On Mon, Apr 6, 2026 at 1:28 PM Adrian Johnston via Std-Proposals <
std-proposals_at_[hidden]> wrote:

>
> If your array is unordered then you can just swap the end element down
> when erasing an element.
>
> From my own code:
>
> template<hxarray_concept_ T_, size_t capacity_>
>
> void hxarray<T_, capacity_>::erase_unordered(const T_* pos_) {
>
> hxassertmsg(pos_ >= this->data() && pos_ < m_end_, "invalid_iterator");
>
> if(pos_ != --m_end_) {
>
> *const_cast<T_*>(pos_) = hxmove(*m_end_);
>
> }
>
> m_end_->~T_();
>
> }
>
> This is something I think the std::vector could definitely use.
>

This is properly an algorithm: `stdx::unstable_remove{,_if}`.
See
Brent Friedman, 2015:
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0041r0.html
Brent Friedman, 2016:
https://iterator.wordpress.com/2016/01/31/algorithms_0/ (archived
<https://archive.is/pd5v6>)
Arthur O'Dwyer, 2023-ish:
https://github.com/Quuxplusone/SG14?tab=readme-ov-file#efficient-removal-algorithms-future--c14
Ted Lyngmo, 2025:
https://discourse.bemanproject.org/t/help-getting-started-writing-a-propsal-for-unstable-remove-and-friends-wanted/335

Note that David Sankel asked (in the last link above) how
std::unstable_remove_if was different from std::partition. The answer is
that std::partition swaps; std::unstable_remove_if leaves the right-hand
elements in a moved-from state (à la std::shift_left).
Note that (AIUI) Ted Lyngmo abandoned his proposal because the benchmark
numbers weren't good enough to justify the standardization effort; see here
<https://lists.isocpp.org/std-proposals/2025/02/12297.php>.

HTH,
Arthur