[Development] QList

[André Somers]

Hi,


Op 29/05/2017 om 14:53 schreef Jason H:
>> Sent: Thursday, May 25, 2017 at 7:03 PM
>> From: "André Somers" <andre at familiesomers.nl>
>> To: "Christoph Feck" <cfeck at kde.org>
>> Cc: development at qt-project.org
>> Subject: Re: [Development] QList
>>
>> Hi,
>>
>> On 25 May 2017, at 18:40, Christoph Feck <cfeck at kde.org> wrote:
>>
>>>> On 25.05.2017 13:53, André Somers wrote:
>>>> Op 25/05/2017 om 12:38 schreef Konstantin Tokarev:
>>>>> Other problem, that IMO is more serious, is that Qt *requires* user to use QList,
>>>>> by returning or taking it as and argument in various places. That's almost only
>>>>> reason why I use QList in my code[*].
>>>>>
>>>>> If Qt 6 APIs are changed from QList to QVector, lots of user code dealing with
>>>>> this APIs will break, unless QList will become an alias of QVector.
>>>>>
>>>>> [*] And, fwiw, almost only reason I use QString, but that's off-topic here
>>>>>
>>>> I think you bring up a good point there. Would not the best way out be
>>>> to fix exactly this problem? If these functions would not return a
>>>> container, but some type of view into such a container, that would leave
>>>> users free to choose the type of container they need for their job
>>>> instead of being forced into the direction Qt choose for its API. A view
>>>> might take the form of a pair of iterators, a range, or perhaps even
>>>> some specialized class that basicaly wraps a pair or iterators and that
>>>> provides convenience functions to/from the Qt containers.
>>> If you only return a view to the container, then if the container is modified, the return value is no longer valid. Returning a full container (referenced, with copy-on-write semantics) will not have this problem.
>> Sure, but do you always or even most of the time need that feature? If not, why always pay for it? And it would be easy to turn it into a container when needed, but then you can choose the most appropriate for your task instead of always getting a QList (now) or a QVector (Qt6?)
>
>
>
> I wonder how gsl::span plays into this. I just learned about span, quick seems to be wet we need here?
>
Not at all, I think. gsl::span is "a non-owning range of contiguous
memory" according to
https://www.quora.com/What-is-the-span-T-in-the-CppCoreGuidelines. As
QList does not obey that definition, it would rule out being a view into
QList (or its successor with the same semantics) already. 

André