Fausto Papandrea (13 December 2018 12:48)
> Hi, I would like to understand the logic of the addDays function of
> QDateTime.
>
> I mean, why doesn't it modify the calling object, but returns a copy of
> a new object instead?
At this point, it does what it does because it's done so for years
(since 5.0, at least) and changing it would break various compatibility
promises. I guess the reason for it originally would be a general
preference for non-mutating methods; think of the add*() methods as
operator+() specialisations, rather than as operator+=(). If you need
to advance a QDateTime's day, you can always use
when->setDate(when.date().addDays(n));
or simply
when = when.addDays(n);
to achieve the mutating variant.
Eddy.
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