Re: Should boost have ofind(_if), that returns boost::optional<T&>?

From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2022-04-03 19:46:15

On Mar 22, 2022, at 2:09 PM, Ivan Matek via Boost <boost_at_[hidden]> wrote:
> 
> Hi,
> I have been thinking for this for a long time so I wanted to get the
> feedback from others.
> 
> As you probably know better than me there is a bit of a drama
> <https://brevzin.github.io/c++/2021/12/13/optional-ref-ptr/>when it comes
> to std::optional<T&> and from what I see it will not be in C++23 for sure.
> I believe this gives an opportunity to boost to provide something nice for
> the users.
> 
> Now the issues are the following:
> AFAIK boost only has old ranges and iterator based algorithms, ideally we
> would just have something like std:: ranges and add the ofind/ofind_if to
> those, but AFAIK those do not exist.
> So I think best thing would be to add it to boost::algorithm
> <https://github.com/boostorg/algorithm/tree/develop/include/boost/algorithm>
> .
> There are further questions like, should boost containers like
> map/unordered_map gain similar functionality, but I think deciding if we
> want the general algorithm is the first step.
> 
> Another option I can think of is that those algorithms return something
> like a 0 or 1 element view(so you could access the optional value with
> range based for loop). This seems weird to me, so I would prefer
> boost::optional<T&>.
> 
> There is s a short example on godbolt <https://godbolt.org/z/W9K3na9Gc>,
> but don't look at implementation too much, it was just something I hacked
> quickly, I am mostly interested in in feedback on if functionality would be
> nice addition to boost.

Personally, I’m not really that enthusiastic about this interface.
However, if someone wants to make a PR for boost.Algorithm, I will certainly review it.

— Marshall