[Development] Another integer typedef OR how to prepare for 64-bit in Qt 5

[Иван Комиссаров]

Yeah, forget my argument. Go for 4.

Иван Комиссаров

> 2 нояб. 2018 г., в 16:02, Thiago Macieira <thiago.macieira at intel.com> написал(а):
> 
>> On Friday, 2 November 2018 06:50:50 PDT Jedrzej Nowacki wrote:
>>> On Friday, November 2, 2018 4:42:52 AM CET Thiago Macieira wrote:
>>> 
>>> We have a lot of API that, for Qt 6, we've already decided to extend to
>>> 64-bit on 64-bit platforms, but keep as decently-sized 32-bit on 32-bit
>>> ones.
>> 
>> Smells like qreal, with all problems that it causes... We could reconsider 
>> costs of using 64bit everywhere, it would streamline debugging of edge
>> cases. 
> 
> [Intel hat on]
> I don't mind this. All Intel processors are 64-bit, all Linux workloads are 
> 64-bit.
> 
> [Qt maintainer hat on]
> Sorry, that would mean 32-bit builds use a larger-than-a-register type which 
> means extra carry operations and slower multiplications. That's probably not a 
> good idea.
> 
>> If I have to I would also pick option 4, but:
>> 1. qsizetype can _not_ be a built in metatype in Qt5 (at best an alias).
> 
> It's not going to be. It's a typedef to either int or long long, depending on 
> your pointer's size.
> 
>> 2.  qsizetype needs to have QDataStream operators so it doesn't fallback to
>> a  platform dependent size
> 
> Since it's a typedef, that can't happen. But you've got a point: we need to 
> serialise in explicit 64-bit widths.
> 
>> 3. QDataStream stream autotests of class that uses the type would need to be
>> extended.
>> 4. I bet there is more, issues to solve, caused by pointer arithmetic ...
> 
> No doubt. That's why I wanted to start now.
> 
>> I would not try to trick qdoc to not see it. The consequences of size
>> changing  "randomly" are far too important, to be hidden.
> 
> So you want users to know now, in Qt 5, that this particular type in the API 
> will become qsizetype in Qt 6?
> 
> -- 
> Thiago Macieira - thiago.macieira (AT) intel.com
>  Software Architect - Intel Open Source Technology Center
> 
> 
> 
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