On Wed, Aug 30, 2023 at 5:40 AM Hewill Kang via Std-Proposals <std-proposals@lists.isocpp.org> wrote:

As a classic bit operation utility in C++, std::bitset has always been recommended for bit storage representation.

FWIW, I don't think that's true. std::bitset has some weird failings, and lots of projects have invented their own "better bitsets." std::bitset isn't quite in the same bucket as std::regex or std::function or std::unordered_map, but I still don't think it's exactly "always been recommended." I'd agree it has always existed.

Although it lacks begin()/end() member, its interface still looks like a container to me. I'm curious if there has been a proposal to turn it into a C++20 range? [...] Is this an enhancement worth considering, or is it a bad idea?

Bad idea. See

std::bitset is one of those “not quite really STL” types, like std::string and std::valarray, that tries to fit a couple of use-cases but none of them are “STL iterable container.” Arguably, the hint is in its name: whereas vector<bool> is clearly a vector, a sequence container, of boolean values, bitset is a set, a collection of small integer indices. bs.test(42) is the equivalent of s.find(42)bs.set(42) is the equivalent of s.insert(42); and so on. (As usual, these named methods throw std::out_of_range on error, and bitset provides operator[] for faster unchecked access.)
If you were going to iterate over the “contents” of such an object, what would you expect to see?
  std::bitset<1000> bs;
  for (auto elt : bs) {
    std::cout << bs;
Surely you wouldn’t expect to see “false, false, false, false, …”!