On Tuesday 13 March 2007 23:55 pm, braddock wrote:
I'm looking for input. I'd be willing to add additional functionality needed and progress it to the point where it could be formally submitted into boost if there is interest. It could perhaps be merged into the existing futures implementation in the vault to add combined groups, etc.
-add_callback() permits arbitrary functions to be called when the future is set. This is needed to build non-intrusive compound waiting structures, like future_groups, or to better support continuation scheduling concepts, as in coroutines.
I'd prefer a signal/slot to add_callback(). That is: thread_safe_signals and moving to Boost.Signals when a thread-safe version is accepted.
TODO:
The following class of sub-type assignments should be made possible, as discussed by Frank Hess and Peter Dimov on the list.
class A {}; class B : public A {}; promise<shared_ptr<B> > p; future<shared_ptr<A> > f(p);
That isn't what I was talking about (although I agree it should be made possible). But B doesn't have to be derived from A. If you can do A a; B b = a; then you should be able to do (without blocking) promise<A> p; future<A> fa(p); future<B> fb = fa; For example, if I have an active_function that returns a future<unsigned> then I should be able to pass that return value to an active_function that takes a future<int> as a parameter and it should "just work". Another suggestion is to rename promise::set() (boring) to promise::fulfill() (makes me smile). And if there is an opportunity to work the name "empty_promise" in as a class or a concept, that would be clever too. Other things I would need to replace poet::future with your future class: -Constructing a future from another with an incompatible template type via a user-supplied conversion function. Useful for extracting future elements from future containers, for example. -Adding a promise::fulfill() that accepts a future with a compatible template type. The effect would be that promise::fulfill() would be called with the value from the future when it is ready. -- Frank