[{"id":3675252,"web_url":"http://patchwork.ozlabs.org/comment/3675252/","msgid":"","list_archive_url":null,"date":"2026-04-09T11:02:55","subject":"Re: [PATCH v2] libstdc++: Implement structured binding support for\n integer_sequence","submitter":{"id":90409,"url":"http://patchwork.ozlabs.org/api/people/90409/","name":"Tomasz Kamiński","email":"tkaminsk@redhat.com"},"content":"On Thu, Apr 9, 2026 at 10:04 AM Tomasz Kamiński wrote:\n\n> From: Matthias Wippich \n>\n> This implements P1789R3 Library Support for Expansion Statements.\n> https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p1789r3.pdf\n>\n> libstdc++-v3/ChangeLog:\n>\n> * include/bits/utility.h (std::tuple_size, std::tuple_element):\n> Add partrial specializations for integer_sequence.\n> (std::get(integer_sequence<_Tp, _Idx...>)): Define.\n> * include/bits/version.def (integer_sequence): Bump to 202511L.\n> * include/bits/version.h: Regenerate.\n> * testsuite/20_util/integer_sequence/tuple_access.cc: New test.\n> * testsuite/20_util/integer_sequence/tuple_access_neg.cc: New test.\n> * testsuite/experimental/feat-cxx14.cc: Updated check for\n> __cpp_lib_integer_sequence value.\n>\n> Co-authored-by: Ivan Lazaric \n> Signed-off-by: Matthias Wippich \n> ---\n> v3:\n> - updates changelog\n> - fixes __cpp_lib_integer_sequence check in feat-cxx14.cc\n> - replaces dg-excess-errors in tuple_access_neg.cc\n> - add few testcasse to tuple_access.cc\n>\n> Testing on x86_64-linux. OK for trunk when all test passes?\n>\nAll test passed (noting this also for myself as I have many patches in\nflight).\n\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 | 143 ++++++++++++++++++\n> .../integer_sequence/tuple_access_neg.cc | 22 +++\n> .../testsuite/experimental/feat-cxx14.cc | 4 +-\n> 6 files changed, 208 insertions(+), 3 deletions(-)\n> create mode 100644\n> libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n> create mode 100644\n> libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n>\n> diff --git a/libstdc++-v3/include/bits/utility.h\n> b/libstdc++-v3/include/bits/utility.h\n> index 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\n> diff --git a/libstdc++-v3/include/bits/version.def\n> b/libstdc++-v3/include/bits/version.def\n> index 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;\n> diff --git a/libstdc++-v3/include/bits/version.h\n> b/libstdc++-v3/include/bits/version.h\n> index 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) ||\n> 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) ||\n> defined(__glibcxx_want_integer_sequence)\n> # define __cpp_lib_integer_sequence 201304L\n> diff --git\n> a/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n> b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n> new file mode 100644\n> index 00000000000..afa644e7dab\n> --- /dev/null\n> +++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n> @@ -0,0 +1,143 @@\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> );\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 8, 16>{};\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> + {\n> + static constexpr auto&& [...elems] = std::integer_sequence 4, 8, 16>{};\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> + /* Unimplemented, see PR117784\n> + {\n> + constexpr auto&& [...elems] = std::integer_sequence 11>{};\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> +\n> + {\n> + auto idx = 0;\n> + static constexpr auto seq = std::make_index_sequence<4>{};\n> + template for (constexpr auto elem : seq)\n> + {\n> + VERIFY( elem == idx );\n> + ++idx;\n> + }\n> + VERIFY( idx == 4 );\n> + }\n> +\n> +\n> + /* Unimplemented, see PR117784\n> + {\n> + auto idx = 0;\n> + constexpr auto seq = std::make_index_sequence<4>{};\n> + template for (constexpr auto elem : seq)\n> + {\n> + VERIFY( elem == idx );\n> + ++idx;\n> + }\n> + VERIFY( idx == 4 );\n> + }\n> +\n> + {\n> + auto idx = 0;\n> + template for (constexpr auto elem : std::make_index_sequence<4>{})\n> + {\n> + VERIFY( elem == idx );\n> + ++idx;\n> + }\n> + VERIFY( idx == 4 );\n> + }\n> + */\n> +\n> + return true;\n> +}\n> +\n> +static_assert( test_basic() );\n> diff --git\n> a/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n> b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n> new file mode 100644\n> index 00000000000..8640114e7d3\n> --- /dev/null\n> +++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n> @@ -0,0 +1,22 @@\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> ); //\n> { dg-error \"here\" }\n> +static_assert( std::is_same_v, int>\n> ); // { dg-error \"here\" }\n> +\n> +using size4 = std::integer_sequence;\n> +static_assert( std::is_same_v, int> ); //\n> { dg-error \"here\" }\n> +static_assert( std::is_same_v, int>\n> ); // { 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-error \"cannot index an empty pack\" \"\" { target *-*-* } 0 }\n> +// { dg-error \"pack index '.' is out of range for pack of length\" \"\" {\n> target *-*-* } 0 }\n> diff --git a/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n> b/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n> index c009062b55c..4cc56c5f76e 100644\n> --- a/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n> +++ b/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n> @@ -18,8 +18,8 @@\n>\n> #ifndef __cpp_lib_integer_sequence\n> # error \"__cpp_lib_integer_sequence\"\n> -#elif __cpp_lib_integer_sequence != 201304\n> -# error \"__cpp_lib_integer_sequence != 201304\"\n> +#elif __cpp_lib_integer_sequence < 201304\n> +# error \"__cpp_lib_integer_sequence < 201304\"\n> #endif\n>\n> #ifndef __cpp_lib_exchange_function\n> --\n> 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[PATCH v2] libstdc++: Implement structured binding support for\n integer_sequence","To":"libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org","Cc":"Matthias Wippich ,\n Ivan Lazaric ","X-Mimecast-Spam-Score":"0","X-Mimecast-MFC-PROC-ID":"mEjm4CV9DM7S2eXrbTSYiQna2Wk9PffYaRWa37E4z24_1775732587","X-Mimecast-Originator":"redhat.com","Content-Type":"multipart/alternative; boundary=\"0000000000000350fb064f04f66f\"","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"}},{"id":3675353,"web_url":"http://patchwork.ozlabs.org/comment/3675353/","msgid":"","list_archive_url":null,"date":"2026-04-09T14:32:06","subject":"Re: [PATCH v2] libstdc++: Implement structured binding support for\n integer_sequence","submitter":{"id":93063,"url":"http://patchwork.ozlabs.org/api/people/93063/","name":"Matthias Wippich","email":"mfwippich@gmail.com"},"content":"whoops, sorry for the extraneous whitespace. Thanks for taking care of\nit. There's a typo in the updated changelog: `partrial` should be\n`partial`.\n\nIn libc++ we did put `[[nodiscard]]` on `get` as an extension. Would\nthat be desirable for libstdc++ as well?\n\nOn Thu, Apr 9, 2026 at 1:03 PM Tomasz Kaminski wrote:\n>\n>\n>\n> On Thu, Apr 9, 2026 at 10:04 AM Tomasz Kamiński wrote:\n>>\n>> From: Matthias Wippich \n>>\n>> This implements P1789R3 Library Support for Expansion Statements.\n>> https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p1789r3.pdf\n>>\n>> libstdc++-v3/ChangeLog:\n>>\n>> * include/bits/utility.h (std::tuple_size, std::tuple_element):\n>> Add partrial specializations for integer_sequence.\n>> (std::get(integer_sequence<_Tp, _Idx...>)): Define.\n>> * include/bits/version.def (integer_sequence): Bump to 202511L.\n>> * include/bits/version.h: Regenerate.\n>> * testsuite/20_util/integer_sequence/tuple_access.cc: New test.\n>> * testsuite/20_util/integer_sequence/tuple_access_neg.cc: New test.\n>> * testsuite/experimental/feat-cxx14.cc: Updated check for\n>> __cpp_lib_integer_sequence value.\n>>\n>> Co-authored-by: Ivan Lazaric \n>> Signed-off-by: Matthias Wippich \n>> ---\n>> v3:\n>> - updates changelog\n>> - fixes __cpp_lib_integer_sequence check in feat-cxx14.cc\n>> - replaces dg-excess-errors in tuple_access_neg.cc\n>> - add few testcasse to tuple_access.cc\n>>\n>> Testing on x86_64-linux. OK for trunk when all test passes?