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.
These changes caused some new FAILs due to invalid uses of
pointer_traits that the standard says should be ill-formed but didn't
fail before. The patch fixes those tests.
Tested powerpc64le-linux, committed to trunk.
commit 9014ff9e72ef2d0048e1985d282341a3c37162ef
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Wed Jul 1 12:27:46 2015 +0100
* include/bits/ptr_traits.h (__ptrtr_elt_type, __ptrtr_diff_type,
__ptrtr_rebind, __ptrtr_not_void): Remove
(__get_first_arg, __replace_first_arg, __make_not_void): Define new
transformations.
(__detected_or_): New detection trait.
(pointer_traits): Use new traits.
* testsuite/20_util/pointer_traits/pointer_to.cc: Add rebind member.
* testsuite/20_util/pointer_traits/requirements/
explicit_instantiation.cc: Use valid arguments to pointer_traits.
diff --git a/libstdc++-v3/include/bits/ptr_traits.h b/libstdc++-v3/include/bits/ptr_traits.h
index 9fd6bf8..84cc4da 100644
--- a/libstdc++-v3/include/bits/ptr_traits.h
+++ b/libstdc++-v3/include/bits/ptr_traits.h
@@ -32,114 +32,86 @@
#if __cplusplus >= 201103L
-#include <type_traits> // For _GLIBCXX_HAS_NESTED_TYPE
+#include <type_traits>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
-_GLIBCXX_HAS_NESTED_TYPE(element_type)
-_GLIBCXX_HAS_NESTED_TYPE(difference_type)
-
- template<typename _Tp, bool = __has_element_type<_Tp>::value>
- struct __ptrtr_elt_type;
+ class __undefined;
+ // Given Template<T, ...> return T, otherwise invalid.
template<typename _Tp>
- struct __ptrtr_elt_type<_Tp, true>
- {
- typedef typename _Tp::element_type __type;
- };
-
- template<template<typename, typename...> class _SomePtr, typename _Tp,
- typename... _Args>
- struct __ptrtr_elt_type<_SomePtr<_Tp, _Args...>, false>
- {
- typedef _Tp __type;
- };
+ struct __get_first_arg
+ { using type = __undefined; };
- template<typename _Tp, bool = __has_difference_type<_Tp>::value>
- struct __ptrtr_diff_type
- {
- typedef typename _Tp::difference_type __type;
- };
+ template<template<typename, typename...> class _Template, typename _Tp,
+ typename... _Types>
+ struct __get_first_arg<_Template<_Tp, _Types...>>
+ { using type = _Tp; };
template<typename _Tp>
- struct __ptrtr_diff_type<_Tp, false>
- {
- typedef ptrdiff_t __type;
- };
-
- template<typename _Ptr, typename _Up>
- class __ptrtr_rebind_helper
- {
- template<typename _Ptr2, typename _Up2>
- static constexpr true_type
- _S_chk(typename _Ptr2::template rebind<_Up2>*);
-
- template<typename, typename>
- static constexpr false_type
- _S_chk(...);
-
- public:
- using __type = decltype(_S_chk<_Ptr, _Up>(nullptr));
- };
-
- template<typename _Tp, typename _Up,
- bool = __ptrtr_rebind_helper<_Tp, _Up>::__type::value>
- struct __ptrtr_rebind;
+ using __get_first_arg_t = typename __get_first_arg<_Tp>::type;
+ // Given Template<T, ...> and U return Template<U, ...>, otherwise invalid.
