cxx1y-deduced-return-type.cpp revision 25d8c856681120581315edcdb48257c99af6b45c
1// RUN: %clang_cc1 -std=c++1y -verify -fsyntax-only %s 2 3auto f(); // expected-note {{previous}} 4int f(); // expected-error {{differ only in their return type}} 5 6auto &g(); 7auto g() -> auto &; 8 9auto h() -> auto *; 10auto *h(); 11 12struct Conv1 { 13 operator auto(); // expected-note {{declared here}} 14} conv1; 15int conv1a = conv1; // expected-error {{function 'operator auto' with deduced return type cannot be used before it is defined}} 16// expected-error@-1 {{no viable conversion}} 17Conv1::operator auto() { return 123; } 18int conv1b = conv1; 19int conv1c = conv1.operator auto(); 20int conv1d = conv1.operator int(); // expected-error {{no member named 'operator int'}} 21 22struct Conv2 { 23 operator auto() { return 0; } // expected-note 2{{previous}} 24 operator auto() { return 0.; } // expected-error {{cannot be redeclared}} expected-error {{redefinition of 'operator auto'}} 25}; 26 27struct Conv3 { 28 operator auto() { int *p = nullptr; return p; } // expected-note {{candidate}} 29 operator auto*() { int *p = nullptr; return p; } // expected-note {{candidate}} 30} conv3; 31int *conv3a = conv3; // expected-error {{ambiguous}} 32int *conv3b = conv3.operator auto(); 33int *conv3c = conv3.operator auto*(); 34 35template<typename T> 36struct Conv4 { 37 operator auto() { return T(); } 38}; 39Conv4<int> conv4int; 40int conv4a = conv4int; 41int conv4b = conv4int.operator auto(); 42 43auto a(); 44auto a() { return 0; } 45using T = decltype(a()); 46using T = int; 47auto a(); // expected-note {{previous}} 48using T = decltype(a()); 49auto *a(); // expected-error {{differ only in their return type}} 50 51auto b(bool k) { 52 if (k) 53 return "hello"; 54 return "goodbye"; 55} 56 57auto *ptr_1() { 58 return 100; // expected-error {{cannot deduce return type 'auto *' from returned value of type 'int'}} 59} 60 61const auto &ref_1() { 62 return 0; // expected-warning {{returning reference to local temporary}} 63} 64 65auto init_list() { 66 return { 1, 2, 3 }; // expected-error {{cannot deduce return type from initializer list}} 67} 68 69auto fwd_decl(); // expected-note 2{{here}} 70 71int n = fwd_decl(); // expected-error {{function 'fwd_decl' with deduced return type cannot be used before it is defined}} 72int k = sizeof(fwd_decl()); // expected-error {{used before it is defined}} 73 74auto fac(int n) { 75 if (n <= 2) 76 return n; 77 return n * fac(n-1); // ok 78} 79 80auto fac_2(int n) { // expected-note {{declared here}} 81 if (n > 2) 82 return n * fac_2(n-1); // expected-error {{cannot be used before it is defined}} 83 return n; 84} 85 86auto void_ret() {} 87using Void = void; 88using Void = decltype(void_ret()); 89 90auto &void_ret_2() {} // expected-error {{cannot deduce return type 'auto &' for function with no return statements}} 91const auto void_ret_3() {} // ok, return type 'const void' is adjusted to 'void' 92 93const auto void_ret_4() { 94 if (false) 95 return void(); 96 if (false) 97 return; 98 return 0; // expected-error {{'auto' in return type deduced as 'int' here but deduced as 'void' in earlier return statement}} 99} 100 101namespace Templates { 102 template<typename T> auto f1() { 103 return T() + 1; 104 } 105 template<typename T> auto &f2(T &&v) { return v; } 106 int a = f1<int>(); 107 const int &b = f2(0); 108 double d; 109 float &c = f2(0.0); // expected-error {{non-const lvalue reference to type 'float' cannot bind to a value of unrelated type 'double'}} 110 111 template<typename T> auto fwd_decl(); // expected-note {{declared here}} 112 int e = fwd_decl<int>(); // expected-error {{cannot be used before it is defined}} 113 template<typename T> auto fwd_decl() { return 0; } 114 int f = fwd_decl<int>(); 115 template<typename T> auto fwd_decl(); 116 int g = fwd_decl<char>(); 117 118 auto (*p)() = f1; // expected-error {{incompatible initializer}} 119 auto (*q)() = f1<int>; // ok 120 121 typedef decltype(f2(1.2)) dbl; // expected-note {{previous}} 122 typedef float dbl; // expected-error {{typedef redefinition with different