[libcxx-commits] [libcxx] [libc++][sstream] Add deleted special member functions (PR #80254)

[Mark de Wever via libcxx-commits]

https://github.com/mordante requested changes to this pull request.

Thanks for working on this! A few minor things, I'd like to have another look before approving.
Even when this is implicit I strongly prefer to follow the wording of the Standard. 
I'm also happy we test these properties since it seems we didn't do that either.

https://github.com/llvm/llvm-project/pull/80254