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[ER] Three Vec functions #82336
Description
Some member functions that could be added to Vec:
This is similar to Vec::remove but like Vec::pop it returns an Option, avoiding panics:
pub fn Vec::pop_index(&mut self, index: usize) -> Option<T>;(In alternative Vec::pop_front could often suffice).
Probably this was already suggested elsewhere:
pub unsafe fn get_debug<I>(&self, index: I) -> &<I as SliceIndex<[T]>>::Output;
pub unsafe fn get_debug_mut<I>(&mut self, index: I) -> &mut <I as SliceIndex<[T]>>::Output;They contain a debug_assert!() to test the bounds only in debug builds. I think such debug_assert can't be added to get_unchecked/get_unchecked_mut because the semantics is different. They are unsafe, but they add a bit of safety during debug runs.
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jyn514 commentedon Feb 20, 2021
@leonardo-m this can't work because the standard library isn't recompiled between debug and release builds, it's always compiled in release mode. Adding a
debug_assert!to get_unchecked seems fine but it won't affect anything other than testing the standard library itself.the8472 commentedon Feb 20, 2021
I think
Vecdoesn't implement it because it would be a performance footgun as it has to move the entire Vec on each invocation, i.e. it's O(n), it's better to use VecDeque in such a case where pop_front is O(1).leonardo-m commentedon Feb 20, 2021
I see, thank for the answers.
Regarding Vec::pop_index, it's not slower than Vec::remove, the difference is just in the API, it returns an Option...
jyn514 commentedon Feb 20, 2021
This was discussed and rejected in #77480. Some relevant comments:
So
pop_indexwould need an RFC, and the others are not possible to write.