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* [gcc r13-2830] libstdc++: Simplify detection idiom using concepts
@ 2022-09-24 14:18 Jonathan Wakely
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From: Jonathan Wakely @ 2022-09-24 14:18 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:2b667beba693e876322af7c6682f9bc885c5ec28
commit r13-2830-g2b667beba693e876322af7c6682f9bc885c5ec28
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Sep 23 23:16:30 2022 +0100
libstdc++: Simplify detection idiom using concepts
Add a simpler definition of std::__detected_or using concepts. This
also replaces the __detector::value_t member which should have been using
a reserved name.
Use __detected_or in pointer_traits.
libstdc++-v3/ChangeLog:
* include/bits/alloc_traits.h (allocator_traits::is_always_equal):
Only instantiate is_empty if needed.
* include/bits/ptr_traits.h (__ptr_traits_impl::difference_type)
(__ptr_traits_impl::rebind): Use __detected_or.
* include/experimental/type_traits (is_same_v): Add a partial
specialization instead of instantiating the std::is_same class
template.
(detected_t): Redefine in terms of detected_or_t.
(is_detected, is_detected_v): Redefine in terms of detected_t.
* include/std/type_traits [__cpp_concepts] (__detected_or): Add
new definition using concepts.
(__detector::value_t): Rename to __is_detected.
* testsuite/17_intro/names.cc: Check value_t isn't used.
Diff:
---
libstdc++-v3/include/bits/alloc_traits.h | 4 ++--
libstdc++-v3/include/bits/ptr_traits.h | 27 +++++----------------------
libstdc++-v3/include/experimental/type_traits | 24 ++++++++++++------------
libstdc++-v3/include/std/type_traits | 27 ++++++++++++++++++++++++---
libstdc++-v3/testsuite/17_intro/names.cc | 1 +
5 files changed, 44 insertions(+), 39 deletions(-)
diff --git a/libstdc++-v3/include/bits/alloc_traits.h b/libstdc++-v3/include/bits/alloc_traits.h
index 507e8f1b6b2..8479bfd612f 100644
--- a/libstdc++-v3/include/bits/alloc_traits.h
+++ b/libstdc++-v3/include/bits/alloc_traits.h
@@ -74,7 +74,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Tp>
using __pocs = typename _Tp::propagate_on_container_swap;
template<typename _Tp>
- using __equal = typename _Tp::is_always_equal;
+ using __equal = __type_identity<typename _Tp::is_always_equal>;
};
template<typename _Alloc, typename _Up>
@@ -209,7 +209,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* otherwise @c is_empty<Alloc>::type
*/
using is_always_equal
- = __detected_or_t<typename is_empty<_Alloc>::type, __equal, _Alloc>;
+ = typename __detected_or_t<is_empty<_Alloc>, __equal, _Alloc>::type;
template<typename _Tp>
using rebind_alloc = __alloc_rebind<_Alloc, _Tp>;
diff --git a/libstdc++-v3/include/bits/ptr_traits.h b/libstdc++-v3/include/bits/ptr_traits.h
index 8360c3b6557..ae8810706ab 100644
--- a/libstdc++-v3/include/bits/ptr_traits.h
+++ b/libstdc++-v3/include/bits/ptr_traits.h
@@ -144,29 +144,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
struct __ptr_traits_impl : __ptr_traits_ptr_to<_Ptr, _Elt>
{
private:
- template<typename _Tp, typename = void>
- struct __difference { using type = ptrdiff_t; };
-
template<typename _Tp>
-#if __cpp_concepts
- requires requires { typename _Tp::difference_type; }
- struct __difference<_Tp>
-#else
- struct __difference<_Tp, __void_t<typename _Tp::difference_type>>
-#endif
- { using type = typename _Tp::difference_type; };
-
- template<typename _Tp, typename _Up, typename = void>
- struct __rebind : __replace_first_arg<_Tp, _Up> { };
+ using __diff_t = typename _Tp::difference_type;
template<typename _Tp, typename _Up>
-#if __cpp_concepts
- requires requires { typename _Tp::template rebind<_Up>; }
- struct __rebind<_Tp, _Up>
-#else
- struct __rebind<_Tp, _Up, __void_t<typename _Tp::template rebind<_Up>>>
-#endif
- { using type = typename _Tp::template rebind<_Up>; };
+ using __rebind = __type_identity<typename _Tp::template rebind<_Up>>;
public:
/// The pointer type.
@@ -176,11 +158,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using element_type = _Elt;
/// The type used to represent the difference between two pointers.
