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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/103295] constexpr std::string does not work for clang
Date: Wed, 17 Nov 2021 12:02:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103295

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #7)
> It just doesn't allow assignment through the pointer.

I think that's correct according to [class.union.general] p6:

"When the left operand of an assignment operator involves a member access
expression ([expr.ref]) that nominates a union member, it may begin the
lifetime of that union member, as described below."

`_M_local_buf[0] =3D 0;` is OK, but `auto p =3D _M_local_buf; p[0] =3D 0;` =
is not.=