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

i wrote my answer below. it's used ObjectMapper, not AlamofireObjectMapper. you can refer if you still need this solution. — wagng, May 08 '18 at 11:47

score 12 · Answer 1 · answered Aug 23 '18 at 10:01

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)

I got this error `Cannot convert value of type '(DataResponse) -> ()' to expected argument type '(DataResponse) -> Void'`. Please advise. — Nizzam, Jul 24 '19 at 16:52

score 6 · Answer 2 · edited Dec 23 '17 at 17:16

6

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.

edited Dec 23 '17 at 17:16

Dávid Pásztor

51,403
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answered Oct 19 '17 at 05:58

Tharindu Ketipearachchi

1,046
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26

score 2 · Answer 3 · answered May 08 '18 at 11:58

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
        }

score 1 · Answer 4 · answered May 22 '17 at 16:07

1

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>.

answered May 22 '17 at 16:07

Dávid Pásztor

51,403
9
85
116

it's solved the error but when i called it like that `doSomething(myCustomClass:Promotions)` i got another error **Argument type 'Promotions.Type' does not conform to expected type 'BaseMappable** – Muhammed May 22 '17 at 16:22
That error is quite straightforward, it says exactly what is wrong... You need to make the class `Promotions` conform to the `Protocol BaseMappable`. – Dávid Pásztor May 22 '17 at 16:28
Promotions is inherit from Mappable and Mappable inherits from BaseMappable – Muhammed May 22 '17 at 16:33
How do you expect anyone to give you a more detailed answer if you don't even include the piece of code in your question/comment that you are asking about? – Dávid Pásztor May 22 '17 at 16:43
Edited my question – Muhammed May 22 '17 at 16:48

Trying to pass Generic type as parameter in Swift

4 Answers4