Public Class aClass
        Private _anObject As Object
 
        Public Property AnObject As Object
            Set(value As Object)
                If Not IsTypeAllowed(value) Then
                    Throw New ArgumentException("Illegal Datatype")
                End If
                _anObject = value
            End Set
            Get
                Return _anObject
            End Get
        End Property
 
        Private Function IsTypeAllwed(ByVal value As Object) As Boolean
            Dim ty As Type = value.GetType
            If Not ty.IsPrimitive And _
               Not ty.Equals(GetType(Decimal)) And
               Not ty.Equals(GetType(String)) Then
                Return False
            End If
            Return True
        End Function
    End Class