I want to use a signals/slots library in a project that doesn't use QT. I have pretty basic requirements:
First, try with boost::signal anyway. Don't assume it will not be fast enough until you try in your specific case that is your application
If it's not efficient enough, maybe something like FastDelegate will suit your needs? (i did'nt try it but heard it was a nice solution in some cases where boost::signal don't seem to suit).
Anyway, if in your application use the signal each frame, it may be worth to replace the signal system by something more simple, like a container that hold objects/functors that will be called each frame. Signal is more made to allow immediate "events" management than to make a loop cycle dynamic (allowing changing the functions called each frame). (I have my own solution (UPDATE: it's very old and archaic now) that i heavily use in a game and for instance i've no problem with the performance, so maybe something similar could help).