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From: "de34 at live dot cn" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/104443] New: common_iterator<I, S>::operator-> is not
 correctly implemented
Date: Tue, 08 Feb 2022 17:40:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104443

            Bug ID: 104443
           Summary: common_iterator<I, S>::operator-> is not correctly
                    implemented
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: de34 at live dot cn
  Target Milestone: ---

When the adapted iterator type I is a pointer type or has operator->,
std::common_iterator<I, S>::operator-> is required to return the iterator by
reference ([common.iter.access]/(5.1), and std::get for std::variant always
returns reference).

However, currently libstdc++'s implementation returns the iterator by value=
 in
these cases, because "return _M_it;" is used and the return type is specifi=
ed
by decltype(auto). "return (_M_it);" should be used instead.

Currently only libc++ correctly implements both common_iterator<I,
S>::operator-> and iterator_traits<common_iterator<I, S>>::pointer. See
https://gcc.godbolt.org/z/1Tn5cGrhh.=