[Development] gsl::owner (Was: Setters: Clarifying the ownership)

[Konstantin Tokarev]

31.07.2018, 21:35, "Иван Комиссаров" <abbapoh at gmail.com>:
> I prefer the solution from the thread "unique_ptr and Qt" about using smart pointers for transferring ownership explicitly. We can use std::observer_ptr from c++20 to indicate the places that do not take ownership.
> I think, using gsl::owner is a wrong way of doing things, it's the way that can be source and (maybe) binary compatible, but that's a workaround, not a solution.

It's binary compatible, because owner<T> = T. It's not a solution, just annotation for people static analyzers (like e.g. "emit" keyword in Qt)

> However, the solution can require too much work to do.

It also requires changic public APIs, which can only be done in Qt 6.

>
> Иван Комиссаров
>
> 31 июля 2018 г., в 16:04, Eric Lemanisser <eric.lemanissier at gmail.com> написал(а):
>
>> Please, don't introduce another type alias. It would loose the advantage of static analysis like http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-owning-memory.html
>>
>> Le mar. 31 juil. 2018 à 14:52, Giuseppe D'Angelo via Development <development at qt-project.org> a écrit :
>>> Hi,
>>>
>>> On 31/07/18 13:11, Sérgio Martins via Development wrote:
>>>> I would recommend however that our docs show T* instead of gsl::owner<T>
>>>> and continue to include "Takes ownership of foo" in the text.
>>>> While I believe in self-documenting signatures I think it's too much
>>>> noise and hurts readability, and most devs never heard of gsl.
>>>>
>>>> Should be just an aid for tooling IMO.
>>>
>>> I agree with the rest of your email, but I kind of disagree with this
>>> particular point, for different reasons:
>>>
>>> * Because we need to educate our users that there's more C++ than Qt out
>>> there, and the Core Guidelines and the GSL are a fundamental part of
>>> knowledge for a C++ developer.
>>>
>>> * Even if we consider talking about the GSL too much of a "distraction"
>>> in the docs, we can simply add our own qOwner type alias, with identical
>>> semantics, and document what it does and what it means in signatures.
>>>
>>> * Leaving gsl::owner in the signature of a function documentation can
>>> help clarify situations where the textual documentation does not say
>>> anything about the ownership. At least, it's one more safeguard against
>>> adding functions that take/return pointers and don't clearly document
>>> the ownership.
>>>
>>> However, from a practical point of view, unless someone adds gsl::owner
>>> _everywhere_ to Qt, we can't report it in the docs, as they would
>>> otherwise be inconsistent :-(
>>>
>>> My 2 c,
>>> --
>>> Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
>>> KDAB (France) S.A.S., a KDAB Group company
>>> Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
>>> KDAB - The Qt, C++ and OpenGL Experts
>>>
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-- 
Regards,
Konstantin