\n>\n> All test passed (noting this also for myself as I have many patches in flight).\n>>\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 | 143 ++++++++++++++++++\n>> .../integer_sequence/tuple_access_neg.cc | 22 +++\n>> .../testsuite/experimental/feat-cxx14.cc | 4 +-\n>> 6 files changed, 208 insertions(+), 3 deletions(-)\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\n>>\n>> diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h\n>> index 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\n>> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def\n>> index 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;\n>> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h\n>> index 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\n>> diff --git a/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n>> new file mode 100644\n>> index 00000000000..afa644e7dab\n>> --- /dev/null\n>> +++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n>> @@ -0,0 +1,143 @@\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>> + {\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>> + /* Unimplemented, see PR117784\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>> +\n>> + {\n>> + auto idx = 0;\n>> + static constexpr auto seq = std::make_index_sequence<4>{};\n>> + template for (constexpr auto elem : seq)\n>> + {\n>> + VERIFY( elem == idx );\n>> + ++idx;\n>> + }\n>> + VERIFY( idx == 4 );\n>> + }\n>> +\n>> +\n>> + /* Unimplemented, see PR117784\n>> + {\n>> + auto idx = 0;\n>> + constexpr auto seq = std::make_index_sequence<4>{};\n>> + template for (constexpr auto elem : seq)\n>> + {\n>> + VERIFY( elem == idx );\n>> + ++idx;\n>> + }\n>> + VERIFY( idx == 4 );\n>> + }\n>> +\n>> + {\n>> + auto idx = 0;\n>> + template for (constexpr auto elem : std::make_index_sequence<4>{})\n>> + {\n>> + VERIFY( elem == idx );\n>> + ++idx;\n>> + }\n>> + VERIFY( idx == 4 );\n>> + }\n>> + */\n>> +\n>> + return true;\n>> +}\n>> +\n>> +static_assert( test_basic() );\n>> diff --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\n>> new file mode 100644\n>> index 00000000000..8640114e7d3\n>> --- /dev/null\n>> +++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n>> @@ -0,0 +1,22 @@\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-error \"cannot index an empty pack\" \"\" { target *-*-* } 0 }\n>> +// { dg-error \"pack index '.' is out of range for pack of length\" \"\" { target *-*-* } 0 }\n>> diff --git a/libstdc++-v3/testsuite/experimental/feat-cxx14.cc b/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n>> index c009062b55c..4cc56c5f76e 100644\n>> --- a/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n>> +++ b/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n>> @@ -18,8 +18,8 @@\n>>\n>> #ifndef __cpp_lib_integer_sequence\n>> # error \"__cpp_lib_integer_sequence\"\n>> -#elif __cpp_lib_integer_sequence != 201304\n>> -# error \"__cpp_lib_integer_sequence != 201304\"\n>> +#elif __cpp_lib_integer_sequence < 201304\n>> +# error \"__cpp_lib_integer_sequence < 201304\"\n>> #endif\n>>\n>> #ifndef __cpp_lib_exchange_function\n>> --\n>> 2.53.0\n>>","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 header.a=rsa-sha256\n header.s=20251104 header.b=r1t3k0BF;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (2048-bit key,\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 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gcc-patches@gcc.gnu.org,\n Ivan Lazaric ","Content-Type":"text/plain; charset=\"UTF-8\"","Content-Transfer-Encoding":"quoted-printable","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"}},{"id":3677102,"web_url":"http://patchwork.ozlabs.org/comment/3677102/","msgid":"","list_archive_url":null,"date":"2026-04-14T09:50:49","subject":"Re: [PATCH v2] libstdc++: Implement structured binding support for\n integer_sequence","submitter":{"id":48004,"url":"http://patchwork.ozlabs.org/api/people/48004/","name":"Jonathan Wakely","email":"jwakely@redhat.com"},"content":"On Thu, 09 Apr 2026 at 10:01 +0200, Tomasz Kamiński wrote:\n>From: Matthias Wippich \n>\n>This implements P1789R3 Library Support for Expansion Statements.