C# Interface to create Optional property -

i have interface written in c# , implemented classes. possible can add 1 more property optional in interface , without modifying exiting implemented classes?

e.g

public interface ishape {     int area { get; } }  public class findwindow : ishape {     public int area     {                 {             return 10;         }     } } 

in findwindow written. possible can add 1 optional property , not implementing in existing class.

ie,

public interface ishape {     int area { get; }     //optional     //string windowname{get;} }  public class findwindow : ishape {     public int area     {                 {             return 10;         }     }      //windowname not implementing here }  public class findwindowname : ishape {     public int area     {         { return 20; }     }      public string windowname     {         { return "stack overflow"; }     } } 

there's no concept of optional members of interface.

what need here define 2 interfaces. 1 contains area, , other contains windowname. this:

public interface ishape {     int area { get; } }  public interface ifindwindow: ishape {     string windowname { get; } } 

then implementing classes can choose implement either ishape or ifindwindow.

at runtime use is operator determine whether or not ifindwindow implemented object @ hand.

ishape shape = ...; if (shape ifindwindow)     .... 

and use more derived interface use as operator:

ishape shape = ...; ifindwindow findwindow = shape ifindwindow; if (findwindow != null)     string windowname = findwindow.windowname;