Empty IEnumerable or null

Gideon Engelberth

I have a data model where each record has a "next version pointer" to track updates to the items. As it stands now, the object looks something like this:

Public MustInherit Class VersionedDataObject(Of T As VersionedDataObject(Of T))

Private \_next As T
Public Property NextVersion() As T
    Get
        Return \_next
    End Get
    Set(ByVal value As T)
        If value Is \_next Then Exit Property
        \_next = value

        If \_next Is Nothing Then
            \_nextVersions = Nothing
        Else
            \_nextVersions = New NextVersionIterator(Me)
        End If
    End Set
End Property

Private \_nextVersions As IEnumerable(Of T)
Public ReadOnly Property NextVersions() As IEnumerable(Of T)
    Get
        Return \_nextVersions
    End Get
End Property

'other common stuff

End Class

The question is, when NextVersion is Nothing, would you return Nothing from NextVersions (as I am doing now) or an IEnumerable with no items?

Luc Pattyn

Why don't you look at what .NET does itself, e.g. the methods operating on a Queue, such as Dequeue. :)

Luc Pattyn

I only read code that is properly indented, and rendered in a non-proportional font; hint: use PRE tags in forum messages

David Skelly

I would return an empty enumerable from NextVersions. That way, the consumer of this property does not have to include a test for whether the IEnumerable is Nothing, but can just go ahead use it. If it's empty, then the iteration over the enumerator will simply do nothing. That makes life simpler for the person using your VersionedDataObject and takes away the risk of getting a NullReferenceException when someone forgets to check for Nothing. So, you can just do something like:

For Each version In myVersionedObject.NextVersions
' do something with version
Next

Gideon Engelberth

Not a bad idea. My object does not directly implement IEnumerable like Queue or List (and isn't a 'collection' type of object), so I'll have to look for other objects to find some examples. For now I think I will go with suggestion from the other response.

Gideon Engelberth

I think I will go with this approach. Like you said, it gives less room for error ("pit of success" and all that).