{

{

boost::promise<int> promise;

boost::future<int> future = promise.get_future();

boost::future<int> result =

future.then

(

boost::launch::deferred,

[](boost::future<int> && f)

{

std::cout << std::this_thread::get_id() << ": callback" << std::endl;

std::cout << "The value is: " << f.get() << std::endl;

return f.get();

}

);

// We could not reach here.

std::cout << std::this_thread::get_id() << ": function" << std::endl;

promise.set_value(0);

}

{

boost::promise<int> promise;

boost::shared_future<int> future = promise.get_future().share();

boost::future<int> result =

future.then

(

boost::launch::deferred,

[](boost::shared_future<int> && f)

{

std::cout << std::this_thread::get_id() << ": callback" << std::endl;

std::cout << "The value is: " << f.get() << std::endl;

return f.get();

}

);

// We could not reach here.

std::cout << std::this_thread::get_id() << ": function" << std::endl;

promise.set_value(0);

}

return 0;