mapper.swift

                let session = URLSession.shared
                
                let task = session.dataTask(with: request as URLRequest, completionHandler: {(data, response, error) in
                    
                    if (error == nil) {
                        do {
                            let json = try! JSONSerialization.jsonObject(with: data!, options: [])
                            let books = Mapper<BookResponse>.mapArray(json) // ERROR: Argument labels '(_:)' do not match any available overloads
                            
                            if let jsonResult = try JSONSerialization.jsonObject(with: data!, options: []) as? NSDictionary {
                                print(jsonResult)
                                DispatchQueue.main.async {
                                    success(jsonResult)}
                            }
                        } 
                    }
                    
                });
                
                task.resume()

BookResponse.swift:

import Foundation
import ObjectMapper

class BookResponse : Mappable {
    var books : [Book]?
    
    /// This function can be used to validate JSON prior to mapping. Return nil to cancel mapping at this point
    required init?(map: Map) {
        
    }
    
    func mapping(map: Map) {
        books  <- map["result"]
    }
    
}

let books = Mapper<BookResponse>().mapArray(json)