Re: [boost] Common future base class (was Re: Boost.Fiber mini-review September 4-13)

Subject: Re: [boost] Common future base class (was Re: Boost.Fiber mini-review September 4-13)
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2015-09-06 09:14:24

> The problem exist already for any library proposing a standard future
> implementation. How can this new implementation works with a standard
> implementation. This is the case for Boost.Thread, HPX, Boost.AFIO,
> Boost.Fiber, or your own implementation.
> What I meant is that we need to change the standard to be able to solve
> this problem, as the standard don't take it in account.

I believe the solution to is not so much to change (std::)future, but to
push forward 'await' instead. It already has (most) of a
future-type-agnostic synchronization mechanism specified. Granted, the
proposal will change, but I'm certain it will get into C++ in the C++17
timeframe. The 'await' allows to rewrite when_all, etc. such that it works
for any combination of input futures. Here's a sketch (sans decay, etc.):

namespace foobar
{
    template <typename Future...>
        requires(is_future<Future>)...
    future<tuple<Future...>> when_all(Future &&... f)
    {
        (await f)...;
        return make_tuple(std::forward<Future>(f)...);
    }
}

i.e. every library which exposes its future type provides this trivial
implementation of when_all(), etc. It can consume any future from any other
place, however.

Regards Hartmut
---------------
http://boost-spirit.com
http://stellar.cct.lsu.edu