C#

Compiler Error CS0553'conversion routine' : user defined conversion to/from base class
User-defined conversions to values of a base class are not allowed; you do not need such an operator.
The following sample generates CS0553:

// CS0553.cs
namespace x
{   
  public class ii   
  {   
  }   
  public class a : ii   
  {      // delete the conversion routine to resolve CS0553      
    public static implicit operator ii(a aa) // CS0553      
    {         
      return new ii();      
    }      
    public static void Main(){}
  }
}

public MyAudio
{
   public MyAudio(string url, bool autoPlay)
   {
      audio = Audio.FromUrl(url, autoPlay);
      file = "???"; // Not sure what you should put here...doesn't really make sense      
   }

   public Audio
   {
      get
      {
         return audio;
      }
   }

   private Audio audio;
   private string file;
}