std::not_fn (3) - Linux Man Pages

std::not_fn: std::not_fn

NAME

std::not_fn - std::not_fn

Synopsis


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


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)
T(T&& f) = default; (2)
T(const T& f) = default;


1) The constructor 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()


template<class... Args> auto operator()(Args&&... args) &
-> decltype(!std::declval<std::invoke_result_t<std::decay_t<F>&, Args...>>()); (1)
template<class... Args> auto operator()(Args&&... args) const&
-> decltype(!std::declval<std::invoke_result_t<std::decay_t<F> const&, Args...>>());
template<class... Args> auto operator()(Args&&... args) &&
-> decltype(!std::declval<std::invoke_result_t<std::decay_t<F>, Args...>>()); (2)
template<class... Args> auto operator()(Args&&... args) const&&
-> decltype(!std::declval<std::invoke_result_t<std::decay_t<F> const, Args...>>());


1) Equivalent to return !std::invoke(fd, std::forward<Args>(args)...)
2) Equivalent to return !std::invoke(std::move(fd), std::forward<Args>(args)...)
where fd is the member object of type std::decay_t<F>

Exceptions


Throws no exceptions, unless the construction of fd throws.

Notes


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

See also


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


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