Hi Everyone, Once again, thank you Joaquín for this contribution to the community. This is not really a review, but I wanted to talk about this idea to implement a specialized algorithm for iterating over the container elements in the form of hub::visit. First, should we draw from this a more general observation that iterators are an abstraction with overhead, and other containers (deque?) would also benefit from this inversion-of-control approach? Second, I think that the most natural naming choice for this operation is "for each", not "visit". It does practically the same thing as `std::for_each`. Third, the interface is rather unusual, and it allows one hub to iterate over another hub's elements: hub<T> h, g; h.visit(g.begin(), g.end(), fun); https://godbolt.org/z/bbb765bb1 It looks like this function should be a free function rather than a member function. And if there is a reason to make it a member function, at minimum add a precondition that both the iterators should point inside the container. Regards, &rzej;