future<future<T>>::then Has No Implementation

[code@…]

Linker errors when using .then() on a future<future<T>>

Undefined symbols for architecture x86_64:
  "boost::future<boost::result_of<TestCallback (boost::future<boost::future<void> >)>::type> boost::future<boost::future<void> >::then<TestCallback>(TestCallback&&)", referenced from:
      _main in test_100000.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Example:

struct TestCallback
{
    typedef boost::future<void> result_type;

    result_type operator()(boost::future<void> future) const
    {
        future.get();
        return boost::make_ready_future();
    }

    result_type operator()(boost::future<boost::future<void>> future) const
    {
       future.get();
       return boost::make_ready_future();
    }
};

int main()
{
    boost::promise<void> test_promise;
    boost::future<void> test_future(test_promise.get_future());
    test_future.then(TestCallback()).then(TestCallback());
    return 0;
}

[viboes]

This is weird. The result of

test_future.then(TestCallback())

should be future<void> and so future<future<void>::then will not necessary in this case.

I'm not saying that there is no problem. I will add the test and check it.

[viboes]

Hrr, I have not implemented yet the implicit unwrap when calling future::then.

[viboes]

​https://github.com/boostorg/thread/commit/b77eac3e379332e3a1752596dd12b90ff9303fb4

[viboes]

​https://github.com/boostorg/thread/commit/71997bd9aa43e1da2f05cdd46219d152a1c2321f