Design, Programming

Simplicity via Redundancy

Typically when we do a time versus space tradeoff analysis for solving a computational problem, we have to give up one for the sake of the other. By definition, you trade reduced memory usage for slower execution or vice versa, faster execution for increased memory usage. Caching responses from a web server is a good example of space traded for time efficiency. You can store the response of a web request in a cache store hoping that you could reuse it, if the same request needs to be served again. On the other hand, if you wanted to be space efficient, you would not cache anything and perform the necessary computations on every request.

When I am having a discussion with my colleagues, this time versus space tradeoff analysis comes up quite frequently ending in a time efficient solution or a space efficient solution based on the problem requirements. Recently I got into a discussion which gave me a new way of thinking about the problem. How about if we also include simplicity of the solution as another dimension which directly contributes to development efficiency. In an industrial setting, simplicity is just as important or the lack thereof costs money just as time or space inefficient solutions would.

So the recent discussion I had was about a problem that involved some serious computation at the end of a workflow that spanned multiple web requests in a web application. This computation would have been considerably simpler, if we stored some extra state on a model in the middle of the workflow. It started to turn into a classic time versus space efficiency debate. Time was not an issue in this case and hence giving up that extra space was considered unnecessary. But I was arguing for the sake of simplicity. Quite understandably, there was some resistance to this approach. The main argument was “We dont have to store that intermediate result, then why are we storing it”. I can understand that. If there is no need, then why do it. But if it makes the solution simple, why not?

I admit there might be certain pitfalls in storing redundant information in the database, because it is not classic normalized data. Also, there could be inconsistencies in the data, if one piece changes and the other piece is not updated along with it. Also it might be a little weird storing random pieces of information on a domain. Luckily in my favor, none of these were true. The data made sense on the model and could be made immutable as it had no reason to change once set and hence guaranteeing data consistency.

Extending this principle to code, I sometimes prefer redundancy over DRYness (Don’t Repeat Yourself), if it buys me simplicity. Some developers obsess over DRYness and in the process make the code harder to read. They would put unrelated code in some shared location just to avoid duplication of code. Trying to reduce the lines of code, by generating methods on the fly that are similar to each other, using meta-programming can take it to a whole new level. It might certainly be justified in some cases but I am not sure how many developers think about the added complexity brought on by this approach.

A good way to think about reusability is thinking about common reason for change. If two classes have a similar looking method, and you want to create a reusable method and have it share between the two, then you should also think about if those two classes have a common reason for that method to change. If yes, then very clearly that method should be shared, if not, may be not so much, especially if it makes the code hard to understand.

I feel redundancy has value sometimes and simplicity should get precedence over eliminating redundancy. Thank you for reading. Comments welcome.

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