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std::experimental::packaged_task::packaged_task (library fundamentals TS)

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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.


[edit] 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.

[edit] 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

[edit] Exceptions

2-3) Any exceptions thrown by copy/move constructor of f and possiblly std::bad_alloc if the allocation fails.
4) (none)