Async: allow appending existing Job objects to the Job chain

Now it's possible to do something like

Job<int, int> job = createSomeJob();
auto main = Async::start<int>(....).then(job);

Previously the 'job' would have to be wrapped in a ThenTask-like lambda (which
is what we still do internally), but with this new syntax it's possible to append
another job chain to existing chain easilly. This syntax is available for all
task types.

1 files changed, 15 insertions, 0 deletions

diff --git a/async/src/async_impl.h b/async/src/async_impl.h
index 58f6ced..eccbc9b 100644
--- a/async/src/async_impl.h
+++ b/async/src/async_impl.h
@@ -19,6 +19,7 @@
 #define ASYNC_IMPL_H
 
 #include "async.h"
+#include <type_traits>
 
 namespace Async {
 
@@ -45,6 +46,20 @@ struct prevOut {
     using type = typename std::tuple_element<0, std::tuple<T ..., void>>::type;
 };
 
+template<typename T>
+inline typename std::enable_if<!std::is_void<T>::value, void>::type
+copyFutureValue(const Async::Future<T> &in, Async::Future<T> &out)
+{
+    out.setValue(in.value());
+}
+
+template<typename T>
+inline typename std::enable_if<std::is_void<T>::value, void>::type
+copyFutureValue(const Async::Future<T> &in, Async::Future<T> &out)
+{
+    // noop
+}
+
 } // namespace Detail
 
 } // namespace Async