NAME¶

std::experimental::not_fn - std::experimental::not_fn

Synopsis¶

Defined in header <experimental/functional>
template< class F> (library fundamentals TS v2)
/*unspecified*/ not_fn( F&& f );

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

Parameters¶

f - the object from which the Callable object held by the wrapper is constructed

Return value¶

Let FD be std::decay_t<F> and fd be an lvalue of type FD constructed from
std::forward<F>(f).

not_fn returns a forwarding call wrapper fn of unspecified type such that fn(a1, a2,
..., aN) is equivalent to !INVOKE(fd, a1, ..., aN), where INVOKE is the operation
described in Callable.

The returned call wrapper is always MoveConstructible, and is CopyConstructible if
FD is CopyConstructible.

Remarks

If fd is not Callable, or std::is_constructible<FD, F>::value is not true, the
behavior is undefined.

Exceptions¶

Throws no exceptions, unless the construction of fd throws.

Possible implementation¶

namespace detail {
template<class F>
struct not_fn_t {
F f;
template<class... Args>
auto operator()(Args&&... args)
noexcept(noexcept(!std::invoke(f, std::forward<Args>(args)...)))
-> decltype(!std::invoke(f, std::forward<Args>(args)...)) {
return !std::invoke(f, std::forward<Args>(args)...);
}

// cv-qualified overload for QoI
template<class... Args>
auto operator()(Args&&... args) const
noexcept(noexcept(!std::invoke(f, std::forward<Args>(args)...)))
-> decltype(!std::invoke(f, std::forward<Args>(args)...)) {
return !std::invoke(f, std::forward<Args>(args)...);
}

template<class... Args>
auto operator()(Args&&... args) volatile
noexcept(noexcept(!std::invoke(f, std::forward<Args>(args)...)))
-> decltype(!std::invoke(f, std::forward<Args>(args)...)) {
return !std::invoke(f, std::forward<Args>(args)...);
}
template<class... Args>
auto operator()(Args&&... args) const volatile
noexcept(noexcept(!std::invoke(f, std::forward<Args>(args)...)))
-> decltype(!std::invoke(f, std::forward<Args>(args)...)) {
return !std::invoke(f, std::forward<Args>(args)...);
}
};
}

template<class F>
detail::not_fn_t<std::decay_t<F>> not_fn(F&& f) { return { std::forward<F>(f) }; }

Notes¶

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

See also¶

not_fn creates a function object that returns the complement of the result of the
(C++17) function object it holds
(function template)