Compiler Error CS0552

'conversion routine' : user defined conversion to/from interface

You cannot create a user-defined conversion to or from an interface. If you need the conversion routine, resolve this error by making the interface a class or derive a class from the interface.

The following sample generates CS0552:

// CS0552.cs  
public interface ii  
{  
}  

public class a  
{  
   // delete the routine to resolve CS0552  
   public static implicit operator ii(a aa) // CS0552  
   {  
      return new ii();  
   }  

   public static void Main()  
   {  
   }  
}