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

From: Anthony Williams (anthony_w.geo_at_[hidden])
Date: 2008-05-13 16:03:30

"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());
}

Anthony
-- 
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