Allow splitting of futures holding std::tuple

[severinstrobl]

Analogous to the case of std::pair, it should be possible to split a hpx::future<std::tuple<Ts...>> into std::tuple<hpx::future<Ts>...>.

[jenkins-cscs]

Can one of the admins verify this patch?

[hkaiser]

Will this work even if HPX_DATASTRUCTURES_WITH_ADAPT_STD_TUPLE=Off? Our support for hpx::get supporting std::tuple relies on having this enabled (see for instance https://github.com/STEllAR-GROUP/hpx/blob/master/libs/core/datastructures/include/hpx/datastructures/tuple.hpp#L107-L125)

[severinstrobl]

Ah, completely missed that part. So would wrapping the respective sections using #if defined()/#endif be acceptable or is there a more elegant solution that would somehow allow the conversion between the tuple types (if enabled)?

[hkaiser]

Ah, completely missed that part. So would wrapping the respective sections using #if defined()/#endif be acceptable or is there a more elegant solution that would somehow allow the conversion between the tuple types (if enabled)?

That would be perfectly acceptable, thanks!

[hkaiser]

LGTM, thanks!

[hkaiser]

retest

[severinstrobl]

As far as I can tell, the failed CI jobs are unrelated to the changes introduced here, but maybe an admin can have a look?

[msimberg]

As far as I can tell, the failed CI jobs are unrelated to the changes introduced here, but maybe an admin can have a look?

This looks good, the remaining failures are unrelated to your changes. Thanks!