On Tue, May 6, 2025 at 8:30 PM Magnus Fromreide via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
Hello!

One problem with friendship is that it is all or nothing.
I think there should exist a kind of limited friendship as follows:

There is; check out the "passkey idiom."
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2893r3.html#passkey-idiom
https://playfulprogramming.com/posts/a-forgotten-idiom-revisited-pass-key

HTH,
Arthur