"vicente.botet" <vicente.botet@wanadoo.fr> writes:
Imagine now we had a function which returs a value and had an out parameter (maybe by reference)
Result f(InOut& ref);
Now we want to refactor this function (either because the new implementation will introduce an IO wait, or because the old blocking implementation could not be supported. Which should be the interface of the new function. The first thing could be to try with
future<Result> f(InOut& ref);
but nothing forbids the caller to use the ref parameter before the operation has completed and which could be invalid. If we want consistency what we would need is something like
future<Result> f(future<InOut&>& ref);
IMO this do not works in any proposal?
You can write it with my proposal, but I'm not sure it means what you intend, given what you write below.
Do we need future to works with in/out references?
Yet another example future<Out&> f();
Note that future<Out&> and future<InOut&> should not mean the same. Do we need two future of reference classes? future<InOut&> will need a constructor future<InOut&>(InOut&), but the assocaited promise should copy the value when doint the set_value.
If the promise associated with your future<InOut&> should copy the value, then what you want is a future<InOut>. If you had a future<InOut&>(InOut&) constructor, then you could /still/ use the original InOut& before the future had returned, just as if you passed a plain reference to the function. With my (updated) proposal, unique_future<T>::get() returns an rvalue-reference, so you could move/copy this into the InOut value you intend to use, or you could use shared_future<T>, where get() returns a const reference.
Anthony, sorry for short cut (futures instead of unique_future or shared_future). In order to be coherent with the thread library (mutex/shared_mutex), should't unique_future be named future?
unique_future/shared_future is by analogy to unique_ptr/shared_ptr, which I think is a closer match than mutex/shared_mutex. Anthony -- Anthony Williams | Just Software Solutions Ltd Custom Software Development | http://www.justsoftwaresolutions.co.uk Registered in England, Company Number 5478976. Registered Office: 15 Carrallack Mews, St Just, Cornwall, TR19 7UL