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

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

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

1-2) Creates an empty function.
3-4) Copies (3) or moves (4) the target of `other` to the target of *this. If `other` is empty, *this will be empty after the call too.
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).

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()`.

### 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

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