[istream.assign]
31 Input/output library [input.output]
31.7 Formatting and manipulators [iostream.format]
31.7.5 Input streams [input.streams]
31.7.5.2 Class template basic_istream [istream]
31.7.5.2.3 Assignment and swap [istream.assign]
basic_istream& operator=(basic_istream&& rhs);
void swap(basic_istream& rhs);