Artyom wrote:

...

weak_ptr< A > p;

bind(&A::foo, throw_if_invalid(p)); bind(&A::foo, ignore_if_invalid(p)); bind(&A::foo, call_if_invalid(p, bar)); // bar

I think this is little bit problematic, because proxy weak_ptr_caller should know the signature of A::foo to provide correct "R operator()(args...)"

It will know it since it's instantiated from weak_ptr_proxy::operator->*, which is called with the bound function pointer.

Maybe, additional policy for weak_fn would be better

void A::foo(int); function<void(int)> bar;

bind(weak_fn(&A::foo,p),_1); // default ignore bind(weak_fn(&A::foo,p,throw_on_invalid()),_1); bind(weak_fn(&A::foo,p,bar),_1); // call bar on invalid

This would not require changes in bind and also weak_fn would be useful without bind as well.

Like function<void(int)> foobar=weak_fn(&A::foo,p); It would be simple to update weak_fn to add policy

I find this interface inconsistent with mem_fn. If this approach is chosen, I'd vote to change the naming in order to reduce confusion.