Dim dt As New System.Data.DataTable
        Dim r As System.Data.DataRow
        dt.Columns.Add("Column").AllowDBNull = False
        dt.Columns("Column").DefaultValue = "{DefaultValue}"
        r = dt.NewRow
        dt.Rows.Add(r)
        MessageBox.Show(r("Column").ToString())

'// MyDataTable
Class MyDataTable
    Inherits DataTable
    Public Shadows Function NewRow() As MyDataRow
        Dim r As MyDataRow = DirectCast(MyBase.NewRow, myDataRow)
        Return r
    End Function
    Protected Overrides Function NewRowFromBuilder(ByVal builder As _
      DataRowBuilder) As DataRow
        Return New MyDataRow(builder)
    End Function
End Class
 
'// MyDataRow
Class MyDataRow
    Inherits DataRow
    Function GetValue(ByVal o As Object) As Object
        If o Is Nothing OrElse o Is System.DBNull.Value Then
            Return CObj("{DefaultValue}")
        End If
        Return o
    End Function
 
    Friend Sub New(ByVal builder As DataRowBuilder)
        MyBase.New(builder)
    End Sub
 
    Default Public Shadows Property Item(ByVal Index As Integer) As Object
        Get
            Return GetValue(MyBase.Item(Index))
        End Get
        Set(ByVal Value As Object)
            MyBase.Item(Index) = Value
        End Set
    End Property
 
    Default Public Shadows Property Item(ByVal ColumnName As String) As Object
        Get
            Return GetValue(MyBase.Item(ColumnName))
        End Get
        Set(ByVal Value As Object)
            MyBase.Item(ColumnName) = Value
        End Set
    End Property
End Class

        Dim dt As New MyDataTable
        Dim r As MyDataRow
        dt.Columns.Add("Column")
        r = dt.NewRow
        dt.Rows.Add(r)
        MessageBox.Show(r("Column").ToString())