Ask HN: What do you think of reusing code you write between diferent jobs?

Code that's in production use is proven.

Conventional wisdom is that you can always improve your code, but sometimes it's already as good as it will get. I'll only rewrite code if I find I can improve it considerably. I always try to write the cleanest, best code possible, and I think I do a pretty good job at it.

Though I have been thinking that if someone competing with someone I'd already been paid to deliver code for, they could ask for (almost) the same exact features, possibly giving them a competitive advantage. I could obviously decline, but where to draw the line would be iffy.

For context, my situation is special in that I do contractual work, and all of my code remains my intellectual property, so it's all unquestionably legal. I do tell clients that I reuse my code often, though I don't go on a monologue about it. All code is written by me. This is more a question on "if you could, would you?".

An employee also owns the copyright to his/her code (at least in most European countries), the company often just gains the exclusive right to use that code through the contract with the employee (or the law, in some countries). So whether or not it is you intellectual property does not matter that much, what is important is what's actually written in your freelancer contract. If you build a custom software system for a company I'd assume they will not simply let you sell "your" exact code to their competitor afterwards, at least if it's something that has some inherent competitive value (e.g. not simply an off-the-shelf solution like a CRM or website). Most companies make sure this can't happen even when working with a freelancer, so have a close look at your contract (if you have one). If there's no explicit contract it'll depend on the country you're in.

Why can't someone re-use the knowledge they have to write code that has the desired functionality?