types ('float' vs 'decltype(f2(1.2))' (aka 'double &'))}} 123 124 extern template auto fwd_decl<double>(); 125 int k1 = fwd_decl<double>(); 126 extern template int fwd_decl<char>(); // expected-error {{does not refer to a function template}} 127 int k2 = fwd_decl<char>(); 128 129 template<typename T> auto instantiate() { T::error; } // expected-error {{has no members}} 130 extern template auto instantiate<int>(); // ok 131 int k = instantiate<int>(); // expected-note {{in instantiation of}} 132 template<> auto instantiate<char>() {} // ok 133 template<> void instantiate<double>() {} // expected-error {{no function template matches}} 134 135 template<typename T> auto arg_single() { return 0; } 136 template<typename T> auto arg_multi() { return 0l; } 137 template<typename T> auto arg_multi(int) { return "bad"; } 138 template<typename T> struct Outer { 139 static auto arg_single() { return 0.f; } 140 static auto arg_multi() { return 0.; } 141 static auto arg_multi(int) { return "bad"; } 142 }; 143 template<typename T> T &take_fn(T (*p)()); 144 145 int &check1 = take_fn(arg_single); // expected-error {{no matching}} expected-note@-2 {{couldn't infer}} 146 int &check2 = take_fn(arg_single<int>); 147 int &check3 = take_fn<int>(arg_single); // expected-error {{no matching}} expected-note@-4{{no overload of 'arg_single'}} 148 int &check4 = take_fn<int>(arg_single<int>); 149 long &check5 = take_fn(arg_multi); // expected-error {{no matching}} expected-note@-6 {{couldn't infer}} 150 long &check6 = take_fn(arg_multi<int>); 151 long &check7 = take_fn<long>(arg_multi); // expected-error {{no matching}} expected-note@-8{{no overload of 'arg_multi'}} 152 long &check8 = take_fn<long>(arg_multi<int>); 153 154 float &mem_check1 = take_fn(Outer<int>::arg_single); 155 float &mem_check2 = take_fn<float>(Outer<char>::arg_single); 156 double &mem_check3 = take_fn(Outer<long>::arg_multi); 157 double &mem_check4 = take_fn<double>(Outer<double>::arg_multi); 158 159 namespace Deduce1 { 160 template<typename T> auto f() { return 0; } // expected-note {{candidate}} 161 template<typename T> void g(T(*)()); // expected-note 2{{candidate}} 162 void h() { 163 auto p = f<int>; 164 auto (*q)() = f<int>; 165 int (*r)() = f; // expected-error {{does not match}} 166 g(f<int>); 167 g<int>(f); // expected-error {{no matching function}} 168 g(f); // expected-error {{no matching function}} 169 } 170 } 171 172 namespace Deduce2 { 173 template<typename T> auto f(int) { return 0; } // expected-note {{candidate}} 174 template<typename T> void g(T(*)(int)); // expected-note 2{{candidate}} 175 void h() { 176 auto p = f<int>; 177 auto (*q)(int) = f<int>; 178 int (*r)(int) = f; // expected-error {{does not match}} 179 g(f<int>); 180 g<int>(f); // expected-error {{no matching function}} 181 g(f); // expected-error {{no matching function}} 182 } 183 } 184 185 namespace Deduce3 { 186 template<typename T> auto f(T) { return 0; } 187 template<typename T> void g(T(*)(int)); // expected-note {{couldn't infer}} 188 void h() { 189 auto p = f<int>; 190 auto (*q)(int) = f<int>; 191 int (*r)(int) = f; // ok 192 g(f<int>); 193 g<int>(f); // ok 194 g(f); // expected-error {{no matching function}} 195 } 196 } 197 198 namespace DeduceInDeducedReturnType { 199 template<typename T, typename U> auto f() -> auto (T::*)(U) { 200 int (T::*result)(U) = nullptr; 201 return result; 202 } 203 struct S {}; 204 int (S::*(*p)())(double) = f; 205 int (S::*(*q)())(double) = f<S, double>; 206 } 207} 208 209auto fwd_decl_using(); 210namespace N { using ::fwd_decl_using; } 211auto fwd_decl_using() { return 0; } 212namespace N { int k = N::fwd_decl_using(); } 213 214namespace OverloadResolutionNonTemplate { 215 auto f(); 216 auto f(int); // expected-note {{here}} 217 218 int &g(int (*f)()); // expected-note {{not viable: no overload of 'f' matching 'int (*)()'}} 219 char &g(int (*f)(int)); // expected-note {{not viable: no overload of 'f' matching 'int (*)(int)'}} 220 221 int a = g(f); // expected-error {{no matching function}} 222 223 auto f() { return 0; } 224 225 // FIXME: It's not completely clear whether this should be ill-formed. 