- using difference_type = typename __difference<_Ptr>::type;
+ using difference_type = __detected_or_t<ptrdiff_t, __diff_t, _Ptr>;
/// A pointer to a different type.
template<typename _Up>
- using rebind = typename __rebind<_Ptr, _Up>::type;
+ using rebind = typename __detected_or_t<__replace_first_arg<_Ptr, _Up>,
+ __rebind, _Ptr, _Up>::type;
};
// _GLIBCXX_RESOLVE_LIB_DEFECTS
diff --git a/libstdc++-v3/include/experimental/type_traits b/libstdc++-v3/include/experimental/type_traits
index af5970e80d0..fa25a1c2be2 100644
--- a/libstdc++-v3/include/experimental/type_traits
+++ b/libstdc++-v3/include/experimental/type_traits
@@ -223,7 +223,9 @@ template <typename _Tp, unsigned _Idx = 0>
// See C++14 20.10.6, type relations
template <typename _Tp, typename _Up>
- constexpr bool is_same_v = is_same<_Tp, _Up>::value;
+ constexpr bool is_same_v = false;
+template <typename _Tp>
+ constexpr bool is_same_v<_Tp, _Tp> = true;
template <typename _Base, typename _Derived>
constexpr bool is_base_of_v = is_base_of<_Base, _Derived>::value;
template <typename _From, typename _To>
@@ -266,23 +268,21 @@ struct nonesuch : private __nonesuchbase
};
#pragma GCC diagnostic pop
-template<template<typename...> class _Op, typename... _Args>
- using is_detected
- = typename std::__detector<nonesuch, void, _Op, _Args...>::value_t;
-
-template<template<typename...> class _Op, typename... _Args>
- constexpr bool is_detected_v = is_detected<_Op, _Args...>::value;
-
-template<template<typename...> class _Op, typename... _Args>
- using detected_t
- = typename std::__detector<nonesuch, void, _Op, _Args...>::type;
-
template<typename _Default, template<typename...> class _Op, typename... _Args>
using detected_or = std::__detected_or<_Default, _Op, _Args...>;
template<typename _Default, template<typename...> class _Op, typename... _Args>
using detected_or_t = typename detected_or<_Default, _Op, _Args...>::type;
+template<template<typename...> class _Op, typename... _Args>
+ using detected_t = detected_or_t<nonesuch, _Op, _Args...>;
+
+template<template<typename...> class _Op, typename... _Args>
+ using is_detected = typename detected_or<void, _Op, _Args...>::__is_detected;
+
+template<template<typename...> class _Op, typename... _Args>
+ constexpr bool is_detected_v = is_detected<_Op, _Args...>::value;
+
template<typename _Expected, template<typename...> class _Op, typename... _Args>
using is_detected_exact = is_same<_Expected, detected_t<_Op, _Args...>>;
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 7c635313a95..c5853fcad90 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2551,13 +2551,34 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// @cond undocumented
+ // Detection idiom.
+ // Detect whether _Op<_Args...> is a valid type, use default _Def if not.
+
+#if __cpp_concepts
+ // Implementation of the detection idiom (negative case).
+ template<typename _Def, template<typename...> class _Op, typename... _Args>
+ struct __detected_or
+ {
+ using type = _Def;
+ using __is_detected = false_type;
+ };
+
+ // Implementation of the detection idiom (positive case).
+ template<typename _Def, template<typename...> class _Op, typename... _Args>
+ requires requires { typename _Op<_Args...>; }
+ struct __detected_or<_Def, _Op, _Args...>
+ {
+ using type = _Op<_Args...>;
+ using __is_detected = true_type;
+ };
+#else
/// Implementation of the detection idiom (negative case).
template<typename _Default, typename _AlwaysVoid,
template<typename...> class _Op, typename... _Args>
struct __detector
{
- using value_t = false_type;
using type = _Default;
+ using __is_detected = false_type;
};
/// Implementation of the detection idiom (positive case).
@@ -2565,14 +2586,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
typename... _Args>
struct __detector<_Default, __void_t<_Op<_Args...>>, _Op, _Args...>
{
- using value_t = true_type;
using type = _Op<_Args...>;
+ using __is_detected = true_type;
};
- // Detect whether _Op<_Args...> is a valid type, use _Default if not.
template<typename _Default, template<typename...> class _Op,
typename... _Args>
using __detected_or = __detector<_Default, void, _Op, _Args...>;
+#endif // __cpp_concepts
// _Op<_Args...> if that is a valid type, otherwise _Default.
template<typename _Default, template<typename...> class _Op,
diff --git a/libstdc++-v3/testsuite/17_intro/names.cc b/libstdc++-v3/testsuite/17_intro/names.cc
index 82e201c71b0..6490cd63307 100644
--- a/libstdc++-v3/testsuite/17_intro/names.cc
+++ b/libstdc++-v3/testsuite/17_intro/names.cc
@@ -112,6 +112,7 @@
#define tmp (
#define sz (
#define token (
+#define value_t (
#if __cplusplus < 201103L
#define uses_allocator (
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