[Development] Question about QCoreApplicationData::*_libpaths

Ziller Eike Eike.Ziller at theqtcompany.com
Tue Jan 19 15:21:57 CET 2016

> On Jan 19, 2016, at 16:09, Marc Mutz <marc.mutz at kdab.com> wrote:
> On Tuesday 19 January 2016 14:33:46 Giuseppe D'Angelo wrote:
>> On Tue, Jan 19, 2016 at 3:07 PM, Marc Mutz <marc.mutz at kdab.com> wrote:
>>> I'd aggregate the std container instead of inheriting it, but yes, that's
>>> a good idea. I just wrote a mail suggesting essentially the same, only
>>> slower.
>>> But I'd have nothing against going all-in, either.
>> We can't "suddenly" break CoW, though. Who's going to review the millions
>> of lines of code where copies where happily taken assuming they were cheap?
> Who's reviewing the millions of lines of code where hidden detaches are 
> happily incurred even though they are not cheap?
> I'd say that if you took copies in a tight loop, you'll notice and the profiler 
> will find it for you. And the rest don't matter, or they will be found by 
> Clazy.
> I doubt many people actively use the fact that Qt containers are cheap to 
> copy.

Each and every developer that uses Qt uses the fact that Qt containers are cheap to “copy"

class A
    QVector<B> something() const;
    QVector<B> m_something;

QVector<B> A::something() const
    return m_something;

Br, Eike

> But yes, Qt API needs to be reviewed with an eye towards this. Then 
> again, Non-Qt C++ would be horribly slow if copying containers was so 
> prohibitly expensive.
> 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
> KDAB - The Qt Experts
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