Question

I saw in a projekt many interfaces which just wrapped a generic class.

An example:

public interface IAssertionViewModelMapper : IMapper<Assertion, AssertionViewModel>
{}

public interface ISearchPageViewModelMapper : IMapper<IList<Tag>, SearchPageViewModel>
{}

Could someone explain why they did this ? I mean I can just straight implement the IMapper interface.

Answer 1

Microsoft Code Analysis (a.k.a. FxCop) contains a rule against doing this. However, creating a new interface like this has a few advantages:

1. The new name can describe the intent of the interface better (however, aliasing in C# can do the same).
2. This saves you a few minutes when new methods are needed on that interface, because you already defined it.
3. It can make your code base more consistent when most interfaces that derive from IMapper<T, TViewModel> actually define new methods. It’s easy to spot the interfaces, even if they don’t define new members.