Question

I have a class called Foo that has a function that looks like the following

List<Bar> LoadData();

Both Foo and Bar are in a library that I want to reuse in other projects. Now I am working on a new project and I want to subclass Bar. Let’s call it NewBar.

What is a simple and flexible way to get Foo.LoadData to return a list of NewBar? I think that a factory is needed or perhaps just a delegate function. Can anyone provide an example?

Thanks, Andy

Answer 1

There are a few problems here. Since you are using List<Bar> this would not work if you return List<Baz> since List<> does not do covariance.

My suggestion is to redesign it to return IEnumerable<Bar> and make it virtual so that in the new project create a SubFoo and you can return IEnumerable<Baz>.

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UPDATE

OK, according to the new information you provided (you use it for populating list from XML), I would create a virtual protected CreateBar() which creates a new bar object and is called by LoadData() to create new Bar in the loop. In the SubFoo I override and return Baz instead. In the SubFoo I will call base.LoadData() and populate the Baz list and then add the logic to populate new properties of Baz which are not in Bar.

Or perhaps

just use XML Serilization and I get all of that for free!