[libcxx-commits] [libcxx] [libc++] P1789R3: Library Support for Expansion Statements (PR #167184)

[Matthias Wippich via libcxx-commits]

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@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+
+// <utility>
+
+// template<size_t I, class T, T... Values>
+//   struct tuple_element<I, integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+//   struct tuple_element<I, const integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+//   constexpr T get(integer_sequence<T, Values...>) noexcept;
+
+// Expect failures for tuple_element and get with empty integer_sequence
+
+#include <utility>
+
+void f() {
+  // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (std::integer_sequence)}}
+  using test1 = std::tuple_element_t<0, std::integer_sequence<int>>;
+  // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (const std::integer_sequence)}}
+  using test2 = std::tuple_element_t<0, const std::integer_sequence<int>>;
+
+  auto empty = std::integer_sequence<int>();
+  // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::get<> (std::integer_sequence)}}
+  // expected-error-re@*:* {{invalid index 0 for pack {{.*}} of size 0}}
+  (void)std::get<0>(empty);
----------------
Tsche wrote:

I think naming it `empty` makes it more obvious why `get` is expected to fail. It reads more naturally than `std::get<0>(_)` imo.

https://github.com/llvm/llvm-project/pull/167184