return type deduction now with result_of

as suggested by https://github.com/n00btime
return type deduction now uses std::result_of
which allows return type deduction for pointer
to members (and looks cleaner anyway).

ThreadPool.h

@@ -16,7 +16,7 @@ class ThreadPool {
     ThreadPool(size_t);
     template<class F, class... Args>
     auto enqueue(F&& f, Args&&... args) 
-        -> std::future<decltype(std::forward<F>(f)(std::forward<Args>(args)...))>;
+        -> std::future<typename std::result_of<F(Args...)>::type>;
     ~ThreadPool();
 private:
     // need to keep track of threads so we can join them
@@ -35,7 +35,7 @@ inline ThreadPool::ThreadPool(size_t threads)
     :   stop(false)
 {
     for(size_t i = 0;i<threads;++i)
-        workers.push_back(std::thread(
+        workers.emplace_back(
             [this]
             {
                 while(true)
@@ -51,15 +51,15 @@ inline ThreadPool::ThreadPool(size_t threads)
                     task();
                 }
             }
-        ));
+        );
 }
 
 // add new work item to the pool
 template<class F, class... Args>
 auto ThreadPool::enqueue(F&& f, Args&&... args) 
-    -> std::future<decltype(std::forward<F>(f)(std::forward<Args>(args)...))>
+    -> std::future<typename std::result_of<F(Args...)>::type>
 {
-    typedef decltype(std::forward<F>(f)(std::forward<Args>(args)...)) return_type;
+    typedef typename std::result_of<F(Args...)>::type return_type;
 
     // don't allow enqueueing after stopping the pool
     if(stop)