async_promise<Value, Event> provides a standard way to expose the
future ability to acquire a value, wrapping the ordinary
construct of a Value that is available after some Event
has been signalled.
The default Event type is async_manual_reset_event<>. The Value type is returned by reference when co_await'ing the async_promise<>. The value can be provided either at construction time
or by calling the emplace method.
async_promise<std::wstring> myDelayedString;
task<> UseDelayedString()
{
std::cout << co_await myDelayedString;
}
task<> AcquireTheString()
{
// ... do some things here
myDelayedString.emplace(L"Hello world");
// ... do some more things here
co_return;
}
task<> HelloWorld()
{
async_scope<> scope;
scope.spawn(UseDelayedString());
scope.spawn(AcquireTheString());
co_await scope.join();
}