# std::experimental::function<R(Args...)>::function

From cppreference.com
< cpp‎ | experimental‎ | function

function() noexcept; | (1) | (library fundamentals TS)
function( std::nullptr_t ) noexcept; | (2) | (library fundamentals TS)
function( const function& other ); | (3) | (library fundamentals TS)
function( function&& other ); | (4) | (library fundamentals TS)
template< class F > function( F f ); | (5) | (library fundamentals TS)
| (6) |
template< class Alloc > function( std::allocator_arg_t, const Alloc& alloc ) noexcept; |  | (library fundamentals TS)
function( std::allocator_arg_t, const allocator_type& alloc ) noexcept; |  | (library fundamentals TS v3)
| (7) |
template< class Alloc > function( std::allocator_arg_t, const Alloc& alloc, std::nullptr_t ) noexcept; |  | (library fundamentals TS)
function( std::allocator_arg_t, const allocator_type& alloc, std::nullptr_t ) noexcept; |  | (library fundamentals TS v3)
| (8) |
template< class Alloc > function( std::allocator_arg_t, const Alloc& alloc, const function& other ); |  | (library fundamentals TS)
function( std::allocator_arg_t, const allocator_type& alloc, const function& other ); |  | (library fundamentals TS v3)
| (9) |
template< class Alloc > function( std::allocator_arg_t, const Alloc& alloc, function&& other ); |  | (library fundamentals TS)
function( std::allocator_arg_t, const allocator_type& alloc, function&& other ); |  | (library fundamentals TS v3)
| (10) |
template< class F, class Alloc > function( std::allocator_arg_t, const Alloc& alloc, F f ); |  | (library fundamentals TS)
function( std::allocator_arg_t, const allocator_type& alloc, F f ); |  | (library fundamentals TS v3)

Constructs a `std::experimental::function` from a variety of sources.

1-2) Creates an empty function.
3) Copies the target of other to the target of *this. If other is empty, *this will be empty after the call too.
4) Moves the target of other to the target of *this. If other is empty, *this will be empty after the call too. After construction, *this stores a copy of other.get_allocator(). (library fundamentals TS v3)
5) Initializes the target with a copy of f. If f is a null pointer to function or null pointer to member, *this will be empty after the call. This constructor does not participate in overload resolution unless f is Callable for argument types `Args...` and return type `R`.
6-10) Same as (1-5) except that alloc is used to allocate memory for any internal data structures that the `function` might use. These constructors treat alloc as a type-erased allocator (see below). (until library fundamentals TS v3)

After construction via (1-5), this->get_memory_resource() returns the same value as std::experimental::pmr::get_default_resource() during construction. | (library fundamentals TS) (until library fundamentals TS v3)
After construction via (1-3) and (5), *this stores a default constructed std::pmr::polymorphic_allocator<>. | (library fundamentals TS v3)

When the target is a function pointer or a std::reference_wrapper, small object optimization is guaranteed, that is, these targets are always directly stored inside the std::experimental::function object, no dynamic allocation takes place. Other large objects may be constructed in dynamic allocated storage and accessed by the std::experimental::function object through a pointer.

If a constructor moves or copies a function object, including an instance of `std::experimental::function`, then that move or copy is performed by using-allocator construction with allocator this->get_memory_resource() (until library fundamentals TS v3)this->get_allocator() (library fundamentals TS v3).

### Type-erased allocator

The constructors of `function` taking an allocator argument `alloc` treats that argument as a type-erased allocator. The memory resource pointer used by `function` 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 `function` object.
None of the above | The program is ill-formed.

### Parameters

other | - | the function object used to initialize *this
f | - | a callable used to initialize *this
alloc | - | an allocator used for internal memory allocation
Type requirements
- `F` must meet the requirements of Callable and CopyConstructible.

### Exceptions

3,8) Does not throw if other's target is a function pointer or a std::reference_wrapper, otherwise may throw std::bad_alloc or any exception thrown by the copy constructor of the stored callable object.
4) (none)
5,10) Does not throw if f is a function pointer or a std::reference_wrapper, otherwise may throw std::bad_alloc or any exception thrown by the copy constructor of the stored callable object.
9) (none)

### Example

| This section is incomplete Reason: no example

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/experimental/function/function&oldid=154957"