The CORBA union indicates (TBD) .....  . 

It maps to VB's union type.

// CORBA IDL

union Nums switch (char)
{
   case 'f': float f;
   case 'l': long l;
   default: short s;
};

e.g.
Nums
NumsHelper

// VB
Imports System

Namespace demo.unions
   '
   ' Union definition : Nums
   ' 
   ' @author TomORB VB Native Compiler 1.0rc1
   '
   <Serializable()> _
   Public NotInheritable Class Nums
      Implements Org.Omg.CORBA.Portable.IDLEntity
      ' 
      ' Union member _d
      ' 
      Private __d As Char
      
      ' 
      ' Union member f
      ' 	
      Private _f As Single
      
      ' 
      ' Union member l
      ' 	
      Private _l As Integer
      
      ' 
      ' Union member s
      ' 

      Private _s As Short
      '
      ' Default constructor
      ' 
      Public Sub New()
         __d = "1"c
      End Sub

      ' 
      '  Get/Set discriminator value 
      ' 
      Public Property discriminator As Char		
         Get
            Return __d
         End Get
         Set
            __d = value
         End Set
      End Property

      ' 
      ' Get/Set f value
      ' 
      Public Property f As Single
         Set
            __d = "f"c
            _f = value
         End Set
         Get
            Return _f
         End Get
      End Property

      ' 
      ' Get/Set l value
      ' 
      Public Property l As Integer
         Set
            __d = "l"c
            _l = value
         End Set
         Get
            Return _l
         End Get
      End Property

      ' 
      ' Get/Set s value
      ' 
      Public Property s As Short
         Set
            __d = "1"c
            _s = value
         End Set
         Get
            Return _s
         End Get
      End Property

      ' 
      '  Set s value
      ' 
      Public Sub Set_Discriminator_And_S(dvalue As  Char, value  As Short)
         __d = dvalue
         _s = value
      End Sub

   End Class

End Namespace

Namespace demo.unions 
   ' 
   ' Helper class for : Nums
   '  
   ' @author TomORB VB Native Compiler 1.0rc1
   ' 
   Public Class NumsHelper
      '
      ' Insert Nums into an any
      ' param name="a" an any
      ' param name="t" Nums value
      '
      Public Shared Sub Insert(a As Org.Omg.CORBA.Any, t As demo.unions.Nums)
         a.Type(Type())
         Write(a.Create_Output_Stream(),t)
      End Sub

      '
      ' Extract Nums from an any
      ' @param a an any
      ' @return the extracted Nums value
      '
      Public Shared Function Extract(a As Org.Omg.CORBA.Any) As demo.unions.Nums
         If Not(a.Type().Equal(Type())) Then
            Throw New Org.Omg.CORBA.MARSHAL()
         End If
         Return Read(a.Create_Input_Stream())
      End Function

      '
      ' Internal TypeCode value
      '
      Private Shared _tc As Org.Omg.CORBA.TypeCode = Nothing
      Private Shared _working As Boolean = false

      '
      ' Return the Nums TypeCode
      ' @return a TypeCode
      '
      Public Shared Function Type() As Org.Omg.CORBA.TypeCode
         If _tc Is Nothing Then
            SyncLock (GetType(Org.Omg.CORBA.TypeCode))
               If Not(_tc Is Nothing) Then
                  Return _tc
               End If
               If _working Then
                  Return Org.Omg.CORBA.ORB.Init().Create_Recursive_TC(Id())
               End If
               _working = True
               Dim orb As Org.Omg.CORBA.ORB = Org.Omg.CORBA.ORB.Init()
               Dim _members() As Org.Omg.CORBA.UnionMember = New Org.Omg.CORBA.UnionMember(2){}
               Dim any As Org.Omg.CORBA.Any

               any = orb.Create_Any()
               any.Insert_Char("f"c)
               _members(0) = New Org.Omg.CORBA.UnionMember()
               _members(0).name = "f"
               _members(0).label = any
               _members(0).type = orb.Get_Primitive_TC(Org.Omg.CORBA.TCKind.tk_float)
               any = orb.Create_Any()
               any.Insert_Char("l"c)
               _members(1) = New Org.Omg.CORBA.UnionMember()
               _members(1).name = "l"
               _members(1).label = any
               _members(1).type = orb.Get_Primitive_TC(Org.Omg.CORBA.TCKind.tk_long)
               any = orb.Create_Any()
               any.Insert_Octet(Convert.ToByte(0))
               _members(2) = New Org.Omg.CORBA.UnionMember()
               _members(2).name = "s"
               _members(2).label = any
               _members(2).type = orb.Get_Primitive_TC(Org.Omg.CORBA.TCKind.tk_short)
               _tc = orb.Create_Union_TC(Id(),"Nums",orb.Get_Primitive_TC(
                                         Org.Omg.CORBA.TCKind.tk_char),_members)
               _working = False
            End SyncLock
         End If
         Return _tc
      End Function

      '
      ' Return the Nums IDL ID
      ' @return an ID
      '
      Public Shared Function Id() As String
         Return _id
      End Function

      Private Shared _id As String = "IDL:demo/unions/Nums:1.0"

      '
      ' Read Nums from a marshalled stream
      ' @param istream the input stream
      ' @return the readed Nums value
      '
      Public Shared Function Read(istream As Org.Omg.CORBA.Portable.InputStream) 
                             As demo.unions.Nums
                             
         Dim new_one As demo.unions.Nums = New demo.unions.Nums()
         new_one.discriminator = istream.Read_Char()
         If new_one.discriminator = CType("f"c, Char) Then
            new_one.f = istream.Read_Float()
         ElseIf new_one.discriminator = CType("l"c, Char) Then
            new_one.l = istream.Read_Long()
         Else
            new_one.s = istream.Read_Short()
         End If
         Return new_one
      End Function

      '
      ' Write Nums into a marshalled stream
      ' @param ostream the output stream
      ' @param value Nums value
      '
      Public Shared Sub Write(ostream As Org.Omg.CORBA.Portable.OutputStream, 
                              value As demo.unions.Nums)
         ostream.Write_Char(value.discriminator)
         If value.discriminator = CType( "f"c, Char) Then
            ostream.Write_Float(value.f)
         ElseIf value.discriminator = CType( "l"c, Char) Then
            ostream.Write_Long(value.l)
         Else
            ostream.Write_Short(value.s)
         End If
      End Sub

   End Class

End Namespace