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[libc++] Require fancy pointer to be correctly convertible #152989

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[libc++] Require fancy pointer to be correctly convertible #152989

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10 changes: 5 additions & 5 deletions libcxx/include/__hash_table
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Original file line number Diff line number Diff line change
Expand Up @@ -96,7 +96,7 @@ struct __hash_node_base {
__next_pointer __next_;
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Please add a release note and mention the potential for breakage. In particular, what kind of code would break after this change and what users should do to fix it.


_LIBCPP_HIDE_FROM_ABI __next_pointer __ptr() _NOEXCEPT {
return static_cast<__next_pointer>(pointer_traits<__node_base_pointer>::pointer_to(*this));
return pointer_traits<__node_base_pointer>::pointer_to(*this);
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Do I understand correctly that this would be the "right" way to perform this cast if we only want to use the requirements in https://eel.is/c++draft/allocator.requirements.general ?

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return pointer_traits<__node_base_pointer>::pointer_to(*this);
return static_cast<__next_pointer>(static_cast<void_pointer>(pointer_traits<__node_base_pointer>::pointer_to(*this)));

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Conversion via void_pointer is constexpr-unfriendly (while these details need to be constexpr since C++26).

}

_LIBCPP_HIDE_FROM_ABI __node_pointer __upcast() _NOEXCEPT {
Expand Down Expand Up @@ -1499,9 +1499,9 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_multi(const_iterator __p
while (__pp->__next_ != __np)
__pp = __pp->__next_;
__cp->__next_ = __np;
__pp->__next_ = static_cast<__next_pointer>(__cp);
__pp->__next_ = __cp;
++size();
return iterator(static_cast<__next_pointer>(__cp));
return iterator(__cp);
}
return __node_insert_multi(__cp);
}
Expand Down Expand Up @@ -1547,9 +1547,9 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::__emplace_unique_key_args(_Key const&
__bucket_list_[std::__constrain_hash(__h->__next_->__hash(), __bc)] = __h.get()->__ptr();
} else {
__h->__next_ = __pn->__next_;
__pn->__next_ = static_cast<__next_pointer>(__h.get());
__pn->__next_ = __h.get();
}
__nd = static_cast<__next_pointer>(__h.release());
__nd = __h.release();
// increment size
++size();
__inserted = true;
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12 changes: 0 additions & 12 deletions libcxx/include/__memory/pointer_traits.h
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Original file line number Diff line number Diff line change
Expand Up @@ -252,18 +252,6 @@ concept __resettable_smart_pointer_with_args = requires(_Smart __s, _Pointer __p

#endif

// This function ensures safe conversions between fancy pointers at compile-time, where we avoid casts from/to
// `__void_pointer` by obtaining the underlying raw pointer from the fancy pointer using `std::to_address`,
// then dereferencing it to retrieve the pointed-to object, and finally constructing the target fancy pointer
// to that object using the `std::pointer_traits<>::pinter_to` function.
template <class _PtrTo, class _PtrFrom>
_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI _PtrTo __static_fancy_pointer_cast(const _PtrFrom& __p) {
using __ptr_traits = pointer_traits<_PtrTo>;
using __element_type = typename __ptr_traits::element_type;
return __p ? __ptr_traits::pointer_to(*static_cast<__element_type*>(std::addressof(*__p)))
: static_cast<_PtrTo>(nullptr);
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS
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