static void Main( string[] args )
     {
         //not allowed by compiler
         //xxx.Field = 10;
 
         xxx.SetField( 10 );
 
         //prints out 0 !!!! <--- I do think that this is pretty bad
         System.Console.Out.WriteLine( xxx.Field );
 
         using ( var m = new Mutable() )
         {
             // This results in a compiler error.
             //m.Field = 10;
             m.SetField( 10 );
 
             //This prints out 10 !!!
             System.Console.Out.WriteLine( m.Field );
         }
 
         
 
         System.Console.In.ReadLine();
     }