Question

I would like to know how to design a system that can offer a solid framework to handle signals and the connection between the signal/s and the method/s without writing a really unpleasant cycle that iterates over and over with some statement for forking the flow of the application.

In other words I would like to know the theory behind the signal slot mechanism of Qt or similar.

I’m naming Qt for no particular reason, it’s just probably one of the most used and well tested library for this so it’s a reference in the C++ world, but any idea about the design of this mechanism will be good.

Thanks.

Answer 1

At a high level, Qt’s signal/slots and boost’s signal library work like the Observer Pattern (they just avoid needing an Observer base class).

Each “signal” keeps track of what “slots” are observing it, and then iterates over all of them when the signal is emitted.

As for how to specifically implement this, the C++ is pretty similar to the Java code in the Wikipedia article. If you want to avoid using an interface for all observers, boost uses templates and Qt uses macros and a special pre-compiler (called moc).