[Development] Is qsizetype *documented* to be ptrdiff_t?

Giuseppe D'Angelo giuseppe.dangelo at kdab.com
Thu Sep 3 06:37:23 CEST 2020

On 03/09/2020 06:08, Thiago Macieira wrote:
> Because qsizetype is the same type as qint64, which is the same type as
> qlonglong (which exists for historical reasons, because older VC++ didn't
> support "long long").

I'm very sorry, I'm lost now -- are you using as a postulate "on 64 bit 
systems"? I would've expected qsizetype to be 32 bits (on 32 bit systems)...

But while qint64 should not change / still be the same type of 
qlonglong, why qsizetype has to be the same type qint64 and cannot be a 
different type (say, ptrdiff_t)?

> I don't have a problem changing the actual type those are aliases of. But I do
> have a problem making them different types. A lot of code assumes that qint64
> and qlonglong are the same type. While they're always the same size, having
> them be different types could result in warnings and problems with overload
> sets.
> For example, say I've added QRandomGenerator::bounded(qint64) and quint64.
>    qint64 v = QRandomGenerator::system()->bounded(str.toLongLong());
> Does this compile or not?

Devil's advocate: next to "toLongLong", why there isn't also "toInt64"?
Or why does bounded() take int64, not long long? Do we have a policy on 
which one to use where? This smells like we're making the situation 
worse by increasing the mix&matching types in the APIs rather than 

My 2 c,
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - The Qt, C++ and OpenGL Experts

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