philwave at gmail.com
Fri Aug 9 08:58:39 CEST 2019
Interesting and subtle indeed.
This also relates to constant-ness AFAIU...
When a method is non-const, then we can assume the object can't be concurrently
Therefore we can assume the state can't pass from detached to shared
while the method is executed.
On Thu, 8 Aug 2019 15:32:00 -0700
Thiago Macieira <thiago.macieira at intel.com> wrote:
> On Thursday, 8 August 2019 02:43:07 PDT Mutz, Marc via Development wrote:
> > If there _was_ a QIntrusiveSharedPointer::isDetached(), _then_ it would
> > have the same problem as shared_ptr::unique() in that the result becomes
> > meaningless upon return to the caller. Such a method might still useful,
> > but it's not currently proposed; qIntrusiveDetached() is _not_ that
> > function.
> Not really, because of different semantics.
> isDetached() = false can have changed before you make use of the result.
> But isDetached() = true is useful. If an object is detached, it *stays*
> detached. This allows you to optimise for that case, while still supporting
> the non-detached case albeit slower.
> The examples are the in-place helper functions in QtCore that are called from
> rvalue-ref members. Like:
> QByteArray QString::toLatin1_helper_inplace(QString &s)
> if (!s.isDetached())
> return qt_convert_to_latin1(s);
> [... modify s ...]
> Thiago Macieira - thiago.macieira (AT) intel.com
> Software Architect - Intel System Software Products
> Development mailing list
> Development at qt-project.org
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