[Development] templates as QObjects

[Peter Kümmel]

On 26.06.2012 23:17, Olivier Goffart wrote:
>
> I'm not sure the class name is that important.
> I mean, if  Foo<int>().metaObject()->className() is just "Foo" it is still ok.
> Because it is hard to support, and hardly usefull.

OK, I thought className() is used by qobject_cast, but it isn't,
so it's maybe really not that important.

But I could imagine when you do alot gui stuff dynamically the
class name would be usefully. A simple grep and wc in qtbase/src
gives 158 hits, so it is used.

>
> Also remember that template parametter can be more complex than just a type.
> It probably should support stuff as complicated as this
>
> template<template<typename ... U>  class T,
>            typename T<>::size_type = sizeof(T<>)>  class Bar;
> (I think i made that quite complicated already)

Yes, currently removing 'class' and 'typename' within <...> must
give valid signature, anything else is not supported. But this is
an isolated piece of code, and could be replaced by a more
sophisticated code later.

>
> The fact that you have that macro Q_QOBJECT_TEMPLATE_USED limit you to only
> one parametter (because you cannot have coma in macro)
> (But we could say it is ok to only support multple parametter with compiler
> that support variadic macros)

Or we introduce
Q_QOBJECT_TEMPLATE_USED_1(x)
Q_QOBJECT_TEMPLATE_USED_2(x,y) ...

>
>
> But to answer your question, the extraData is not being used currently and is
> reserved for future use, so yes, it can be used.
>

What is missing atm, are some tests for linking. I assume there will
be linker errors because of the statics when the header is included
in multiple files. And for Dlls it would be even more complicated.

Peter