Hi Everyone, This is a short review of Boost.Hub. First, I wanted to yet again thank Joaquín for this contribution. Also, thanks to Ion for managing the review. I personally never had a need for a container with colony/hive/hub properties, so I do not speak as an expert in the problem domain. I have read the docs for the library, investigated the API, compared against std::hive, and played with the library on Compiler Explorer (GCC 15.2) trying to break it. I recommend accepting Hub into Boost. For me, it is equally fine whether this would be a separate library or part of Boost.Container. The library is clearly useful. It belongs in Boost more than in the Standard Library. Regarding the design, there is not much flexibility here: it has already been designed while standardizing std::hive. Although the STD has this impractical type requirements Container and SequenceContainer that (i) are not useful and (ii) do not play well with std::hive, so Boost.Hub has a chance to set things straight. For instance, neither hub nor hive are SequenceContainers, as pointed out in another thread. As indicated in another thread, I recommend making the `visit` functions free functions and renaming them to `for_each` and `for_each_while` (as per Joaquí's suggestion). While the latter name is funny, it is the most adequate one also. This could also be a customization point for all containers: it would default to regular `std::for_each` but offer container authors to provide a faster implementation. We are encouraged to prefer Boost's Hub over Hive based on numbers, but it is not clear to me if the better numbers are due to the necessary API changes, or because Joaquín is a better implementer. What was the primary motivation to scrap the block size control? Regarding the documentation, I find the one currently present in the README satisfactory (modulo the SequenceContainer requirements), and friendlier than these in Boost.Container. So I wonder what the effect of merging would be. Regarding the implementation, I didn't have time to follow all of it but: 1. It is impressive that it is only 1800 lines. 2. It is easy to read and understand; also well documented, where needed. 3. I am concerned about the usage of BOOST_LIKELY. Are these the source of performance? It is my understanding that they are very fragile and may give opposite effects once something changes in the compiler implementation. Plus it is easy to fabricate the data that will make the program go slow when the "negative" branches are deliberately triggered. 4. There is this line: `size_type memory() const noexcept // TODO: remove` Is this something to be fixed? 5. Compiling with -Wall gives me a warning in GCC when sorting an empty hub: a zero-sized heap array is allocated: https://godbolt.org/z/dWvxv9n8s This is technically fine to allocate such arrays, but maybe it is worth to make -Wall clean. I know that Joaquín is responsive and am confident that the Hub implementation will be maintained. Regards, &rzej;