On Tue, Jun 20, 2023 at 6:05 AM Nikl Kelbon via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> I've been working on improving trivial relocation proposals and I think
> I've found a new tool in a language we don't use
>
> About relocation:
>
> There are few possibilities to create move ctor:
> 1. trivial memcpy
> 2. exchange with default state
> 3. self reference scenario
> 4. do not have move ctor at all
>

...and many more. :) You should read Appendix C:
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p1144r8.html#non-trivial-samples


[...] then we can add trait
> is_not_self_reference<T>
> (traits checks if T has field or base class with non 'swap'/'default' move
> recursivelly)
>

We need a solution that can reliably distinguish MSVC's std::list from
libc++/libstdc++'s std::list.
(The former uses the "sentinel node" technique; the latter two use the
"dummy node" technique. You need to learn the difference between them.)


What if we add trait is_trivially_destructible_after_move?
>

You're describing Niall Douglas's P1029. Watch "Trivially Relocatable"
(2019) <https://www.youtube.com/watch?v=SGdfPextuAU&ab_channel=CppNow>,
particularly slide 109.

–Arthur