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From: "sshannin at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/96269] optional comparison with nullopt fails
Date: Tue, 21 Jul 2020 16:17:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96269

--- Comment #2 from sshannin at gmail dot com ---
(In reply to Jonathan Wakely from comment #1)
> Your operator=3D=3D should be const-qualified.

I don't disagree. I can also fully remove the operator=3D=3D and it compile=
s as
well (why should the presence of the non-const operator=3D=3D cause the com=
parison
with nullopt in one direction to instantiate it).

But yeah, I lost something in my reduction in there. I think the main point=
 is
that one direction of the comparison instantiates the templated operator=3D=
=3D and
the other doesn't.

Consider this version of X instead, which avoids the const issues:
struct X {
  int y;

  template <typename T>
  bool operator=3D=3D(const T&o) const {
    return y =3D=3D o.summary();
  }
};

We again end up instantiating X's operator=3D=3D (even though we wouldn't c=
all it)
in the FLIP case (and thus fail to compile), but in the non-flip case
everything seems fine.=