add original source

source/listing_4.14.cpp

@@ -0,0 +1,12 @@
+template<typename F,typename A>
+std::future<std::result_of<F(A&&)>::type>
+spawn_task(F&& f,A&& a)
+{
+    typedef std::result_of<F(A&&)>::type result_type;
+    std::packaged_task<result_type(A&&)>
+        task(std::move(f));
+    std::future<result_type> res(task.get_future());
+    std::thread t(std::move(task),std::move(a));
+    t.detach();
+    return res;
+}