Change unique check to use_count for buffer

[bjeurissen]

Replaces deprecated unique() (https://en.cppreference.com/w/cpp/memory/shared_ptr/unique) with use_count() == 1 (https://en.cppreference.com/w/cpp/memory/shared_ptr/use_count.html). Avoids deprecation warnings on modern compilers.

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[daljit46]

I'm not opposed to this change as a temporary solution, but as mentioned in #2894, perhaps we should take a moment to check why we need this in the first place.

[bjeurissen]

I'm not opposed to this change as a temporary solution, but as mentioned in #2894, perhaps we should take a moment to check why we need this in the first place.

The main purpose of this change would be to silence the deprecation warnings on recent compilers and avoid compilation failures on even newer ones.

As far as I can tell .use_count()==1 and .unique() are identical, apart from the deprecation (warning). This also means that it does not alleviate potential issues with unique() in multi-threaded environments.

[daljit46]

The main purpose of this change would be to silence the deprecation warnings on recent compilers and avoid compilation failures on even newer ones.

Yes, I understand, but I think the compiler warnings and the deprecation of unique() point out that we should not rely on these functions. Substituting with use_count() == 1 just sweeps the issue under the rug without having to deal with the problem.

[bjeurissen]

That is exactly what I meant.