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Re: [v3 patch] Implement N4502 Standard Library Support for the C++ Detection Idiom
- From: Jonathan Wakely <jwakely at redhat dot com>
- To: libstdc++ at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Wed, 1 Jul 2015 13:26:54 +0100
- Subject: Re: [v3 patch] Implement N4502 Standard Library Support for the C++ Detection Idiom
- Authentication-results: sourceware.org; auth=none
- References: <20150701122354 dot GD18520 at redhat dot com> <20150701122553 dot GE18520 at redhat dot com>
On 01/07/15 13:25 +0100, Jonathan Wakely wrote:
On 01/07/15 13:23 +0100, Jonathan Wakely wrote:
This adds the "detection idiom" API from N4502
http://open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4502.pdf
I've added the low-level parts to <type_traits>, with public aliases
in <experimental/type_traits>, so that I can use them elsewhere in the
library.
For example this uses the new features to simplify pointer_traits.
And this does the same for allocator_traits.
Tested powerpc64le-linux, committed to trunk.
commit bdccabb2604c4a2f714cea5846ad8526cd2eb496
Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Wed Jul 1 12:24:09 2015 +0000
* include/bits/alloc_traits.h (__alloctr_rebind): Remove.
(__allocator_traits_base): New base class.
(__alloc_rebind): Reimplement in terms of detection idiom.
(allocator_traits): Derive from __allocator_traits_base. Reimplement
nested types in terms of detection idiom. Simplify SFINAE constraints
on overloaded static member functions.
* include/bits/hashtable.h (_Hashtable): Use __alloc_rebind instead
of __alloctr_rebind.
* testsuite/20_util/scoped_allocator/propagation.cc: Define rebind.
* testsuite/23_containers/unordered_set/instantiation_neg.cc: Adjust
dg-error line number.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@225244 138bc75d-0d04-0410-961f-82ee72b054a4
diff --git a/libstdc++-v3/include/bits/alloc_traits.h b/libstdc++-v3/include/bits/alloc_traits.h
index bb98c1d..e5ed92b 100644
--- a/libstdc++-v3/include/bits/alloc_traits.h
+++ b/libstdc++-v3/include/bits/alloc_traits.h
@@ -40,72 +40,57 @@ namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
- template<typename _Alloc, typename _Tp>
- class __alloctr_rebind_helper
- {
- template<typename _Alloc2, typename _Tp2>
- static constexpr true_type
- _S_chk(typename _Alloc2::template rebind<_Tp2>::other*);
-
- template<typename, typename>
- static constexpr false_type
- _S_chk(...);
-
- public:
- using __type = decltype(_S_chk<_Alloc, _Tp>(nullptr));
- };
-
- template<typename _Alloc, typename _Tp,
- bool = __alloctr_rebind_helper<_Alloc, _Tp>::__type::value>
- struct __alloctr_rebind;
-
- template<typename _Alloc, typename _Tp>
- struct __alloctr_rebind<_Alloc, _Tp, true>
- {
- typedef typename _Alloc::template rebind<_Tp>::other __type;
- };
-
- template<template<typename, typename...> class _Alloc, typename _Tp,
- typename _Up, typename... _Args>
- struct __alloctr_rebind<_Alloc<_Up, _Args...>, _Tp, false>
- {
- typedef _Alloc<_Tp, _Args...> __type;
- };
-
- template<typename _Alloc, typename _Tp>
- using __alloc_rebind = typename __alloctr_rebind<_Alloc, _Tp>::__type;
+ struct __allocator_traits_base
+ {
+ template<typename _Alloc, typename _Up>
+ using __rebind = typename _Alloc::template rebind<_Up>::other;
+
+ protected:
+ template<typename _Tp>
+ using __pointer = typename _Tp::pointer;
+ template<typename _Tp>
+ using __c_pointer = typename _Tp::const_pointer;
+ template<typename _Tp>
+ using __v_pointer = typename _Tp::void_pointer;
+ template<typename _Tp>
+ using __cv_pointer = typename _Tp::const_void_pointer;
+ template<typename _Tp>
+ using __diff_type = typename _Tp::difference_type;
+ template<typename _Tp>
+ using __size_type = typename _Tp::size_type;
+ template<typename _Tp>
+ using __pocca = typename _Tp::propagate_on_container_copy_assignment;
+ template<typename _Tp>
+ using __pocma = typename _Tp::propagate_on_container_move_assignment;
+ template<typename _Tp>
+ using __pocs = typename _Tp::propagate_on_container_swap;
+ template<typename _Tp>
+ using __equal = typename _Tp::is_always_equal;
+ };
+
+ template<typename _Alloc, typename _Up>
+ using __alloc_rebind = __detected_or_t_<__replace_first_arg_t,
+ __allocator_traits_base::__rebind,
+ _Alloc, _Up>;
/**
* @brief Uniform interface to all allocator types.
