Hidden Features of VB.NET?

I have learned quite a bit browsing through Hidden Features of C# and was surprised when I couldn't find something similar for VB.NET.

So what are some of its hidden or lesser known features?

Solution 1:

The Exception When clause is largely unknown.

Consider this:

Public Sub Login(host as string, user as String, password as string, _
                            Optional bRetry as Boolean = False)
Try
   ssh.Connect(host, user, password)
Catch ex as TimeoutException When Not bRetry
   ''//Try again, but only once.
   Login(host, user, password, True)
Catch ex as TimeoutException
   ''//Log exception
End Try
End Sub

Solution 2:

Custom Enums

One of the real hidden features of VB is the completionlist XML documentation tag that can be used to create own Enum-like types with extended functionality. This feature doesn't work in C#, though.

One example from a recent code of mine:

'
''' <completionlist cref="RuleTemplates"/>
Public Class Rule
    Private ReadOnly m_Expression As String
    Private ReadOnly m_Options As RegexOptions

    Public Sub New(ByVal expression As String)
        Me.New(expression, RegexOptions.None)
    End Sub

    Public Sub New(ByVal expression As String, ByVal options As RegexOptions)
        m_Expression = expression
        m_options = options
    End Sub

    Public ReadOnly Property Expression() As String
        Get
            Return m_Expression
        End Get
    End Property

    Public ReadOnly Property Options() As RegexOptions
        Get
            Return m_Options
        End Get
    End Property
End Class

Public NotInheritable Class RuleTemplates
    Public Shared ReadOnly Whitespace As New Rule("\s+")
    Public Shared ReadOnly Identifier As New Rule("\w+")
    Public Shared ReadOnly [String] As New Rule("""([^""]|"""")*""")
End Class

Now, when assigning a value to a variable declared as Rule, the IDE offers an IntelliSense list of possible values from RuleTemplates.

/EDIT:

Since this is a feature that relies on the IDE, it's hard to show how this looks when you use it but I'll just use a screenshot:

Completion list in action http://page.mi.fu-berlin.de/krudolph/stuff/completionlist.png

In fact, the IntelliSense is 100% identical to what you get when using an Enum.