Encapsulate Member Objects

Objects frequently contain member objects that need to be exposed.Often, these are not correctly encapsulated, which could lead to problems that are difficult to track down.

Consider a Circus object, which has a private collection of the names of its clowns. We could expose this Collection with a public property:

    Public Property Get GetAllClowns() As Collection      set GetAllClowns = m_colClowns   End Property


This passes a pointer to the private collection to the caller. This private collection might as well have been declared public, because the caller can get a reference to the private object and do whatever it wants with it. Therefore, the code above does NOT encapsulate its clowns. A better way to get our clowns would be to return a new collection:

    Public Property Get GetAllClowns() As Collection      Dim colClowns   As Collection      Dim sClown      As String      Set colClowns = New Collection      For Each sClown In m_colClowns         colClowns.Add sClown      Next      Set GetAllClowns = colClowns   End Property


If you are dealing with your own objects, rather than Collections, you could provide a Clone method in the object you will be exposing through a property. Clone() should return a copy of its object. Then, instead of returning a member object in the Property Get, simply Clone it and return the clone.

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