Using The For-Each Syntax On A Private Collection Object

Using The For-Each Syntax On A Private Collection Object

Creating an object that looks and acts like a collection is a good wayto implement a form of inheritance in VB4, where inheritance is not providedby the language. Creating properties for the Count and Item propertiesof your collection is not difficult. Likewise, creating an Add and Removemethod is fairly easy. You can restrict the type of data added to a collection,and you can encapsulate all of the object handling in your class. However,there are two problems. You can expose the Item property, but you can’t make the Item thedefault property. Instead of writing:

 val = MyCollection("Fubar")

you must always write:

 val = MyCollection.Item("Fubar")

There is no way to allow a VB user to use the For-Each syntax andstill keep your encapsulation complete. If you are willing to break yourencapsulation, you can provide an Items property, like this:

 Property Get Items() As Collection	Set Items = collMyInternalCollectionEnd Property

Users can iterate your collection object like this:

 For Each obj in MyCollection.Items	' Do somethingNext

The problem with this method is that your users can now invoke the Addand Remove methods directly on the exposed collection. You have lost controlof the data, and your encapsulation is broken. If you are willing to trustthat your users will not use either the Add or Remove properties on thisobject, then this is a possible workaround.

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