// RUN: %clang_cc1 -std=c++17 -Wc++20-extensions -verify=expected %s
// RUN: %clang_cc1 -std=c++20 -Wpre-c++20-compat -verify=expected %s
// RUN: %clang_cc1 -std=c++20 -Wpre-c++20-compat -fexperimental-new-constant-interpreter -verify=expected %s
void use_from_own_init() {
auto [a] = a; // expected-error {{binding 'a' cannot appear in the initializer of its own decomposition declaration}}
}
void num_elems() {
struct A0 {} a0;
int a1[1], a2[2];
auto [] = a0; // expected-warning {{does not allow a decomposition group to be empty}}
auto [v1] = a0; // expected-error {{type 'struct A0' decomposes into 0 elements, but 1 name was provided}}
auto [] = a1; // expected-error {{type 'int[1]' decomposes into 1 element, but no names were provided}} expected-warning {{empty}}
auto [v2] = a1;
auto [v3, v4] = a1; // expected-error {{type 'int[1]' decomposes into 1 element, but 2 names were provided}}
auto [] = a2; // expected-error {{type 'int[2]' decomposes into 2 elements, but no names were provided}} expected-warning {{empty}}
auto [v5] = a2; // expected-error {{type 'int[2]' decomposes into 2 elements, but only 1 name was provided}}
auto [v6, v7] = a2;
auto [v8, v9, v10] = a2; // expected-error {{type 'int[2]' decomposes into 2 elements, but 3 names were provided}}
}
// As a Clang extension, _Complex can be decomposed.
float decompose_complex(_Complex float cf) {
static _Complex float scf;
auto &[sre, sim] = scf;
// ok, this is references initialized by constant expressions all the way down
static_assert(&sre == &__real scf);
static_assert(&sim == &__imag scf);
auto [re, im] = cf;
return re*re + im*im;
}
// As a Clang extension, vector types can be decomposed.
typedef float vf3 __attribute__((ext_vector_type(3)));
float decompose_vector(vf3 v) {
auto [x, y, z] = v;
auto *p = &x; // expected-error {{address of vector element requested}}
return x + y + z;
}
struct S { int a, b; };
constexpr int f(S s) {
auto &[a, b] = s;
return a * 10 + b;
}
static_assert(f({1, 2}) == 12);
constexpr bool g(S &&s) {
auto &[a, b] = s;
return &a == &s.a && &b == &s.b && &a != &b;
}
static_assert(g({1, 2}));
struct S1 {
int a, b;
};
struct S2 {
int a : 1; // expected-note 2{{bit-field is declared here}}
int b;
};
auto [outer1, outer2] = S1{1, 2};
auto [outerbit1, outerbit2] = S1{1, 2}; // expected-note {{declared here}}
void enclosing() {
struct S { int a = outer1; };
auto [n] = S(); // expected-note 3{{'n' declared here}}
struct Q {
int f() { return n; } // expected-error {{reference to local binding 'n' declared in enclosing function 'enclosing'}}
};
(void)[&] { return n; }; // expected-warning {{C++20}}
(void)[n] { return n; }; // expected-warning {{C++20}}
static auto [m] = S(); // expected-note {{'m' declared here}} \
// expected-warning {{C++20}}
struct R { int f() { return m; } };
(void) [&] { return m; };
(void)[m]{}; // expected-error {{'m' cannot be captured because it does not have automatic storage duration}}
(void)[outerbit1]{}; // expected-error {{'outerbit1' cannot be captured because it does not have automatic storage duration}}
auto [bit, var] = S2{-1, 1}; // expected-note 2{{'bit' declared here}}
(void)[&bit] { // expected-error {{non-const reference cannot bind to bit-field 'a'}} \
// expected-warning {{C++20}}
return bit;
};
union { // expected-note {{declared here}}
int u;
};
(void)[&] { return bit + u; } // expected-error {{unnamed variable cannot be implicitly captured in a lambda expression}} \
