Every interface is public

A few days ago, I posted a comment on timm's blog. I made a remark about the difficulties that most .NET developers had and still have when they have to handle with Stream objects to read and write text files; especially in the early days of the .NET framework, when methods such as File.ReadAllText and File.ReadAllLines did not exist yet.

Then, I remembered reading that on the book written by Brad Adams and Krzysztof Cwalina: "Framework Design Guidelines".

Although published already two years ago, this is still an excellent reference about naming conventions, sane type design and class library extensibility. Perhaps it would deserve a second edition with additional stuff about C#3, Linq, WPF, WCF, etc. This book is also a source of valuable comments and amusing little stories from various actors in the .NET framework world, explaining why some classes were designed the way they are, or which were the difficulties they met while designing the class library. Delightful…

However, there is a little point in that book which I tend to disagree with. It is apparently only a detail, but which hides perhaps an entirely different philosophical point of view about code design. The authors say about naming guidelines:
Although adopting these naming conventions as general code development guidelines would result in more consistent naming throughout your code, you are required only to apply them to APIs that are publicly exposed.

As a corporate developer, I write code that has little chance to be read or to be reused by other developers outside my work place. The question I ask myself, is what exactly "publicly exposed APIs" mean? Technically speaking, it should be any type or member with a public scope. But actually, when my colleague reads my code, he has also access to objects with private or internal scope. When I download the code of an open-source project such as Rhino or the promising Gallio, I also have access to internal types. In VS2008, we have also the possibility to see the source code of the class library, which has not a public scope. And finally, when I stop working for a while on a project of mine, the person I am when I resume the job is not exactly the same. I have perhaps forgotten how the system was designed; so I come with a new fresh eye and new recently acquired experience.

I believe that "publicly exposed APIs" is not synonym of "types and members with a public scope". In fact, I tend to consider every single line of code as public at a certain level: public to other anonymous developers, public to your colleagues, or only public to you. As soon as a line of code is written, it can obviously be read as well. Maybe not by everyone, but at least by you and the other developers who work with you.

That's why I think it does not make sense to apply partially such a guideline. It's like pushing dust under the carpet. For sure, people passing next to the house will never know you do that. They will only see the "public interface", that is the front of your home. But your family might discover it, or your neighbor, who will visit you one day or another. But more important, YOU will know it. If you can live with that mess in your code, I have the bad feeling that you are not rigorous enough to become a good developer.

No comments: