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Make array<const T, 0> non-CopyAssignable and make swap and fill ill-formed.

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The standard isn't exactly clear how std::array should handle zero-sized arrays
with const element types. In particular W.R.T. copy assignment, swap, and fill.

This patch takes the position that those operations should be ill-formed,
and makes changes to libc++ to make it so.

This follows up on commit r324182.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@324185 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier
2018-02-04 02:17:02 +00:00
parent f3224ac007
commit 122c064a76
5 changed files with 181 additions and 10 deletions
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31
include/array
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@@ -122,7 +122,8 @@ struct __array_traits {
typedef _Tp _StorageT[_Size];
_LIBCPP_INLINE_VISIBILITY
static _LIBCPP_CONSTEXPR_AFTER_CXX14 _Tp* __data(_StorageT& __store) {
static _LIBCPP_CONSTEXPR_AFTER_CXX14 typename remove_const<_Tp>::type*
__data(typename remove_const<_StorageT>::type& __store) {
return __store;
}
@@ -144,12 +145,16 @@ struct __array_traits {
template <class _Tp>
struct __array_traits<_Tp, 0> {
typedef typename aligned_storage<sizeof(_Tp), alignment_of<_Tp>::value>::type _StorageT;
typedef typename aligned_storage<sizeof(_Tp), alignment_of<_Tp>::value>::type
_NonConstStorageT;
typedef typename conditional<is_const<_Tp>::value, const _NonConstStorageT,
_NonConstStorageT>::type _StorageT;
typedef typename remove_const<_Tp>::type _NonConstTp;
_LIBCPP_INLINE_VISIBILITY
static _Tp* __data(_StorageT& __store) {
static _NonConstTp* __data(_NonConstStorageT& __store) {
_StorageT *__ptr = std::addressof(__store);
return reinterpret_cast<_Tp*>(__ptr);
return reinterpret_cast<_NonConstTp*>(__ptr);
}
_LIBCPP_INLINE_VISIBILITY
@@ -162,8 +167,7 @@ struct __array_traits<_Tp, 0> {
static void __swap(_StorageT&, _StorageT&) {}
_LIBCPP_INLINE_VISIBILITY
static void __fill(_StorageT&, _Tp const&) {
}
static void __fill(_StorageT&, _Tp const&) {}
};
template <class _Tp, size_t _Size>
@@ -187,12 +191,19 @@ struct _LIBCPP_TEMPLATE_VIS array
typename _Traits::_StorageT __elems_;
// No explicit construct/copy/destroy for aggregate type
_LIBCPP_INLINE_VISIBILITY void fill(const value_type& __u)
{_Traits::__fill(__elems_, __u);}
_LIBCPP_INLINE_VISIBILITY void fill(const value_type& __u) {
static_assert(_Size != 0 || !is_const<_Tp>::value,
"cannot fill zero-sized array of type 'const T'");
_Traits::__fill(__elems_, __u);
}
_LIBCPP_INLINE_VISIBILITY
void swap(array& __a) _NOEXCEPT_(_Size == 0 || __is_nothrow_swappable<_Tp>::value)
{ _Traits::__swap(__elems_, __a.__elems_); }
void swap(array& __a)
_NOEXCEPT_(_Size == 0 || __is_nothrow_swappable<_Tp>::value) {
static_assert(_Size != 0 || !is_const<_Tp>::value,
"cannot swap zero-sized array of type 'const T'");
_Traits::__swap(__elems_, __a.__elems_);
}
// iterators:
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14