Async ref

[sean-parent]

@FelixPetriconi - can you take a look at this? Added support for std::ref per issue #80. Required quite a bit of meta- scaffolding.

[codecov]

Codecov Report

Merging #81 into develop will increase coverage by 0.09%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop      #81      +/-   ##
===========================================
+ Coverage    94.74%   94.83%   +0.09%     
===========================================
  Files           33       34       +1     
  Lines         4206     4280      +74     
  Branches       214      214              
===========================================
+ Hits          3985     4059      +74     
  Misses          85       85              
  Partials       136      136

Impacted Files	Coverage Δ
stlab/concurrency/future.hpp	87.98% <100%> (-0.03%)	⬇️
test/future_tests.cpp	97.97% <100%> (+3.69%)	⬆️
stlab/test/model.hpp	94.11% <100%> (+6.61%)	⬆️
stlab/utility.hpp	100% <100%> (ø)
test/channel_test_helper.hpp	92.5% <0%> (-1.25%)	⬇️
test/future_then_tests.cpp	99.51% <0%> (+0.24%)	⬆️

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[FelixPetriconi]

The line wrapping here is strange. Probably a result of clangformat?

[sean-parent]

Yes, clang-format is getting lost on that line.

[FelixPetriconi]

The changes are fine for me. But I think we should add a test for this as well so that we will have this as regression as well.

[ahcox]

You guys are efficient! Note I think this also addresses std::cref().
(An object passed to std::async() by const reference is copied unless std::cref() is used to wrap it)
I updated my repro to have a std::cref() example (https://gist.github.com/ahcox/0e76d32a0a87ac24160bf50298052a1d). This all compiles fine now using the async-ref branch.

[sean-parent]

I will add some test cases.
@ahcox, this also handles the cref() case correctly without copies. Simple test:

#include <stlab/concurrency/future.hpp>
#include <stlab/concurrency/immediate_executor.hpp>
#include <stlab/test/model.hpp>

int main() {
    stlab::annotate a;
    stlab::async(stlab::immediate_executor, [](const auto& x) -> const auto& { return x; },
                 std::cref(a));
}

[sean-parent]

I added test cases and reworked annotate to make it more useful for generating tests. See the new future tests for async to see how to use it.