Hello, I don't know if there is a first or second class library in Boost to do with this already. Or at least a C++ mechanism I could leverage. Basically, I want to hook or intercept when a function call is made. I do not want to change the underlying call, although I suppose that hook could be done as well. For now, I just want a callback when that function calls is made. For instance, a vector push_back listener. I want to listen when items are push_back-ed onto the vector. The items should still land in the vector. I just want the notification when that occurs. I've dug around for different "callback" flavors, but these just seem to be wrappers to an underlying method pointer, bound function, along these lines. I can do that easy enough but it doesn't buy me the interception when the push back is actually called. The tricky part with push_back as well, is that it comes in two flavors, so there needs to be a stand in lambda, something to declare the actual kind of argument(s) I want. Then there's the matter of Variadics. But for now I am not concerned with either of these. Thank you... Best regards, Michael Powell