Comment by throwaway173738
9 hours ago
I look at Postel’s law more as advice on how to parse input. At some point you’re going to have to upgrade a client or a server to add a new field. If you’ve been strict, then you’ve created a big coordination problem, because the new field is a breaking change. But if you’re liberal, then your systems ignore components of the input that they don’t recognize. And that lets you avoid a fully coordinated update.
Yes, what Postel's Law is about. That's the whole point of contrasting it with Hyrum's Law, no?
Hyrum's Law is pointing out that sometimes the new field is a breaking change in the liberal scenario as well, because if you used to just ignore the field before and now you don't, your client that was including it before will see a change in behavior now. At least by being strict, (not accepting empty arrays, extra fields, empty strings, incorrect types that can be coerced, etc), you know that expanding the domain of valid inputs won't conflict with some unexpected-but-previously-papered-over stuff that current clients are sending.