[Development] HEADS UP: Don't use QList, use Q_DECLARE_TYPEINFO

[Marc Mutz]

On Friday 10 July 2015 21:33:30 Thiago Macieira wrote:
> You really want to use a vector for everything except if:
>  - you NEED O(1) insertion or deletion anywhere → use QLinkedList
>  - you want stable element pointers even if the container is modified
>  - copying your type is expensive and your container gets modified a lot
> 
> The first two are extremely rare.

Indeed. So rare that in my professional career, with lots of STL use (I even 
wrote a custom allocator once - yes, in production code), I have only ever 
used std::list only to implement a poor man's concurrent queue (and that 
requires splice(), which QLinkedList doesn't have):

    // pop_front:
    std::list<C> next;
    {
        const QMutexLocker locker(queueMutex);
        next.splice(next.begin(), queue, queue.begin());
    }
    // use next.front()

    // push_back
    std::list<C> newItem = { ... };
    {
        const QMutexLocker locker(queueMutex);
        queue.splice(queue.end(), newItem);
    }

And the third is so hard to predict that one shouldn't try, but see whether 
QVector doesn't offer enough performance.

So im my book, using QLinkedList or QList-for-list-behaviour or std::list is 
almost certainly a premature optimisation, and in need of defending in the 
commit message.

Thanks,
Marc

-- 
Marc Mutz <marc.mutz at kdab.com> | Senior Software Engineer
KDAB (Deutschland) GmbH & Co.KG, a KDAB Group Company
Tel: +49-30-521325470
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