absl::FunctionRef<R const(Args...)>::FunctionRef

template<
    auto F,
    typename Obj,
    typename = EnableIfCompatible<decltype(F), std::remove_reference_t<Obj>&>,
    absl::functional_internal::EnableIf<! std::is_rvalue_reference_v<Obj &&>> = 0>
FunctionRef(
    nontype_t<F> arg,
    Obj&& obj) noexcept;