[Interest] QVariant compare operator

[André Pönitz]

On Mon, Apr 20, 2020 at 10:04:38AM -0400, Matthew Woehlke wrote:
> On 19/04/2020 08.23, André Pönitz wrote:
> > QVariant(TypeA) and QVariant(TypeB) can be ordered for different TypeA and
> > TypeB based e.g. on alphabetical order of their .typeName().
> > 
> > If wanted, this can be refined to make e.g. all integral types comparable.
> 
> No:
> 
>   int{5} <=> JsonObject{...} => lesser
>   int{5} <=> long{3} => greater
>   long{3} <=> JsonObject{...} => greater
> 
> ...oops.

"make comparable" means lumping them into a common "type", say
"@integral", with values covering the union set of the values
of the original type.

   int{5} == "@integral"{5} <=> JsonObject{...} => lesser
   int{5} == "@integral"{5} <=> "@integral{3}" == long{3} => greater
   long{3} == "@integral"{3} <=> JsonObject{...} =>  lesser! // not greater

> You'd have to make all integral types sort before (or after) all other
> types, but then you're back to not having a reliable ordering by type name.

No.

> It makes *much* more sense that some comparisons just come back
> "incomparable".

Possible, but not needed on the type level, and restricts use
unnecessarily.

Andre'