[Interest] Are slots even needed these days?

[Henry Skoglund]

Hi, I thought I was the only one disliking the PMF syntax.
But there's hope, to aid my feeble brain I wrote some macros, so that 
the new syntax resembles the old, but still catching errors in compile time:

#define COMPOSEPMF(QOBJPTR,FUNC) \
&std::decay<decltype(*QOBJPTR)>::type::FUNC

#define CONNECT(SENDER,FUNC1,RECEIVER,FUNC2) \
connect(SENDER,COMPOSEPMF(SENDER,FUNC1),RECEIVER,COMPOSEPMF(RECEIVER,FUNC2))


Those macros let you write code like this:
...
CONNECT(ui->pushButton,clicked,this,buttonClicked);
...


Less horrid (!) they use std::decay to retrieve the type and prefix it 
to the function, thus setting up correct PMF syntax in all its glory.

However, it wasn't long before I stumbled upon the casting problem, like 
in QCombobox and QSignalMapper. So I had to write 3 more macros:


#define COMPOSECASTPMF(QOBJPTR,ARGS,FUNC) \
static_cast<void (std::decay<decltype(*QOBJPTR)>::type::*)(ARGS)> \
(COMPOSEPMF(QOBJPTR,FUNC))

#define CONNECTSCAST(SENDER,ARGS,FUNC1,RECEIVER,FUNC2) \
connect(SENDER,COMPOSECASTPMF(SENDER,ARGS,FUNC1),RECEIVER,COMPOSEPMF(RECEIVER,FUNC2))

#define CONNECTRCAST(SENDER,FUNC1,RECEIVER,ARGS,FUNC2) \
connect(SENDER,COMPOSEPMF(SENDER,FUNC1),RECEIVER,COMPOSECASTPMF(RECEIVER,ARGS,FUNC2))


With those I can write code like so:
...
ui->comboBox->addItems({"Now","is","the","time"});
CONNECTSCAST(ui->comboBox,const QString &,
currentIndexChanged,this,indexChanged);
...
auto sm = new QSignalMapper(ui->pushButton);
CONNECTRCAST(ui->pushButton,clicked,sm,void,map);
...

So yeah, the cast wreaks a bit of a havoc, but you only have to specify 
the casting argument(s), std::decay takes care of prefixing the type.
Note: the macros only support either a sending or a receiving cast, 
hopefully a cast on both sides will never be needed...

Also, beginning now with 5.6 you don't even have to specify CONFIG += 
c++11 in your .pro file, the macros work right out of the box.

Rgrds Henry


On 2016-03-16 18:24, John Weeks wrote:
> Nobody's mentioned the fact that an overridden virtual slot requires an
 > absolutely horrid cast in order to use the new PMF syntax.
>
 > John Weeks
 >
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