{"id":2221265,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2221265/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260409024128.421442-4-mfwippich@gmail.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/1.1/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null},"msgid":"<20260409024128.421442-4-mfwippich@gmail.com>","date":"2026-04-09T02:41:31","name":"[v2] libstdc++: Implement structured binding support for integer_sequence","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"8759f215622fb5a25a8eae6a2b7e415621c80fda","submitter":{"id":93063,"url":"http://patchwork.ozlabs.org/api/1.1/people/93063/?format=json","name":"Matthias Wippich","email":"mfwippich@gmail.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/20260409024128.421442-4-mfwippich@gmail.com/mbox/","series":[{"id":499231,"url":"http://patchwork.ozlabs.org/api/1.1/series/499231/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=499231","date":"2026-04-09T02:41:31","name":"[v2] libstdc++: Implement structured binding support for integer_sequence","version":2,"mbox":"http://patchwork.ozlabs.org/series/499231/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2221265/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2221265/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com 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Statements.\nhttps://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p1789r3.pdf\n\nCorresponding C++ draft commit: 3d71a838ed2a1689dd329f964ec4d58152487151\nFeature-test macro integer_sequence has been bumped to 202511L.\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/bits/utility.h:\n Implement structured bindings protocol for std::integer_sequence.\n\t* include/bits/version.def: Bump integer_sequence feature-test macro.\n\t* include/bits/version.h: Regenerate.\n\t* testsuite/20_util/integer_sequence/tuple_access.cc: New test.\n\t* testsuite/20_util/integer_sequence/tuple_access_neg.cc: New test.\n\nCo-authored-by: Ivan Lazaric \nSigned-off-by: Matthias Wippich \n---\n libstdc++-v3/include/bits/utility.h | 30 ++++++\n libstdc++-v3/include/bits/version.def | 5 +\n libstdc++-v3/include/bits/version.h | 7 +-\n .../20_util/integer_sequence/tuple_access.cc | 96 +++++++++++++++++++\n .../integer_sequence/tuple_access_neg.cc | 21 ++++\n 5 files changed, 158 insertions(+), 1 deletion(-)\n create mode 100644 libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n create mode 100644 libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc","diff":"diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h\nindex 93e9e9f9dba..363aed478c5 100644\n--- a/libstdc++-v3/include/bits/utility.h\n+++ b/libstdc++-v3/include/bits/utility.h\n@@ -481,6 +481,36 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n static constexpr size_t size() noexcept { return sizeof...(_Idx); }\n };\n \n+#if __glibcxx_integer_sequence >= 202511L // C++ >= 26\n+\n+ /// Structured binding support\n+ template\n+ struct tuple_size>\n+ : integral_constant { };\n+\n+ template\n+ struct tuple_element<__i, integer_sequence<_Tp, _Idx...>>\n+ {\n+ static_assert(__i < sizeof...(_Idx));\n+ using type = _Tp;\n+ };\n+\n+ template\n+ struct tuple_element<__i, const integer_sequence<_Tp, _Idx...>>\n+ {\n+ static_assert(__i < sizeof...(_Idx));\n+ using type = _Tp;\n+ };\n+\n+ template\n+ constexpr _Tp\n+ get (integer_sequence<_Tp, _Idx...>) noexcept\n+ {\n+ static_assert(__i < sizeof...(_Idx));\n+ return _Idx...[__i];\n+ }\n+#endif // __glibcxx_integer_sequence >= 202511L\n+\n /// Alias template make_integer_sequence\n template\n using make_integer_sequence\ndiff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def\nindex cfb90533ce4..8db3c1d2df3 100644\n--- a/libstdc++-v3/include/bits/version.def\n+++ b/libstdc++-v3/include/bits/version.def\n@@ -184,6 +184,11 @@ ftms = {\n \n ftms = {\n name = integer_sequence;\n+ values = {\n+ v = 202511;\n+ cxxmin = 26;\n+ extra_cond = \"__cpp_pack_indexing\";\n+ };\n values = {\n v = 201304;\n cxxmin = 14;\ndiff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h\nindex 22dd31b9d32..455d7190e90 