[libc++] [C++2b] [P1682] Add to_underlying.
* https://wg21.link/P1682
Reviewed By: ldionne, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D97365
GitOrigin-RevId: 43e421417378bab378eccdf88a66a0a46304fa13
diff --git a/docs/Cxx2bStatusPaperStatus.csv b/docs/Cxx2bStatusPaperStatus.csv
index c6efa20..79b5db0 100644
--- a/docs/Cxx2bStatusPaperStatus.csv
+++ b/docs/Cxx2bStatusPaperStatus.csv
@@ -4,7 +4,7 @@
"`P1048R1 <https://wg21.link/P1048R1>`__","LWG","A proposal for a type trait to detect scoped enumerations","Autumn 2020","|Complete|","12.0"
"`P1679R3 <https://wg21.link/P1679R3>`__","LWG","string contains function","Autumn 2020","|Complete|","12.0"
"","","","","",""
-"`P1682R3 <https://wg21.link/P1682R3>`__","LWG","std::to_underlying for enumerations","February 2021","",""
+"`P1682R3 <https://wg21.link/P1682R3>`__","LWG","std::to_underlying for enumerations","February 2021","|Complete|","13.0"
"`P2017R1 <https://wg21.link/P2017R1>`__","LWG","Conditionally borrowed ranges","February 2021","",""
"`P2160R1 <https://wg21.link/P2160R1>`__","LWG","Locks lock lockables","February 2021","",""
"`P2162R2 <https://wg21.link/P2162R2>`__","LWG","Inheriting from std::variant","February 2021","",""
diff --git a/docs/FeatureTestMacroTable.rst b/docs/FeatureTestMacroTable.rst
index 77010b5..693a668 100644
--- a/docs/FeatureTestMacroTable.rst
+++ b/docs/FeatureTestMacroTable.rst
@@ -301,5 +301,7 @@
``__cpp_lib_stdatomic_h`` *unimplemented*
------------------------------------------------- -----------------
``__cpp_lib_string_contains`` ``202011L``
+ ------------------------------------------------- -----------------
+ ``__cpp_lib_to_underlying`` ``202102L``
================================================= =================
diff --git a/include/utility b/include/utility
index 6f27af7..ca3d3fe 100644
--- a/include/utility
+++ b/include/utility
@@ -191,6 +191,10 @@
template <size_t I>
inline constexpr in_place_index_t<I> in_place_index{};
+// [utility.underlying], to_underlying
+template <class T>
+ constexpr underlying_type_t<T> to_underlying( T value ) noexcept; // C++2b
+
} // std
*/
@@ -1622,8 +1626,21 @@
using __enable_hash_helper _LIBCPP_NODEBUG_TYPE = _Type;
#endif
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr typename underlying_type<_Tp>::type
+__to_underlying(_Tp __val) noexcept {
+ return static_cast<typename underlying_type<_Tp>::type>(__val);
+}
#endif // !_LIBCPP_CXX03_LANG
+#if _LIBCPP_STD_VER > 20
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr underlying_type_t<_Tp>
+to_underlying(_Tp __val) noexcept {
+ return _VSTD::__to_underlying(__val);
+}
+#endif
+
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP_UTILITY
diff --git a/include/version b/include/version
index 49648a0..becbfa5 100644
--- a/include/version
+++ b/include/version
@@ -150,6 +150,7 @@
__cpp_lib_to_address 201711L <memory>
__cpp_lib_to_array 201907L <array>
__cpp_lib_to_chars 201611L <utility>
+__cpp_lib_to_underlying 202102L <utility>
__cpp_lib_transformation_trait_aliases 201304L <type_traits>
__cpp_lib_transparent_operators 201510L <functional> <memory>
201210L // C++14
@@ -365,6 +366,7 @@
// # define __cpp_lib_stacktrace 202011L
// # define __cpp_lib_stdatomic_h 202011L
# define __cpp_lib_string_contains 202011L
+# define __cpp_lib_to_underlying 202102L
#endif
// clang-format on
diff --git a/test/std/language.support/support.limits/support.limits.general/utility.version.pass.cpp b/test/std/language.support/support.limits/support.limits.general/utility.version.pass.cpp
index ab495be..1ec2f43 100644
--- a/test/std/language.support/support.limits/support.limits.general/utility.version.pass.cpp
+++ b/test/std/language.support/support.limits/support.limits.general/utility.version.pass.cpp
@@ -22,6 +22,7 @@
__cpp_lib_integer_comparison_functions 202002L [C++20]
__cpp_lib_integer_sequence 201304L [C++14]
__cpp_lib_to_chars 201611L [C++17]
+ __cpp_lib_to_underlying 202102L [C++2b]
