1353     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {  in partial_cmp()
1944     fn next(&mut self) -> Option<I::Item> {  in next()
1947     fn size_hint(&self) -> (usize, Option<usize>) {  in size_hint()
1950     fn nth(&mut self, n: usize) -> Option<I::Item> {  in nth()
1953     fn last(self) -> Option<I::Item> {  in last()
1960     fn last(self) -> Option<Self::Item>;  in last()
1965     default fn last(self) -> Option<I::Item> {  in last()
1967         fn some<T>(_: Option<T>, x: T) -> Option<T> {  in last()
1979     fn last(self) -> Option<I::Item> {  in last()
1986     fn next_back(&mut self) -> Option<I::Item> {  in next_back()
1989     fn nth_back(&mut self, n: usize) -> Option<I::Item> {  in nth_back()
2155     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {  in poll_next()
2159     fn size_hint(&self) -> (usize, Option<usize>) {  in size_hint()
2444     fn cause(&self) -> Option<&dyn core::error::Error> {  in cause()
2448     fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {  in source()