I would suggest that not modifying capacity is the better default.
Even clear() doesn't deallocate element blocks.

As for insert(num, element) when size() == 0, I would be surprised
that if the operation that caused the size to go to zero didn't change
the capacity, that the next time I added even 1 element to the
container would cause the capacity to drop.

For list, I expect the capacity to decrease because list doesn't have
a capacity different than size.

On Wed, Mar 5, 2025 at 2:06 PM Matt Bentley via SG14
<sg14_at_[hidden]> wrote:
>
> Hi all,
>
> I'm just wondering what people's assumptions are around hive::assign()/fill-insert/range-insert and capacity. This is not a standardisation question.
>
> The standard ([sequence.reqmts]) does not specify one way or another whether capacity changes as a result of a call to assign(), but obviously if the assigned range is larger than capacity(), capacity() will increase.
>
> However, if the assigned range is smaller than capacity, would capacity be expected to decrease? Or rather, what would you expect to happen? Leave capacity as-is, avoid deallocations and put the burden on the developer to call trim()? This has implications for whether or not assign does the right thing by cache locality ie. maintaining the minimum number of larger contiguous blocks, or by allocation/deallocation.
>
> For vector, we would possibly expect capacity to stay the same in this case. For list, we expect it to decrease.
>
> Similarly, would you expect a call to hive::insert(num, element) when size() == 0 but capacity() > num to potentially decrease capacity()?
>
> Thanks,
>
> Matt
>
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