CODEWITHSUNDEEP
swiftpromisekit
Vasil Garov
Vasil Garov

Reputation: 4931

PromiseKit unwrapping optional before chaining

Just started using PromiseKit 6 with Swift. I've checked some examples and read the documentation. I have a scenario that seems trivial but I can't get around it. I have the following scenario:

func addModel(_ model: Model, image: UIImage?, completion: @escaping (Error?) -> Void) {
   var modelToSet = model
   var id = ""

   firstly {
        serviceWrapper.setImage(image!)     
   }.map { path in
        modelToSet.imagePath = path
   }.then { [serviceWrapper]
        serviceWrapper.setModel(modelToSet)
   }.map { documentId in
        id = documentId
   }.then {
        CLLocationManager.promise()
   }.done { [serviceWrapper] location in
        serviceWrapper.setLocation(GeoPoint(latitude: location.lat, longitude: location.long), id: id)
   }.catch { error in
        completion(error)
   }
}

As you can see, in this pseudo code I am force unwrapping the image. Any ideas how I can start the chain with the setImage method only if there is an image passed? Otherwise start from setModel directly. Or probably just return empty string if there is no image? What am I missing here?

Upvotes: 0

Views: 635

Answers (2)

Vasil Garov
Vasil Garov

Reputation: 4931

After asking the PromiseKit community, I got what I needed. So this is how you can go with solving it with a local function:

func addModel(_ model: Model, image: UIImage?, completion: @escaping (Error?) -> Void) {
    var modelToSet = model
    var id = ""

    func start() -> Promise<Void> {
        guard let image = image else {
            return Promise()
        }
        return serviceWrapper.uploadImage(image).map { path in
            dishToSet.imagePath = path
        }
    }

    firstly {
        start()
    }.then { [serviceWrapper]
        serviceWrapper.setModel(modelToSet)
    }.map { documentId in
        id = documentId
    }.then {
        CLLocationManager.promise()
    }.done { [serviceWrapper] location in
        serviceWrapper.setLocation(GeoPoint(latitude: location.lat, longitude: location.long), id: id)
    }.catch { error in
        completion(error)
    }
}

Upvotes: 1

user9749232
user9749232

Reputation:

Any ideas how I can start the chain with the setImage method only if there is an image passed?

You can use a guard statement to check the image is nil or not. If it is nil, execute the code needed to return. If not, continue the flow with a warpped image.

func addModel(_ model: Model, image: UIImage?, completion: @escaping (Error?) -> Void) {
   var modelToSet = model
   var id = ""

   guard let image = image else {
       // insert code to return if needed
       return
   }

   firstly {
        serviceWrapper.setImage(image)     
   }.map { path in
        modelToSet.imagePath = path
   }.then { [serviceWrapper]
        serviceWrapper.setModel(modelToSet)
   }.map { documentId in
        id = documentId
   }.then {
        CLLocationManager.promise()
   }.done { [serviceWrapper] location in
        serviceWrapper.setLocation(GeoPoint(latitude: location.lat, longitude: location.long), id: id)
   }.catch { error in
        completion(error)
   }
}

Upvotes: 0

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