Then I noticed people were using them, preventing me from making important changes. So I created a pseudo-"private" facility using macros, where people had to write FOOLIB_PRIVATE(var) to get at the internal var.
Then I noticed (I kid you not) people started writing FOOLIB_PRIVATE(var) in their own code. Completely circumventing my attempt to hide these internal members. And I can't entirely blame them, they were trying to get something done, and they felt it was the fastest way to do it.
After this experience, I consider it an absolute requirement to have a real "private" struct member facility in a language.
I respect Andrew and I think he's done a hell of a job with Zig. I also understand the concern with the Java precedent and lots of wordy getters/setters around trivial variables. But I feel like Rust (and even C++) is a great counterexample that private struct variables can be done in a reasonable way. Most of the time there's no need to have getters/setters for every individual struct member.