__cpp_lib_tuples_by_type 201304L [C++14]
*/
@@ -54,6 +55,10 @@
# error "__cpp_lib_to_chars should not be defined before c++17"
# endif
+# ifdef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should not be defined before c++2b"
+# endif
+
# ifdef __cpp_lib_tuples_by_type
# error "__cpp_lib_tuples_by_type should not be defined before c++14"
# endif
@@ -90,6 +95,10 @@
# error "__cpp_lib_to_chars should not be defined before c++17"
# endif
+# ifdef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should not be defined before c++2b"
+# endif
+
# ifndef __cpp_lib_tuples_by_type
# error "__cpp_lib_tuples_by_type should be defined in c++14"
# endif
@@ -141,6 +150,10 @@
# endif
# endif
+# ifdef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should not be defined before c++2b"
+# endif
+
# ifndef __cpp_lib_tuples_by_type
# error "__cpp_lib_tuples_by_type should be defined in c++17"
# endif
@@ -204,6 +217,10 @@
# endif
# endif
+# ifdef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should not be defined before c++2b"
+# endif
+
# ifndef __cpp_lib_tuples_by_type
# error "__cpp_lib_tuples_by_type should be defined in c++20"
# endif
@@ -267,6 +284,13 @@
# endif
# endif
+# ifndef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should be defined in c++2b"
+# endif
+# if __cpp_lib_to_underlying != 202102L
+# error "__cpp_lib_to_underlying should have the value 202102L in c++2b"
+# endif
+
# ifndef __cpp_lib_tuples_by_type
# error "__cpp_lib_tuples_by_type should be defined in c++2b"
# endif
diff --git a/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp b/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
index 337714f..3a66876 100644
--- a/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
+++ b/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
@@ -140,6 +140,7 @@
__cpp_lib_to_address 201711L [C++20]
__cpp_lib_to_array 201907L [C++20]
__cpp_lib_to_chars 201611L [C++17]
+ __cpp_lib_to_underlying 202102L [C++2b]
__cpp_lib_transformation_trait_aliases 201304L [C++14]
__cpp_lib_transparent_operators 201210L [C++14]
201510L [C++17]
@@ -642,6 +643,10 @@
# error "__cpp_lib_to_chars should not be defined before c++17"
# endif
+# ifdef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should not be defined before c++2b"
+# endif
+
# ifdef __cpp_lib_transformation_trait_aliases
# error "__cpp_lib_transformation_trait_aliases should not be defined before c++14"
# endif
@@ -1222,6 +1227,10 @@
# error "__cpp_lib_to_chars should not be defined before c++17"
# endif
+# ifdef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should not be defined before c++2b"
+# endif
+
# ifndef __cpp_lib_transformation_trait_aliases
# error "__cpp_lib_transformation_trait_aliases should be defined in c++14"
# endif
@@ -2021,6 +2030,10 @@
# endif
# endif
+# ifdef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should not be defined before c++2b"
+# endif
+
# ifndef __cpp_lib_transformation_trait_aliases
# error "__cpp_lib_transformation_trait_aliases should be defined in c++17"
# endif
@@ -3225,6 +3238,10 @@
# endif
# endif
+# ifdef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should not be defined before c++2b"
+# endif
+
# ifndef __cpp_lib_transformation_trait_aliases
# error "__cpp_lib_transformation_trait_aliases should be defined in c++20"
# endif
@@ -4456,6 +4473,13 @@
# endif
# endif
+# ifndef __cpp_lib_to_underlying
+# error "__cpp_lib_to_underlying should be defined in c++2b"
+# endif
+# if __cpp_lib_to_underlying != 202102L
+# error "__cpp_lib_to_underlying should have the value 202102L in c++2b"
+# endif
+
# ifndef __cpp_lib_transformation_trait_aliases
# error "__cpp_lib_transformation_trait_aliases should be defined in c++2b"
# endif
diff --git a/test/std/utilities/utility/utility.underlying/to_underlying.pass.cpp b/test/std/utilities/utility/utility.underlying/to_underlying.pass.cpp