100644\n--- a/libstdc++-v3/include/bits/version.h\n+++ b/libstdc++-v3/include/bits/version.h\n@@ -186,7 +186,12 @@\n #undef __glibcxx_want_exchange_function\n \n #if !defined(__cpp_lib_integer_sequence)\n-# if (__cplusplus >= 201402L)\n+# if (__cplusplus > 202302L) && (__cpp_pack_indexing)\n+# define __glibcxx_integer_sequence 202511L\n+# if defined(__glibcxx_want_all) || defined(__glibcxx_want_integer_sequence)\n+# define __cpp_lib_integer_sequence 202511L\n+# endif\n+# elif (__cplusplus >= 201402L)\n # define __glibcxx_integer_sequence 201304L\n # if defined(__glibcxx_want_all) || defined(__glibcxx_want_integer_sequence)\n # define __cpp_lib_integer_sequence 201304L\ndiff --git a/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\nnew file mode 100644\nindex 00000000000..a942d1d8396\n--- /dev/null\n+++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n@@ -0,0 +1,96 @@\n+// { dg-do compile { target c++26 } }\n+\n+#include \n+#include \n+#include \n+\n+#if __cpp_lib_integer_sequence < 202511L\n+# error \"Feature-test macro __cpp_lib_integer_sequence is incorrect\"\n+#endif\n+\n+constexpr auto\n+destructure_sum(auto seq)\n+{\n+ auto [...elems] = seq;\n+ return (0 + ... + elems);\n+}\n+\n+using IS1 = std::make_index_sequence<10>;\n+static_assert( std::tuple_size_v == 10 );\n+static_assert( std::is_same_v, std::size_t> );\n+static_assert( std::get<7>(IS1{}) == 7 );\n+static_assert( destructure_sum(IS1{}) == 45 );\n+static_assert( noexcept(get<0>(IS1{})) );\n+\n+using IS2 = std::integer_sequence;\n+static_assert( std::tuple_size_v == 3 );\n+static_assert( std::is_same_v, int> );\n+static_assert( std::get<2>(IS2{}) == -13 );\n+static_assert( destructure_sum(IS2{}) == 130 );\n+static_assert( noexcept(get<0>(IS2{})) );\n+\n+using IS3 = std::integer_sequence;\n+static_assert( std::tuple_size_v == 0 );\n+\n+using IS4 = std::integer_sequence;\n+static_assert( !std::is_constructible_v, IS4> );\n+static_assert( !std::is_constructible_v, IS4> );\n+\n+template\n+constexpr bool\n+test_basic()\n+{\n+ {\n+ auto [...elems] = std::make_index_sequence<0>{};\n+ static_assert( sizeof...(elems) == 0 );\n+ }\n+\n+ {\n+ auto [...elems] = std::integer_sequence{};\n+\n+ static_assert( sizeof...(elems) == 4 );\n+\n+ VERIFY( elems...[0] == 3 );\n+ VERIFY( elems...[1] == 5 );\n+ VERIFY( elems...[2] == 7 );\n+ VERIFY( elems...[3] == 11 );\n+ }\n+\n+ {\n+ static constexpr auto [...elems] = std::integer_sequence{};\n+\n+ static_assert( sizeof...(elems) == 4 );\n+\n+ static_assert( elems...[0] == 2 );\n+ static_assert( elems...[1] == 4 );\n+ static_assert( elems...[2] == 8 );\n+ static_assert( elems...[3] == 16 );\n+ }\n+\n+ {\n+ constexpr auto [...elems] = std::integer_sequence{};\n+\n+ static_assert( sizeof...(elems) == 4 );\n+\n+ static_assert( elems...[0] == 1 );\n+ static_assert( elems...[1] == 8 );\n+ static_assert( elems...[2] == 2 );\n+ static_assert( elems...[3] == 11 );\n+ }\n+\n+ /* Unimplemented, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117784\n+ {\n+ auto idx = 0;\n+ template for (constexpr auto elem : std::make_index_sequence<4>{})\n+ {\n+\tVERIFY( elem == idx );\n+\t++idx;\n+ }\n+ VERIFY( idx == 4 );\n+ }\n+ */\n+\n+ return true;\n+}\n+\n+static_assert( test_basic() );\ndiff --git a/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\nnew file mode 100644\nindex 00000000000..42c57620e91\n--- /dev/null\n+++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n@@ -0,0 +1,21 @@\n+// { dg-do compile { target c++26 } }\n+\n+#include \n+\n+using empty = std::integer_sequence;\n+static_assert( std::is_same_v, int> ); // { dg-error \"here\" }\n+static_assert( std::is_same_v, int> ); // { dg-error \"here\" }\n+\n+using size4 = std::integer_sequence;\n+static_assert( std::is_same_v, int> ); // { dg-error \"here\" }\n+static_assert( std::is_same_v, int> ); // { dg-error \"here\" }\n+\n+void\n+test() \n+{\n+ (void)std::get<0>(empty{}); // { dg-error \"here\" } \n+ (void)std::get<4>(size4{}); // { dg-error \"here\" } \n+}\n+\n+// { dg-error \"static assertion failed\" \"\" { target *-*-* } 0 }\n+// { dg-excess-errors \"\" }\n","prefixes":["v2"]}