Promise

ViewController.swift

import UIKit
import PromiseKit

let GET_POSTS = "https://jsonplaceholder.typicode.com/posts"

struct APIError : Error {
    var message : String?
}

struct Post:Codable  {
    var userId : Int?
    var id : Int?
    var title : String?
    var body : String?
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let list: [Post] = self.asyncGetRequest().value?.then { data -> Void in return data }
        print("\n Posts \(list.first )")
    }
    
    func asyncGetRequest<T: Decodable>() -> Promise<[T]> {
        return Promise { resolve in
            Alamofire.request(GET_POSTS).responseData().done { response in
                guard let result = try? JSONDecoder().decode([T].self, from: response.data) else {
                    let error = APIError(message: "Error: Couldn't decode")
                    resolve.reject(error)
                    return
                }
                resolve.fulfill(result as [T])
                }.ensure {
                    
                }.catch { error in
                    resolve.reject(error)
            }
        }
    }
}