# std::experimental::packaged_task<R(Args...)>::packaged_task (library fundamentals TS)

From cppreference.com
< cpp‎ | experimental‎ | lib extensions‎ | packaged task

packaged_task() noexcept; | (1) | (library fundamentals TS)
template <class F> explicit packaged_task( F&& f ); | (2) | (library fundamentals TS)
template <class F, class Allocator> explicit packaged_task( std::allocator_arg_t, const Allocator& alloc, F&& f ); | (3) | (library fundamentals TS)
packaged_task( const packaged_task& ) = delete; | (4) | (library fundamentals TS)
packaged_task( packaged_task&& rhs ) noexcept; | (5) | (library fundamentals TS)

Constructs a new `std::experimental::packaged_task` object.

1) Constructs a `std::experimental::packaged_task` object with no task and no shared state.
2) Constructs a `std::experimental::packaged_task` object with a shared state and a copy of the task, initialized with std::forward <F>(f). This constructor does not participate in overload resolution if std::decay <F>::type is the same type as std::packaged_task <R(ArgTypes...)>.
3) Constructs a `std::experimental::packaged_task` object with a shared state and a copy of the task, initialized with std::forward <F>(f). Uses the provided allocator to allocate memory necessary to store the task, which is treated as a type-erased allocator (see below). This constructor does not participate in overload resolution if std::decay <F>::type is the same type as std::packaged_task <R(ArgTypes...)>.
4) The copy constructor is deleted, `std::experimental::packaged_task` is move-only.
5) Constructs a `std::experimental::packaged_task` with the shared state and task formerly owned by `rhs`, leaving `rhs` with no shared state and a moved-from task.

### Type-erased allocator

The constructors of `packaged_task` taking an allocator argument `alloc` treats that argument as a type-erased allocator. The memory resource pointer used by `packaged_task` to allocate memory is determined using the allocator argument (if specified) as follows:

Type of `alloc` | value of the memory resource pointer
Non-existent (no allocator specified at time of construction) | The value of std::experimental::pmr::get_default_resource () at time of construction.
std::nullptr_t | The value of std::experimental::pmr::get_default_resource () at time of construction
A pointer type convertible to std::experimental::pmr::memory_resource * | static_cast< std::experimental::pmr::memory_resource *>(alloc)
A specialization of std::experimental::pmr::polymorphic_allocator | alloc.resource()
Any other type meeting the Allocator requirements | A pointer to a value of type std::experimental::pmr::resource_adaptor <A>(alloc), where `A` is the type of `alloc`. The pointer remains valid only for the lifetime of the `packaged_task` object.
None of the above | The program is ill-formed.

### Parameters

f | - | the callable target (function, member function, lambda-expression, functor) to execute
alloc | - | the allocator to use when storing the task
rhs | - | the `std::experimental::packaged_task` to move from

### Exceptions

2-3) Any exceptions thrown by copy/move constructor of `f` and possiblly std::bad_alloc if the allocation fails.
4) (none)
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/experimental/lib_extensions/packaged_task/packaged_task&oldid=98631"