`decode` function comparison without Argo about argo

[michaelmcguire]

I notice you conspicuously left out "Role" in your translation 😉

For the model you have, that looks about right. But when you're dealing with types not handled by NSJSONSerialization, including arrays of those types, you get a lot more help from Argo.

[gfontenot]

Totally valid concern. In addition to what you posted, you'd also need to add the create function to your user models.

Also, keep in mind that pulling Argo in as a dependency of your framework would require users to link Argo (and Runes, and soon Box as well) to your user's apps (assuming they are using frameworks. CocoaPods will do this for them). That might be a deal breaker.

[paulyoung]

I notice you conspicuously left out "Role" in your translation

🙈 - updated to add that and fix one other issue.

[paulyoung]

In addition to what you posted, you'd also need to add the create function to your user models.

Aware of that if using Argo, thanks. I've written too many curried create functions to be able to forget!

[paulyoung]

when you're dealing with types not handled by NSJSONSerialization, including arrays of those types, you get a lot more help from Argo

@michaelmcguire could you elaborate on that?

[michaelmcguire]

Sure, the line:

role = j["role"] as Role,

probably won't do what you want it to do. It is probably another NSDictionary that contains the key/values for the Role that will need to be properly mapped, so you would need code to do that also. Of course, you don't get that "for free" from Argo, as you would need to implement JSONEncodable for that also. But if you do that, then you get handling an array of them.

[gfontenot]

yep. @michaelmcguire is exactly right. You'd have to do something like:

role = Role.decode(j["role"])

[paulyoung]

Yeah, I realized that as soon as I'd asked. That seems totally reasonable though.

Any other concerns or gotchas?

[paulyoung]

As for arrays?

friends = j["friends"].map { User.decode($0) }

[gfontenot]

Yes, but you'd also need to bring in sequence to get the same behavior of Argo (when one decode fails, the entire array fails)

[gfontenot]

You example also probably won't handle the case of actual optional values. The if let will fail if it's .None, where as you'd want to let that succeed. You might want to confirm this.

[paulyoung]

when one decode fails, the entire array fails

TIL.

It looks like map succeeds until the first decode fails rather than all or nothing. In some cases it might actually be desirable to do:

friends = j["friends"].reduce([], combine: { accum, elem in
  if let user = User.decode(elem) {
    return accum + [user]
  } else {
    return accum
  }
})

(specialized for User, could be made generic)

[paulyoung]

You example also probably won't handle the case of actual optional values. The if let will fail if it's .None, where as you'd want to let that succeed. You might want to confirm this.

@gfontenot do you mean if a key is missing from the JSON dictionary? If so, this works:

let j: NSDictionary = [
    "id": 123
]

// prints "success"
if let name = j["name"] as? String?, id = j["id"] as? Int {
    println("success")
} else {
    println("failure")
}

Sorry for the detour. This all helps in weighing things up.

[gfontenot]

Good to know that using as? Foo? works as I'd hope. I hadn't ever tried it, so was taking the more pessimistic route.

re: your map/reduce question, map should return [User?] and your reduce version should return [User]. We chose to go with [User]? (using map/sequence) because it fits in line with the behavior of the rest of the lib (we never fail silently). I think it's probably fine for you to use reduce to get [User], but if you were trying to replicate Argo's behavior exactly, you'd want to use map/sequence.

[paulyoung]

In addition to all of this, Argo also does JSON parsing which I'd need to handle.

I think there's a pretty compelling case for me to continue to use it.

Thanks @michaelmcguire @gfontenot!

[gfontenot]

Argo doesn't actually parse JSON itself, to be clear. We rely on NSJSONSerialization to do the NSData -> AnyObject transformation. We just then turn it into an enum for performance/type safety reasons.