Richard:
boost-users@lists.boost.org spake the secret code <019801c8721d$e1612fc0$6407a80a@pdimov2> thusly:
It is impossible to overload && in such a way so that in e1 && e2, e2 is not evaluated when e1 is false. But it's possible to overload f && g so that in (f && g)(x) :- f(x) && g(x), g(x) is not evaluated when f(x) is false.
I guess I'm still a little lost... why does it work for f && g and not e1 && e2? Is it because f and g are functors and don't evaluate their expressions until their operator() is called?
Yes, exactly. As an example, boost::bind( f, 4 ) creates a function object that will call f(4) when its operator() is called; and with the operator&& defined, bind( f, 4 ) && bind( g, 5 ) will call f(4) && g(5) when called, which will correctly not call g(5) when f(4) returns false.