On Tue, Sep 2, 2025 at 1:11 PM Tomasz Kaminski <tkami...@redhat.com> wrote:
>
>
> On Tue, Sep 2, 2025 at 11:44 AM Jonathan Wakely <jwak...@redhat.com>
> wrote:
>
>> On Tue, 2 Sept 2025 at 09:01, Luc Grosheintz wrote:
>> >
>> > 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.
>>
>> At some point I'd like to split <type_traits> into smaller pieces. Not
>> one header per trait, that would be silly (Boost, I'm looking at you),
>> but we don't need e.g. all the complex invoke_result logic in every
>> header that wants to use std::decay_t.
>>
>> But that is a larger project and isn't made any easier or harder by
>> this small change.
>>
>> > 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.
>>
>> Great, thanks.
>>
>> OK for trunk.
>>
> I will merge the patch today.
>
Pushed to trunk.
>
>>
>> >
>> > 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.
>> >
>> > Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
>> > ---
>> > libstdc++-v3/include/bits/utility.h | 20 --------------------
>> > libstdc++-v3/include/std/type_traits | 22 ++++++++++++++++++++++
>> > 2 files changed, 22 insertions(+), 20 deletions(-)
>> >
>> > diff --git a/libstdc++-v3/include/bits/utility.h
>> b/libstdc++-v3/include/bits/utility.h
>> > index 84d25e0c658..4e574658eba 100644
>> > --- a/libstdc++-v3/include/bits/utility.h
>> > +++ b/libstdc++-v3/include/bits/utility.h
>> > @@ -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
>> > diff --git a/libstdc++-v3/include/std/type_traits
>> b/libstdc++-v3/include/std/type_traits
>> > index ff23544fbf0..4636457eb5a 100644
>> > --- a/libstdc++-v3/include/std/type_traits
>> > +++ b/libstdc++-v3/include/std/type_traits
>> > @@ -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
>> > --
>> > 2.51.0
>> >
>>
>>
