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libstdc++: Move _Index_tuple, _Build_index_tuple to <type_traits>.

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As preparation for implementing std::constant_wrapper that's part of the
C++26 version of the <type_traits> header, the two classes _Index_tuple
and _Build_index_tuple are moved to <type_traits>. These two helpers are
needed by std::constant_wrapper to initialize the elements of one C
array with another.

Since, <bits/utility.h> already includes <type_traits> this solution
avoids creating a very small header file for just these two internal
classes. This approach doesn't move std::index_sequence and related code
to <type_traits> and therefore doesn't change which headers provide
user-facing features.

libstdc++-v3/ChangeLog:

	* include/bits/utility.h (_Index_tuple): Move to <type_traits>.
	(_Build_index_tuple): Ditto.
	* include/std/type_traits (_Index_tuple): Ditto.
	(_Build_index_tuple): Ditto.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>
This commit is contained in:
Luc Grosheintz
2025-09-02 09:59:44 +02:00
committed by Tomasz Kamiński
parent cfc9a42e8b
commit dea668daa2
2 changed files with 22 additions and 20 deletions
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20
libstdc++-v3/include/bits/utility.h
View File

@@ -137,26 +137,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using tuple_element_t = typename tuple_element<__i, _Tp>::type;
#endif
// Stores a tuple of indices. Used by tuple and pair, and by bind() to
// extract the elements in a tuple.
template<size_t... _Indexes> struct _Index_tuple { };
// Builds an _Index_tuple<0, 1, 2, ..., _Num-1>.
template<size_t _Num>
struct _Build_index_tuple
{
#if __has_builtin(__make_integer_seq)
template<typename, size_t... _Indices>
using _IdxTuple = _Index_tuple<_Indices...>;
// Clang defines __make_integer_seq for this purpose.
using __type = __make_integer_seq<_IdxTuple, size_t, _Num>;
#else
// For GCC and other compilers, use __integer_pack instead.
using __type = _Index_tuple<__integer_pack(_Num)...>;
#endif
};
#ifdef __glibcxx_integer_sequence // C++ >= 14
/// Class template integer_sequence

22
libstdc++-v3/include/std/type_traits
View File

@@ -4280,6 +4280,28 @@ template<typename _Ret, typename _Fn, typename... _Args>
#endif // C++2a
#if __cplusplus >= 201103L
// Stores a tuple of indices. Used by tuple and pair, and by bind() to
// extract the elements in a tuple.
template<size_t... _Indexes> struct _Index_tuple { };
// Builds an _Index_tuple<0, 1, 2, ..., _Num-1>.
template<size_t _Num>
struct _Build_index_tuple
{
#if __has_builtin(__make_integer_seq)
template<typename, size_t... _Indices>
using _IdxTuple = _Index_tuple<_Indices...>;
// Clang defines __make_integer_seq for this purpose.
using __type = __make_integer_seq<_IdxTuple, size_t, _Num>;
#else
// For GCC and other compilers, use __integer_pack instead.
using __type = _Index_tuple<__integer_pack(_Num)...>;
#endif
};
#endif // C++11
/// @} group metaprogramming
_GLIBCXX_END_NAMESPACE_VERSION