std::bitset_reference - Man Page

reference (const reference &)=default
constexpr reference & flip () noexcept
constexpr operator bool () const noexcept
constexpr reference & operator= (bool __x) noexcept
constexpr reference & operator= (const reference &__j) noexcept
constexpr bool operator~ () const noexcept

class bitset

class std::bitset< _Nb >::reference"This encapsulates the concept of a single bit. An instance of this class is a proxy for an actual bit; this way the individual bit operations are done as faster word-size bitwise instructions.

Most users will never need to use this class directly; conversions to and from bool are automatic and should be transparent. Overloaded operators help to preserve the illusion.

(On a typical system, this bit reference is 64 times the size of an actual bit. Ha.)