new file mode 100644
index 0000000..0b2bc19
--- /dev/null
+++ b/test/std/utilities/utility/utility.underlying/to_underlying.pass.cpp
@@ -0,0 +1,84 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+
+// [utility.underlying], to_underlying
+// template <class T>
+// constexpr underlying_type_t<T> to_underlying( T value ) noexcept; // C++2b
+
+#include <utility>
+#include <cassert>
+#include <limits>
+
+#include "test_macros.h"
+
+enum class e_default { a = 0, b = 1, c = 2 };
+enum class e_ushort : unsigned short { d = 10, e = 25, f = 50 };
+enum class e_longlong : long long {
+ low = std::numeric_limits<long long>::min(),
+ high = std::numeric_limits<long long>::max()
+};
+enum e_non_class { enum_a = 10, enum_b = 11, enum_c = 12 };
+enum e_int : int {
+ enum_min = std::numeric_limits<int>::min(),
+ enum_max = std::numeric_limits<int>::max()
+};
+enum class e_bool : std::uint8_t { f = 0, t = 1 };
+
+struct WithBitfieldEnums {
+ e_default e1 : 3;
+ e_ushort e2 : 6;
+ e_bool e3 : 1;
+};
+
+constexpr bool test() {
+ ASSERT_NOEXCEPT(std::to_underlying(e_default::a));
+ ASSERT_SAME_TYPE(int, decltype(std::to_underlying(e_default::a)));
+ ASSERT_SAME_TYPE(unsigned short, decltype(std::to_underlying(e_ushort::d)));
+ ASSERT_SAME_TYPE(long long, decltype(std::to_underlying(e_longlong::low)));
+ ASSERT_SAME_TYPE(int, decltype(std::to_underlying(enum_min)));
+ ASSERT_SAME_TYPE(int, decltype(std::to_underlying(enum_max)));
+
+ assert(0 == std::to_underlying(e_default::a));
+ assert(1 == std::to_underlying(e_default::b));
+ assert(2 == std::to_underlying(e_default::c));
+
+ assert(10 == std::to_underlying(e_ushort::d));
+ assert(25 == std::to_underlying(e_ushort::e));
+ assert(50 == std::to_underlying(e_ushort::f));
+
+ // Check no truncating.
+ assert(std::numeric_limits<long long>::min() ==
+ std::to_underlying(e_longlong::low));
+ assert(std::numeric_limits<long long>::max() ==
+ std::to_underlying(e_longlong::high));
+
+ assert(10 == std::to_underlying(enum_a));
+ assert(11 == std::to_underlying(enum_b));
+ assert(12 == std::to_underlying(enum_c));
+ assert(std::numeric_limits<int>::min() == std::to_underlying(enum_min));
+ assert(std::numeric_limits<int>::max() == std::to_underlying(enum_max));
+
+ WithBitfieldEnums bf;
+ bf.e1 = static_cast<e_default>(3);
+ bf.e2 = e_ushort::e;
+ bf.e3 = e_bool::t;
+ assert(3 == std::to_underlying(bf.e1));
+ assert(25 == std::to_underlying(bf.e2));
+ assert(1 == std::to_underlying(bf.e3));
+
+ return true;
+}
+
+int main(int, char**) {
+ test();
+ static_assert(test());
+
+ return 0;
+}
diff --git a/test/std/utilities/utility/utility.underlying/to_underlying.verify.cpp b/test/std/utilities/utility/utility.underlying/to_underlying.verify.cpp
new file mode 100644
index 0000000..9064ba4
--- /dev/null
+++ b/test/std/utilities/utility/utility.underlying/to_underlying.verify.cpp
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++2a
+
+// [utility.underlying], to_underlying
+// template <class T>
+// constexpr underlying_type_t<T> to_underlying( T value ) noexcept; // C++2b
+
+#include <utility>
+
+struct S {};
+
+int main(int, char**) {
+ std::to_underlying(125); // expected-error {{no matching function for call}}
+ std::to_underlying(S{}); // expected-error {{no matching function for call}}
+
+ return 0;
+}
diff --git a/utils/generate_feature_test_macro_components.py b/utils/generate_feature_test_macro_components.py
index 24780f8..7351da3 100755
--- a/utils/generate_feature_test_macro_components.py
+++ b/utils/generate_feature_test_macro_components.py
@@ -594,6 +594,10 @@
"headers": ["utility"],
"unimplemented": True,
}, {
+ "name": "__cpp_lib_to_underlying",
+ "values": { "c++2b": 202102 },
+ "headers": ["utility"],
+ }, {
"name": "__cpp_lib_transformation_trait_aliases",
"values": { "c++14": 201304 },
"headers": ["type_traits"],