std::invoke
std::invoke
| Defined in header | | |
|---|---|---|
| template< class F, class... Args> std::invoke_result_t<F, Args...> invoke(F&& f, Args&&... args) noexcept(/* see below */ | | (since C++17) |
Invoke the Callable object f with the parameters args. As by INVOKE(std::forward<F>(f), std::forward<Args>(args)...).
where INVOKE(f, t1, t2, ..., tN) is defined as follows:
- i
ffis a pointer to memberfunction ofclassT:
Parameters
| f | - | Callable object to be invoked |
|---|---|---|
| args | - | arguments to pass to f |
Exceptions
noexcept specification:
noexcept(std::is_nothrow_invocable_v<F, Args...>)
Possible implementation
namespace detail {
template <class T>
struct is_reference_wrapper : std::false_type {};
template <class U>
struct is_reference_wrapper<std::reference_wrapper<U>> : std::true_type {};
template <class T>
constexpr bool is_reference_wrapper_v = is_reference_wrapper<T>::value;
template <class Base, class T, class Derived, class... Args>
auto INVOKE(T Base::*pmf, Derived&& ref, Args&&... args)
noexcept(noexcept((std::forward<Derived>(ref).*pmf)(std::forward<Args>(args)...)))
-> std::enable_if_t<std::is_function_v<T> &&
std::is_base_of_v<Base, std::decay_t<Derived>>,
decltype((std::forward<Derived>(ref).*pmf)(std::forward<Args>(args)...))>
{
return (std::forward<Derived>(ref).*pmf)(std::forward<Args>(args)...
}
template <class Base, class T, class RefWrap, class... Args>
auto INVOKE(T Base::*pmf, RefWrap&& ref, Args&&... args)
noexcept(noexcept((ref.get().*pmf)(std::forward<Args>(args)...)))
-> std::enable_if_t<std::is_function_v<T> &&
is_reference_wrapper_v<std::decay_t<RefWrap>>,
decltype((ref.get().*pmf)(std::forward<Args>(args)...))>
{
return (ref.get().*pmf)(std::forward<Args>(args)...
}
template <class Base, class T, class Pointer, class... Args>
auto INVOKE(T Base::*pmf, Pointer&& ptr, Args&&... args)
noexcept(noexcept(((*std::forward<Pointer>(ptr)).*pmf)(std::forward<Args>(args)...)))
-> std::enable_if_t<std::is_function_v<T> &&
!is_reference_wrapper_v<std::decay_t<Pointer>> &&
!std::is_base_of_v<Base, std::decay_t<Pointer>>,
decltype(((*std::forward<Pointer>(ptr)).*pmf)(std::forward<Args>(args)...))>
{
return ((*std::forward<Pointer>(ptr)).*pmf)(std::forward<Args>(args)...
}
template <class Base, class T, class Derived>
auto INVOKE(T Base::*pmd, Derived&& ref)
noexcept(noexcept(std::forward<Derived>(ref).*pmd))
-> std::enable_if_t<!std::is_function_v<T> &&
std::is_base_of_v<Base, std::decay_t<Derived>>,
decltype(std::forward<Derived>(ref).*pmd)>
{
return std::forward<Derived>(ref).*pmd;
}
template <class Base, class T, class RefWrap>
auto INVOKE(T Base::*pmd, RefWrap&& ref)
noexcept(noexcept(ref.get().*pmd))
-> std::enable_if_t<!std::is_function_v<T> &&
is_reference_wrapper_v<std::decay_t<RefWrap>>,
decltype(ref.get().*pmd)>
{
return ref.get().*pmd;
}
template <class Base, class T, class Pointer>
auto INVOKE(T Base::*pmd, Pointer&& ptr)
noexcept(noexcept((*std::forward<Pointer>(ptr)).*pmd))
-> std::enable_if_t<!std::is_function_v<T> &&
!is_reference_wrapper_v<std::decay_t<Pointer>> &&
!std::is_base_of_v<Base, std::decay_t<Pointer>>,
decltype((*std::forward<Pointer>(ptr)).*pmd)>
{
return (*std::forward<Pointer>(ptr)).*pmd;
}
template <class F, class... Args>
auto INVOKE(F&& f, Args&&... args)
noexcept(noexcept(std::forward<F>(f)(std::forward<Args>(args)...)))
-> std::enable_if_t<!std::is_member_pointer_v<std::decay_t<F>>,
decltype(std::forward<F>(f)(std::forward<Args>(args)...))>
{
return std::forward<F>(f)(std::forward<Args>(args)...
}
} // namespace detail
template< class F, class... ArgTypes >
auto invoke(F&& f, ArgTypes&&... args)
// exception specification for QoI
noexcept(noexcept(detail::INVOKE(std::forward<F>(f), std::forward<ArgTypes>(args)...)))
-> decltype(detail::INVOKE(std::forward<F>(f), std::forward<ArgTypes>(args)...))
{
return detail::INVOKE(std::forward<F>(f), std::forward<ArgTypes>(args)...
}
Example
Implement the basic functionality of std::mem_fn.
#include <functional>
template< class PM >
class mem_fn_t {
PM p;
public:
mem_fn_t(PM p):p(p){}
template<class... Args>
decltype(auto) operator()(Args&&... args) {
return std::invoke(p, std::forward<Args>(args)...
}
};
template< class R, class T >
auto mem_fn(R T::* pm){
mem_fn_t<R T::*> t {pm};
return t;
}
See also
| mem_fn (C++11) | creates a function object out of a pointer to a member (function template) |
|---|---|
| result_ofinvoke_result (C++11)(deprecated in C++17)(C++17) | deduces the result type of invoking a callable object with a set of arguments (class template) |
| is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17) | checks if a type can be invoked (as if by std::invoke) with the given argument types (class template) |
| apply (C++17) | calls a function with a tuple of arguments (function template) |
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