Edward Diener wrote:
This is similar to the way in the signals2 library that one has to have access to a boost::signals2::signal in order to setup a connection to a slot. So while I like your library I do not immediately understand the advantage it has over signals2.
When you already have an existing third-party object (say, XButton) it's more convenient to not have to think where to place the corresponding signal object. Non-intrusive dispatch is kind of like the library containing the equivalent of map<void*, signal>, automatically managing the signal objects corresponding to an external, third-party, object. In the use case in which you define your buttons, there's not much to gain, you make them contain your signal objects. But third-party buttons don't contain your signal objects, they contain their own functionality for notifying you of events, sometimes that's (their own) signal implementation, sometimes a callback/std::function, sometimes you need to override a virtual method, sometimes they send you messages. With a non-intrusive signal library, you just attach an emit call to the third-party notification mechanism and the rest of the code can connect to the non-intrusive signal. This avoids the need to wrap the external objects in your own types that contain signal objects.