[Development] Converting types in Qt
Eike.Ziller at digia.com
Thu Jul 17 10:51:03 CEST 2014
On Jul 16, 2014, at 1:45 PM, Poenitz Andre <Andre.Poenitz at digia.com> wrote:
> Olivier Goffart wrote:
>> Jędrzej Nowacki wrote:
>>>> What is wrong with string -> int or bytearray -> int?
>>> At the very least, _implicit_ conversions should not lose data,
>>> i.e. a A a1; B b = a1; A a2 = b; round trip ideally should yield
>>> a1 == a2.
>>> If I am ready to give up information, I'd like to need to say so
>>> in the code explicitly. (And yes, part of the deed is done in the
>>> core language, but even there compilers start to nag about it.)
>> André, QVariant conversions are not implicit, they are explicit.
> I am aware of that. I tried to answer the question of "What is wrong
> with string -> int or bytearray -> int”.
QVariant::operator== is not symmetric :( :( :(
QDateTime dateTime = QDateTime::currentDateTime();
QTime time = dateTime.time();
qDebug() << (QVariant(dateTime) == QVariant(time));
qDebug() << (QVariant(time) == QVariant(dateTime));
> We admittedly left the original context here (and in other parts of the
> discussion), but the question was posed in context that I read an
> example of an conversion that one would always consider convenient
> to have, and I started with "At the very least, _implicit.." supposedly
> setting the context of the answer.
> Anyway. To summarize my position in the original context: QVariant
> is as it is. It is convenient at times, and it is already too convenient
> at times. "Easy type conversion" is a different use case than "Type
> agnostic storage". QVariant does a bit of both, only the second one
> has ever been useful _to me_, I have been bitten by the first. As
> there are typically also more direct ways to convert types than to
> pass through QVariant, I consider the possibility to do type conversion
> through QVariant a mis-feature, and adding even more conversion
> abilities would be a step into the wrong direction _for me_. This is
> a personal opinion.
Eike Ziller, Senior Software Engineer - Digia, Qt
Digia Germany GmbH, Rudower Chaussee 13, D-12489 Berlin
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