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]

22.10.17.6.5 Deduction guides [func.wrap.ref.deduct]

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template<class F> function_ref(F*) -> function_ref<F>;
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Constraints: is_function_v<F> is true.
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template<auto c, class F0> function_ref(constant_wrapper<c, F0>) -> function_ref<see below>;
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Let F be remove_pointer_t<F0>.
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Constraints: is_function_v<F> is true.
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Remarks: The deduced type is function_ref<F>.
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template<auto c, class F, class T> function_ref(constant_wrapper<c, F>, T&&) -> function_ref<see below>;
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Constraints:
  • (5.1)
    F is of the form R(G​::​*)(A...) cv & noexcept(E) for a type G, or
  • (5.2)
    F is of the form M 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, and E be true, or
  • (5.3)
    F is of the form R(*)(G, A...) noexcept(E) for a type G.
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Remarks: The deduced type is function_ref<R(A...) noexcept(E)>.