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1 // { dg-do compile { target c++17 } }
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2 // { dg-options "-fconcepts" }
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111
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3
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4 // Test that constraint satisfaction checks work even when
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5 // processing template declarations.
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6
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7 namespace std
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8 {
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9
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10 struct ostream { };
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11 ostream cout;
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12
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13 template<typename T>
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14 auto begin(T& t) -> decltype(t.begin()) { return t.begin(); }
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15
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16 template<typename T>
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17 auto begin(T const& t) -> decltype(t.begin()) { return t.begin(); }
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18
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19 template<typename T>
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20 auto end(T& t) -> decltype(t.end()) { return t.end(); }
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21
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22 template<typename T>
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23 auto end(T const& t) -> decltype(t.end()) { return t.end(); }
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24
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25 } // namespace std
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26
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27
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28 template <typename T>
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29 concept bool Float()
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30 {
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31 return __is_same_as( T, float );
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32 }
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33
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34 template <typename T>
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35 constexpr decltype(auto) project( T t )
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36 {
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37 return t;
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38 }
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39
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40 template <typename T>
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41 concept bool Concept()
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42 {
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43 return requires( T t ) {
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44 requires Float<decltype( project(t) )>();
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45 };
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46 }
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47
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48 template <Concept E, Concept F>
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49 constexpr decltype(auto) operator<<( E&& e, F&& f ) {}
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50
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51 template <Concept T>
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52 void foo( T t )
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53 {
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54 // Try to resolve operator<< from within a template context but
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55 // with non-dependent arguments. We need to ensure that template
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56 // processing is turned off whenever checking for satisfaction.
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57 std::cout << "OK"; // { dg-error "no match" }
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58 }
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59
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60
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61 template <typename R>
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62 concept bool Range()
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63 {
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64 return requires( R r ) {
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65 requires __is_same_as(
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66 decltype(std::begin(r)), decltype(std::end(r)) );
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67 };
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68 }
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69
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70 struct A
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71 {
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72 A() = default;
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73 A( const A& ) = default;
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74
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75 // Derivation from this class forces the instantiation of
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76 // this constructor, which results in the __is_same_as type
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77 // trait above to become error_mark_node in this declaration.
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78 template <Range R>
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79 explicit A( R&& r ) { }
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80 };
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81
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82 struct C : A
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83 {
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84 C() = default;
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85 C( const C& ) = default;
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86 };
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87
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88 int main()
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89 {
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90 C c; // OK
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91 return 0;
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92 }
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