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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/113064] assignement from temporary sometimes invokes
 copy-assign instead of move-assign operator
Date: Tue, 19 Dec 2023 15:54:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113064

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to m.cencora from comment #4)
> This also might be a just another symptom of the same root cause:
>=20
> struct bar
> {
>     bar() =3D default;
>=20
>     bar(const bar&);
>     bar(bar&&);
>=20
>     bar& operator=3D(const bar&);
>     bar& operator=3D(bar&&);
> };
>=20
> struct foo
> {
>     operator const bar& () const &;
>=20
>     operator bar& () &;
>=20
>     operator bar&&() &&;
> };
>=20
> void test()
> {
>     bar a =3D foo{}; // ok
>=20
>     a =3D foo{}; // not ok - ambiguous call, but why? &&-qualified looks =
like
> a better match
>=20
>     foo f;
>     a =3D f; // ok
>=20
>     a =3D static_cast<const foo&>(foo{}); // ok
> }

Here the error showed up in r9-6486:

commit c7e936dbc7f59ad09c28ef57e5399a4256061747
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Mar 11 23:19:22 2019 -0400

    PR c++/86521 - wrong overload resolution with ref-qualifiers.

    Here we were wrongly treating binding a const lvalue ref to an xvalue as
    direct binding, which is wrong under [dcl.init.ref] and [over.match.ref=
].=