Template class used to wrap a function object in conjunction with class structured_task_group.
Class task_handle is used primarily in conjunction with class structured_task_group. For sake of uniformity, class task_group also accepts task_handle arguments.
template<typename Func>
class task_handle {
public:
task_handle( const Func& );
task_handle( Func&& ); // supported since C++11
void operator()() const;
};