std::std::uses_allocator<std::packaged_task>

From cppreference.com
template< class R, class Alloc >
struct uses_allocator<std::packaged_task<R>, Alloc> : true_type { };
(since C++11)

Provides a specialization of the std::uses_allocator type trait for std::packaged_task.

[edit] See also

checks if the specified type supports uses-allocator construction
(class template)