Property is coming up empty when called from another class when using URLSession - ios

Question

For some reason, the products array is coming back empty when I try and access it from another class. What am I doing wrong, and how can I get the products array to populate? Is it something related to the do/catch?
The print statement shown will give me what I'm looking for, but when I try and use the property in another class after the retrieve method has been called, it comes up empty.
For information, "Product" is a struct that has name, description, etc properties attached.
private let productListUrl = URL(string: "https://api/products.json")
var products = [Product]()
func retrieveProductList() {
if let productListUrl = productListUrl {
URLSession.shared.dataTask(with: productListUrl) { (data, response, error) in
if let data = data {
do {
let jsonData = try JSONSerialization.jsonObject(with: data, options: []) as! [String:Any]
let tempArray: Array = jsonData["products"] as! [Any]
for product in tempArray {
let newProduct = Product(json: product as! [String : Any])
self.products.append(newProduct!)
}
print("In ProductService: \(self.products)")
}
catch {
print("An error occured while attempting to read data")
}
}
}.resume()
}
}

Answer 1

As maddy noted, this is because the URL call is asynchronous.
You basically have 3 options:
Use a semaphore approach and make your retrieveProductList method synchronous.
Change your class to have a delegate property that you can ping when the URL request finishes.
Add a completion handler to your retrieveProductList method that is called when the URL request finishes.
I personally would lean towards option 3:
func retrieveProductList(completion: #escaping ([Product])->())
{
// Right after you print the products...
completion(self.products)
}