Equivalent of getters/setters for collections within a class

Question

I have a class as follows:

public class Document
{
    public List<DocumentSection> sections = new List<DocumentSection>();
    ...

Various questions cover the situation where a property needs to be writable from inside the class but readonly from outside it (http://stackoverflow.com/questions/4662180/c-sharp-public-variable-as-writeable-inside-the-clas-but-readonly-outside-the-cl)

I'd like to do the same but for this collection - allow adding to it from within the class, but only allow a user to iterate through it when they are outside it. Is this elegantly doable?

Thanks

Answer 1

Expose the collection as IEnumerable so that users can only iterate through it.

public class Document {
   private List<DocumentSection> sections;

   public IEnumerable<DocumentSection> Sections 
   { 
       get { return sections; }
   }
}

Answer 2

Yes, you have to hide the List and only expose an Add method and a property of type IEnumerable<DocumentSection>:

public class Document
{
    private List<DocumentSection> sections = new List<DocumentSection>();

    public void AddSection(DocumentSection section) {
        sections.Add(section);
    }

    public IEnumerable<DocumentSection> Sections {
        get { return sections; }
    }
}

Answer 3

You could expose the List as an IEnumerable<DocumentSection> and only use the List internally. Like so:

public class Document {
  public IEnumerable<DocumentSection> Sections { get { return list; } }
  private List<DocumentSection> list;
}

Answer 4

If you really want to allow only iteration, you could keep the IList private, but make a public function resolving to GetEnumerator()

Answer 5

public class Document {
   private readonly List<DocumentSection> sections = new List<DocumentSection>();

   public IEnumerable<DocumentSection> Sections 
   { 
       get 
       { 
           lock (this.sections)
           {
               return sections.ToList(); 
           }
       }
   }
}