YAGNI it's not a excuse for badly designed applications.

YAGNI or “You ain’t gonna need it”, is great. It keep people like me to over design systems. Now, every time that I start to write some piece of code I always have that said in mind. You will be surprised how many times I found myself telling me, YAGNI.

Although, sometimes, this can be misused. Sometimes this “rule” may be used as an excuse to write tightly couple systems, difficult to maintain in the long run. I know that this is not the spirit of “YAGNI“, but a week ago somebody said that to me when we were talking about the importance of programming against interfaces.

So let me tell you what my own interpretation of YAGNI is. Do not create that cool feature that nobody requested, but design your system in a way that when (or if) somebody request that cool feature, you will be able to implement it without rewriting the whole system.

So what we do? Well, just apply solid OO design principles. Make your system extensible. This is not as difficult as it sounds. Design from the get go a modular system.

Program against interfaces. This will facilitate the use of Dependency Injection to reduce friction. You should make sure that different compilation units do not depend on each other.

Practice Test First (TDD or BDD) or at least have a good test suite in place so later on you can change your system with confidence.

Make sure that you put your business rules in the right place and not scattered all over your system.

Do not be afraid of aggressively refactor your code to make it more readable, even when the feature works, refactoring your code to make it extensible is not a violation of YAGNI.