<xstd/bits/bit_valarray/bit_slice.hpp>

bit_slice

class bit_slice {
public:
  bit_slice() = default;
  constexpr bit_slice(size_t start, size_t size, size_t stride) noexcept;
  explicit bit_slice(const slice& s) noexcept;

  constexpr auto start() const noexcept -> size_t;
  constexpr auto size() const noexcept -> size_t;
  constexpr auto stride() const noexcept -> size_t;

  friend auto operator==(const bit_slice&, const bit_slice&) -> bool = default;
};

• As [class.slice], usable in a constant expression, where slice's constructors are not, so v[bit_slice(start, size, stride)] runs in one.
• It selects what the slice of the same three numbers selects.