[Development] QVariant comparison in Qt6

[Thiago Macieira]

On Wednesday, 23 September 2020 13:24:24 PDT Milian Wolff wrote:
> > QAbstractItemModelPrivate::isVariantLessThan returns false for BOTH 
orders:
> >  isVariantLessThan(1, "hello") == false
> >  isVariantLessThan("hello", 1) == false
> 
> Right, sorry - I missed the part where you say "a few of the above are
> strings, the others are numbers". Mixed variant types within a single column
> is I believe a super rare case in models.

I explicitly did not mark the ones that were strings with quotes because they 
aren't displayed in a model. If you are mixing, then you want consistent order 
somehow and the string sorting is a good first approximation.

If you're not mixing, then QVariant's upcoming comparison operator suffices.

> So from my side: as long as there's an equivalent to comparing two QVariants
> with matching types, e.g. via a public
> QAbstractItemModelPrivate::isVariantLessThan equivalent which can then be
> used in proxy models etc., then I'm fine.

It's just QVariant::compare and QMetaType::compare.

> Please just make sure there are no string conversions or similar required
> for that common case. That was all I wanted to point our (after
> misunderstanding your example above).

Just note how QVariant(-1) > QVariant(0U), just like -1 > 0U in C++.
-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel DPG Cloud Engineering