Question

I am in the process of converting all my parameters, return types, classes to all use Interfaces instead ie. IUser instead of User.

Besides the extra code required to maintain this, are their any negatives to this approach?

Answer 1

This isn’t an uncommon approach, especially if you do a lot of mocking; however, it has issues with:

• data-binding support (especially when adding rows to tables)
• xml serialization (including comms WCF, asmx, etc), or contract-based serialization in general

You need to figure out whether the advantages of mocking etc outweigh these issues. It might be that you use IUser in most scenarios, but (for example) at the comms layer it may be simpler to use raw DTOs rather than interfaces.

Note that I’m applying the above to classes. If you involve structs, then remember that in most cases this will involve boxing too.