[Development] Proposal: Deprecating platforms in Qt 5.6 that don't support lambda

[Kevin Funk]

On Thursday 19 February 2015 15:41:42 Matthew Woehlke wrote:
> On 2015-02-19 15:21, Marc Mutz wrote:
> > On Thursday 19 February 2015 13:29:48 Daniel Teske wrote:
> >> more than 400 lambdas in Creator's source
> > 
> > Sounds like lambdas are overused (as any new language feature is overused
> > before it's fully understood by the resp. language community).
> 
> Maybe, maybe not.
> 
> I'm not sure I've even *written* 400 lambdas yet :-), but I find myself
> using them most often in QObject::connect. Basically, a lambda saves
> writing a protected (or worse, *private*) slot by allowing the relevant
> code to be written inline. These are rarely more than a few lines long,
> and it's not unusual for them to be one-liners, e.g.:
> 
>   connect(d->UI.scrollBar, &QAbstractSlider::valueChanged,
>           [d](int value){ d->scrollTo(value); });
> 
> The above is basically a private slot that's *actually private*. I've
> also had cases of needing to connect a signal to a slot where the slot
> needs to be called with additional (constant) arguments; these tend to
> look like the above also.
> 
> Of course, the usual caveats of binding to a lambda apply, but in many
> cases those aren't issues (e.g. my MainWindow class is not going to
> disappear without taking its widgets with it, and said widgets aren't
> likely to be emitting signals from other threads).
> 
> p.s. It would be cool if these restrictions could be relaxed by adding
> an overload that takes a QObject that "owns" the slot.

http://doc.qt.io/qt-5/qobject.html#connect-6 (since Qt 5.2)

Isn't that what you need?
- Resolves issues with thread-affinity (via QueuedConnection if req.)
- Automatic disconnect when the receiver/context is destroyed

> 
> >> and have several interfaces
> >> that take a std::function.
> > 
> > What about boost::function?
> 
> Ugh, make Qt depend on boost? No, thanks...

Greets

-- 
Kevin Funk | kfunk at kde.org | http://kfunk.org
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