missing template - to_future

[Nenad Vukicevic]

'to_future' seems to be missing. This code does not compile:

future<int> f[2];
future<int,int,double> result = to_future (f[0], f[1], 1.0);

[Dan Bonachea]

Bug confirmed.

Full example:

#include <upcxx/upcxx.hpp>
using namespace upcxx;

int main() {
future<int> f[2];
future<int,int,double> result = to_future (f[0], f[1], 1.0);
return 0;
}

Too late to fix for this release.

[Dan Bonachea]

In the 1/10/18 meeting, John recommended keeping only the single-argument version and excising the variadic version from the spec.

Note related spec issue 104

[Amir Kamil]

This is what I believe is a spec-compliant implementation of to_future() using make_future() and when_all():

template<typename T>
struct future_collapse {
  using type = future<T>;
  static type make(T arg) {
    return make_future(std::move(arg));
  }
};

template<typename ...T>
struct future_collapse<future<T...>> {
  using type = future<T...>;
  static type make(future<T...> arg) {
    return std::move(arg);
  }
};

template<typename ...Arg>
auto to_future(Arg ...args)
  -> decltype(when_all(future_collapse<Arg>::make(args)...)) {
  return when_all(future_collapse<Arg>::make(args)...);
}

It may need to be modified to account for John's future1 stuff.

[Amir Kamil]

We have modified the spec to match the implementation. See spec issue 104.