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145
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1 // { dg-do compile { target c++2a } }
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2
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3 // Tests constrained decltype(auto).
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4
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5 template<typename T>
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6 concept Type = true;
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7
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8 template<typename T>
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9 concept Int = __is_same_as(T, int);
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10
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11 template<typename T, typename U>
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12 concept SameAs = __is_same_as(T, U);
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13
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14 template<typename T, typename U>
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15 requires SameAs<T, U>
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16 constexpr bool check = true;
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17
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18 int z = 0;
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19 const int cz = 0;
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20
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21 Type decltype(auto) x1 = 0;
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22 static_assert(check<decltype(x1), int>);
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23 Type decltype(auto) x2 = z;
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24 static_assert(check<decltype(x2), int>);
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25 Type decltype(auto) x3 = (z);
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26 static_assert(check<decltype(x3), int&>);
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27 Type decltype(auto) x4 = cz;
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28 static_assert(check<decltype(x4), const int>);
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29 Type decltype(auto) x5 = (cz);
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30 static_assert(check<decltype(x5), const int&>);
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31
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32 Type decltype(auto) f1() { return 0; }
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33 static_assert(check<decltype(f1()), int>);
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34 Type decltype(auto) f2() { return z; }
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35 static_assert(check<decltype(f2()), int>);
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36 Type decltype(auto) f3() { return (z); }
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37 static_assert(check<decltype(f3()), int&>);
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38 Type decltype(auto) f4() { return cz; }
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39 static_assert(check<decltype(f4()), int>); // Top-level const is removed?
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40 Type decltype(auto) f5() { return (cz); }
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41 static_assert(check<decltype(f5()), const int&>);
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42
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43 bool b = true;
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44 const bool cb = true;
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45
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46 Int decltype(auto) b1 = true; // { dg-error "deduced initializer" }
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47 Int decltype(auto) b2 = (b); // { dg-error "deduced initializer" }
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48 Int decltype(auto) b3 = (cb); // { dg-error "deduced initializer" }
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49
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50 Int decltype(auto) g1() { } // { dg-error "deduced return type" }
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51 Int decltype(auto) g2() { return; } // { dg-error "deduced return type" }
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52 Int decltype(auto) g3() { return true; } // { dg-error "deduced return type" }
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53 int g4(Type decltype(auto) x) { return 0; } // { dg-error "cannot declare" }
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54 int g5(decltype(auto) x) { return 0; } // { dg-error "cannot declare" }
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55
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56 template<Type decltype(auto) X, typename T>
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57 requires SameAs<decltype(X), T>
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58 constexpr bool deduced_as = true;
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59
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60 constexpr int Z = 10;
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61
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62 static_assert(deduced_as<0, int>);
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63 static_assert(deduced_as<0, int&>); // { dg-error "invalid variable template" }
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64 static_assert(deduced_as<Z, const int>);
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65 static_assert(deduced_as<(Z), const int>); // { dg-error "invalid variable template" }
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66 static_assert(deduced_as<(Z), const int&>);
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67
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