On Wed, 14 Mar 2007 14:09:37 -0400, Frank Mori Hess wrote:
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.
I would prefer a signal too, although I wanted to minimize the boost-isms in the interface in the hope that it will be closer to whatever future concept gets into C++0x (if any). I'd probably expose a thread_safe_signal once available.
then you should be able to do (without blocking) promise<A> p; future<A> fa(p); future<B> fb = fa;
Does libpoet already do this? Any advice on implementation? I split my future_impl from the actual value type so that I could more easily support this, but haven't worked out the details yet.
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.
Personally, I love your fulfill() name. I would also prefer fail() to set_exception()...it seems more descriptive since it is more than just an accessor method. I didn't want to stray TOO far from Peter's C++ language proposal though. If I add a default constructor to future<T>, I'll be sure to have it throw empty_promise or empty_future if get() is called before it is initialized. ;)
-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.
I think I saw you mention this in another post, and hoped you would come back with it. Can you give me a short example of how this syntax would work that I can work towards?
-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.
So this effectively chains the future's? Ie: promise<T> p1; future<T> f1(p1); promise<U> p2; future<U> f2(p2); p2.fulfill(f1); f2.wait(); //actually waits for f1 to complete.