https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106376
Bug ID: 106376
Summary: The implementation of std::pointer_traits seems wrong
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
[pointer.traits.types]:
using element_type = see below;
Type: Ptr::element_type if the qualified-id Ptr::element_type is valid
and denotes a type ([temp.deduct]); otherwise, T if Ptr is a class template
instantiation of the form SomePointer<T, Args>, where Args is zero or more type
arguments; otherwise, the specialization is *ill-formed*.
So for the following, the instantiation of pointer_traits will be ill-formed,
and static_assert will cause a hard error, just like libc++ and MSVC-STL do.
libstdc++ specifies element_type as a meaningless type, so the static_assert
still passes.
Although the behavior of libstdc++ is incorrect, but I am not feel good about
this static_assert hard error..
#include <iterator>
struct I {
using iterator_category = std::contiguous_iterator_tag;
using difference_type = std::ptrdiff_t;
using value_type = int;
value_type& operator*() const;
I& operator++();
I operator++(int);
I& operator--();
I operator--(int);
I& operator+=(difference_type);
I& operator-=(difference_type);
value_type* operator->() const;
value_type& operator[](difference_type) const;
friend I operator+(I, difference_type);
friend I operator+(difference_type, I);
friend I operator-(I, difference_type);
friend difference_type operator-(I, I);
auto operator<=>(const I&) const = default;
};
static_assert(std::contiguous_iterator<I>);
https://godbolt.org/z/sx763oMn6
