[Development] QList for Qt 6

Иван Комиссаров abbapoh at gmail.com
Wed May 22 18:25:18 CEST 2019


> 4. Use QVector to implement QList<Foo>, if sizeof(Foo) <= sizeof(quint64) and Foo is movable

What about fast prepend in that case? People tend to use QList as a deque because of the fast prepend/take first

Иван Комиссаров

> 22 мая 2019 г., в 15:49, Lars Knoll <lars.knoll at qt.io> написал(а):
> 
> Let’s conclude the topic of QList. I do see the concern about silent source breakages. Here’s what we’ll (I’ll) do then for Qt 6:
> 
> 1. Rename QList to QArrayList and make QList an alias to QArrayList
> 2. Move QStringList and QByteArrayList over to inherit from QVector (that should be source compatible)
> 3. Rename QStringList to QStringVector (keep QStringList as a compatibility name), same for QBAList
> 4. Use QVector to implement QList<Foo>, if sizeof(Foo) <= sizeof(quint64) and Foo is movable. I’m intentionally not using sizeof(void *) here, as types with sizes between 4 and 8 bytes would not have stable references in cross platform code, so I do not believe lots of code would assume that (or it would have broken on 64 bit).
> 5. Add a compile time switch that allows mapping QList completely to QVector or to a compatibility mode where QLists of large/non movable types are mapped to QArrayList
> 6. For now we don’t yet want to explicitly change all our API that uses QList to use QVector (as that would make merging from dev a pain, let’s do that later this year). But to test that everything we have works with QVector, we’ll set the compile switch to default to mapping to QVector.
> 7. Make the implementation of QArrayList fully inline and deprecate the class.
> 
> Let me know if there are any major concerns with this plan. It should give us a good compromise, where we can move all of Qt over to QVector and test things early, as well as providing a compatibility mode for our users (slower but won’t silently break).
> 
> Cheers,
> Lars
> 
>> On 21 May 2019, at 10:38, Giuseppe D'Angelo via Development <development at qt-project.org> wrote:
>> 
>> Il 21/05/19 10:30, Konstantin Shegunov ha scritto:
>>> That's a hard one. Especially since very few could keep in their brain a list of the sizes of each and every one class from Qt. It also differs depending on architecture.
>> 
>> I know. That's my point: we can't just break this level of source compatibility.
>> 
>> Thanks,
>> 
>> -- 
>> 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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