[Qt5-feedback] QVariant::toString() and custom types

[Konstantin Ritt]

why not something simple like:

template <typename T> inline bool QVariant::canConvert() const
{ return m_type >= QVariant::User ? qVariantCanConvert<T>(*this) : /*
internal implementation */; }
 template <typename T> inline T QVariant::convert() const
{ return m_type >= QVariant::User ? qVariantValue<T>(*this) : /* internal
implementation */; }
?
it makes it possible to convert to an arbitrary type rather than just to
QString...

regards,
Konstantin



2011/7/17 Jerome Vizcaino <vizcaino_jerome at yahoo.fr>

> There's a good point on having a generic cast operation but I think this is
> more
> complicated to implement.
>
> QVariant uses templates functions and template specializing to build
> construct
> and delete helper. I think the same can be done to add toString()
> fromString()
> features without actually requiring any modification on encapsulated
> classes (see
> QDataStream or QTextStream operators)
>
> This can lead to :
>
> QString QVariant::toString()
> {
>        if(m_type >= QVariant::User)
>                // cast local pointer to correct encapsulated class
>                // call some specialised template function to do the work
>        else
>                // keep the good old internal implementation for QVariant
> native types
> }
>
> On Friday 15 July 2011, Konrad Rosenbaum wrote:
> > Hi,
> >
> > On Thu, July 14, 2011 13:18, Jerome Vizcaino wrote:
> > > I use QVariant a lot in Qt4 to store native but also custom types.
> > > One thing I find a bit annoying is that there is no way to "extend" the
> > > toString() QVariant functionnality.
> > >
> > > How about adding some sort of operator (à la QDataStream) that custom
> > > types
> > > could provide to help QVariant convert to/from string ?
> > >
> > > This would be really convienent in order to easily print QVariant
> without
> > > actually knowing if it's custom or native content.
> >
> > I have found myself wanting this feature as well. However, I can't think
> > of a way to implement this without adding more requirements on classes
> > that are compatible with QVariant.
> >
> > I.e. it should be done so that classes that cannot be transformed to
> > QString (yet) are still storable in QVariant. This seems to require a lot
> > of dark magic... ...any ideas?
> >
> >
> >
> >     Konrad
> >
> > _______________________________________________
> > Qt5-feedback mailing list
> > Qt5-feedback at qt.nokia.com
> > http://lists.qt.nokia.com/mailman/listinfo/qt5-feedback
>
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