When any function constructor that takes a first argument of type allocator_arg_t is invoked, the second argument shall have a type that conforms to the requirements for Allocator (Table [allocator.requirements]). A copy of the allocator argument is used to allocate memory, if necessary, for the internal data structures of the constructed function object.
function() noexcept;
template <class A> function(allocator_arg_t, const A& a) noexcept;
Postconditions: !*this.
function(nullptr_t) noexcept;
template <class A> function(allocator_arg_t, const A& a, nullptr_t) noexcept;
Postconditions: !*this.
function(const function& f);
template <class A> function(allocator_arg_t, const A& a, const function& f);
Postconditions: !*this if !f; otherwise, *this targets a copy of f.target().
Throws: shall not throw exceptions if f's target is a callable object passed via reference_wrapper or a function pointer. Otherwise, may throw bad_alloc or any exception thrown by the copy constructor of the stored callable object. [ Note: Implementations are encouraged to avoid the use of dynamically allocated memory for small callable objects, for example, where f's target is an object holding only a pointer or reference to an object and a member function pointer. — end note ]
function(function&& f);
template <class A> function(allocator_arg_t, const A& a, function&& f);
Effects: If !f, *this has no target; otherwise, move-constructs the target of f into the target of *this, leaving f in a valid state with an unspecified value.
template<class F> function(F f);
template <class F, class A> function(allocator_arg_t, const A& a, F f);
Requires: F shall be CopyConstructible.
Remarks: These constructors shall not participate in overload resolution unless f is Callable ([func.wrap.func]) for argument types ArgTypes... and return type R.
Otherwise, *this targets a copy of f initialized with std::move(f). [ Note: Implementations are encouraged to avoid the use of dynamically allocated memory for small callable objects, for example, where f's target is an object holding only a pointer or reference to an object and a member function pointer. — end note ]
Throws: shall not throw exceptions when f is a function pointer or a reference_wrapper<T> for some T. Otherwise, may throw bad_alloc or any exception thrown by F's copy or move constructor.
function& operator=(const function& f);
Effects: function(f).swap(*this);
Returns: *this
function& operator=(function&& f);
Effects: Replaces the target of *this with the target of f.
Returns: *this
function& operator=(nullptr_t);
Effects: If *this != nullptr, destroys the target of this.
Postconditions: !(*this).
Returns: *this
template<class F> function& operator=(F&& f);
Effects: function(std::forward<F>(f)).swap(*this);
Returns: *this
Remarks: This assignment operator shall not participate in overload resolution unless declval<typename decay<F>::type&>() is Callable ([func.wrap.func]) for argument types ArgTypes... and return type R.
template<class F> function& operator=(reference_wrapper<F> f) noexcept;
Effects: function(f).swap(*this);
Returns: *this
Effects: If *this != nullptr, destroys the target of this.