let (left, right) = (&mut foo[..split], &mut foo[split..]);
I see these are limitations but not show-stoppers in any way.
Yes, sure, the rule in question may be simple in the abstract (it's a compiler, after all -- they're just software doing straightforward things). But the ability for the poor programmer to detect which rule is being violated where is a lot more limited than the compiler is designed for. Thus the user with the upthread complaint, which is hardly unique.
I mean, at the end of the day if Rust wants to be an everyday language for this kind of everyday problem, the analysis paradigm needs to be communicated much better to everyday hackers (via docs, error messages, whatever). When Rust was new this seemed like just a technical problem to be solved with software maturity. I guess at this point after several years of regularly returning to play with Rust and being frustrated every time, I've mostly given up.
Not to belabor this growing thread, but here's the disconnect. I complained the rules were ad hoc and complicated, you replied that they were simple, and when challenged on an edge case your treatment is to add another clause to re-define a term you used in isolation earlier.
That's what "ad hoc and complicated" means.
Actually, my elaboration of "place", local/field/index, is nearly complete. The only thing missing is upvar, which is local captured in closure. Pre-NLL "live" is simple: expression is live from the definition to the end of the containing statement, and declaration is live from the definition to the end of the containing block. Post-NLL "live" is connected region of control flow graph from the definition to potentially multiple last uses. Really, that is the whole story.
There are two changes currently in development. One changes definition of "place" to include field captured in closure, in addition to local captured in closure. The other is more drastic, changing definition of "live": a loan is live where the loan is origin of a variable and the variable is live. This is great, because current approximation is equivalent to union of all origins.