Re: [hub] on the specialized iteration over elements

El 16/04/2026 a las 21:42, Andrzej Krzemienski escribió:
> 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?


Ion has aready followed up on this subtopic, I'll add my observations on 
that subthread.


>
> 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.


Yes, I think your proposal makes sense, since, as you CE snippet shows, 
the operation can be performed based on the iterators alone.

So, instead of visit and visit_all we can have global functions:

   template<hub_iterator Iterator, typename F>
   Iterator for_each(Iterator first, Iterator last, F f);

   template<typename T, typename Allocator, typename F>
   typename hub<T, Allocator>::iterator for_each(hub<T, Allocator>& x, F f)
   {
     return for_each(x.begin(), x.end(), std:.ref(f));
   }

   // same for const hub

I have a bikeshedding problem with visit_while/visit_all_while, though: 
the morally closest function in <algorithm> would be std::find_if_not, 
which is not a very intuitive equivalent and has, in fact, different 
semantics (predicates can't change the passed element). Ideas on naming? 
for_each_while would be my first option, I guess.

Joaquín M López Muñoz

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