PromiseViewController.swift

import UIKit
import PromiseKit

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

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

extension Alamofire.DataRequest {
    // Return a Promise for a Codable
    public func responseCodable<T: Codable>() -> Promise<T> {
        
        return Promise { resolver in
            responseData(queue: nil) { response in
                switch response.result {
                case .success(let value):
                    let decoder = JSONDecoder()
                    do {
                        resolver.fulfill(try decoder.decode(T.self, from: value))
                    } catch let e {
                        resolver.reject(e)
                    }
                case .failure(let error):
                    resolver.reject(error)
                }
            }
        }
    }
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let data : [Post] = self.getFeed().then { data in
            return data
        }
        print("\n data \(data.first )")

    }
    
    func getFeed() -> Promise<[Post]> {
        return Alamofire.request(GET_POSTS).responseDecodable()
    }
}