vicente.botet:
I don't understand the need of this function. Could you show a use case for promise::get_future() function?
promise::get_future() is the only way to get a future from a promise. Since the whole point of using promise is to get the future, it's rather pointless without it.
why this is not an internal feautre?
You have to have a way to create the initial future, but for the "one time" semantics one can have for example promise::promise( future& f ); instead of get_future. FWIW, Braddock has argued (see the archives) that it's convenient to be able to obtain a future from a promise, without the "one time" restriction. ("His" futures are "shared" though, as are "mine".) I argued that without this feature, a promise can detect that no futures are left and can cancel its task.