Auto merge of #24781 - bluss:vec-drain-range, r=alexcrichton

Implement Vec::drain(\<range type\>) from rust-lang/rfcs#574, tracking issue #23055.

This is a big step forward for vector usability. This is an introduction of an API for removing a range of *m* consecutive elements from a vector, as efficently as possible.

New features:

- Introduce trait `std::collections::range::RangeArgument` implemented by all four built-in range types.
- Change `Vec::drain()` to use `Vec::drain<R: RangeArgument>(R)`

Implementation notes:

- Use @Gankro's idea for memory safety: Use `set_len` on the source vector when creating the iterator, to make sure that the part of the vector that will be modified is unreachable. Fix up things in Drain's destructor — but even if it doesn't run, we don't expose any moved-out-from slots of the vector.
- This `.drain<R>(R)` very close to how it is specified in the RFC.
- Introduced as unstable
- Drain reuses the slice iterator — copying and pasting the same iterator pointer arithmetic again felt very bad
- The `usize` index as a range argument in the RFC is not included. The ranges trait would have to change to accomodate it.

Please help me with:

- Name and location of the new ranges trait.
- Design of the ranges trait
- Understanding Niko's comments about variance (Note: for a long time I was using a straight up &mut Vec in the iterator, but I changed this to permit reusing the slice iterator).

Previous PR and discussion: #23071

0 files changed, 0 insertions, 0 deletions