override init() {

    productIdentifiers = NSSet(objects: "---")
}

func requestProductsWithCompletionHandler(_ completionHandler:@escaping (Bool, [SKProduct]?) -> Void){
    self.completionHandler = completionHandler

    let productsRequest = SKProductsRequest(productIdentifiers: productIdentifiers as Set<NSObject> as Set<NSObject> as Set<NSObject> as! Set<String>)
    productsRequest.delegate = self
    productsRequest.start()
}

//MARK: SKProductsRequestDelegate methods
func productsRequest(_ request: SKProductsRequest, didReceive response: SKProductsResponse) {

    print("product count (response.products.count)")
    print("invalid product IDs (response.invalidProductIdentifiers)")

    if response.products.count > 0 {
        var products: [SKProduct] = []

        for prod in response.products {
            if prod.isKind(of: SKProduct.self) {
                products.append(prod )
            }
        }

        completionHandler(true, products)
    }
}

func request(_ request: SKRequest!, didFailWithError error: Error) {

    completionHandler(false, nil)
}