Philippe Cholet

After discussion on [zulip](https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/Adding.20new.20lints.20.60missing_iterator_*.60) and some reflexion, those lints (if wanted) should at least be part of the same lint pass as `missing_trait_methods`. Alternatively, `missing_trait_methods` could be configurable in `clippy.toml`....

We have a bunch of methods about iterators of results: `map_ok filter_ok filter_map_ok flatten_ok fold_ok` (and related but different `process_results`) and `try_collect` clashing with the nightly `Iterator::try_collect`. I think `try_`...

@jswrenn Merry Xmas. What do you think about adding `product_ok` and `sum_ok`? (There is also #830 about a `fold_while_ok`?)

I think this should be closed, thanks to #699.

Running totals and `0, |x,y| x+y` surely makes me think of python's `itertools.accumulate` which was a bit discussed in #705 and #147. Which is there seen with `scan`: `(0..4).scan(0, |x,...

The name "accumulate" seems a reasonable name to me. I agree that _we should be able to "accumulate" without `Copy`_, making your "successors"-way more general than the "scan"-way but definitely...

In #710, I said that `process_results` "should" take `&mut self` instead of `self`, in which case the lifetime you remove here is useful I think. I'm gonna think about this....

I wonder if _libcore_ would want a `Iterator::tail` (not as straightforward as this implementation in case the iterator generate less than `N` items but it's possible) in which case name...

I fused the iterator instead of checking `data.len() == n` (same as recent fix #900).

I polished the commits and added @scottmcm as co-author. I particularly like his idea of `skip`ping the starting part of the iterator. Is there a better name than `tail`? (see...