\n>https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p1789r3.pdf\n>\n>libstdc++-v3/ChangeLog:\n>\n>\t* include/bits/utility.h (std::tuple_size, std::tuple_element):\n>\tAdd partrial specializations for integer_sequence.\n>\t(std::get(integer_sequence<_Tp, _Idx...>)): Define.\n>\t* include/bits/version.def (integer_sequence): Bump to 202511L.\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>\t* testsuite/experimental/feat-cxx14.cc: Updated check for\n>\t__cpp_lib_integer_sequence value.\n>\n>Co-authored-by: Ivan Lazaric \n>Signed-off-by: Matthias Wippich \n>---\n>v3:\n> - updates changelog\n> - fixes __cpp_lib_integer_sequence check in feat-cxx14.cc\n> - replaces dg-excess-errors in tuple_access_neg.cc\n> - add few testcasse to tuple_access.cc\n>\n>Testing on x86_64-linux. OK for trunk when all test passes?\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 | 143 ++++++++++++++++++\n> .../integer_sequence/tuple_access_neg.cc | 22 +++\n> .../testsuite/experimental/feat-cxx14.cc | 4 +-\n> 6 files changed, 208 insertions(+), 3 deletions(-)\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\n>\n>diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h\n>index 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\nSo that it has a bit more context in the generated Doxygen HTML,\nplease make this comment:\n\n /** @brief Structured binding support for `integer_sequence`\n\n * @since C++26\n * @{\n */\n\nand then after the get overload, add /// @}\n\nThat will create a group so that the same comment applies to all of\ntuple_size, tuple_element, and get.\n\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\nI agree with the suggestion to add [[nodiscard]] here.\n\nOK with those changes (and the \"partial\" typo that Matthias noticed).\n\nThanks to all three of you for doing this.\n\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\n>diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def\n>index 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;\n>diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h\n>index 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\n>diff --git a/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n>new file mode 100644\n>index 00000000000..afa644e7dab\n>--- /dev/null\n>+++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n>@@ -0,0 +1,143 @@\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>+ {\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>+ /* Unimplemented, see PR117784\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>+\n>+ {\n>+ auto idx = 0;\n>+ static constexpr auto seq = std::make_index_sequence<4>{};\n>+ template for (constexpr auto elem : seq)\n>+ {\n>+\tVERIFY( elem == idx );\n>+\t++idx;\n>+ }\n>+ VERIFY( idx == 4 );\n>+ }\n>+\n>+\n>+ /* Unimplemented, see PR117784\n>+ {\n>+ auto idx = 0;\n>+ constexpr auto seq = std::make_index_sequence<4>{};\n>+ template for (constexpr auto elem : seq)\n>+ {\n>+\tVERIFY( elem == idx );\n>+\t++idx;\n>+ }\n>+ VERIFY( idx == 4 );\n>+ }\n>+\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() );\n>diff --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\n>new file mode 100644\n>index 00000000000..8640114e7d3\n>--- /dev/null\n>+++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n>@@ -0,0 +1,22 @@\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-error \"cannot index an empty pack\" \"\" { target *-*-* } 0 }\n>+// { dg-error \"pack index '.' is out of range for pack of length\" \"\" { target *-*-* } 0 }\n>diff --git a/libstdc++-v3/testsuite/experimental/feat-cxx14.cc b/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n>index c009062b55c..4cc56c5f76e 100644\n>--- a/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n>+++ b/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n>@@ -18,8 +18,8 @@\n>\n> #ifndef __cpp_lib_integer_sequence\n> # error \"__cpp_lib_integer_sequence\"\n>-#elif __cpp_lib_integer_sequence != 201304\n>-# error \"__cpp_lib_integer_sequence != 201304\"\n>+#elif __cpp_lib_integer_sequence < 201304\n>+# error \"__cpp_lib_integer_sequence < 201304\"\n> #endif\n>\n> #ifndef __cpp_lib_exchange_function\n>-- \n>2.53.0\n>\n>","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 (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=fOsUQ2ko;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (1024-bit key,\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=fOsUQ2ko","sourceware.org; dmarc=pass (p=quarantine dis=none)\n 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Pratchett","X-Scanned-By":"MIMEDefang 3.0 on 10.30.177.12","X-Mimecast-Spam-Score":"0","X-Mimecast-MFC-PROC-ID":"xwtiDkebkk5Wf1UyY8ydgpIMIas_mhJw_Z6fZYk7xqc_1776160253","X-Mimecast-Originator":"redhat.com","Content-Type":"text/plain; charset=utf-8; format=flowed","Content-Disposition":"inline","Content-Transfer-Encoding":"8bit","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"}},{"id":3677128,"web_url":"http://patchwork.ozlabs.org/comment/3677128/","msgid":"","list_archive_url":null,"date":"2026-04-14T11:06:57","subject":"Re: [PATCH v2] libstdc++: Implement structured binding support for\n integer_sequence","submitter":{"id":90409,"url":"http://patchwork.ozlabs.org/api/people/90409/","name":"Tomasz Kamiński","email":"tkaminsk@redhat.com"},"content":"On Tue, Apr 14, 2026 at 11:50 AM Jonathan Wakely wrote:\n\n> On Thu, 09 Apr 2026 at 10:01 +0200, Tomasz Kamiński wrote:\n> >From: Matthias Wippich \n> >\n> >This implements P1789R3 Library Support for Expansion Statements.\n> >https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p1789r3.pdf\n> >\n> >libstdc++-v3/ChangeLog:\n> >\n> > * include/bits/utility.h (std::tuple_size, std::tuple_element):\n> > Add partrial specializations for integer_sequence.\n> > (std::get(integer_sequence<_Tp, _Idx...>)): Define.\n> > * include/bits/version.def (integer_sequence): Bump to 202511L.\n> > * include/bits/version.h: Regenerate.\n> > * testsuite/20_util/integer_sequence/tuple_access.cc: New test.\n> > * testsuite/20_util/integer_sequence/tuple_access_neg.cc: New test.\n> > * testsuite/experimental/feat-cxx14.cc: Updated check for\n> > __cpp_lib_integer_sequence value.\n> >\n> >Co-authored-by: Ivan Lazaric \n> >Signed-off-by: Matthias Wippich \n> >---\n> >v3:\n> > - updates changelog\n> > - fixes __cpp_lib_integer_sequence check in feat-cxx14.cc\n> > - replaces dg-excess-errors in tuple_access_neg.cc\n> > - add few testcasse to tuple_access.cc\n> >\n> >Testing on x86_64-linux. OK for trunk when all test passes?\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 | 143 ++++++++++++++++++\n> > .../integer_sequence/tuple_access_neg.cc | 22 +++\n> > .../testsuite/experimental/feat-cxx14.cc | 4 +-\n> > 6 files changed, 208 insertions(+), 3 deletions(-)\n> > create mode 100644\n> libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n> > create mode 100644\n> libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n> >\n> >diff --git a/libstdc++-v3/include/bits/utility.h\n> b/libstdc++-v3/include/bits/utility.h\n> >index 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>\n> So that it has a bit more context in the generated Doxygen HTML,\n> please make this comment:\n>\n> /** @brief Structured binding support for `integer_sequence`\n>\n> * @since C++26\n> * @{\n> */\n>\n> and then after the get overload, add /// @}\n>\n> That will create a group so that the same comment applies to all of\n> tuple_size, tuple_element, and get.\n>\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> I agree with the suggestion to add [[nodiscard]] here.\n>\n> OK with those changes (and the \"partial\" typo that Matthias noticed).