Why declare a slot as a slot?

Question

If basically anything can be used as a slot for a signal in Qt (provided that the signatures are compatible), why would I ever want to declare a member function as a slot? Is declaring a member function as a slot really just a hold over from the pre-C++11 days?

Answer 1

It has indeed become a rare situation but there are still some uses to declaring methods as slots, if you want to use the SIGNAL()/SLOT() macros in a connection (aka string-based connection). For example:

• If you use e.g. a factory to create instances of several unrelated classes, you can create a string-based connection without doing introspection on the involved object(s).
  A good example of that is QLineEdit and QTextEdit; they do not inherit one another but both have a textChanged signal and you could make a window where instances of the former or the latter are added dynamically to it.
• If you want to make a signal to slot connection where the slot has more arguments (with default values) than the signal.
  This is explained here.
• For connecting C++ Objects to QML Objects (from the same page), as signals/slots of QML objects are simply text in a .qml file.

The cons of string-based connections (or I guess pros of functor-based connections) are listed in the same page.