Right now Vala allows you doing:

public interface EmailDetails : Object
{
  public abstract Set<FieldDetails> email_addresses { get; set; }
}

public class Person,
   EmailDetails
{
  public Set<FieldDetails> email_addresses
    {
      get { return this._email_addresses_ro; }
      private set
        {
           // ....
        }
    }
}

whereas one would expect that the setter should have the same access type as the interface being implemented... 

But things get really confusing because the set of email_addresses in Person *is* actually public, cause the following code works (!!):

Person p = new Person();
p.email_addresses = emails; // <-- shouldn't be allowed!The interface wins.