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Inheriting from Generics: Set the Datatype ... Or Not

When you're creating a derived class and your base type is a generic class, you have two choices in implementing your derived class: You can set the type of your derived class or you can make your derived class another generic class.

For example, imagine that you have a class called ReadRepository that accepts a variety of types:

Public Class ReadRepository(Of T)

End Class

If you create a CustomerRepository that inherits from ReadRepository, you might choose to set the type of your base class:

Public Class CustomerRepository 
    Inherits ReadRepository(Of Customer)
End Class

That's the strategy to follow when your derived class adds functionality specific to a datatype (in this case, I'm adding functionality specific to the Customer class).

On the other hand, if you wanted to create an UpdateAndReadRepository, you might choose to have your new class also be a generic class. In that case, your derived class also accepts a type placeholder and passes that placeholder to the base class:

Public Class UpdateAndReadRepository(Of T) 
    Inherits ReadRepository(Of T)
End Class

This is the strategy to follow if you're extending the base class with functionality that can be used with a variety of classes. In this case, adding Update capabilities for any class.

Posted by Peter Vogel on 04/02/2018 at 5:44 AM


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