// expected-error {{non-const reference cannot bind to bit-field 'a'}} \
// expected-warning {{C++20}}
();
}
void bitfield() {
struct { int a : 3, : 4, b : 5; } a;
auto &[x, y] = a;
auto &[p, q, r] = a; // expected-error-re {{type 'struct (unnamed struct at {{.*}})' decomposes into 2 elements, but 3 names were provided}}
}
void for_range() {
int x = 1;
for (auto[a, b] : x) { // expected-error {{invalid range expression of type 'int'; no viable 'begin' function available}}
a++;
}
int y[5];
for (auto[c] : y) { // expected-error {{cannot decompose non-class, non-array type 'int'}}
c++;
}
}
int error_recovery() {
auto [foobar]; // expected-error {{requires an initializer}}
return foobar_; // expected-error {{undeclared identifier 'foobar_'}}
}
// PR32172
template <class T> void dependent_foreach(T t) {
for (auto [a,b,c] : t)
a,b,c;
}
struct PR37352 {
int n;
void f() { static auto [a] = *this; } // expected-warning {{C++20}}
};
namespace instantiate_template {
template <typename T1, typename T2>
struct pair {
T1 a;
T2 b;
};
const pair<int, int> &f1();
int f2() {
const auto &[a, b] = f1();
return a + b;
}
} // namespace instantiate_template
namespace lambdas {
void f() {
int n;
auto [a] = // expected-error {{cannot decompose lambda closure type}}
[n] {}; // expected-note {{lambda expression}}
}
auto [] = []{}; // expected-warning {{ISO C++17 does not allow a decomposition group to be empty}}
int g() {
int n = 0;
auto a = [=](auto &self) { // expected-note {{lambda expression}}
auto &[capture] = self; // expected-error {{cannot decompose lambda closure type}}
++capture;
return n;
};
return a(a); // expected-note {{in instantiation of}}
}
int h() {
auto x = [] {};
struct A : decltype(x) {
int n;
};
auto &&[r] = A{x, 0}; // OK (presumably), non-capturing lambda has no non-static data members
return r;
}
int i() {
int n;
auto x = [n] {};
struct A : decltype(x) {
int n;
};
auto &&[r] = A{x, 0}; // expected-error-re {{cannot decompose class type 'A': both it and its base class 'decltype(x)' (aka '(lambda {{.*}})') have non-static data members}}
return r;
}
void j() {
auto x = [] {};
struct A : decltype(x) {};
auto &&[] = A{x}; // expected-warning {{ISO C++17 does not allow a decomposition group to be empty}}
}
}
namespace by_value_array_copy {
struct explicit_copy {
explicit_copy() = default; // expected-note 2{{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
explicit explicit_copy(const explicit_copy&) = default; // expected-note 2{{explicit constructor is not a candidate}}
};
constexpr int direct_initialization_for_elements() {
explicit_copy ec_arr[2];
auto [a1, b1](ec_arr);
int arr[3]{1, 2, 3};
auto [a2, b2, c2](arr);
arr[0]--;
return a2 + b2 + c2 + arr[0];
}
static_assert(direct_initialization_for_elements() == 6);
constexpr int copy_initialization_for_elements() {
int arr[2]{4, 5};
auto [a1, b1] = arr;
auto [a2, b2]{arr}; // GH31813
arr[0] = 0;
return a1 + b1 + a2 + b2 + arr[0];
}
static_assert(copy_initialization_for_elements() == 18);
void copy_initialization_for_elements_with_explicit_copy_ctor() {
explicit_copy ec_arr[2];
auto [a1, b1] = ec_arr; // expected-error {{no matching constructor for initialization of 'explicit_copy[2]'}}
auto [a2, b2]{ec_arr}; // expected-error {{no matching constructor for initialization of 'explicit_copy[2]'}}
// Test prvalue
using T = explicit_copy[2];
auto [a3, b3] = T{};
auto [a4, b4]{T{}};
}
} // namespace by_value_array_copy
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