Re: [boost] Review Request: future library : what does futureofreferences exactly means?

From: vicente.botet (vicente.botet_at_[hidden])
Date: 2008-05-13 18:27:00

----- Original Message ----- 
From: "Anthony Williams" <anthony_w.geo_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Tuesday, May 13, 2008 10:03 PM
Subject: Re: [boost] Review Request: future library : what does 
futureofreferences exactly means?

> "vicente.botet" <vicente.botet_at_[hidden]> writes:
>
>> Well let me come back to my initial example. Supose that I had
>>     Result f(InOut& ref);
>>     // ...
>>         {
>>             InOut v=0;
>>             // ...
>>             v = 13;
>>             Result r = f(v);
>>             // ...     use r or v;
>>             g(r, v);
>>             v = 15;
>>         }
>>
>> Do you mean that the following works with your proposal?
>>
>>     unique_future<Result> f(shared_future<InOut>& ref);
>>     // ...
>>         {
>>             shared_future<InOut> v; v->get()=0;
>>             // ...
>>             v->get() = 13;
>>             unique_future<Result> r = f(v);
>>             // ... use r or v;
>>             g(r->get(), v->get());
>>             v->get() = 15;
>>         }
>
> Not quite. You can't set a value on a future by writing to the result of a
> call to get() - you need a promise or a packaged task for that. However, 
> you
> can write:
>
> void foo()
> {
>    promise<InOut> p;
>    shared_future<InOut> v=p.get_future();
>    p.set_value(13);
>
>    unique_future<Result> r=f(v);
>
>    // v.get() may have changed if f took v by reference
>    g(r.get(),v.get());
> }
>
Sorry, this is exactly the behaviour I wanted to refactor.

Thanks
Vicente