std:: function_ref

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Function wrappers
function (C++11)
move_only_function (C++23)
copyable_function (C++26)
function_ref (C++26)
mem_fn (C++11)
bad_function_call (C++11)

Partial function application
bind_front bind_back (C++20) (C++23)
bind (C++11)
is_bind_expression (C++11)
is_placeholder (C++11)
_1, _2, _3, ... (C++11)

Function invocation
invoke invoke_r (C++17) (C++23)
Identity function object
identity (C++20)

Reference wrappers
reference_wrapper (C++11)
ref cref (C++11) (C++11)
unwrap_reference unwrap_ref_decay (C++20) (C++20)

Operator wrappers

plus
minus
negate
multiplies
divides
modulus
bit_and
bit_or
bit_not (C++14)
bit_xor

equal_to
not_equal_to
greater
less
greater_equal
less_equal
logical_and
logical_or
logical_not

Transparent operator wrappers

plus <> (C++14)
minus <> (C++14)
negate <> (C++14)
multiplies <> (C++14)
divides <> (C++14)
modulus <> (C++14)
bit_and <> (C++14)
bit_or <> (C++14)
bit_not <> (C++14)
bit_xor <> (C++14)

equal_to <> (C++14)
not_equal_to <> (C++14)
greater <> (C++14)
less <> (C++14)
greater_equal <> (C++14)
less_equal <> (C++14)
logical_and <> (C++14)
logical_or <> (C++14)
logical_not <> (C++14)

Negators
not_fn (C++17)
Searchers
default_searcher (C++17)
boyer_moore_searcher (C++17)
boyer_moore_horspool_searcher (C++17)

Constrained comparators
ranges::equal_to (C++20)
ranges::not_equal_to (C++20)
ranges::greater (C++20)
ranges::less (C++20)
ranges::greater_equal (C++20)
ranges::less_equal (C++20)
compare_three_way (C++20)

Old binders and adaptors

unary_function ( until C++17* )
binary_function ( until C++17* )
ptr_fun ( until C++17* )
pointer_to_unary_function ( until C++17* )
pointer_to_binary_function ( until C++17* )
mem_fun ( until C++17* )
mem_fun_t mem_fun1_t const_mem_fun_t const_mem_fun1_t ( until C++17* ) ( until C++17* ) ( until C++17* ) ( until C++17* )
not1 ( until C++20* )
not2 ( until C++20* )

binder1st binder2nd ( until C++17* ) ( until C++17* )
bind1st bind2nd ( until C++17* ) ( until C++17* )

mem_fun_ref ( until C++17* )
mem_fun_ref_t mem_fun1_ref_t const_mem_fun_ref_t const_mem_fun1_ref_t ( until C++17* ) ( until C++17* ) ( until C++17* ) ( until C++17* )
unary_negate ( until C++20* )
binary_negate ( until C++20* )

Defined in header `<functional>`
template < class ... > class function_ref ; // not defined	(1)	(since C++26)
template < class R, class ... Args > class function_ref < R ( Args... ) > ; template < class R, class ... Args > class function_ref < R ( Args... ) noexcept > ; template < class R, class ... Args > class function_ref < R ( Args... ) const > ; template < class R, class ... Args > class function_ref < R ( Args... ) const noexcept > ;	(2)	(since C++26)

Class template std::function_ref is a non-owning function wrapper. std::function_ref objects can store and invoke reference to Callable target - functions, lambda expressions , bind expressions , or other function objects, but not pointers to member functions and pointers to member objects. std:: nontype can be used to construct std::function_ref by passing function pointers, pointers to member functions, and pointers to member objects.

std::function_ref s supports every possible combination of cv-qualifiers (excluding volatile ), and noexcept-specifiers provided in its template parameter.

Every specialization of std::function_ref is a TriviallyCopyable type that satisfies copyable .

Member objects

Member	Definition
`bound-entity`	an object that has an unspecified TriviallyCopyable type `BoundEntityType` , that satisfies `copyable` and is capable of storing a pointer to object value or pointer to function value ( exposition-only member object* )
`thunk-ptr`	a pointer to function of type R ( * ) ( BoundEntityType, Args && ... ) noexcept ( /noex/ ) where /noex/ is true if noexcept is present in function signature as part of the template parameter of `std::function_ref` ( exposition-only member object* )

Member functions

(constructor)	constructs a new `function_ref` object (public member function)
operator=	assigns a `function_ref` (public member function)
operator()	invokes the stored thunk of a `function_ref` (public member function)

Deduction guides

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_function_ref`	202306L	(C++26)	`std::function_ref`

Example

This section is incomplete
Reason: example

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Execution support library (C++26)
Technical specifications
Symbols index
External libraries

Member functions
function_ref::function_ref
function_ref::operator=
function_ref::operator()
Deduction guides

function (C++11)	copyable wrapper of any copy constructible callable object (class template)
copyable_function (C++26)	copyable wrapper of any copy constructible callable object that supports qualifiers in a given call signature (class template)
move_only_function (C++23)	move-only wrapper of any callable object that supports qualifiers in a given call signature (class template)
nontype nontype_t (C++26)	value construction tag (tag)