std::function_ref

 

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External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Function objects Bit manipulation (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23)

 

Function objects

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_frontbind_back (C++20)(C++23) bind (C++11) is_bind_expression (C++11) is_placeholder (C++11) _1, _2, _3, ... (C++11)
Function invocation invokeinvoke_r (C++17)(C++23) Identity function object identity (C++20)	Reference wrappers reference_wrapper (C++11) refcref (C++11)(C++11) unwrap_referenceunwrap_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_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_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*)

 

std::function_ref

Member functions

function_ref::function_ref

function_ref::operator=

function_ref::operator()

Deduction guides

 

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_refs 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 types

Member	Definition
BoundEntityType (private)	unspecified TriviallyCopyable type that satisfies copyable and is capable of storing a pointer to object value or pointer to function value (exposition-only member type*)
FunctionPointerType (private)	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, false otherwise (exposition-only member type*)

Data members

Member	Definition
BoundEntityType bound-entity	a bound entity object (exposition-only member object*)
FunctionPointerType thunk-ptr	a stored pointer to function (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)

Notes

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

See also

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)