[boost] Weak functor: Interested? (How to boost::bind to a weak_ptr)

Subject: [boost] Weak functor: Interested? (How to boost::bind to a weak_ptr)
From: Vladimír Tøebický (vladimir.trebicky_at_[hidden])
Date: 2012-01-10 05:01:38

Hi!

I saw people asking how to do boost::bind using a weak pointer.
Generally it's not possible without first specifying what should
happen if the weak_ptr cannot be converted to shared_ptr. The
"weak_fn" I wrote is a small class holding a member pointer, a weak
pointer and a "policy":

* It is callable so you can insert it to boost::bind.
* You can construct it using free function templates.
* The policy says what should happen when the object is called yet the
weak_ptr cannot be converted to shared_ptr.
* It's implemented both using variadic templates and Boost.Preprocessor.

Copy of the help comment:

/** Returns a callback that can be used eg. in boost::bind. When called, it
 * tries to lock weak_ptr to get a shared_ptr. If successful, it calls
 * given member function with given arguments. If not successful, it calls given
 * policy functor. Built-in policies are:
 *
 * "ignore_if_invalid" - does nothing
 * "throw_if_invalid" - throws "bad_weak_ptr"
 * "return_default_if_invalid" - returns given value
 *
 * Example:
 *
 * struct Foo {
 *     void bar(int i) {
 *         std::cout << i << std::endl;
 *     }
 * };
 *
 * struct do_something {
 *     void operator()() {
 *         std::cout << "outdated reference" << std::endl;
 *     }
 * };
 *
 * int main()
 * {
 *     boost::shared_ptr<Foo> sp(new Foo());
 *     boost::weak_ptr<Foo> wp(sp);
 *
 *     boost::bind(boost::weak_fn(&Foo::bar, wp), _1)(1);
 *     sp.reset();
 *     boost::bind(boost::weak_fn(&Foo::bar, wp), 1)();
 *     boost::bind(boost::weak_fn(&Foo::bar, wp, do_something()), 1)();
 * }
 */

What's missing:

* Cannot point to a free function. Only member functions.
* ?

Wdys?

Vladimir.