This is how I view iterators, but with an extra notch in difficulty. You really need to understand the coroutine model to get anywhere -- and the same is true of iterators. Are these leaky abstractions? I generally think of leaks as "pushing", but this is "pulling" -- I'd call 'em sucky abstractions. But I digress.

I just sat down with the tutorial and banged out what I consider to be a holy grail for quality of life. Alas, it's about 50 lines of ugly boilerplate. I'm omitting it, in part because it's untested, but mostly because I'm embarrassed to share that much C++ in a public forum. If anybody close to the C++ standards is listening... please make this boilerplate not suck so hard.

    template<typename T>
    struct CoroutineIterator {
      left for the reader!
      hint: start with the ReturnObject5 struct in the article,
            and add standard iterator boilerplate
    }

    //! yields the integers 0 through `stop`, except for `skip`
    CoroutineIterator<int> skip_iter(int skip, int stop) {
      for(int i=0;i<stop;i++)
        if(i != skip)
          co_yield i;
    }

    int main() {
      for(auto &i : skip_iter(15, 20)) {
        std::cout << i << std::endl;
      }
    }