Trying to pass Generic type as parameter in Swift

Question

I am Using AlamofireObjectMapper i need to make a func that take a Generic parameter like that :

func doSomething < T : BaseMappable > (myCustomClass : T) 
{
    Alamofire.request("url", method: .get, parameters: nil, encoding: JSONEncoding.default, headers: APIKeys().AuthorizedHeader).responseObject(completionHandler: { ( response :DataResponse<T>) in

             let data = response.result.value

            if let array = data?.objects
            {
                for ar in array
                {
                   self.allPromotions.append(ar)
                }
            }

        })


}

but iam getting error :

Use of undeclared type 'myCustomClass' edit as you guys answer me in the comments i put fixed the error but i got another error when iam trying to call this method

i called the method like that

doSomething(myCustomClass: Promotions)

but i got another error

Argument type 'Promotions.Type' does not conform to expected type 'BaseMappable'

and here's my Promotions class

import ObjectMapper


class Promotions : Mappable  {





        var id:Int?
        var workshop_id:Int?
        var title:String?
        var desc:String?
        var start_date:String?
        var expire_date:String?
        var type:String?

        var objects  = [Promotions]()




        required init?(map: Map){

        }

        func mapping(map: Map) {
            id <- map["id"]
            workshop_id <- map["workshop_id"]
            title <- map["title"]
            desc <- map["desc"]
            start_date <- map["start_date"]
            expire_date <- map["expire_date"]
            type <- map["type"]
            objects <- map["promotions"]
        }




}

How can i fix that

Answer 1

Just pass the Promotions.self as the parameter.

doSomething(myCustomClass: Promotions.self)

This'll overcome the error that you are getting in the function call.

Answer 2

You need to pass as argument the type of Generic Type T. Try changing

myCustomClass : T

by

myCustomClass : T.Type

The result would look like:

Swift 4:

    func doSomething<T>(myCustomClass : T.Type) where T : BaseMappable
    {
        Alamofire.request("url", method: .get, parameters: nil, encoding: JSONEncoding.default, headers: APIKeys().AuthorizedHeader).responseObject(completionHandler: { ( response :DataResponse<T>) in

                 let data = response.result.value

                if let array = data?.objects
                {
                    for ar in array
                    {
                       self.allPromotions.append(ar)
                    }
                }

            })
    }

Then, you should call the method:

doSomething(myCustomClass: Promotions.self)

Answer 3

myCustomClass is just the name of the input parameter to doSomething . The name of the generic type is T , so DataResponse should be DataResponse<T> .

Answer 4

Here is the solution using Alamofire , ObjectMapper and PromiseKit ,

• User Mappable object.

   class User: Mappable { var id: Int! var userName: String! var firstName: String? var lastName: String? required init?(map: Map) { } // Mappable func mapping(map: Map) { id <- map["id"] userName <- map["userName"]\\ firstName <- map["firstName"] lastName <- map["lastName"] } } 

• Class template based function

   func sendRequest<T: Mappable>(_ url: URLConvertible, method: HTTPMethod = .get, parameters: Parameters? = nil, encoding: ParameterEncoding = URLEncoding.default, headers: HTTPHeaders? = nil, responseObject: T.Type) -> Promise<T> { return Promise { resolve, reject in Alamofire.request(url, method: method, parameters: parameters, encoding: encoding, headers: headers) .responseJSON() { response in switch response.result { case .success(let data): let json = JSON(data as Any) let dataObj = json["data"].object let resObj = Mapper<T>().map(JSONObject: dataObj) resolve(resObj!) case .failure(_): reject(self.generateError(message: nil)) } } } } 

• Usage

Define in utility class

    func loginWith(userName: String, and password: String) -> Promise<User> {

        let apiPath = "localhost:3000"

        let parameters: Parameters = [
            "email": userName,
            "password": password
        ]

        return sendRequest(apiPath, method: .post, parameters: parameters, encoding: JSONEncoding.default, headers: nil, responseObject: User.self)
    }

Use in view controllers

    loginWith(userName: name, and: password)
        .then { response -> Void in
            // response is `User` type object!!!
        }
        .catch { error in
            // show error message
        }
        .always {
            // do something like hide activity indicator
        }