Function extern_spec_std_iter_Iterator_next 

pub fn extern_spec_std_iter_Iterator_next<Self_>(
    self_: &mut Self_,
) -> Option<Self_::Item>
where
    Self_: IteratorSpec + ?Sized + Iterator,

extern spec for ::std::iter::Iterator::next

This is not a real function: its only use is for documentation.

ensures

match result {
                    None => self.completed(),
                    Some(v) => (*self).produces(Seq::singleton(v), ^self)
                }