Merge pull request #3681 from softins/cpp17-resultof-deprecation

Fix deprecation of result_of in C++17

Author: pljones

src/threadpool.h

@@ -35,13 +35,24 @@
 #include <functional>
 #include <stdexcept>
 
+// compatibility with C++17 deprecation of result_of
+#if __cplusplus >= 201703L
+// std::invoke_result_t should be used from C++17 onwards, but is not available in C++14 and earlier
+template<class F, class... Args>
+using threadpool_result_t = std::invoke_result_t<F, Args...>;
+#else
+// std::result_of should be used on C++14 and earlier, but is deprecated in C++17
+template<class F, class... Args>
+using threadpool_result_t = typename std::result_of<F ( Args... )>::type;
+#endif
+
 class CThreadPool
 {
 public:
     CThreadPool() = default;
     CThreadPool ( size_t );
     template<class F, class... Args>
-    auto enqueue ( F&& f, Args&&... args ) -> std::future<typename std::result_of<F ( Args... )>::type>;
+    auto enqueue ( F&& f, Args&&... args ) -> std::future<threadpool_result_t<F, Args...>>;
     ~CThreadPool();
 
 private:
@@ -87,9 +98,9 @@ inline CThreadPool::CThreadPool ( size_t threads ) : stop ( false )
 
 // add new work item to the pool
 template<class F, class... Args>
-auto CThreadPool::enqueue ( F&& f, Args&&... args ) -> std::future<typename std::result_of<F ( Args... )>::type>
+auto CThreadPool::enqueue ( F&& f, Args&&... args ) -> std::future<threadpool_result_t<F, Args...>>
 {
-    using return_type = typename std::result_of<F ( Args... )>::type;
+    using return_type = threadpool_result_t<F, Args...>;
 
     auto task = std::make_shared<std::packaged_task<return_type()>> ( std::bind ( std::forward<F> ( f ), std::forward<Args> ( args )... ) );