Under NLL, reference lifetime is defined by the places where the reference is used, and noaccess types can't be used. So then reference lifetime has to devolve to the spans where the reference is live, which is only defined lexically.
replySo for example:
let mut data = vec!['a', 'b', 'c'];
let b: &noaccess [char] = &data[..];
data.push('d'); // Does this error?
Aha, gotcha. I assume that any such reference would either do nothing or would be used by unsafe code (presumably by conversion through a raw pointer but maybe direct unsafe conversion to regular references could also be allowed).
replyYour example is sneaky, though. Lifetime issues aside (suppose the next line of code uses b), that’s a noaccess reference to memory (an object? a place? I’m not sure what the current term is) that is only guaranteed to exist so long as data is not mutated. So the code with a subsequent use of data would error.
But if it were instead:
let b: &noaccess = data;
It may be interesting to focus on how exactly these planned "no-access" references would differ from raw pointers? Access through raw pointers is an unsafe operation already.
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