1 // { dg-do compile { target c++20 } }
2
3 // Tests constrained decltype(auto).
4
5 template<typename T>
6 concept Type = true;
7
8 template<typename T>
9 concept Int = __is_same_as(T, int);
10
11 template<typename T, typename U>
12 concept SameAs = __is_same_as(T, U);
13
14 template<typename T, typename U>
15 requires SameAs<T, U>
16 constexpr bool check = true;
17
18 int z = 0;
19 const int cz = 0;
20
21 Type decltype(auto) x1 = 0;
22 static_assert(check<decltype(x1), int>);
23 Type decltype(auto) x2 = z;
24 static_assert(check<decltype(x2), int>);
25 Type decltype(auto) x3 = (z);
26 static_assert(check<decltype(x3), int&>);
27 Type decltype(auto) x4 = cz;
28 static_assert(check<decltype(x4), const int>);
29 Type decltype(auto) x5 = (cz);
30 static_assert(check<decltype(x5), const int&>);
31
decltype(auto)32 Type decltype(auto) f1() { return 0; }
33 static_assert(check<decltype(f1()), int>);
decltype(auto)34 Type decltype(auto) f2() { return z; }
35 static_assert(check<decltype(f2()), int>);
decltype(auto)36 Type decltype(auto) f3() { return (z); }
37 static_assert(check<decltype(f3()), int&>);
decltype(auto)38 Type decltype(auto) f4() { return cz; }
39 static_assert(check<decltype(f4()), int>); // Top-level const is removed?
decltype(auto)40 Type decltype(auto) f5() { return (cz); }
41 static_assert(check<decltype(f5()), const int&>);
42
43 bool b = true;
44 const bool cb = true;
45
46 Int decltype(auto) b1 = true; // { dg-error "deduced initializer" }
47 Int decltype(auto) b2 = (b); // { dg-error "deduced initializer" }
48 Int decltype(auto) b3 = (cb); // { dg-error "deduced initializer" }
49
decltype(auto)50 Int decltype(auto) g1() { } // { dg-error "deduced return type" }
decltype(auto)51 Int decltype(auto) g2() { return; } // { dg-error "deduced return type" }
decltype(auto)52 Int decltype(auto) g3() { return true; } // { dg-error "deduced return type" }
g4(Type decltype (auto)x)53 int g4(Type decltype(auto) x) { return 0; } // { dg-error "cannot declare" }
g5(decltype (auto)x)54 int g5(decltype(auto) x) { return 0; } // { dg-error "cannot declare" }
55
56 template<Type decltype(auto) X, typename T>
57 requires SameAs<decltype(X), T>
58 constexpr bool deduced_as = true;
59
60 constexpr int Z = 10;
61
62 static_assert(deduced_as<0, int>);
63 static_assert(deduced_as<0, int&>); // { dg-error "invalid variable template" }
64 static_assert(deduced_as<Z, int>);
65 static_assert(deduced_as<(Z), const int>); // { dg-error "invalid variable template" }
66 static_assert(deduced_as<(Z), const int&>);
67
68