Add keep_future algorithm #5323
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msimberg
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hkaiser
previously approved these changes
May 15, 2021
Note that this includes #5274. No further comments on that? |
… continuations when futures are used as senders keep_future passes the future instead of the value to help manage future lifetimes. Especially shared_future | on | ... is not possible without this helper if the wrapped value in the future is noncopyable (since shared_future::get returns a const& and on cannot store a const&, nor does it need to keep the operation state alive long enough).
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This solves the problem of trying to use a
shared_future<noncopyable_type>with e.g.onorsync_waitwhich fails because the algorithms have to copy the value internally (which obviously does not work with noncopyable types). This adds a wrapper algorithmkeep_future(other name suggestions?) which callsset_valueon receivers connected to futures with the future instead of the contained value.Note: This could very well be a better default than the current implementation of futures as senders. There's always
unwrappingfor dealing with futures in continuations.Builds on #5274 since it requires some fixes to
on. Only the last commit is new.