On Jul 16, 2014, at 11:28 AM, Jędrzej Nowacki <jedrzej.nowa...@digia.com> wrote:
> On Wednesday 16 of July 2014 06:37:25 Ziller Eike wrote: >> [...] >>> When one use QVariant, it is because we want to enjoy dynamic typing and >>> nice conversions. >> >> >> I don’t think we have a single place in Qt Creator where we want automatic >> conversions when using QVariant. A search for QVariant(Map) returns 5400 >> hits. In the map case, we usually expect the one retrieving the value for >> a key to know the exact type of what was thrown in (that’s usually the same >> class, or related classes), and then we use item models and QSettings which >> we use in the same way. >> Even if automatic conversion might be interesting (when, actually?), then >> the point is: > >> There is no API in QVariant to support the common use case of getting the >> value *without* automatic conversion. > > Nobody asked for it, It should be easy to implement something equal to this; > > Q_ASSUME(variant.userType() == qMetaType<TargetType>()); > TargetType data = variant.value<TargetType>(); > > I believe such new api make sense, we can add it. > >> >>>>> We use common sense on a case by case basic. >> >> >> >> Either there is no “common sense” common to me, or this rule has failed in >> the past already ;) > >> bool -> string ? >> bytearray -> int/long/double ? >> keysequence -> int ? >> string -> bool ? >> string -> bytearray ? >> string -> int ? >> >> Br, Eike > > What is wrong with string -> int or bytearray -> int? First of all I wondered what bytearray -> int does at all. Convert the first byte in the byte array to an int, if bytearray.size() == 1 (which would be consistent with QStringList->QString)? bytearrays are not strings after all… Otherwise bytearray/string -> int has similar problems as string -> bool and string -> bytearray: There is no canonical “right” way to do it, and it can fail depending on the actual *value*. Does QVariant::canConvert actually take that into account? Is there any other possibility to find out if it went wrong? Does it interpret 0xa1 ? Will 076 be interpreted as octal or decimal? Does it convert “𝟷” (U+1D7F7) to 1 ? ;) All in all it creates more questions than it solves problems. There are no QKeySequence::toInt(), QString::toBool(), QString::toByteArray() functions btw, and QString/QByteArray::toInt(…) take arguments. I think one prerequisite for possible conversions (automatic or not) should be, that a corresponding ::to… function without any arguments in the corresponding type would survive an API review, and actually is added as well. Then one also has a place to look for documentation how the actual conversion is done. Br, Eike >> -- >> Eike Ziller, Senior Software Engineer - Digia, Qt >> Digia Germany GmbH, Rudower Chaussee 13, D-12489 Berlin >> Geschäftsführer: Mika Pälsi, Juha Varelius, Anja Wasenius >> Sitz der Gesellschaft: Berlin. Registergericht: Amtsgericht Charlottenburg, >> HRB 144331 B > >> _______________________________________________ >> Development mailing list >> Development@qt-project.org >> http://lists.qt-project.org/mailman/listinfo/development -- Eike Ziller, Senior Software Engineer - Digia, Qt Digia Germany GmbH, Rudower Chaussee 13, D-12489 Berlin Geschäftsführer: Mika Pälsi, Juha Varelius, Anja Wasenius Sitz der Gesellschaft: Berlin. Registergericht: Amtsgericht Charlottenburg, HRB 144331 B _______________________________________________ Development mailing list Development@qt-project.org http://lists.qt-project.org/mailman/listinfo/development
