Re: [optional] Feedback on the range interface for Boost.Optional

From: Steve Downey (sdowney_at_[hidden])
Date: 2024-10-05 15:02:01

On Sat, Oct 5, 2024, 10:42 Andrzej Krzemienski <akrzemi1_at_[hidden]> wrote:

>
>
> czw., 3 paź 2024 o 00:51 Vinnie Falco <vinnie.falco_at_[hidden]> napisał(a):
>
>> On Mon, Sep 16, 2024 at 8:32 AM Steve Downey via Boost <
>> boost_at_[hidden]> wrote:
>>
>>> ...
>>
>>
>> For what it is worth, I rather like p3168r2 over the alternative. The
>> design of ranges seems such that it anticipates an open set of library and
>> user-defined adaptors, and long pipelines containing many small
>> transformations to achieve a desired result. The `views::maybe` and
>> `views::nullable` adaptors look very much like in the spirit of the ranges
>> design: small, focused algorithms to achieve a specific well-defined
>> purpose.
>>
>> p3168r2 claims that this:
>>
>>     // Compute eye colors of 'people'.
>>     vector<string> eye_colors = people
>>       | views::transform(&Person::eye_color)
>>       | views::transform(views::nullable)
>>       | views::join
>>       | ranges::to<set>()
>>       | ranges::to<vector>();
>>
>> is worse than this:
>>
>>     // Compute eye colors of 'people'.
>>     vector<string> eye_colors = people
>>       | views::transform(&Person::eye_color)
>>       // no extra wrapping necessary
>>       | views::join
>>       | ranges::to<set>()
>>       | ranges::to<vector>();
>>
>> I prefer the first one, since the transformation is explicit. p3168r2
>> suggests that the new syntax is "dramatically more straightforward" which
>> seems exaggerated to me. It is in fact less straightforward, as now the
>> reader is expected to know about std::optional's expanded role as a range.
>>
>> I'm all for simplicity, but when you choose C++ you are opting in to a
>> certain minimum level of complexity. views::maybe and views::nullable seem
>> like just the right level of complexity for C++. A rangeful std::optional
>> does not do much for me.
>>
>
> Ok, I now have a paper to revert the range interface from Optional:
> https://isocpp.org/files/papers/D3415R0.html
>
> Regards,
> &rzej;
>
I think when you say
Whether [P2988R7]
<https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2988r7.pdf> should
be added instead, we have no strong opinion.

You mean P1255, view maybe?  P2988 is optional<T&>

Are you going to be at Wroclaw?

>