Dan Gohman (May 21 2020 at 20:53): Dan Gohman (May 21 2020 at 20:53):if I have a Vec<Val> that I can consume, can I move the elements into a &mut [Val]?
fitzgen (he/him) (May 21 2020 at 20:55):like you have dst: &mut [Val] and src: Vec<Val>?
if so, then {copy,clone}_from_slice should do the trick
Alex Crichton (May 21 2020 at 20:55):@Dan Gohman for (slot, val) in slots.iter_mut().zip(values) { *slot = val; } I think?
Alex Crichton (May 21 2020 at 20:56):oh, do what fitzgen says
Dan Gohman (May 21 2020 at 20:57):ah, I guess I was hoping to avoid copy/clone since the old copy is going away anyway, but I can do that
Chris Fallin (May 21 2020 at 20:57):if you want to avoid the clone and Val's type has a cheap default (e.g. it's a nested Vec or something) you might also be able to use mem::replace
Dan Gohman (May 21 2020 at 20:57):I tried Alex's thing, changing it to values.into_iter(), but it doesn't like that: cannot move out of *result which is behind a shared reference
Chris Fallin (May 21 2020 at 20:58):in the worst case you could always do some hackery with unsafe, a memcpy, and mem::forget
fitzgen (he/him) (May 21 2020 at 20:58):@Dan Gohman can you share the snippet with a tiny bit more context?
Chris Fallin (May 21 2020 at 20:58):though the actual Rust people here will please toss me overboard if that has caveats (Pin would break I think?)
Dan Gohman (May 21 2020 at 21:01):ok, heh, tried to make a reduced case of this and it compiled without error. let me see what's different...
fitzgen (he/him) (May 21 2020 at 21:01):are you destructuring out of a type that has a Drop implementation, by chance?
Dan Gohman (May 21 2020 at 21:02):cannot move out of *command_result which is behind a shared referenc
Dan Gohman (May 21 2020 at 21:03):oops
Dan Gohman (May 21 2020 at 21:03): Dan Gohman (May 21 2020 at 21:03):It looks like I can do it if I have a Vec, but I actually have a Box<[T]>
Alex Crichton (May 21 2020 at 21:04):@Dan Gohman Vec::from(ins)
Alex Crichton (May 21 2020 at 21:04):in that you can create a Vec from a Box<[T]> w/ a zero-cost cast
fitzgen (he/him) (May 21 2020 at 21:05): Dan Gohman (May 21 2020 at 21:06):oh, cool
Dan Gohman (May 21 2020 at 21:06):That works!
fitzgen (he/him) (May 21 2020 at 21:07):I think what was happening is that Box<[T]> doesn't implement IntoIter, and it just derefs to the slice's IntoIter; would need specialization to special case Box<[T]> over Box<T> for choosing an IntoIter, which I'm not sure std ever does at the public level (although definitely internally uses specialization)
maybe you can clarify, @Alex Crichton
Alex Crichton (May 21 2020 at 21:08):that sounds right yeah
Last updated: Nov 22 2024 at 16:03 UTC