[libcxx-commits] [libcxx] [DRAFT] [libc++] Add `__is_transparently_comparable_v` specializations for `basic_string_view` (PR #195871)
Michael Levine via libcxx-commits
libcxx-commits at lists.llvm.org
Tue May 5 08:34:52 PDT 2026
https://github.com/levinem updated https://github.com/llvm/llvm-project/pull/195871
>From a25cc50d919a949e3403f91b499f2db76a0f463b Mon Sep 17 00:00:00 2001
From: mlevine55 <mlevine55 at bloomberg.net>
Date: Tue, 5 May 2026 11:15:47 -0400
Subject: [PATCH 1/2] Added the optimizations
Signed-off-by: mlevine55 <mlevine55 at bloomberg.net>
---
libcxx/include/string | 23 +++++++++++++++
libcxx/include/string_view | 27 ++++++++++++++++++
..._transparently_comparable.compile.pass.cpp | 28 +++++++++++++++++++
3 files changed, 78 insertions(+)
diff --git a/libcxx/include/string b/libcxx/include/string
index a00b824e5150a..82deee9085027 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -2599,6 +2599,29 @@ template <class _Comparator, class _CharT, class _Traits, class _Alloc, size_t _
inline const bool __is_transparently_comparable_v<_Comparator, _CharT[_Np], basic_string<_CharT, _Traits, _Alloc> > =
__is_transparently_comparable_v<_Comparator, basic_string<_CharT, _Traits, _Alloc>, const _CharT*>;
+template <class _Comparator, class _CharT, class _Traits, class _Alloc>
+inline const bool
+ __is_transparently_comparable_v<_Comparator,
+ basic_string<_CharT, _Traits, _Alloc>,
+ basic_string_view<_CharT, _Traits> > =
+ __desugars_to_v<__less_tag,
+ _Comparator,
+ basic_string<_CharT, _Traits, _Alloc>,
+ basic_string<_CharT, _Traits, _Alloc> > ||
+ __desugars_to_v<__greater_tag,
+ _Comparator,
+ basic_string<_CharT, _Traits, _Alloc>,
+ basic_string<_CharT, _Traits, _Alloc> >;
+
+template <class _Comparator, class _CharT, class _Traits, class _Alloc>
+inline const bool
+ __is_transparently_comparable_v<_Comparator,
+ basic_string_view<_CharT, _Traits>,
+ basic_string<_CharT, _Traits, _Alloc> > =
+ __is_transparently_comparable_v<_Comparator,
+ basic_string<_CharT, _Traits, _Alloc>,
+ basic_string_view<_CharT, _Traits> >;
+
# if _LIBCPP_STD_VER >= 17
template <class _InputIterator,
class _CharT = __iterator_value_type<_InputIterator>,
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
index 5dd04a9ba8479..0ea8b5f3965f5 100644
--- a/libcxx/include/string_view
+++ b/libcxx/include/string_view
@@ -217,6 +217,7 @@ namespace std {
# include <__cstddef/ptrdiff_t.h>
# include <__cstddef/size_t.h>
# include <__functional/hash.h>
+# include <__functional/is_transparent.h>
# include <__functional/unary_function.h>
# include <__fwd/ostream.h>
# include <__fwd/string.h>
@@ -234,11 +235,13 @@ namespace std {
# include <__ranges/size.h>
# include <__string/char_traits.h>
# include <__type_traits/is_array.h>
+# include <__type_traits/desugars_to.h>
# include <__type_traits/is_convertible.h>
# include <__type_traits/is_same.h>
# include <__type_traits/is_standard_layout.h>
# include <__type_traits/is_trivially_constructible.h>
# include <__type_traits/is_trivially_copyable.h>
+# include <__type_traits/remove_cv.h>
# include <__type_traits/remove_cvref.h>
# include <__type_traits/remove_reference.h>
# include <__type_traits/type_identity.h>
@@ -933,6 +936,30 @@ template <>
struct hash<basic_string_view<wchar_t, char_traits<wchar_t> > > : __string_view_hash<wchar_t> {};
# endif
+template <class _Comparator, class _CharT2, class _CharT, class _Traits>
+inline const bool __is_transparently_comparable_v<_Comparator, basic_string_view<_CharT, _Traits>, _CharT2*> =
+ is_same<_CharT, __remove_cv_t<_CharT2> >::value &&
+ (__desugars_to_v<__less_tag,
+ _Comparator,
+ basic_string_view<_CharT, _Traits>,
+ basic_string_view<_CharT, _Traits> > ||
+ __desugars_to_v<__greater_tag,
+ _Comparator,
+ basic_string_view<_CharT, _Traits>,
+ basic_string_view<_CharT, _Traits> >);
+
+template <class _Comparator, class _CharT2, class _CharT, class _Traits>
+inline const bool __is_transparently_comparable_v<_Comparator, _CharT2*, basic_string_view<_CharT, _Traits> > =
+ __is_transparently_comparable_v<_Comparator, basic_string_view<_CharT, _Traits>, _CharT2*>;
+
+template <class _Comparator, class _CharT, class _Traits, size_t _Np>
+inline const bool __is_transparently_comparable_v<_Comparator, basic_string_view<_CharT, _Traits>, _CharT[_Np]> =
+ __is_transparently_comparable_v<_Comparator, basic_string_view<_CharT, _Traits>, const _CharT*>;
+
+template <class _Comparator, class _CharT, class _Traits, size_t _Np>
+inline const bool __is_transparently_comparable_v<_Comparator, _CharT[_Np], basic_string_view<_CharT, _Traits> > =
+ __is_transparently_comparable_v<_Comparator, basic_string_view<_CharT, _Traits>, const _CharT*>;
+
# if _LIBCPP_STD_VER >= 14
inline namespace literals {
inline namespace string_view_literals {
diff --git a/libcxx/test/libcxx/type_traits/is_transparently_comparable.compile.pass.cpp b/libcxx/test/libcxx/type_traits/is_transparently_comparable.compile.pass.cpp
index 8ab8cb0be8418..870a77cf33abc 100644
--- a/libcxx/test/libcxx/type_traits/is_transparently_comparable.compile.pass.cpp
+++ b/libcxx/test/libcxx/type_traits/is_transparently_comparable.compile.pass.cpp
@@ -10,8 +10,10 @@
#include <functional>
#include <string>
+#include <string_view>
#include <__type_traits/desugars_to.h>
+// basic_string with char pointers/arrays
static_assert(std::__is_transparently_comparable_v<std::less<std::string>, std::string, const char*>, "");
static_assert(std::__is_transparently_comparable_v<std::less<std::string>, std::string, char*>, "");
static_assert(std::__is_transparently_comparable_v<std::less<std::string>, std::string, char[5]>, "");
@@ -30,3 +32,29 @@ static_assert(
static_assert(
!std::__is_transparently_comparable_v<std::less<std::reference_wrapper<std::string> >, char const*, std::string>,
"");
+
+// basic_string_view with char pointers/arrays
+static_assert(
+ std::__is_transparently_comparable_v<std::less<std::string_view>, std::string_view, const char*>, "");
+static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, std::string_view, char*>, "");
+static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, std::string_view, char[5]>, "");
+
+static_assert(
+ std::__is_transparently_comparable_v<std::less<std::string_view>, const char*, std::string_view>, "");
+static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, char*, std::string_view>, "");
+static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, char[5], std::string_view>, "");
+
+static_assert(
+ !std::__is_transparently_comparable_v<std::less<std::reference_wrapper<std::string_view> >,
+ std::string_view,
+ const char*>,
+ "");
+static_assert(
+ !std::__is_transparently_comparable_v<std::less<std::reference_wrapper<std::string_view> >,
+ const char*,
+ std::string_view>,
+ "");
+
+// Cross-type: basic_string key with basic_string_view argument
+static_assert(std::__is_transparently_comparable_v<std::less<std::string>, std::string, std::string_view>, "");
+static_assert(std::__is_transparently_comparable_v<std::less<std::string>, std::string_view, std::string>, "");
>From 5346d22c9a0b48debfa51a701acad833858f2d6d Mon Sep 17 00:00:00 2001
From: mlevine55 <mlevine55 at bloomberg.net>
Date: Tue, 5 May 2026 11:34:11 -0400
Subject: [PATCH 2/2] clang-format
Signed-off-by: mlevine55 <mlevine55 at bloomberg.net>
---
libcxx/include/string | 54 +++++++++----------
libcxx/include/string_view | 2 +-
..._transparently_comparable.compile.pass.cpp | 24 ++++-----
3 files changed, 37 insertions(+), 43 deletions(-)
diff --git a/libcxx/include/string b/libcxx/include/string
index 82deee9085027..c9bc3336e8be4 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1735,8 +1735,8 @@ public:
_LIBCPP_CONSTEXPR_SINCE_CXX20 size_type copy(value_type* __s, size_type __n, size_type __pos = 0) const;
# if _LIBCPP_STD_VER <= 20
- [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
- _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string substr(size_type __pos = 0, size_type __n = npos) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string
+ substr(size_type __pos = 0, size_type __n = npos) const {
return basic_string(*this, __pos, __n);
}
# else
@@ -2600,27 +2600,25 @@ inline const bool __is_transparently_comparable_v<_Comparator, _CharT[_Np], basi
__is_transparently_comparable_v<_Comparator, basic_string<_CharT, _Traits, _Alloc>, const _CharT*>;
template <class _Comparator, class _CharT, class _Traits, class _Alloc>
-inline const bool
- __is_transparently_comparable_v<_Comparator,
- basic_string<_CharT, _Traits, _Alloc>,
- basic_string_view<_CharT, _Traits> > =
- __desugars_to_v<__less_tag,
- _Comparator,
- basic_string<_CharT, _Traits, _Alloc>,
- basic_string<_CharT, _Traits, _Alloc> > ||
- __desugars_to_v<__greater_tag,
- _Comparator,
- basic_string<_CharT, _Traits, _Alloc>,
- basic_string<_CharT, _Traits, _Alloc> >;
+inline const bool __is_transparently_comparable_v<_Comparator,
+ basic_string<_CharT, _Traits, _Alloc>,
+ basic_string_view<_CharT, _Traits> > =
+ __desugars_to_v<__less_tag,
+ _Comparator,
+ basic_string<_CharT, _Traits, _Alloc>,
+ basic_string<_CharT, _Traits, _Alloc> > ||
+ __desugars_to_v<__greater_tag,
+ _Comparator,
+ basic_string<_CharT, _Traits, _Alloc>,
+ basic_string<_CharT, _Traits, _Alloc> >;
template <class _Comparator, class _CharT, class _Traits, class _Alloc>
-inline const bool
+inline const bool __is_transparently_comparable_v<_Comparator,
+ basic_string_view<_CharT, _Traits>,
+ basic_string<_CharT, _Traits, _Alloc> > =
__is_transparently_comparable_v<_Comparator,
- basic_string_view<_CharT, _Traits>,
- basic_string<_CharT, _Traits, _Alloc> > =
- __is_transparently_comparable_v<_Comparator,
- basic_string<_CharT, _Traits, _Alloc>,
- basic_string_view<_CharT, _Traits> >;
+ basic_string<_CharT, _Traits, _Alloc>,
+ basic_string_view<_CharT, _Traits> >;
# if _LIBCPP_STD_VER >= 17
template <class _InputIterator,
@@ -2635,8 +2633,8 @@ template <class _CharT,
class _Traits,
class _Allocator = allocator<_CharT>,
class = enable_if_t<__is_allocator_v<_Allocator>>>
-explicit basic_string(basic_string_view<_CharT, _Traits>, const _Allocator& = _Allocator())
- -> basic_string<_CharT, _Traits, _Allocator>;
+explicit basic_string(basic_string_view<_CharT, _Traits>,
+ const _Allocator& = _Allocator()) -> basic_string<_CharT, _Traits, _Allocator>;
template <class _CharT,
class _Traits,
@@ -3977,21 +3975,21 @@ operator""s(const char* __str, size_t __len) {
}
# if _LIBCPP_HAS_WIDE_CHARACTERS
-[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI
-_LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<wchar_t> operator""s(const wchar_t* __str, size_t __len) {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<wchar_t>
+operator""s(const wchar_t* __str, size_t __len) {
return basic_string<wchar_t>(__str, __len);
}
# endif
# if _LIBCPP_HAS_CHAR8_T
-[[__nodiscard__]] inline
- _LIBCPP_HIDE_FROM_ABI constexpr basic_string<char8_t> operator""s(const char8_t* __str, size_t __len) {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI constexpr basic_string<char8_t>
+operator""s(const char8_t* __str, size_t __len) {
return basic_string<char8_t>(__str, __len);
}
# endif
-[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI
-_LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<char16_t> operator""s(const char16_t* __str, size_t __len) {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<char16_t>
+operator""s(const char16_t* __str, size_t __len) {
return basic_string<char16_t>(__str, __len);
}
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
index 0ea8b5f3965f5..6dc3af94bb99f 100644
--- a/libcxx/include/string_view
+++ b/libcxx/include/string_view
@@ -234,8 +234,8 @@ namespace std {
# include <__ranges/enable_view.h>
# include <__ranges/size.h>
# include <__string/char_traits.h>
-# include <__type_traits/is_array.h>
# include <__type_traits/desugars_to.h>
+# include <__type_traits/is_array.h>
# include <__type_traits/is_convertible.h>
# include <__type_traits/is_same.h>
# include <__type_traits/is_standard_layout.h>
diff --git a/libcxx/test/libcxx/type_traits/is_transparently_comparable.compile.pass.cpp b/libcxx/test/libcxx/type_traits/is_transparently_comparable.compile.pass.cpp
index 870a77cf33abc..d02f5713ce777 100644
--- a/libcxx/test/libcxx/type_traits/is_transparently_comparable.compile.pass.cpp
+++ b/libcxx/test/libcxx/type_traits/is_transparently_comparable.compile.pass.cpp
@@ -34,26 +34,22 @@ static_assert(
"");
// basic_string_view with char pointers/arrays
-static_assert(
- std::__is_transparently_comparable_v<std::less<std::string_view>, std::string_view, const char*>, "");
+static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, std::string_view, const char*>, "");
static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, std::string_view, char*>, "");
static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, std::string_view, char[5]>, "");
-static_assert(
- std::__is_transparently_comparable_v<std::less<std::string_view>, const char*, std::string_view>, "");
+static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, const char*, std::string_view>, "");
static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, char*, std::string_view>, "");
static_assert(std::__is_transparently_comparable_v<std::less<std::string_view>, char[5], std::string_view>, "");
-static_assert(
- !std::__is_transparently_comparable_v<std::less<std::reference_wrapper<std::string_view> >,
- std::string_view,
- const char*>,
- "");
-static_assert(
- !std::__is_transparently_comparable_v<std::less<std::reference_wrapper<std::string_view> >,
- const char*,
- std::string_view>,
- "");
+static_assert(!std::__is_transparently_comparable_v<std::less<std::reference_wrapper<std::string_view> >,
+ std::string_view,
+ const char*>,
+ "");
+static_assert(!std::__is_transparently_comparable_v<std::less<std::reference_wrapper<std::string_view> >,
+ const char*,
+ std::string_view>,
+ "");
// Cross-type: basic_string key with basic_string_view argument
static_assert(std::__is_transparently_comparable_v<std::less<std::string>, std::string, std::string_view>, "");
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