std::not_fn
From cppreference.com
< cpp | utility | functional
Defined in header
<functional>
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template< class F>
/*unspecified*/ not_fn( F&& f ); |
(since C++17) | |
Creates a forwarding call wrapper that returns the complement of the callable object it holds.
Contents |
[edit] Parameters
f | - | the object from which the Callable object held by the wrapper is constructed
|
[edit] 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
.
[edit] Remarks
If fd
is not Callable
, or std::is_constructible<FD, F>::value is not true
, the behavior is undefined.
[edit] Exceptions
Throws no exceptions, unless the construction of fd
throws.
[edit] 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) }; } |
[edit] Notes
not_fn
is intended to replace the C++03-era negators std::not1 and std::not2.
[edit] See also
(deprecated)
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constructs custom std::unary_negate object (function template) |
(deprecated)
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constructs custom std::binary_negate object (function template) |