Why I think Marcus is wrong
March 18, 2014

Marcus Zarra’s NSConference talk today - about how reinventing the wheel is ok, maybe even to be encouraged - was thought provoking. In fact, I think it was downright provocative. Which is great :)

I recognise a lot of the sentiment behind what he was saying, and have undoubtedly had that same urge to reinvent on many occasions.

I generally feel that it’s useful to understand at least one level below the one at which you are working. If you’re using Objective C, understand C. If you’re using C, understand assembler. If you’re using an open source framework, understand how it works or the technology on which it is implemented.

And yes, it’s hard to really understand a coding problem until you’ve tackled it yourself.

Also it’s quite true that generic code is never going to be as optimal as a bespoke solution.


When you use an open source library, you are typically using code that has shipped in existing products. In multiple existing products. Products that have provided the code with hours/days/months of testing with real world data. Is that worth something? Hell yes.

There is code out there which is broken, unused, or just plain rubbish. Undeniable. That’s an argument for choosing carefully, it’s not an argument for not using other people’s code.

The fact that it’s hard to understand a problem until you’ve tackled it yourself makes it tempting to rewrite. Very tempting. I have ripped out and rewritten plenty of other people’s code in my time. Many’s the time I have simplified “unnecessarily complicated code”: “what an idiot this guy is, look at all this crazy shit he’s doing…”.

That same fact is also why you really shouldn’t, most of the time. Unless you have the luxury of enough hours to rewrite the same thing more than once on the same project, or the luxury of doing the same thing repeatedly on each project. When you rewrite, you will fuck up. The fuck up rate will probably never get to zero, but it will almost certainly only reach an acceptable level after two or more attempts.

It’s uncanny how often that “weird shit” that you ripped out near the beginning makes a quiet return (with the variable names changed to protect the innocent), when the subtlety of your understanding of the problem finally catches up with that of the person who wrote the original version.

When we use someone else’s code, the trade off we’re making is to exchange that deeper understanding that we would have gained by doing it ourselves for the luxury of not having to go down all the blind alleys first.

When it comes to the risk that comes with using someone else’s code, I agree with Marcus that it’s always good to understand it.

But if you’re selling your client on the idea of doing an upfront rewrite of something now on the basis that there’s a 20% chance that they might conceivably need to do it later… well, that’s nice work if you can get it, but 80% of the time it’s stuff that they didn’t need to pay for. Sure the cost of that 20% scenario might be much worse than up-front rewrite, but there are other ways to mitigate against that worst case.

Marcus seemed to be describing a situation where you’re basically doing similar projects again and again. In that case I can also see the attraction of starting from scratch each time. Like a master craftsperson essentially making the same chair over and over again, that zen-like quest for perfection is seductive.

Most of us don’t live in that world though.

I’m not saying that we write code once and let it ossify for ever more, or that we grab the first thing off Github that looks vaguely ok and never question it again. There’s a hell of a lot of room in between that and what Marcus seemed to be advocating though.

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