[Development] Should QVariant be doing fuzzy comparisons on doubles?

Mathias Hasselmann mathias at taschenorakel.de
Thu Sep 22 06:04:58 CEST 2016

Am 22.09.2016 um 00:58 schrieb André Pönitz:
> On Wed, Sep 21, 2016 at 08:57:01AM +0200, Olivier Goffart wrote:
>>> No, it's not. It's changing undefined behavior into defined
>>> behavior.
>> But in many case, we want to put something in a QVariant, and we
>> never compare this variant.  Forbidding types that do not have an
>> operator== to be in a QVariant might be to strict.
> Forbidding types without operator== in QVariants is not needed,
> not even if one wanted to use associative container with
> QVariants as keys.
> [Pseudocode]
> bool operator(QVariant(Foo) a, QVariant(Bar) b)
> {
>     if Foo != Bar:
>         return false
>     if Foo has no operator==():
>         return true
>     return (Foo)a == (Foo)b
> }
> establishes an equivalance relation by lumping all "uncomparable"
> objects into a single equivalency class.

I rather was considering to return false. But indeed. Forcing all that 
types into a single equivalency class feels that unnatural, that users 
should notice that issue much quicker, than if we'd return false.

Would that be sufficient to warn Qt users, or would we also have to 
print a warning?


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