Difference between revisions of "cpp/utility/functional/not fn"
m (→Notes: ~FTM; fmt) |
m (→See also) |
||
| Line 161: | Line 161: | ||
{{dsc end}} | {{dsc end}} | ||
| − | {{langlinks|es|ja|zh}} | + | {{langlinks|es|ja|ru|zh}} |
Revision as of 02:53, 17 March 2023
| Defined in header <functional>
|
||
template< class F> /*unspecified*/ not_fn( F&& f ); |
(since C++17) (until C++20) |
|
| template< class F> constexpr /*unspecified*/ not_fn( F&& f ); |
(since C++20) | |
Creates a forwarding call wrapper that returns the negation of the callable object it holds.
Contents |
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
| (1) | ||
explicit T(F&& f); // exposition only |
(since C++17) (until C++20) |
|
| explicit constexpr T(F&& f); // exposition only |
(since C++20) | |
| T(T&& f) = default; T(const T& f) = default; |
(2) | |
Member function operator()
| (1) | ||
template<class... Args> auto operator()(Args&&... args) & -> decltype( |
(since C++17) (until C++20) |
|
| template<class... Args> constexpr auto operator()(Args&&... args) & noexcept(/*see below*/) |
(since C++20) | |
| (2) | ||
template<class... Args> auto operator()(Args&&... args) && -> decltype( |
(since C++17) (until C++20) |
|
| template<class... Args> constexpr auto operator()(Args&&... args) && noexcept(/*see below*/) |
(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>
Expression-equivalent
Expression e is expression-equivalent to expression f, if
- e and f have the same effects, and
- either both are constant subexpressions or else neither is a constant subexpression, and
- either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).
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> constexpr 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)...); } template<class... Args> constexpr 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> constexpr auto operator()(Args&&... args) && noexcept(noexcept(!std::invoke(std::move(f), std::forward<Args>(args)...))) -> decltype(!std::invoke(std::move(f), std::forward<Args>(args)...)) { return !std::invoke(std::move(f), std::forward<Args>(args)...); } template<class... Args> constexpr auto operator()(Args&&... args) const&& noexcept(noexcept(!std::invoke(std::move(f), std::forward<Args>(args)...))) -> decltype(!std::invoke(std::move(f), std::forward<Args>(args)...)) { return !std::invoke(std::move(f), std::forward<Args>(args)...); } }; } template<class F> constexpr 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.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_not_fn |
201603L | (C++17) | std::not_fn()
|
Example
| This section is incomplete Reason: no example |
See also
| (deprecated in C++17)(removed in C++20) |
constructs custom std::unary_negate object (function template) |
| (deprecated in C++17)(removed in C++20) |
constructs custom std::binary_negate object (function template) |
