On Wednesday, July 15, 2009, Stewart, Robert <Robert.Stewart@sig.com> wrote:
Gottlob Frege wrote:
My standard answer has now become: 1. use a traits/policy class 2. have the default traits/policy call a free functinon
eg:
// default free function // or yours will found by ADL if you supply your own // template<class T> bool is_null_pointer(T p) { return (p == 0); };
// default policy class, calls whatever it finds by ADL // feel free to supply your own policy class instead // template<class T> struct default_smart_pointer_traits : public smart_pointer_traits<T> { static bool is_null(pointer p) { return is_null_pointer(p); } };
That's a very nice approach. You seem to lump traits and policy classes together, but they are clearly not equivalent. I think a policy class is superior to a traits class, so your numbered bullets should not contain "traits/".
Yes I really mean policy. But the original example had a class called 'traits' being passed as a policy and I wanted to make sure it was understood which class I was talking about. I should have clarified more.
What about function templates? The above seems to apply to class templates only. Overloading permits one function template to rely on a default functor type while another can take a functor as an argument. (The former can call the latter, of course.) The functor argument can be defaulted, provided the default functor is stateless.
I think we could make something work. Do you want to start with an example?
_____ Rob Stewart
Tony