At first wasn’t very concerned about this example. It’s typical of examples meant to illustrate the rampant incorrectness.
In general the function is called like map!(c, a, b). In the examples in the doc string, the input and output are clearly not aliased. In fact c is freshly initialized. Many numerical libraries work like this. It is very common to read something like “output must not be aliased to input”. So if I see the doc to map!(c, a, b) and thought, “well it didnt say I cant alias, I guess I just do it and move on”, I’m asking for trouble. If I didn’t read the doc string, I’d never assume it. I’d check it first or ask or something.
If this were the end of the story, I’d say it’s not such a big deal.
The bigger problem, apparently, is that
- behavior with aliasing is not documented.
- behavior with aliasing was not properly tested.
- behavior with aliasing changed in a (non-breaking) release.
Now there’s nothing I can do to avoid a bug in my code, even if I’m careful.
It’s possible that documenting it more carefully may have avoided this. It would have made it less likely that adequate tests were overlooked, and that a breaking change would be introduced.
Note that although the previous behavior has been restored, it’s still not documented.
More generally: I won’t put much stock in the idea that Julia is really buggy based on anecdotes. I’d have to see some attempt at an analysis. And discussion of which languages you’re comparing to.
EDIT: