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[libcxx] removes unnecessary traits from has_unique_object_representations #69241

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May 21, 2024
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[libcxx] removes unnecessary traits from has_unique_object_representations #69241

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[libcxx] removes unnecessary traits from `has_unique_object_represent…
cjdb Oct 16, 2023
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ldionne Apr 12, 2024
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4 changes: 1 addition & 3 deletions libcxx/include/__type_traits/has_unique_object_representation.h
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,6 @@

#include <__config>
#include <__type_traits/integral_constant.h>
#include <__type_traits/remove_all_extents.h>
#include <__type_traits/remove_cv.h>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
Expand All @@ -24,7 +22,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS has_unique_object_representations
: public integral_constant<bool, __has_unique_object_representations(remove_cv_t<remove_all_extents_t<_Tp>>)> {};
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I assume you've checked that we have tests for const arrays or w/e to make sure the patch is still exercised.

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Yes to both questions, but I wouldn't be upset if someone wanted to double check the tests' existence.

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There is libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/has_unique_object_representations.pass.cpp, but we seem to be missing a test for a multi-dimensional array.

: public integral_constant<bool, __has_unique_object_representations(_Tp)> {};

template <class _Tp>
inline constexpr bool has_unique_object_representations_v = has_unique_object_representations<_Tp>::value;
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Suggested change
inline constexpr bool has_unique_object_representations_v = has_unique_object_representations<_Tp>::value;
inline constexpr bool has_unique_object_representations_v = __has_unique_object_representations(_Tp);

Might as well while we're here.

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Very happy to do this if we're okay with doing it elsewhere (I can lead the clean-up for that).

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Depends on what you mean by "it". If you just mean cases where we always have the builtins available, sure (although I think I removed those cases). In other cases I'm not sure it's a good idea.

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I mean applying the same change to all other traits where the trait is how the builtin is surfaced (so mostly stuff in <type_traits>). Anything else deserves a proper discussion.

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I think what Nikolas tried explaining is that in most cases, we already call the builtin directly from the _v alias if there's a builtin (for example libcxx/include/__type_traits/is_reference.h). So I think there should be no other places where we want to make the same change, unless of course we forgot to do it in other places.

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