[Development] Q_DECLARE_TYPEINFO and namespaced Qt

[Jedrzej Nowacki]

On Wednesday 11. July 2012 02.10.28 ext Olivier Goffart wrote:
> On Tuesday 10 July 2012 18:37:20 Marc Mutz wrote:
> > Hi,
> > 
> > as seen on IRC:
> > [18:18:43] <ossi|tt> thiago: how about we make Q_DECLARE_TYPEINFO
> > automatically use the qt namespace, like Q_DECLARE_METATYPE does? it is
> > massively SIC, except that probably not many outside qt/creator use it
> > ... [18:20:09] <marc_kdab_> ossi|tt: errhm, I used it in many projects,
> > and the Q_DECLARE_METATYPE solution is also not the best one
> > [18:20:22] <marc_kdab_> though I'm all for consistency, too
> > [18:20:34] <ossi|tt> marc_kdab_: but you probably didn't use qt in
> > namespace? [18:21:08] <marc_kdab_> could someone with VS 2005 and/or 2008
> > please test-drive https://codereview.qt-project.org/#/t/35/ ?
> > [18:21:42] <marc_kdab_> ossi|tt: I made KDTools work with a namespaced
> > Qt, and hit the problem of Q_DECLARE_TYPEINFO there
> > [18:22:23] <ossi|tt> marc_kdab_: yeah. i'd instantly change it. not sure
> > about the amount of opposition to expect, though
> > [18:22:50] <marc_kdab_> ossi|tt: the question is: change which way?
> > [18:23:26] <ossi|tt> marc_kdab_: have it in the namespace transparently.
> > it's insane that user code needs to be aware of this in this context
> > [18:24:21] <marc_kdab_> ossi|tt: but user code needs to be aware of a
> > namespaced Qt in any case. Wrapping the QClass forward-declarations was
> > the most work, and then wrapping Q_DECLARE_TYPEINFO, too, is just
> > consistent [18:24:47] <marc_kdab_> (wrapping in QT_BEGIN_NAMESPACE /
> > QT_END_NAMESPACE, that is)
> > [18:25:06] <ossi|tt> marc_kdab_: yes, but it's stupid that i need to wrap
> > a macro with another macro pair
> > [18:26:12] <marc_kdab_> ossi|tt: depends how your take is on consistency,
> > I guess [18:27:42] <marc_kdab_> I don't have an opinion myself; both
> > ways have pros and cons... [18:27:59] <marc_kdab_> if in doubt, stay
> > with the status quo, I guess [18:28:06] <ossi|tt> marc_kdab_: this macro
> > is clearly optimized for the use in qt, where everything is wrapped in
> > these macros anyway
> > [18:28:35] <ossi|tt> marc_kdab_: the easiest way out would be
> > Q_DECLARE_NAMESPACED_TYPEINFO
> > 
> > As I said, I'm undecided. On one hand, I always have to look at the
> > implementation to see whether I need to wrap the macro in
> > QT_BEGIN_NAMESPACE /
> > QT_END_NAMESPACE, and I would like to see consistency here, on the other
> > hand, in a way it's Q_DECLARE_METATYPE that's inconsistent, since it
> > violates the "put Qt stuff into QT_BEGIN_NAMESPACE if you want to be
> > compatible with a namespaced Qt, otherwise don't bother" assumption.
> > 
> > What's the general opinion on this?
> 
> My opinion is to fix Q_DECLARE_TYPEINFO to do the same as in
> Q_DECLATE_METATYPE (as ossi says)
> 
> It is source incompatible only with namespaced Qt, that are not that common
> anyway.
> 
> 
> 
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It only shows how difficult is to work with namespaced Qt :-) In general I agree 
with Olivier, let's fix Q_DECLARE_TYPEINFO, or just leave it as it is. I 
suspect that changing Q_DECLARE_METATYPE will have a bigger impact on source 
compatibility.

Cheers,
  Jędrek
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