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1 // PR c++/82565
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2 // { dg-do compile { target c++2a } }
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3
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4 struct string
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5 {
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6 string();
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7 string(const char *);
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8 bool empty() const;
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9 };
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10
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11 template<class From, class To>
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12 concept convertible_to = requires(From (&f)(), void (&g)(To)) { g(f()); };
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13
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14 template<typename T, typename ReturnType>
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15 concept Concept =
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16 requires(T t, const string& s) {
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17 { t(s) } -> convertible_to<ReturnType>;
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18 };
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19
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20 struct test {
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21 string _str;
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22
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23 template<typename Visitor>
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24 requires Concept<Visitor, bool>
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25 decltype(auto) visit(Visitor&& visitor) const {
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26 return visitor(_str);
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27 }
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28
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29 };
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30
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31 int main() {
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32 test().visit([] (auto& x) { return x.empty(); });
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33 }
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