment on why.

1 Answer 1