| // C++26 P2686R4 - constexpr structured bindings |
| // { dg-do compile { target c++11 } } |
| // { dg-options "-fno-implicit-constexpr" } |
| |
| namespace std { |
| template <typename T> struct tuple_size; |
| template <int, typename> struct tuple_element; |
| } |
| |
| struct A { |
| int i, j; |
| template <int I> int &get () { return I == 1 ? j : i; } |
| }; |
| |
| template <> struct std::tuple_size <A> { static const int value = 3; }; |
| template <int I> struct std::tuple_element <I, A> { using type = int; }; |
| template <> struct std::tuple_size <const A> { static const int value = 3; }; |
| template <int I> struct std::tuple_element <I, const A> { using type = int; }; |
| |
| struct B { |
| int i, j; |
| long long k, l; |
| } a[3] = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 } }; // { dg-message "'a' was not declared 'constexpr'" "" } |
| |
| struct C { |
| int i, j; |
| template <int I> const int &get () const { return I == 1 ? j : i; } |
| }; |
| |
| template <> struct std::tuple_size <const C> { static const int value = 3; }; |
| template <int I> struct std::tuple_element <I, const C> { using type = const int; }; |
| |
| constexpr auto [ b, c, d ] = a; // { dg-warning "structured bindings only available with" "" { target c++14_down } } |
| // { dg-warning "structured binding declaration can be 'constexpr' only with" "" { target c++23_down } .-1 } |
| // { dg-error "the value of 'a' is not usable in a constant expression" "" { target *-*-* } .-2 } |
| #if __cpp_constinit >= 201907 |
| constinit auto [ e, f, g ] = a; // { dg-warning "'constinit' can be applied to structured binding only with" "" { target { c++20 && c++23_down } } } |
| // { dg-error "'constinit' variable '<structured bindings>' does not have a constant initializer" "" { target c++20 } .-1 } |
| // { dg-error "the value of 'a' is not usable in a constant expression" "" { target c++20 } .-2 } |
| #endif |
| constexpr auto [ h, i, j, k ] = a[1]; // { dg-warning "structured bindings only available with" "" { target c++14_down } } |
| // { dg-warning "structured binding declaration can be 'constexpr' only with" "" { target c++23_down } .-1 } |
| // { dg-error "the value of 'a' is not usable in a constant expression" "" { target *-*-* } .-2 } |
| #if __cpp_constinit >= 201907 |
| constinit auto [ l, m, n, o ] = a[2]; // { dg-warning "'constinit' can be applied to structured binding only with" "" { target { c++20 && c++23_down } } } |
| // { dg-error "'constinit' variable '<structured bindings>' does not have a constant initializer" "" { target c++20 } .-1 } |
| // { dg-error "the value of 'a' is not usable in a constant expression" "" { target c++20 } .-2 } |
| #endif |
| constexpr auto & [ p, q, r ] = a; // { dg-warning "structured bindings only available with" "" { target c++14_down } } |
| // { dg-warning "structured binding declaration can be 'constexpr' only with" "" { target c++23_down } .-1 } |
| #if __cpp_constinit >= 201907 |
| constinit auto & [ s, t, u ] = a; // { dg-warning "'constinit' can be applied to structured binding only with" "" { target { c++20 && c++23_down } } } |
| #endif |
| constexpr auto & [ v, w, x, y ] = a[1]; // { dg-warning "structured bindings only available with" "" { target c++14_down } } |
| // { dg-warning "structured binding declaration can be 'constexpr' only with" "" { target c++23_down } .-1 } |
| #if __cpp_constinit >= 201907 |
| constinit auto & [ aa, ab, ac, ad ] = a[2]; // { dg-warning "'constinit' can be applied to structured binding only with" "" { target { c++20 && c++23_down } } } |
| #endif |
| |
| A z = { 42, -42 }; // { dg-message "'z' was not declared 'constexpr'" "" } |
| constexpr auto [ ae, af, ag ] = z; // { dg-warning "structured bindings only available with" "" { target c++14_down } } |
| // { dg-warning "structured binding declaration can be 'constexpr' only with" "" { target c++23_down } .-1 } |
| // { dg-error "the value of 'z' is not usable in a constant expression" "" { target *-*-* } .-2 } |
| // { dg-error "passing 'const A' as 'this' argument discards qualifiers" "" { target *-*-* } .-3 } |
| // { dg-error "call to non-'constexpr' function 'int\\\& A::get\\\(\\\)" "" { target *-*-* } .-4 } |
| #if __cpp_constinit >= 201907 |
| constinit const auto [ ah, ai, aj ] = z; // { dg-warning "'constinit' can be applied to structured binding only with" "" { target { c++20 && c++23_down } } } |
| // { dg-error "'constinit' variable '<structured bindings>' does not have a constant initializer" "" { target c++20 } .-1 } |