226 int &b = g(f); // expected-error {{used before it is defined}} 227 228 auto f(int) { return 0.0; } 229 230 int &c = g(f); // ok 231} 232 233namespace OverloadResolutionTemplate { 234 auto f(); 235 template<typename T> auto f(T); 236 237 int &g(int (*f)()); // expected-note {{not viable: no overload of 'f' matching 'int (*)()'}} expected-note {{candidate}} 238 char &g(int (*f)(int)); // expected-note {{not viable: no overload of 'f' matching 'int (*)(int)'}} expected-note {{candidate}} 239 240 int a = g(f); // expected-error {{no matching function}} 241 242 auto f() { return 0; } 243 244 int &b = g(f); // ok (presumably), due to deduction failure forming type of 'f<int>' 245 246 template<typename T> auto f(T) { return 0; } 247 248 int &c = g(f); // expected-error {{ambiguous}} 249} 250 251namespace DefaultedMethods { 252 struct A { 253 auto operator=(const A&) = default; // expected-error {{must return 'DefaultedMethods::A &'}} 254 A &operator=(A&&); // expected-note {{previous}} 255 }; 256 auto A::operator=(A&&) = default; // expected-error {{differs from the declaration in the return type}} 257} 258 259namespace Constexpr { 260 constexpr auto f1(int n) { return n; } 261 struct NonLiteral { ~NonLiteral(); } nl; // expected-note {{user-provided destructor}} 262 constexpr auto f2(int n) { return nl; } // expected-error {{return type 'Constexpr::NonLiteral' is not a literal type}} 263} 264 265// It's not really clear whether these are valid, but this matches g++. 266using size_t = decltype(sizeof(0)); 267auto operator new(size_t n, const char*); // expected-error {{must return type 'void *'}} 268auto operator delete(void *, const char*); // expected-error {{must return type 'void'}} 269 270namespace Virtual { 271 struct S { 272 virtual auto f() { return 0; } // expected-error {{function with deduced return type cannot be virtual}} expected-note {{here}} 273 }; 274 // Allow 'auto' anyway for error recovery. 275 struct T : S { 276 int f(); 277 }; 278 struct U : S { 279 auto f(); // expected-error {{different return}} 280 }; 281 282 // And here's why... 283 struct V { virtual auto f(); }; // expected-error {{cannot be virtual}} 284 struct W : V { virtual auto f(); }; // expected-error {{cannot be virtual}} 285 auto V::f() { return 0; } // in tu1.cpp 286 auto W::f() { return 0.0; } // in tu2.cpp 287 W w; 288 int k1 = w.f(); 289 int k2 = ((V&)w).f(); 290} 291 292namespace std_examples { 293 294namespace NoReturn { 295 auto f() {} 296 void (*p)() = &f; 297 298 auto f(); // ok 299 300 auto *g() {} // expected-error {{cannot deduce return type 'auto *' for function with no return statements}} 301 302 auto h() = delete; // expected-note {{explicitly deleted}} 303 auto x = h(); // expected-error {{call to deleted}} 304} 305 306namespace UseBeforeComplete { 307 auto n = n; // expected-error {{variable 'n' declared with 'auto' type cannot appear in its own initializer}} 308 auto f(); // expected-note {{declared here}} 309 void g() { &f; } // expected-error {{function 'f' with deduced return type cannot be used before it is defined}} 310 auto sum(int i) { 311 if (i == 1) 312 return i; 313 else 314 return sum(i - 1) + i; 315 } 316} 317 318namespace Redecl { 319 auto f(); 320 auto f() { return 42; } 321 auto f(); // expected-note 2{{previous}} 322 int f(); // expected-error {{functions that differ only in their return type cannot be overloaded}} 323 decltype(auto) f(); // expected-error {{cannot be overloaded}} 324 325 template<typename T> auto g(T t) { return t; } // expected-note {{candidate}} 326 template auto g(int); 327 template char g(char); // expected-error {{does not refer to a function}} 328 template<> auto g(double); 329 330 template<typename T> T g(T t) { return t; } // expected-note {{candidate}} 331 template char g(char); 332 template auto g(float); 333 334 void h() { return g(42); } // expected-error {{ambiguous}} 335} 336 337namespace ExplicitInstantiationDecl { 338 template<typename T> auto f(T t) { return t; } 339 extern template auto f(int); 340 int (*p)(int) = f; 341} 342 343} 344