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1 // PR c++/69066
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2 // { dg-do compile { target c++14 } }
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3
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4 template <typename T> T&& declval();
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5
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6 template<typename T, T v>
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7 struct integral_constant
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8 {
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9 static constexpr T value = v;
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10 typedef T value_type;
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11 typedef integral_constant<T, v> type;
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12 constexpr operator value_type() const { return value; }
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13 };
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14
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15 typedef integral_constant<bool, true> true_type;
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16 typedef integral_constant<bool, false> false_type;
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17
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18 template <typename...>
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19 using void_t = void;
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20
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21 template <typename, typename = void>
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22 class is_zero_callable : public false_type
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23 {
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24 };
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25
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26 template <typename T>
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27 class is_zero_callable<T, void_t<decltype(declval<T>()())>>
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28 : public true_type
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29 {
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30 };
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31
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32 template <typename TF, bool TLastStep>
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33 struct curry_impl
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34 {
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35 static auto exec(TF f)
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36 {
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37 // Bind `x` to subsequent calls.
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38 return [=](auto x)
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39 {
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40 auto bound_f = [=](auto... xs) -> decltype(f(x, xs...))
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41 {
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42 return f(x, xs...);
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43 };
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44
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45 // Recursive step.
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46 return curry_impl<decltype(bound_f),
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47 is_zero_callable<decltype(bound_f)>{}>::exec(bound_f);
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48 };
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49 }
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50 };
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51
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52 template <typename TF>
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53 struct curry_impl<TF, true>
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54 {
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55 static auto exec(TF f)
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56 {
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57 return f();
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58 }
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59 };
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60
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61 template <typename TF>
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62 auto curry(TF f)
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63 {
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64 return curry_impl<TF, is_zero_callable<decltype(f)>{}>::exec(f);
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65 }
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66
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67 int main()
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68 {
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69 auto sum = [](int x, int y)
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70 {
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71 return x + y;
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72 };
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73
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74 (void)curry(sum)(1)(1);
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75 }
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