| // { dg-error "the value of 'z' is not usable in a constant expression" "" { target c++20 } .-2 } |
| // { dg-error "passing 'const A' as 'this' argument discards qualifiers" "" { target c++20 } .-3 } |
| // { dg-error "call to non-'constexpr' function 'int\\\& A::get\\\(\\\)" "" { target c++20 } .-4 } |
| // { dg-error "'constinit' variable 'ah' does not have a constant initializer" "" { target c++20 } .-5 } |
| // { dg-error "'constinit' variable 'ai' does not have a constant initializer" "" { target c++20 } .-6 } |
| // { dg-error "'constinit' variable 'aj' does not have a constant initializer" "" { target c++20 } .-7 } |
| #endif |
| constexpr auto & [ ak, al, am ] = z; // { dg-warning "structured bindings only available with" "" { target c++14_down } } |
| // { dg-warning "structured binding declaration can be 'constexpr' only with" "" { target c++23_down } .-1 } |
| // { dg-error "call to non-'constexpr' function 'int\\\& A::get\\\(\\\)" "" { target *-*-* } .-2 } |
| #if __cpp_constinit >= 201907 |
| constinit auto & [ an, ao, ap ] = z; // { dg-warning "'constinit' can be applied to structured binding only with" "" { target { c++20 && c++23_down } } } |
| // { dg-error "'constinit' variable 'an' does not have a constant initializer" "" { target c++20 } .-1 } |
| // { dg-error "'constinit' variable 'ao' does not have a constant initializer" "" { target c++20 } .-2 } |
| // { dg-error "'constinit' variable 'ap' does not have a constant initializer" "" { target c++20 } .-3 } |
| // { dg-message "call to non-'constexpr' function 'int\\\& A::get\\\(\\\)" "" { target c++20 } .-4 } |
| #endif |
| |
| constexpr C zz = { 42, -42 }; |
| constexpr auto [ aq, ar, as ] = zz; // { dg-warning "structured bindings only available with" "" { target c++14_down } } |
| // { dg-warning "structured binding declaration can be 'constexpr' only with" "" { target c++23_down } .-1 } |
| // { dg-error "call to non-'constexpr' function 'const int\\\& C::get\\\(\\\) const" "" { target *-*-* } .-2 } |
| #if __cpp_constinit >= 201907 |
| constinit const auto [ at, au, av ] = zz; // { dg-warning "'constinit' can be applied to structured binding only with" "" { target { c++20 && c++23_down } } } |
| // { dg-error "call to non-'constexpr' function 'const int\\\& C::get\\\(\\\) const" "" { target c++20 } .-1 } |
| // { dg-error "'constinit' variable 'at' does not have a constant initializer" "" { target c++20 } .-2 } |
| // { dg-error "'constinit' variable 'au' does not have a constant initializer" "" { target c++20 } .-3 } |
| // { dg-error "'constinit' variable 'av' does not have a constant initializer" "" { target c++20 } .-4 } |
| #endif |
| constexpr auto & [ aw, ax, ay ] = zz; // { dg-warning "structured bindings only available with" "" { target c++14_down } } |
| // { dg-warning "structured binding declaration can be 'constexpr' only with" "" { target c++23_down } .-1 } |
| // { dg-error "call to non-'constexpr' function 'const int\\\& C::get\\\(\\\) const" "" { target *-*-* } .-2 } |
| #if __cpp_constinit >= 201907 |
| constinit auto & [ az, ba, bb ] = zz; // { dg-warning "'constinit' can be applied to structured binding only with" "" { target { c++20 && c++23_down } } } |
| // { dg-error "'constinit' variable 'az' does not have a constant initializer" "" { target c++20 } .-1 } |
| // { dg-error "'constinit' variable 'ba' does not have a constant initializer" "" { target c++20 } .-2 } |
| // { dg-error "'constinit' variable 'bb' does not have a constant initializer" "" { target c++20 } .-3 } |
| // { dg-message "call to non-'constexpr' function 'const int\\\& C::get\\\(\\\) const" "" { target c++20 } .-4 } |
| #endif |
| |
| void |
| foo () |
| { |
| #if __cpp_constinit >= 201907 |
| constexpr B a[3] = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 } }; |
| constinit auto [ b, c, d ] = a; // { dg-error "'constinit' can only be applied to a variable with static or thread storage duration" "" { target c++20 } } |
| constinit auto & [ e, f, g ] = a; // { dg-error "'constinit' can only be applied to a variable with static or thread storage duration" "" { target c++20 } } |
| constinit auto [ h, i, j, k ] = a[1]; // { dg-error "'constinit' can only be applied to a variable with static or thread storage duration" "" { target c++20 } } |
| constinit auto & [ l, m, n, o ] = a[2]; // { dg-error "'constinit' can only be applied to a variable with static or thread storage duration" "" { target c++20 } } |
| #endif |
| } |
