On Wed, 14 Mar 2007 07:27:06 -0500, Hartmut Kaiser wrote:
Braddock Gaskill wrote: These operators should create a new (composite)future, exposing the same interface as the (simple) futures you're composing. This composite future should handle the exceptions in a similar way as the embedded ones, i.e. propagate the exceptions catched in the embedded futures to the caller, as appropriate.
So, that would mean that for f3 = f1 || f2, if f1 propagates an exception while f2 succeeds, f3 still propagates an exception?
Also, does your implementation of operator|| allow for constructs like f1 || f2 || f3 ?
I don't have a real implementation of composition, I posted that simple operator|| example out to show that it can be done without any changes to the base future<T>/promise<T> implementation, so that they can proceed more or less independently. I'm hoping we can make use of an existing composition implemenation. As I understand it, the point you riase is if you want f1 || f2 || f3 to have the semantics of returning a future<variant<T1, T2, T3> > without modifiation to the base future class. I would think that could be done if operator||(future<T1>, future<T2) actually returns a proxy class which is implicitly convertible to a future, and properly specialized operator|| functions are provided. I haven't given this much thought yet though. But that raises another point with the variant/tuple semantics...if I do f3 = f1 || f2; f3 would then have the type future<variant<f1::type, f2::type> >. If I then do a seperate f5 = f3 || f4; then does f5 have the type future<variant<f1::type, f2::type, f4::type> >, or future<variant<variant<f1:type, f2::type>, f4::type> >? Should there be a seperate future_group concept to disambiguate? Composition overloading with || or && gets very hairy or impossible if the current proposal to have a future implicitly convertable to it's value, with blocking, goes through. Maybe Peter has thoughts on this. I like the tuples/variant idea of composition, but how do you handle exceptions? The semantics of composition still seems far less settled than the basic future concept, at least in my mind. Any references are appreciated, I have seen very few. I would like to discuss it. Thanks for the feedback! Braddock Gaskill Dockside Vision Inc