[Development] Adding more Datetime classes to Qt

[Mark De Wit]

> From: Development <development-bounces at qt-project.org> On Behalf Of
> Thiago Macieira
> > On Tuesday, 9 April 2019 05:11:03 PDT Pouya Shahinfar wrote:
> > You open a project which is developed by someone else, and he/she used
> > QDateTime for holding time and date. The problem here is you as a
> > newcomer to project do not know the value in the class is based on UTC
> > or local time, etc. if there was a class like QLocalDateTime, the code
> > was more maintainable.
> 
> Why is the code unmaintainable or unreadable just because the information
> is not in the class name? The information *is* there, held inside the object.
> You can ask it (timeSpec(), offsetFromUtc() and timeZone()) what it is.
> 
> So what is the problem?

We fell into the same QDateTime trap recently.  The documentation on QDateTime is perhaps a bit too obscure and/or does not sufficiently highlight possible pitfalls?   

It might be good to highlight, for instance, that MSecsSinceEpoch is not share-able between users in different timezones unless QDateTime is instantiated with a timespec of Qt::UTC (which is not the default).

The defaults (local time w. timezone conversion) are perhaps more likely to lead to error than the plain C time since epoch with no hours being added/subtracted.

Mark