[Development] moc 4.8.6 & macros

[Olivier Goffart]

On Thursday 11 September 2014 22:03:03 Samuel Gaist wrote:
> On 11 sept. 2014, at 21:49, Thiago Macieira <thiago.macieira at intel.com> 
wrote:
> > On Thursday 11 September 2014 21:44:15 Samuel Gaist wrote:
> >> What would be the correct procedure to handle QT_DEPRECATED_SINCE ?
> >> Removing it from around the signal declaration would make the code a bit
> >> inconsistent.
> >> 
> >> By the way, how is it handled in Qt 5 since building goes without any
> >> problem even with the macros around the signal ?
> > 
> > moc is smarter in Qt 5: it expands macros.
> > 
> > But the recommendation stands: do not #if (of any kind) anything that
> > isn't
> > #defined in the same source, in a header next to the one being compiled,
> > or
> > passed as -D in the command-line.
> > 
> > That means: don't hide signals and slots with #if, even for deprecation.
> 
> I thought I've read somewhere that moc got better at this job :-)

I would not be as strict as Thiago.  
In Qt5 it's fine to use the preprocessor as long as moc can see the defines 
(that is, if they don't rely on compiler built-in or need special include 
paths.)
QT_DEPRECATED_SINCE should be fine.

It is strange it does not work with Qt4.  Are you sure that all the include 
paths are passed to moc?
Otherwise, you will have to work around it somehow.
try #if not QT_DEPRECATED_SINCE() #else
Or some other trick with Q_MOC_RUN


You can also use the QT_MOC_COMPAT macro in front of a declaration so QObject 
will throw a runtime warning when connecting to this signal. (in debug mode)


> It seems that the new moc doesn't use much of the Qt 5 only classes, would
> it be useful to backport it to Qt 4 to avoid having to "break" the code
> style for modules supporting both series ?

This is out of question.
This is a behaviour change as Qt4 code relied on moc not expending the macro 
in some cases.

(At some point it will be time to switch fully to Qt5 and drop Qt4 support)


-- 
Olivier

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