"Software licenses" aren't their own subject. They are instruments of copyright law. Without copyright, there is nothing to be licensed. And clean room implementations are the best way to ensure that no copyright violation has occurred.
Looking at GPL code doesn't poison your mind forever. Of course, you cannot directly copy GPL code and call it MIT. And you arguably cannot have GPL code open in one window and write your version in a separate window. Copyright protects a specific set of symbols in some order, not an underlying idea or algorithm. You can look at a GPL hashtable one day and write an MIT one the next, no problem.
However, it is my opinion that having a project posted on HN, being directed to look at the "internals" of another software project (such project being licensed under the GPL), and subsequently modifying your own project with what you've learned, is legally risky.
Specifically, if I were corporate counsel at a company looking to use MIT-licensed code in a product of ours, and our due diligence uncovered that just such a thing had happened, I would advise against using that code. The risk—that is, likelihood multiplied by the magnitude of the severity of the consequences—of being compelled to license our software under the GPL would be far too high.
As a result, I stand by my assessment that it is probably best—albeit not mandatory—for the OP author not to take a look at how GPL'd code accomplishes what OP author is trying to accomplish.
> Specifically, if I were corporate counsel at a company looking to use MIT-licensed code in a product of ours, and our due diligence uncovered that just such a thing had happened, I would advise against using that code.
I get that corporate counsel is extremely conservative (do you practice in this area?) and often insensitive to the costs of following their advice (as opposed to the costs of not following it) and you may well be right that this is what they would advise if asked explicitly. But I don't think the end result is good advice for an engineer.
> The risk—that is, likelihood multiplied by the magnitude of the severity of the consequences—of being compelled to license our software under the GPL would be far too high.
I think you're overestimating both likelihood and severity. Likelihood -- I mean, your internal hash table is never going to see GPL enforcement action. Severity -- the least expensive path to remediation is unlikely to be GPL'ing your software. You could replace the component, for example.
A human beings right to enlighten themselves trumps any other human beings right to enrich themselves.
You're calling for a reduction in agency over a potential for legal action - self-censorship, essentially - in a way, forming a pre-judiciary "pre-crime" conclusion of guilt.
Code is language. Restrictions on its use are human rights violations, no matter what legal-ese can be trotted out to FUD the arena.
> Looking at GPL code doesn't poison your mind forever.
If you purposely go through the source code of a project to get inspiration and afterwards you are so inspired that you end up implementing the same thing in your code, you're literally reusing the code. If the project that inspired you so much does not grant you the right to reuse the code in the way you are reusing it, you're violating the licensing terms.
"Clean room implementation" does not mean "I may or may not have copy/pasted the code". It literally means replicating a design without infringing copyright related to the work you're replicating. Directly accessing the code and lift the good parts in different degrees of verbatim-ness is the textbook definition of copyright violation.
Software licenses are the greatest legal psych out of my lifetime. US law permits anyone who has a legally acquired copy of a piece of software to copy it further[1], such
that such a new copy or adaptation is created as an essential step in the utilization of the computer program in conjunction with a machine and that it is used in no other manner
As anyone can see, this completely obviates any need to be licensed to use software once the seller has lawfully sold you a copy. It's yours and you can execute it as you see fit. Interestingly, this doesn't really affect the GPL because the GPL doesn't attempt to kick in unless you further redistribute. And that, of course, is not protected by section 117 and does require a license.
Of course we live in a regime where the process is the punishment, so if you're high profile you'll probably get hit with a ruinous lawsuit anyhow. C'est la vie.
