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YAGNI – "You Aren't Going To Need It". This is an acronym commonly used in software development to remind developers to only write what they need. This acronym exists because software developers have gotten into the habit of writing everything they need to solve a problem and then everything they think they're going to possibly need in the future.

Since we can't predict the future this results in a large portion of the code that we write never being used. That extra code causes unnecessary complexity, which makes it harder to understand and harder to modify when we inevitably have to write something that we didn't think of.

I've known about YAGNI for some time now but I never really got it. The words made sense and the idea was clear but the concept never sank in. I was one of those devs who'd happily write a ton of code in the anticipation of future needs. In my mind this was an essential part of writing high quality code. I didn't realise that in doing so I was actually writing low quality code.

If you are anything like me you are probably thinking "Lies and propaganda! High quality code needs to be future proof." I agree! But what makes code future proof? If we could see into the future the answer would be simple, code that allows for or meets all future requirements. Since we can't see the future the best we can do is write code that can easily adapt to future requirements, this means writing flexible code.

Flexible code is:

  • Fast to understand.
  • Fast to add to.
  • Fast to modify.

To be flexible code has to be simple, this means only making it as complex as it needs to be to meet those 3 criteria. That is high quality code. YAGNI!

The art is in deciding where to place the seams (abstractions) that will give you flexibility without making decisions about future functionality. Robert C Martin explains it very nicely, he says a good architecture allows you to defer decisions because if you can defer a decision then you have the flexibility to change it.

I've recently had a YAGNI experience which brought this all into perspective. I was working on a new project which had multiple clients that connect to a server hosted in the cloud. I was tasked with adding a feature to the desktop client that would allow users to capture items that would then be saved to the cloud. My immediate thought was "Hey we have multiple clients so I should build a web service for these items, that way we can access them from other clients", so I went to work and this is what I created.


I stood back and gazed upon what I'd created with a warm fuzzy feeling. It was beautiful! Then the time came for the team to use the design I'd created for another feature with a new entity. Let's just say that they didn't get the same warm fuzzy feeling that I did when they looked at the design. After much discussion they eventually got it through to me that I'd bloated the design based on an assumption of future functionality. After much more discussion we cut the design down to the following.

This design gives us future flexibility with no extra work, it is as complex as it needs to be.

It has been a couple of months since this incident and we still haven't needed to access either of the entities from other clients. Using the simpler design allowed us to do more stuff with less stuff!


Posted on Friday, November 8, 2013 8:25 AM software development , software development process , YAGNI | Back to top

Comments on this post: More Stuff less Fluff

# re: More Stuff less Fluff
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For me YAGNI is a life's journey in the search for simplification.
Left by Brett on Nov 14, 2013 5:37 PM

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