ServiceUsage.swift

let serverAdress = "https://countries.trevorblades.com/"

guard let url = URL(string: serverAdress) else {
    return nil
}

let factory = World.Factory()
// You will neet to retain the service object with a strong
// reference to recieve the callbacks with the data.
self.store = factory.makeStore(with: url)

// Next, call the service: 
store.fetchAllCountries(cachePolicy: .returnCacheDataElseFetch) { [weak self] result in
switch result {
     case let .success(countries):
         // handle data 
         return
     case let .failure(error):
        // handle error
        return
     }
}