This isn't directly possible, since you can't inspect a class to see which members it has.
However, you can do something close:
Logging<Widget> w(widget);
w([&](Widget& w){
return w.computeAnswer();
});
Where Logging::operator()
looks like follows:
/* somewhere in class: T wrapped; */
template<class F>
auto operator()(F&& f)
-> decltype(f(wrapped))
{
pre_log();
auto&& result = f(wrapped);
post_log(result);
return result;
}
It won't get better much better than this for totally generic code, since C++ has no (static) reflection.