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From: "pkasting at google dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/109242] New: C++2b std::optional::transform omits
 required std::remove_cv_t from return optional type
Date: Tue, 21 Mar 2023 23:31:31 +0000
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X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109242

            Bug ID: 109242
           Summary: C++2b std::optional::transform omits required
                    std::remove_cv_t from return optional type
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pkasting at google dot com
  Target Milestone: ---

The implementation of C++2b's std::optional::transform() on HEAD omits a ca=
ll
to std::remove_cv_t when determining the value type of the returned optiona=
l.
As a result valid code such as the following example is rejected:
https://godbolt.org/z/hG5hnz59e

#include <optional>

struct S {
  int i;
};

void foo() {
  std::optional<S>().transform(&S::i);
}

Per https://en.cppreference.com/w/cpp/utility/optional/transform, the retur=
ned
type should always be computed via std::remove_cv_t<> on the invoke_result,=
 but
per
https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dblob;f=3Dlibstdc%2B%2B-v3/include/=
std/optional;hb=3DHEAD,
_Up consistently omits this.=