public static int Main() { SimpleTest.Prefix("foo", "1"); string s = "foo".Prefix("1"); Type ex_attr = typeof(System.Runtime.CompilerServices.ExtensionAttribute); if (!typeof(SimpleTest).IsDefined(ex_attr, false)) { return(1); } if (!typeof(SimpleTest).Assembly.IsDefined(ex_attr, false)) { return(2); } if (!typeof(SimpleTest).GetMethod("Prefix").IsDefined(ex_attr, false)) { return(3); } if (s != "1foo") { return(9); } Console.WriteLine(s); return(0); }