13 KiB
[func.wrap.ref]
22 General utilities library [utilities]
22.10 Function objects [function.objects]
22.10.17 Polymorphic function wrappers [func.wrap]
22.10.17.6 Non-owning wrapper [func.wrap.ref]
22.10.17.6.1 General [func.wrap.ref.general]
The header provides partial specializations of function_ref for each combination of the possible replacements of the placeholders cv and noex where:
cv is either const or empty, and
noex is either true or false.
22.10.17.6.2 Class template function_ref [func.wrap.ref.class]
namespace std {template<class R, class... ArgTypes>class function_ref<R(ArgTypes...) cv noexcept(noex)> {public:// [func.wrap.ref.ctor], constructors and assignment operatorstemplate function_ref(F*) noexcept; template constexpr function_ref(F&&) noexcept; template constexpr function_ref(nontype_t) noexcept; template<auto f, class U> constexpr function_ref(nontype_t, U&&) noexcept; template<auto f, class T> constexpr function_ref(nontype_t, cv T*) noexcept; constexpr function_ref(const function_ref&) noexcept = default; constexpr function_ref& operator=(const function_ref&) noexcept = default; template function_ref& operator=(T) = delete; // [func.wrap.ref.inv], invocation R operator()(ArgTypes...) const noexcept(noex); private:template<class... T>static constexpr bool is-invocable-using = see below; // exposition only R (thunk-ptr)(BoundEntityType, Args&&...) noexcept(noex); // *exposition only*BoundEntityType* bound-entity; // exposition only}; // [func.wrap.ref.deduct], deduction guidestemplate function_ref(F*) -> function_ref; template function_ref(nontype_t) -> function_ref<see below>; template<auto f, class T> function_ref(nontype_t, T&&) -> function_ref<see below>;}
An object of classfunction_ref<R(Args...) cv noexcept(noex)> stores a pointer to function thunk-ptr and an object bound-entity.
bound-entity has an unspecified trivially copyable type BoundEntityType, that models copyable and is capable of storing a pointer to object value or a pointer to function value.
The type of thunk-ptr isR(*)(BoundEntityType, Args&&...) noexcept(noex).
Each specialization of function_ref is a trivially copyable type ([basic.types.general]) that models copyable.
Within [func.wrap.ref],call-args is an argument pack with elements such thatdecltype((call-args))... denoteArgs&&... respectively.
22.10.17.6.3 Constructors and assignment operators [func.wrap.ref.ctor]
template<class... T> static constexpr bool is-invocable-using = see below;
If noex is true,is-invocable-using<T...> is equal to:is_nothrow_invocable_r_v<R, T..., ArgTypes...>
Otherwise, is-invocable-using<T...> is equal to:is_invocable_r_v<R, T..., ArgTypes...>
template<class F> function_ref(F* f) noexcept;
Constraints:
is_function_v is true, and
is-invocable-using is true.
Preconditions: f is not a null pointer.
Effects: Initializesbound-entity with f, andthunk-ptr with the address of a function thunk such thatthunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) toinvoke_r(f, call-args...).
template<class F> constexpr function_ref(F&& f) noexcept;
Let T be remove_reference_t.
Constraints:
remove_cvref_t is not the same type as function_ref,
is_member_pointer_v is false, and
is-invocable-using<cv T&> is true.
Effects: Initializesbound-entity with addressof(f), andthunk-ptr with the address of a function thunk such thatthunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) toinvoke_r(static_cast<cv T&>(f), call-args...).
template<auto f> constexpr function_ref(nontype_t<f>) noexcept;
Let F be decltype(f).
Constraints: is-invocable-using is true.
Mandates: If is_pointer_v || is_member_pointer_v is true, then f != nullptr is true.
Effects: Initializesbound-entity with a pointer to an unspecified object or null pointer value, andthunk-ptr with the address of a function thunk such thatthunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) toinvoke_r(f, call-args...).
template<auto f, class U> constexpr function_ref(nontype_t<f>, U&& obj) noexcept;
Let T be remove_reference_t andF be decltype(f).
Constraints:
is_rvalue_reference_v<U&&> is false, and
is-invocable-using<F, cv T&> is true.
Mandates: If is_pointer_v || is_member_pointer_v is true, then f != nullptr is true.
Effects: Initializesbound-entity with addressof(obj), andthunk-ptr with the address of a function thunk such thatthunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) toinvoke_r(f, static_cast<cv T&>(obj), call-args...).
template<auto f, class T> constexpr function_ref(nontype_t<f>, cv T* obj) noexcept;
Let F be decltype(f).
Constraints: is-invocable-using<F, cv T*> is true.
Mandates: If is_pointer_v || is_member_pointer_v is true, then f != nullptr is true.
Preconditions: If is_member_pointer_v is true,obj is not a null pointer.
Effects: Initializesbound-entity with obj, andthunk-ptr with the address of a function thunk such thatthunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) toinvoke_r(f, obj, call-args...).
template<class T> function_ref& operator=(T) = delete;
Constraints:
T is not the same type as function_ref,
is_pointer_v is false, and
T is not a specialization of nontype_t.
22.10.17.6.4 Invocation [func.wrap.ref.inv]
R operator()(ArgTypes... args) const noexcept(noex);
Effects: Equivalent to:return thunk-ptr(bound-entity, std::forward(args)...);
22.10.17.6.5 Deduction guides [func.wrap.ref.deduct]
template<class F> function_ref(F*) -> function_ref<F>;
Constraints: is_function_v is true.
template<auto f> function_ref(nontype_t<f>) -> function_ref<see below>;
Let F be remove_pointer_t<decltype(f)>.
Constraints: is_function_v is true.
Remarks: The deduced type is function_ref.
template<auto f, class T> function_ref(nontype_t<f>, T&&) -> function_ref<see below>;
Let F be decltype(f).
Constraints:
F is of the formR(G::*)(A...) cv &opt noexcept(E) for a type G, or
F is of the formM G::* for a type G and an object type M, in which case let R be invoke_result_t<F, T&>,A... be an empty pack, andE be false, or
F is of the formR(*)(G, A...) noexcept(E) for a type G.
Remarks: The deduced type is function_ref<R(A...) noexcept(E)>.