std::function<R(Args...)>::function
function() noexcept; |
(1) | (since C++11) |
function( std::nullptr_t ) noexcept; |
(2) | (since C++11) |
function( const function& other ); |
(3) | (since C++11) |
(4) | ||
function( function&& other ); |
(since C++11) (until C++20) |
|
function( function&& other ) noexcept; |
(since C++20) | |
template< class F > function( F f ); |
(5) | (since C++11) |
template< class Alloc > function( std::allocator_arg_t, const Alloc& alloc ) noexcept; |
(6) | (since C++11) (removed in C++17) |
template< class Alloc > function( std::allocator_arg_t, const Alloc& alloc, |
(7) | (since C++11) (removed in C++17) |
template< class Alloc > function( std::allocator_arg_t, const Alloc& alloc, |
(8) | (since C++11) (removed in C++17) |
template< class Alloc > function( std::allocator_arg_t, const Alloc& alloc, |
(9) | (since C++11) (removed in C++17) |
template< class F, class Alloc > function( std::allocator_arg_t, const Alloc& alloc, F f ); |
(10) | (since C++11) (removed in C++17) |
Constructs a std::function
from a variety of sources.
other
to the target of *this. If other
is empty, *this will be empty after the call too. For (4), other
is in a valid but unspecified state after the call.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
. (since C++14)alloc
is used to allocate memory for any internal data structures that the function
might use.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::function object, no dynamic allocation takes place. Other large objects may be constructed in dynamic allocated storage and accessed by the std::function object through a pointer.
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.
| ||
-Alloc must meet the requirements of Allocator.
|
Exceptions
other
's target is a function pointer or a std::reference_wrapper, otherwise may throw std::bad_alloc or any exception thrown by the constructor used to copy or move the stored callable object.
4) 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 constructor used to copy or move the stored callable object. |
(until C++20) |
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.Notes
std::function
's allocator support was poorly specified and inconsistently implemented. Some implementations do not provide overloads (6-10) at all, some provide the overloads but ignore the supplied allocator argument, and some provide the overloads and use the supplied allocator for construction but not when the std::function
is reassigned. As a result, allocator support was removed in C++17.
Example
This section is incomplete Reason: no example |