[Qt-interest] QVariant comparisons and custom types?

[Daniel Price]

This is really crap. I can see no-reason why QVariant cannot call custom operators.

Is it worth raising as a bug/suggestion? I can imagine a lot of people running into this.


> -----Original Message-----
> From: qt-interest-bounces at trolltech.com [mailto:qt-interest-
> bounces at trolltech.com] On Behalf Of Dan Milburn
> Sent: 13 September 2010 12:00
> To: qt-interest at trolltech.com
> Subject: Re: [Qt-interest] QVariant comparisons and custom types?
>
> Daniel Price wrote:
> > Hi List,
> >
> >
> >
> > I'm trying to use custom types (enums and structs) with QVariant. To
> cut
> > a long story short, I'm storing custom data in the userData field of
> > combox box rows. I have an interface that wraps the combox that must
> set
> > the list to the index corresponding to the row with specific data.
> This
> > interface is generic and can't know about the specific custom data
> being
> > passed in - only that it's a variant that matches another variant
> > already in the list.
> >
> >
> >
> > For reasons that escape me, QVariant's equality operator doesn't call
> > the equality operator of custom types. Rather it compares the
> addresses
> > of the data stored. This makes no sense given that all of Qt other
> > container classes behave as expected. In what situations would the
> > addresses be the same?!
> >
> >
> >
> > So I need to find a way around this. I've thought about templates or
> > using other variant classes (boost any) but I still need to store
> them
> > inside Qt's interface as a QVariant.
> >
> >
> >
> > The interface needs to be able to compare the contents of the
> variants
> > without having to be hard-coded with all the type cases.
> >
> >
> >
> > Any help appreciated!
>
> Hi,
>
> Yes, this is an issue I've run into before as well.  It seems like it
> should be possible to extend QMetaType to be able to handle equality in
> a similar way as it deals with the QDataStream operators, but there's
> no
> solution available at the moment that I know of.
>
> The only thing I can think of would be to create your own functions for
> testing QVariant equality which knows about your custom types and
> manually casts the variant and compares equality.
>
> Dan
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