I strongly believe, that the main reason why `span` is strongly constrained
initially is exactly the same why `vector` didn't allow incomplete element
type before C++11 -- it was just easier to add one strong constraint than
elaborate what methods could work with incomplete element type and what
ones couldn't.

On Thu, Jul 6, 2023 at 6:27 PM Jason McKesson via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> On Thu, Jul 6, 2023 at 2:50 AM Andrey Davydov via Std-Proposals
> <std-proposals_at_[hidden]> wrote:
> >
> > Hello everyone!
> >
> > I'd like to propose a support span of elements of incomplete type.
> > The draft of the proposal (
> https://github.com/AndreyG/cpp-papers/blob/main/span-of-incomplete-element-type.md)
> contains motivation. What do you think about it?
>
> The proposal needs to investigate why the limitation exists at all. I
> didn't know about it until you brought it up. You should spend some
> time looking into older versions of `span` or asking the people who
> made those proposals why the type is required to be complete.
>
> There could be some good-yet-esoteric reason why this limitation is here.
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>

-- 
Andrey Davydov