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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/103923] is_invocable<const T &, ...> inexplicably fails
Date: Thu, 06 Jan 2022 16:00:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103923

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Maybe we don't actually need to do anything here. As the original testcase
shows, trying to actually use the map is still ill-formed:

        //T().m[T::K()]; // for extra fun

I'm not going to work on this for now, because the code is undefined, it's =
just
that we don't give a clear diagnostic about what the problem is. There's a
simple workaround, which is to not use the 'auto' return type.=