Std::not_fn (3) Linux Manual Page

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.

std::not_fn (3) Linux Manual Page