I’ve toyed with QT connections trying to create anonymous function when connecting a slot to a signal. For instance, I am trying to do the following:

Qt Signal Slot Lambda Functions Python
Qt Signal Slot Lambda

So far so good, but sometime I find it cumbersome to define all the slots. Create a declaration, a definition, etc…

I would like to declare the body right there! Here’s what I would like to do using std::function or a c++ lambda:

When the user clicks a button, the custom widget will emit a single clicked signal whose argument is the text of the button the user clicked. This class was mostly useful before lambda functions could be used as slots. The example above can be rewritten simpler without QSignalMapper by connecting to a lambda function. The Qt signals/slots and property system are based on the ability to introspect the objects at runtime. Introspection means being able to list the methods and properties of an object and have all kinds of information about them such as the type of their arguments. QtScript and QML would have hardly been possible without that ability.

I’ve achieved that by creating a global object named _Q which is responsible to maintained the QT meta object information about all connection that needs to be called.

How to connect a signal with int parameter to a slot with enum parameter WITHOUT using lambdas in QT5? 3 How does Qt handle call-by-reference for signals and slots?
Connecting overloaded signals/slots. While being better in many regards, the new connection syntax in Qt5 has one big weakness: Connecting overloaded signals and slots. In order to let the compiler resolve the overloads we need to use staticcasts to member function pointers, or (starting in Qt 5.7) qOverload and friends.

Here’s the header of the class in question:

And here’s the implementation:

The idea here is that we maintain the QMetaObject needed to dispatch the call, when qt_metacall is called, to the proper anonymous functions. The magic is done in FillMetaStructs() to maintain the meta object structure each time a new connection is made when Call(...) is called.

Qt Signal Slot Lambda Functions Python