Qt connect new syntax error

[Volebab]

I tried to use connect with a signal that has arguments, like this:

connect(response, &QNetworkReply::error, this, &Webservice::error);

But I'm getting an error:

error: C2664: 'QMetaObject::Connection QObject::connect(const QObject *,const char *,const char *,Qt::ConnectionType) const' : cannot convert argument 2 from 'overloaded-function' to 'const char *'
Context does not allow for disambiguation of overloaded function

[mrjj]

Hi
If error is overloaded then its why,
( overloaded = more than one error function exists with different parameters)
You need extra (ugly) syntax to force compiler to use the correct one
https://forum.qt.io/topic/20998/qt5-new-signals-slots-syntax-does-not-work-solved/8

in such cases i just use the old SLOT & SIGNAL macros as the typecast needed
is very ugly and confusing to read later.

[Volebab]

@mrjj I prefer to use the old syntax, this one is really ugly. lol, but thank you.

[mrjj]

@Volebab
Yeah, when overloaded signals, new syntax is ugly.
else it looks nice and is type safe
You can also connect to a function. :)

[Volebab]

@mrjj You are right, it works nicely with functions without arguments

[mrjj]

@Volebab
also with arguments as long as its the only one with that name :)

[hskoglund]

Hi, I also faced this dilemma; whether to use the old syntax (which is easier) or the new (which gives you better/more error messages when compiling). I wrote 2 macros:

#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))

Example on how to use them:

CONNECT(ui->pushButton,clicked,this,buttonClicked);

So you use them like the old macros but they give you the new syntax (i.e. having the cake and eating it too :-)

Ok, what about using overloading functions? I wrote 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))

Use them for overload functions like this:

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);

Ok still complicated, but maybe not as ugly as the new syntax, when dealing with overloaded functions. Also note: you need a C++11 (or later) compiler.

[Volebab]

@hskoglund That is amazing actually, the second I saw your code I thought about putting it in a global header file and call it the day. Perhaps I would change a few names though. What you mean with PMF?

[mrjj]

Much nicer to look at :)
Thx for sharing

• having the cake and eating it too :-)

My favorite concept :)

[A Former User]

@hskoglund Looks like a really good idea. Thank you so much for sharing! :-*