You would think so, but it actually doesn't. last time I checked, libstdc++ could only optimize std::bind closures. A trivial test with a stateless lambda shows this is still the case in GCC14 and 15. In fact I can't even seem to trigger the library optimization with bind.

Differently from GCC14, GCC15 itself does seem to be able to optimize the allocation (and the whole std::function) in trivial cases though (independently of what the library does).