[Bug libstdc++/103904] [defect fix] Please backport P2325R3 to 10 and 11

["h2+bugs at fsfe dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103904

--- Comment #6 from Hannes Hauswedell <h2+bugs at fsfe dot org> ---
Yes, I understand that, and I know that it is your role to uphold these rules
(which I believe make a lot of sense in general) and that you have other
interests to consider beyond mine :)

I would still like to sum up the points that I see in favour of deviating from
that rule:
* GCC10 is still young, the chances that codebases have come to rely on exactly
this behaviour is lower now than it will be when e.g. the next Debian stable is
released. Backporting will reduce breakage in the long run.
* As you have pointed out, the feature has been hidden behind the non-standard
c++20-flag. People had to explicitly opt-in to use this feature and were made
aware that it is experimental.
* The concept becomes more general than before, and all standard library types
that previously met its requirements still meet the old requirements (standard
library views are still default-initializable). So I expect *most* old code
that uses views to just keep working.
* I don't know if this counts as an argument, but I would argue that people
whose code breaks because they rely on something not being a view that is now
considered a view, are also the kind of people who will be able to fix this
quickly ;-)