static void Main(string[] args) { IReadOnlyInterface iexample = new ReadAndWriteImplementation(); //iexample.Value = 1; Console.WriteLine(iexample.Value); var example = (ReadAndWriteImplementation)iexample; example.Value = 2; Console.WriteLine($"original {iexample.Value}"); Console.WriteLine($"changed {example.Value}"); Console.ReadKey(); }