template<typename _Tp, typename _Up>
- struct __ptrtr_rebind<_Tp, _Up, true>
- {
- typedef typename _Tp::template rebind<_Up> __type;
- };
+ struct __replace_first_arg
+ { using type = __undefined; };
- template<template<typename, typename...> class _SomePtr, typename _Up,
- typename _Tp, typename... _Args>
- struct __ptrtr_rebind<_SomePtr<_Tp, _Args...>, _Up, false>
- {
- typedef _SomePtr<_Up, _Args...> __type;
- };
+ template<template<typename, typename...> class _Template, typename _Up,
+ typename _Tp, typename... _Types>
+ struct __replace_first_arg<_Template<_Tp, _Types...>, _Up>
+ { using type = _Template<_Up, _Types...>; };
- template<typename _Tp, typename = typename remove_cv<_Tp>::type>
- struct __ptrtr_not_void
- {
- typedef _Tp __type;
- };
+ template<typename _Tp, typename _Up>
+ using __replace_first_arg_t = typename __replace_first_arg<_Tp, _Up>::type;
template<typename _Tp>
- struct __ptrtr_not_void<_Tp, void>
- {
- struct __type { };
- };
-
- template<typename _Ptr>
- class __ptrtr_pointer_to
- {
- typedef typename __ptrtr_elt_type<_Ptr>::__type __orig_type;
- typedef typename __ptrtr_not_void<__orig_type>::__type __element_type;
-
- public:
- static _Ptr pointer_to(__element_type& __e)
- { return _Ptr::pointer_to(__e); }
- };
+ using __make_not_void
+ = typename conditional<is_void<_Tp>::value, __undefined, _Tp>::type;
/**
* @brief Uniform interface to all pointer-like types
* @ingroup pointer_abstractions
*/
template<typename _Ptr>
- struct pointer_traits : __ptrtr_pointer_to<_Ptr>
+ struct pointer_traits
{
- /// The pointer type
- typedef _Ptr pointer;
- /// The type pointed to
- typedef typename __ptrtr_elt_type<_Ptr>::__type element_type;
- /// Type used to represent the difference between two pointers
- typedef typename __ptrtr_diff_type<_Ptr>::__type difference_type;
+ private:
+ template<typename _Tp>
+ using __element_type = typename _Tp::element_type;
+
+ template<typename _Tp>
+ using __difference_type = typename _Tp::difference_type;
+
+ template<typename _Tp, typename _Up>
+ using __rebind = typename _Tp::template rebind<_Up>;
+
+ public:
+ /// The pointer type.
+ using pointer = _Ptr;
+
+ /// The type pointed to.
+ using element_type
+ = __detected_or_t_<__get_first_arg_t, __element_type, _Ptr>;
+ /// The type used to represent the difference between two pointers.
+ using difference_type
+ = __detected_or_t<ptrdiff_t, __difference_type, _Ptr>;
+
+ /// A pointer to a different type.
template<typename _Up>
- using rebind = typename __ptrtr_rebind<_Ptr, _Up>::__type;
+ using rebind
+ = __detected_or_t_<__replace_first_arg_t, __rebind, _Ptr, _Up>;
+
+ static _Ptr
+ pointer_to(__make_not_void<element_type>& __e)
+ { return _Ptr::pointer_to(__e); }
+
+ static_assert(!is_same<element_type, __undefined>::value,
+ "pointer type defines element_type or is like SomePointer<T, Args>");
+ static_assert(!is_same<rebind<element_type>, __undefined>::value,
+ "pointer type defines rebind<U> or is like SomePointer<T, Args>");
};
/**
@@ -165,10 +137,14 @@ _GLIBCXX_HAS_NESTED_TYPE(difference_type)
* @return @c addressof(__r)
*/
static pointer
- pointer_to(typename __ptrtr_not_void<element_type>::__type& __r) noexcept
+ pointer_to(__make_not_void<element_type>& __r) noexcept
{ return std::addressof(__r); }
};
+ /// Convenience alias for rebinding pointers.
+ template<typename _Ptr, typename _Tp>
+ using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
diff --git a/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to.cc b/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to.cc
index 843adbd..6782f79 100644
--- a/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to.cc
+++ b/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to.cc
@@ -26,6 +26,8 @@ struct Ptr
typedef bool element_type;
bool* value;
+ template<typename> using rebind = Ptr;
+
static Ptr pointer_to(bool& b) { return Ptr{&b}; }
};
diff --git a/libstdc++-v3/testsuite/20_util/pointer_traits/requirements/explicit_instantiation.cc b/libstdc++-v3/testsuite/20_util/pointer_traits/requirements/explicit_instantiation.cc
index f47bed0..d9c808f 100644
--- a/libstdc++-v3/testsuite/20_util/pointer_traits/requirements/explicit_instantiation.cc
+++ b/libstdc++-v3/testsuite/20_util/pointer_traits/requirements/explicit_instantiation.cc
@@ -22,10 +22,25 @@
#include <memory>
+template<typename T>
+struct P1
+{
+ using element_type = T;
+ using difference_type = long;
+ template<typename U> using rebind = P1<U>;
+ static P1 pointer_to(T&) { return {}; }
+};
+
+template<typename T>
+struct P2
+{
+ static P2 pointer_to(T&) { return {}; }
+};
+
namespace std
{
typedef short test_type;
template struct pointer_traits<test_type*>;
- template struct pointer_traits<shared_ptr<test_type>>;
- template struct pointer_traits<unique_ptr<test_type>>;
+ template struct pointer_traits<P1<test_type>>;
+ template struct pointer_traits<P2<test_type>>;
}
