std::not_fn

 

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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)
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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*)

 

Defined in header <functional>
template< class F > /* unspecified */ not_fn( F&& f );		(since C++17) (constexpr since C++20)

Creates a forwarding call wrapper that returns the negation of the callable object it holds.

Parameters

f	-	the object from which the Callable object held by the wrapper is constructed
Type requirements
- std::decay_t<F> must meet the requirements of Callable and MoveConstructible.
- std::is_constructible_v<std::decay_t<F>, F> is required to be true.

Return value

A function object of unspecified type T. It has the following members:

std::not_fn return type

Member objects

The return type of std::not_fn holds a member object of type std::decay_t<F>.

Constructors

explicit T( F&& f );	(1)	(since C++17) (constexpr since C++20) (exposition only*)
T( T&& f ) = default; T( const T& f ) = default;	(2)

1) The constructor direct-non-list-initializes the member object (of type std::decay_t<F>) from std::forward<F>(f). Throws any exception thrown by the constructor selected.

2) Because std::decay_t<F> is required to be MoveConstructible, the returned call wrapper is always MoveConstructible, and is CopyConstructible if std::decay_t<F> is CopyConstructible.

Member function operator()

	(1)
template< class... Args > auto operator()( Args&&... args ) & -> decltype(!std::declval<     std::invoke_result_t<std::decay_t<F>&, Args...>>()); template< class... Args > auto operator()( Args&&... args ) const& -> decltype(!std::declval<     std::invoke_result_t<std::decay_t<F> const&, Args...>>());			(since C++17) (until C++20)
template< class... Args > constexpr auto operator()( Args&&... args ) &     noexcept(/* see below */) -> decltype(!std::declval<     std::invoke_result_t<std::decay_t<F>&, Args...>>()); template< class... Args > constexpr auto operator()( Args&&... args ) const&     noexcept(/* see below */) -> decltype(!std::declval<     std::invoke_result_t<std::decay_t<F> const&, Args...>>());			(since C++20)
		(2)
template< class... Args > auto operator()( Args&&... args ) && -> decltype(!std::declval<     std::invoke_result_t<std::decay_t<F>, Args...>>()); template< class... Args > auto operator()( Args&&... args ) const&& -> decltype(!std::declval<     std::invoke_result_t<std::decay_t<F> const, Args...>>());				(since C++17) (until C++20)
template< class... Args > constexpr auto operator()( Args&&... args ) &&     noexcept(/* see below */) -> decltype(!std::declval<     std::invoke_result_t<std::decay_t<F>, Args...>>()); template< class... Args > constexpr auto operator()( Args&&... args ) const&&     noexcept(/* see below */) -> decltype(!std::declval<     std::invoke_result_t<std::decay_t<F> const, Args...>>());				(since C++20)

1) Equivalent to return !std::invoke(fd, std::forward<Args>(args)...); 2) Equivalent to return !std::invoke(std::move(fd), std::forward<Args>(args)...);	(since C++17) (until C++20)
1) Expression-equivalent to !std::invoke(fd, std::forward<Args>(args)...) 2) Expression-equivalent to !std::invoke(std::move(fd), std::forward<Args>(args)...)	(since C++20)

where fd is the member object of type std::decay_t<F>.

Exceptions

Throws no exceptions, unless the construction of fd throws.

Possible implementation

namespace detail { template<class V, class F, class... Args> constexpr bool negate_invocable_impl = false; template<class F, class... Args> constexpr bool negate_invocable_impl<std::void_t<decltype( !std::invoke(std::declval<F>(), std::declval<Args>()...))>, F, Args...> = true;   template<class F, class... Args> constexpr bool negate_invocable_v = negate_invocable_impl<void, F, Args...>;   template<class F> struct not_fn_t { F f;   template<class... Args, std::enable_if_t<negate_invocable_v<F&, Args...>, int> = 0> constexpr decltype(auto) operator()(Args&&... args) & noexcept(noexcept(!std::invoke(f, std::forward<Args>(args)...))) { return !std::invoke(f, std::forward<Args>(args)...); }   template<class... Args, std::enable_if_t<negate_invocable_v<const F&, Args...>, int> = 0> constexpr decltype(auto) operator()(Args&&... args) const& noexcept(noexcept(!std::invoke(f, std::forward<Args>(args)...))) { return !std::invoke(f, std::forward<Args>(args)...); }   template<class... Args, std::enable_if_t<negate_invocable_v<F, Args...>, int> = 0> constexpr decltype(auto) operator()(Args&&... args) && noexcept(noexcept(!std::invoke(std::move(f), std::forward<Args>(args)...))) { return !std::invoke(std::move(f), std::forward<Args>(args)...); }   template<class... Args, std::enable_if_t<negate_invocable_v<const F, Args...>, int> = 0> constexpr decltype(auto) operator()(Args&&... args) const&& noexcept(noexcept(!std::invoke(std::move(f), std::forward<Args>(args)...))) { return !std::invoke(std::move(f), std::forward<Args>(args)...); }   // Deleted overloads are needed for preventing a non-equivalent but well-formed // overload to be selected.   template<class... Args, std::enable_if_t<!negate_invocable_v<F&, Args...>, int> = 0> void operator()(Args&&...) & = delete;   template<class... Args, std::enable_if_t<!negate_invocable_v<F&, Args...>, int> = 0> void operator()(Args&&...) const& = delete;   template<class... Args, std::enable_if_t<!negate_invocable_v<F&, Args...>, int> = 0> void operator()(Args&&...) && = delete;   template<class... Args, std::enable_if_t<!negate_invocable_v<F&, Args...>, int> = 0> void operator()(Args&&...) const&& = delete; }; }   template<class F> constexpr detail::not_fn_t<std::decay_t<F>> not_fn(F&& f) { return {std::forward<F>(f)}; }

Notes

std::not_fn is intended to replace the C++03-era negators std::not1 and std::not2.

Feature-test macro	Value	Std	Feature
__cpp_lib_not_fn	201603L	(C++17)	std::not_fn()
	202306L	(C++26)	Allow passing callable objects as non-type template arguments to std::not_fn

See also

not1 (deprecated in C++17)(removed in C++20)	constructs custom std::unary_negate object (function template)
not2 (deprecated in C++17)(removed in C++20)	constructs custom std::binary_negate object (function template)