* @ingroup allocators
*/
template<typename _Alloc>
- struct allocator_traits
+ struct allocator_traits : __allocator_traits_base
{
/// The allocator type
typedef _Alloc allocator_type;
/// The allocated type
typedef typename _Alloc::value_type value_type;
-#define _GLIBCXX_ALLOC_TR_NESTED_TYPE(_NTYPE, _ALT) \
- private: \
- template<typename _Tp> \
- static typename _Tp::_NTYPE _S_##_NTYPE##_helper(_Tp*); \
- static _ALT _S_##_NTYPE##_helper(...); \
- typedef decltype(_S_##_NTYPE##_helper((_Alloc*)0)) __##_NTYPE; \
- public:
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(pointer, value_type*)
-
/**
* @brief The allocator's pointer type.
*
* @c Alloc::pointer if that type exists, otherwise @c value_type*
*/
- typedef __pointer pointer;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(const_pointer,
- typename pointer_traits<pointer>::template rebind<const value_type>)
+ using pointer = __detected_or_t<value_type*, __pointer, _Alloc>;
/**
* @brief The allocator's const pointer type.
@@ -113,10 +98,9 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(const_pointer,
* @c Alloc::const_pointer if that type exists, otherwise
* <tt> pointer_traits<pointer>::rebind<const value_type> </tt>
*/
- typedef __const_pointer const_pointer;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(void_pointer,
- typename pointer_traits<pointer>::template rebind<void>)
+ using const_pointer
+ = __detected_or_t<__ptr_rebind<pointer, const value_type>,
+ __c_pointer, _Alloc>;
/**
* @brief The allocator's void pointer type.
@@ -124,10 +108,8 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(void_pointer,
* @c Alloc::void_pointer if that type exists, otherwise
* <tt> pointer_traits<pointer>::rebind<void> </tt>
*/
- typedef __void_pointer void_pointer;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(const_void_pointer,
- typename pointer_traits<pointer>::template rebind<const void>)
+ using void_pointer
+ = __detected_or_t<__ptr_rebind<pointer, void>, __v_pointer, _Alloc>;
/**
* @brief The allocator's const void pointer type.
@@ -135,10 +117,9 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(const_void_pointer,
* @c Alloc::const_void_pointer if that type exists, otherwise
* <tt> pointer_traits<pointer>::rebind<const void> </tt>
*/
- typedef __const_void_pointer const_void_pointer;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(difference_type,
- typename pointer_traits<pointer>::difference_type)
+ using const_void_pointer
+ = __detected_or_t<__ptr_rebind<pointer, const void>, __cv_pointer,
+ _Alloc>;
/**
* @brief The allocator's difference type
@@ -146,10 +127,9 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(difference_type,
* @c Alloc::difference_type if that type exists, otherwise
* <tt> pointer_traits<pointer>::difference_type </tt>
*/
- typedef __difference_type difference_type;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(size_type,
- typename make_unsigned<difference_type>::type)
+ using difference_type
+ = __detected_or_t<typename pointer_traits<pointer>::difference_type,
+ __diff_type, _Alloc>;
/**
* @brief The allocator's size type
@@ -157,10 +137,9 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(size_type,
* @c Alloc::size_type if that type exists, otherwise
* <tt> make_unsigned<difference_type>::type </tt>
*/
- typedef __size_type size_type;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(propagate_on_container_copy_assignment,
- false_type)
+ using size_type
+ = __detected_or_t<typename make_unsigned<difference_type>::type,
+ __size_type, _Alloc>;
/**
* @brief How the allocator is propagated on copy assignment
@@ -168,11 +147,8 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(propagate_on_container_copy_assignment,
* @c Alloc::propagate_on_container_copy_assignment if that type exists,
* otherwise @c false_type
*/
- typedef __propagate_on_container_copy_assignment
- propagate_on_container_copy_assignment;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(propagate_on_container_move_assignment,
- false_type)
+ using propagate_on_container_copy_assignment
+ = __detected_or_t<false_type, __pocca, _Alloc>;
/**
* @brief How the allocator is propagated on move assignment
@@ -180,11 +156,8 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(propagate_on_container_move_assignment,
* @c Alloc::propagate_on_container_move_assignment if that type exists,
* otherwise @c false_type
*/
- typedef __propagate_on_container_move_assignment
- propagate_on_container_move_assignment;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(propagate_on_container_swap,
- false_type)
+ using propagate_on_container_move_assignment
+ = __detected_or_t<false_type, __pocma, _Alloc>;
/**
* @brief How the allocator is propagated on swap
@@ -192,10 +165,8 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(propagate_on_container_swap,
* @c Alloc::propagate_on_container_swap if that type exists,
* otherwise @c false_type
*/
- typedef __propagate_on_container_swap propagate_on_container_swap;
-
-_GLIBCXX_ALLOC_TR_NESTED_TYPE(is_always_equal,
- typename is_empty<_Alloc>::type)
+ using propagate_on_container_swap
+ = __detected_or_t<false_type, __pocs, _Alloc>;
/**
* @brief Whether all instances of the allocator type compare equal.
