[Development] Meaning of Q_PRIMITIVE_TYPE?

[Thiago Macieira]

On terça-feira, 3 de abril de 2012 10.20.11, Marc Mutz wrote:
> Hi,
> 
> On Tuesday April 3 2012, jedrzej.nowacki at nokia.com wrote:
> [...]
> 
> > > Also, QVarLengthArray should zero-initialise, but it doesn't.
> > 
> > I like this feature it allows to avoid double initialization in some
> > cases,
> > but maybe it is not the most intuitive behavior. Anyway it is a bit out of
> > scope.
> 
> If you want to avoid double initialisation, the correct way is
> reserve()+push_back(), not resize()+operator[]. That works even for complex
> types.

The thing is that, like Lars said, QVarLengthArray was invented to replace the 
C99 feature of variable-length arrays, hence the name. In C99 but not in C++98 
or C++11, you can write:

	char buffer[length];

where length is not a constant expression (to borrow a C++11 term). That buffer 
is not initialised because char has no constructor.

So like Jędrzej says, the users expect that an array of chars is uninitialised 
to garbage, but an array of QUuid is properly zeroed because this produces a 
zero QUuid:

	QUuid uuid;

My experience producing a type that doesn't initialise by default 
(QElapsedTimer) is that users really don't expect C++ types to remain 
uninitialised.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
     Intel Sweden AB - Registration Number: 556189-6027
     Knarrarnäsgatan 15, 164 40 Kista, Stockholm, Sweden
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