<xstd/bits/bit_set/bit_set_view.hpp>

bit_set_view

template<bit_blocks Blocks, size_t N>
class bit_set_view {
public:
  // types, lookups, iterators and set algebra as basic_bit_set's, with
  template<class W>
      requires see below
    constexpr explicit bit_set_view(W&& blocks) noexcept;
  template<class Owner>
      requires see below
    constexpr bit_set_view(Owner& c) noexcept;
};

template<class Owner>
    requires see below
  bit_set_view(Owner&) -> bit_set_view<see below>;
template<class W>
    requires see below
  bit_set_view(W&&) -> bit_set_view<see below>;

namespace std::ranges {
  template<class Blocks, size_t N>
    constexpr bool enable_view<xstd::bit_set_view<Blocks, N>> = true;
  template<class Blocks, size_t N>
    constexpr bool enable_borrowed_range<xstd::bit_set_view<Blocks, N>> = true;
}

The set reading of bits another object owns, as basic_bit_set over size_t keys, with:

• Blocks names the blocks the view refers to: a block, a span of blocks, or the block container of the owner it views, const where they are; N is their width in bits, or dynamic_extent.
• The constructor from blocks is explicit. It takes an lvalue block, or a range of blocks that is an lvalue or a borrowed range, and its guide deduces a block as itself and a range as the span that lends it, so bit_set_view(board) over a uint64_t is a bit_set_view<uint64_t>.
• The constructor from an owner is implicit, and takes an lvalue owner of the set reading; a const owner gives a view of const bits. A view of mutable bits converts implicitly to a view of the same bits as const.
• It has no default constructor, owns nothing, and is a ranges::view and a borrowed range.
• Its modifiers write the bits it refers to, and exist only where those bits are not const. insert over a run-time width grows the owner's storage. The compound operators take any set over the same storage and keys, owner or view; the non-member operators, which copy, are the owner's alone.
• == and <=> compare it with whatever converts to it, its owner and lent blocks included, as string_view compares.
• It hashes what it presents: hash<bit_set_view<Blocks, N>> and the Hash2 hook answer as for its owner.