@@ -203,44 +174,27 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(is_always_equal,
* @c Alloc::is_always_equal if that type exists,
* otherwise @c is_empty<Alloc>::type
*/
- typedef __is_always_equal is_always_equal;
-
-#undef _GLIBCXX_ALLOC_TR_NESTED_TYPE
+ using is_always_equal
+ = __detected_or_t<typename is_empty<_Alloc>::type, __equal, _Alloc>;
template<typename _Tp>
- using rebind_alloc = typename __alloctr_rebind<_Alloc, _Tp>::__type;
+ using rebind_alloc = __alloc_rebind<_Alloc, _Tp>;
template<typename _Tp>
using rebind_traits = allocator_traits<rebind_alloc<_Tp>>;
- private:
- template<typename _Alloc2>
- struct __allocate_helper
- {
- template<typename _Alloc3,
- typename = decltype(std::declval<_Alloc3*>()->allocate(
- std::declval<size_type>(),
- std::declval<const_void_pointer>()))>
- static true_type __test(int);
-
- template<typename>
- static false_type __test(...);
-
- using type = decltype(__test<_Alloc>(0));
- };
+ static_assert(!is_same<rebind_alloc<value_type>, __undefined>::value,
+ "allocator defines rebind or is like Alloc<T, Args>");
+ private:
template<typename _Alloc2>
- using __has_allocate = typename __allocate_helper<_Alloc2>::type;
-
- template<typename _Alloc2,
- typename = _Require<__has_allocate<_Alloc2>>>
- static pointer
- _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer __hint)
+ static auto
+ _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer __hint, int)
+ -> decltype(__a.allocate(__n, __hint))
{ return __a.allocate(__n, __hint); }
- template<typename _Alloc2, typename _UnusedHint,
- typename = _Require<__not_<__has_allocate<_Alloc2>>>>
+ template<typename _Alloc2>
static pointer
- _S_allocate(_Alloc2& __a, size_type __n, _UnusedHint)
+ _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer, ...)
{ return __a.allocate(__n); }
template<typename _Tp, typename... _Args>
@@ -273,57 +227,24 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(is_always_equal,
_S_construct(_Alloc&, _Tp* __p, _Args&&... __args)
{ ::new((void*)__p) _Tp(std::forward<_Args>(__args)...); }
- template<typename _Tp>
- struct __destroy_helper
- {
- template<typename _Alloc2,
- typename = decltype(std::declval<_Alloc2*>()->destroy(
- std::declval<_Tp*>()))>
- static true_type __test(int);
-
- template<typename>
- static false_type __test(...);
-
- using type = decltype(__test<_Alloc>(0));
- };
-
- template<typename _Tp>
- using __has_destroy = typename __destroy_helper<_Tp>::type;
-
- template<typename _Tp>
- static _Require<__has_destroy<_Tp>>
- _S_destroy(_Alloc& __a, _Tp* __p)
+ template<typename _Alloc2, typename _Tp>
+ static auto
+ _S_destroy(_Alloc2& __a, _Tp* __p, int)
+ -> decltype(__a.destroy(__p))
{ __a.destroy(__p); }
- template<typename _Tp>
- static _Require<__not_<__has_destroy<_Tp>>>
- _S_destroy(_Alloc&, _Tp* __p)
+ template<typename _Alloc2, typename _Tp>
+ static void
+ _S_destroy(_Alloc2&, _Tp* __p, ...)
{ __p->~_Tp(); }
template<typename _Alloc2>
- struct __maxsize_helper
- {
- template<typename _Alloc3,
- typename = decltype(std::declval<_Alloc3*>()->max_size())>
- static true_type __test(int);
-
- template<typename>
- static false_type __test(...);
-
- using type = decltype(__test<_Alloc2>(0));
- };
-
- template<typename _Alloc2>
- using __has_max_size = typename __maxsize_helper<_Alloc2>::type;
-
- template<typename _Alloc2,
- typename = _Require<__has_max_size<_Alloc2>>>
- static size_type
+ static auto
_S_max_size(_Alloc2& __a, int)
+ -> decltype(__a.max_size())
{ return __a.max_size(); }
- template<typename _Alloc2,
- typename = _Require<__not_<__has_max_size<_Alloc2>>>>
+ template<typename _Alloc2>
static size_type
_S_max_size(_Alloc2&, ...)