\n>\n> Thanks to all three of you for doing this.\n>\nMerged to trunk. Thanks!\n\n>\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\n> >diff --git a/libstdc++-v3/include/bits/version.def\n> b/libstdc++-v3/include/bits/version.def\n> >index 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;\n> >diff --git a/libstdc++-v3/include/bits/version.h\n> b/libstdc++-v3/include/bits/version.h\n> >index 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) ||\n> 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) ||\n> defined(__glibcxx_want_integer_sequence)\n> > # define __cpp_lib_integer_sequence 201304L\n> >diff --git\n> a/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n> b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n> >new file mode 100644\n> >index 00000000000..afa644e7dab\n> >--- /dev/null\n> >+++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access.cc\n> >@@ -0,0 +1,143 @@\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> );\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 4, 8, 16>{};\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 11>{};\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> >+ {\n> >+ static constexpr auto&& [...elems] = std::integer_sequence 4, 8, 16>{};\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> >+ /* Unimplemented, see PR117784\n> >+ {\n> >+ constexpr auto&& [...elems] = std::integer_sequence 11>{};\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> >+\n> >+ {\n> >+ auto idx = 0;\n> >+ static constexpr auto seq = std::make_index_sequence<4>{};\n> >+ template for (constexpr auto elem : seq)\n> >+ {\n> >+ VERIFY( elem == idx );\n> >+ ++idx;\n> >+ }\n> >+ VERIFY( idx == 4 );\n> >+ }\n> >+\n> >+\n> >+ /* Unimplemented, see PR117784\n> >+ {\n> >+ auto idx = 0;\n> >+ constexpr auto seq = std::make_index_sequence<4>{};\n> >+ template for (constexpr auto elem : seq)\n> >+ {\n> >+ VERIFY( elem == idx );\n> >+ ++idx;\n> >+ }\n> >+ VERIFY( idx == 4 );\n> >+ }\n> >+\n> >+ {\n> >+ auto idx = 0;\n> >+ template for (constexpr auto elem : std::make_index_sequence<4>{})\n> >+ {\n> >+ VERIFY( elem == idx );\n> >+ ++idx;\n> >+ }\n> >+ VERIFY( idx == 4 );\n> >+ }\n> >+ */\n> >+\n> >+ return true;\n> >+}\n> >+\n> >+static_assert( test_basic() );\n> >diff --git\n> a/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n> b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n> >new file mode 100644\n> >index 00000000000..8640114e7d3\n> >--- /dev/null\n> >+++ b/libstdc++-v3/testsuite/20_util/integer_sequence/tuple_access_neg.cc\n> >@@ -0,0 +1,22 @@\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> ); //\n> { dg-error \"here\" }\n> >+static_assert( std::is_same_v, int>\n> ); // { dg-error \"here\" }\n> >+\n> >+using size4 = std::integer_sequence;\n> >+static_assert( std::is_same_v, int> ); //\n> { dg-error \"here\" }\n> >+static_assert( std::is_same_v, int>\n> ); // { 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-error \"cannot index an empty pack\" \"\" { target *-*-* } 0 }\n> >+// { dg-error \"pack index '.' is out of range for pack of length\" \"\" {\n> target *-*-* } 0 }\n> >diff --git a/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n> b/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n> >index c009062b55c..4cc56c5f76e 100644\n> >--- a/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n> >+++ b/libstdc++-v3/testsuite/experimental/feat-cxx14.cc\n> >@@ -18,8 +18,8 @@\n> >\n> > #ifndef __cpp_lib_integer_sequence\n> > # error \"__cpp_lib_integer_sequence\"\n> >-#elif __cpp_lib_integer_sequence != 201304\n> >-# error \"__cpp_lib_integer_sequence != 201304\"\n> >+#elif __cpp_lib_integer_sequence < 201304\n> >+# error \"__cpp_lib_integer_sequence < 201304\"\n> > #endif\n> >\n> > #ifndef __cpp_lib_exchange_function\n> >--\n> >2.53.0\n> >\n> >\n>\n>","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 (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com 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