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]

22.10.17.6.3 Constructors and assignment operators [func.wrap.ref.ctor]

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template<class... T> static constexpr bool is-invocable-using = see below;
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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...>
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template<class F> function_ref(F* f) noexcept;
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Constraints:
  • (2.1)
    is_function_v<F> is true, and
  • (2.2)
    is-invocable-using<F> is true.
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Preconditions: f is not a null pointer.
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Effects: Initializes bound-entity with f, and thunk-ptr with the address of a function thunk such that thunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) to invoke_r<R>(f, call-args...).
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template<class F> constexpr function_ref(F&& f) noexcept;
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Let T be remove_reference_t<F>.
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Constraints:
  • (6.1)
    remove_cvref_t<F> is not the same type as function_ref,
  • (6.2)
    is_member_pointer_v<T> is false, and
  • (6.3)
    is-invocable-using<cv T&> is true.
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Effects: Initializes bound-entity with addressof(f), and thunk-ptr with the address of a function thunk such that thunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) to invoke_r<R>(static_cast<cv T&>(f), call-args...).
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template<auto f> constexpr function_ref(nontype_t<f>) noexcept;
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Let F be decltype(f).
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Constraints: is-invocable-using<F> is true.
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Mandates: If is_pointer_v<F> || is_member_pointer_v<F> is true, then f != nullptr is true.
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Effects: Initializes bound-entity with a pointer to an unspecified object or null pointer value, and thunk-ptr with the address of a function thunk such that thunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) to invoke_r<R>(f, call-args...).
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template<auto f, class U> constexpr function_ref(nontype_t<f>, U&& obj) noexcept;
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Let T be remove_reference_t<U> and F be decltype(f).
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Constraints:
  • (13.1)
    is_rvalue_reference_v<U&&> is false, and
  • (13.2)
    is-invocable-using<F, cv T&> is true.
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Mandates: If is_pointer_v<F> || is_member_pointer_v<F> is true, then f != nullptr is true.
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Effects: Initializes bound-entity with addressof(obj), and thunk-ptr with the address of a function thunk such that thunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) to invoke_r<R>(f, static_cast<cv T&>(obj), call-args...).
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template<auto f, class T> constexpr function_ref(nontype_t<f>, cv T* obj) noexcept;
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Let F be decltype(f).
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Constraints: is-invocable-using<F, cv T*> is true.
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Mandates: If is_pointer_v<F> || is_member_pointer_v<F> is true, then f != nullptr is true.
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Preconditions: If is_member_pointer_v<F> is true, obj is not a null pointer.
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Effects: Initializes bound-entity with obj, and thunk-ptr with the address of a function thunk such that thunk(bound-entity, call-args...) is expression-equivalent ([defns.expression.equivalent]) to invoke_r<R>(f, obj, call-args...).
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template<class T> function_ref& operator=(T) = delete;
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Constraints:
  • (21.1)
    T is not the same type as function_ref,
  • (21.2)
    is_pointer_v<T> is false, and
  • (21.3)
    T is not a specialization of nontype_t.