{
@@ -334,30 +255,12 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(is_always_equal,
}
template<typename _Alloc2>
- struct __select_helper
- {
- template<typename _Alloc3, typename
- = decltype(std::declval<_Alloc3*>()
- ->select_on_container_copy_construction())>
- static true_type __test(int);
-
- template<typename>
- static false_type __test(...);
-
- using type = decltype(__test<_Alloc2>(0));
- };
-
- template<typename _Alloc2>
- using __has_soccc = typename __select_helper<_Alloc2>::type;
-
- template<typename _Alloc2,
- typename = _Require<__has_soccc<_Alloc2>>>
- static _Alloc2
+ static auto
_S_select(_Alloc2& __a, int)
+ -> decltype(__a.select_on_container_copy_construction())
{ return __a.select_on_container_copy_construction(); }
- template<typename _Alloc2,
- typename = _Require<__not_<__has_soccc<_Alloc2>>>>
+ template<typename _Alloc2>
static _Alloc2
_S_select(_Alloc2& __a, ...)
{ return __a; }
@@ -388,7 +291,7 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(is_always_equal,
*/
static pointer
allocate(_Alloc& __a, size_type __n, const_void_pointer __hint)
- { return _S_allocate(__a, __n, __hint); }
+ { return _S_allocate(__a, __n, __hint, 0); }
/**
* @brief Deallocate memory.
@@ -398,7 +301,8 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(is_always_equal,
*
* Calls <tt> a.deallocate(p, n) </tt>
*/
- static void deallocate(_Alloc& __a, pointer __p, size_type __n)
+ static void
+ deallocate(_Alloc& __a, pointer __p, size_type __n)
{ __a.deallocate(__p, __n); }
/**
@@ -427,7 +331,7 @@ _GLIBCXX_ALLOC_TR_NESTED_TYPE(is_always_equal,
*/
template <class _Tp>
static void destroy(_Alloc& __a, _Tp* __p)
- { _S_destroy(__a, __p); }
+ { _S_destroy(__a, __p, 0); }
/**
* @brief The maximum supported allocation size
diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h
index 31d237e..4881004 100644
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -179,15 +179,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
public __detail::_Equality<_Key, _Value, _Alloc, _ExtractKey, _Equal,
_H1, _H2, _Hash, _RehashPolicy, _Traits>,
private __detail::_Hashtable_alloc<
- typename __alloctr_rebind<_Alloc,
- __detail::_Hash_node<_Value,
- _Traits::__hash_cached::value> >::__type>
+ __alloc_rebind<_Alloc,
+ __detail::_Hash_node<_Value,
+ _Traits::__hash_cached::value>>>
{
using __traits_type = _Traits;
using __hash_cached = typename __traits_type::__hash_cached;
using __node_type = __detail::_Hash_node<_Value, __hash_cached::value>;
- using __node_alloc_type =
- typename __alloctr_rebind<_Alloc, __node_type>::__type;
+ using __node_alloc_type = __alloc_rebind<_Alloc, __node_type>;
using __hashtable_alloc = __detail::_Hashtable_alloc<__node_alloc_type>;
diff --git a/libstdc++-v3/testsuite/20_util/scoped_allocator/propagation.cc b/libstdc++-v3/testsuite/20_util/scoped_allocator/propagation.cc
index e1e5946..a3da6c0 100644
--- a/libstdc++-v3/testsuite/20_util/scoped_allocator/propagation.cc
+++ b/libstdc++-v3/testsuite/20_util/scoped_allocator/propagation.cc
@@ -41,6 +41,10 @@ template<typename T>
template<typename T, bool copy, bool move, bool swap>
struct test_allocator : minimal_allocator<T>
{
+ template<typename U>
+ struct rebind
+ { using other = test_allocator<U, copy, move, swap>; };
+
struct propagate_on_container_copy_assignment
: std::integral_constant<bool, copy> { };
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_set/instantiation_neg.cc b/libstdc++-v3/testsuite/23_containers/unordered_set/instantiation_neg.cc
index 61848de..ac19900 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_set/instantiation_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_set/instantiation_neg.cc
@@ -19,7 +19,7 @@
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
-// { dg-error "with noexcept" "" { target *-*-* } 266 }
+// { dg-error "with noexcept" "" { target *-*-* } 265 }
#include <unordered_set>