[throwaway894345]

> What exactly happens in these cases? How can I trust myself, as a fallible human being, to reason about such cases when I'm trying to efficiently roll up a list of results. :-/

For me: minimize shared mutable data. If I really can’t get rid of some shared mutable data, I mutex it or use atomics or similar. This works very well—I almost never run into data races this way, but it is a discipline rather than a technical control, so you might have to deal with coworkers who lack this particular discipline.

[metadat]

Absolutely, the disappointing part is that as code authors, we need to constantly remember about various (otherwise appealing and even encouraged by the language syntax and control constructs) footguns and "never approach such areas" of (totally valid) syntax.

Reminds me of programming in Javascript (it's extreme example, but the similarity is there).

[throwaway894345]

Yeah, it’s a bit disappointing. It doesn’t bother me too much, but it could be improved by a linter which could help you find shared mutable state. Without a concept of “const” (for complex types, anyway), I’m not sure how feasible such a linter would be.