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1 // { dg-do compile { target c++2a } }
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2 // { dg-additional-options "-fconcepts-ts" }
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3
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4 #include <type_traits>
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5
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6 inline constexpr bool and_impl() { return true; }
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7
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8 template <class OperandFirst, class... OperandsRest>
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9 constexpr bool and_impl(OperandFirst operand_first,
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10 OperandsRest... operands_rest) {
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11 return operand_first && and_impl(operands_rest...);
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12 }
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13
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14 template <class... Operands> constexpr bool and_(Operands... operands) {
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15 return and_impl(operands...);
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16 }
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17
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18 template <class X> concept bool C() { return true; }
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19
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20 // v1
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21 template<int, class... Xs>
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22 requires and_(C<Xs>()...)
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23 constexpr int f(const Xs&... xs) {
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24 return 0;
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25 }
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26
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27 // v2
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28 template<int, class... Xs>
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29 constexpr int f(const Xs&... xs) {
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30 return 1;
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31 }
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32
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33 int main() {
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34 static_assert(f<10>(3.0, 2.0f) == 0);
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35 return 0;
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36 }
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37
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38 // 2nd example
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39
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40 template <typename T, typename... Us>
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41 concept bool AreType() {
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42 return (std::is_same<T,Us>::value && ...);
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43 // return true; gives the same overloaded error
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44 }
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45
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46 // Function with constraint
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47 template<typename T, AreType<T>... Us>
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48 constexpr bool isValid(Us... us) {
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49 return true;
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50 }
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51
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52 // Function with no constraint
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53 template<typename T, typename... U>
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54 constexpr bool isValid(U... u) {
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55 return false;
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56 }
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57
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58 int main2() {
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59 static_assert(isValid<int>(1)); // also isValid<int>(1, 2, 3); etc
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60 return 0;
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61 }
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