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From: "andysem at mail dot ru" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/98978] Consider packing _M_Engaged in the tail
 padding of T in optional<>
Date: Fri, 05 Feb 2021 20:44:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98978

--- Comment #3 from andysem at mail dot ru ---
(In reply to Jonathan Wakely from comment #1)
> This would be an ABI break, and so not going to happen.

Is there no way to improve standard components implementation? I'd imagine =
you
could provide the new implementation in the new version inline namespace and
still support the old ABI for backward compatibility.

(In reply to Jonathan Wakely from comment #2)
> If we were going to do this, we could also make std::optional<bool> occup=
y a
> single byte, using one bit for the value and one for the engaged flag.

This would be more problematic as emplace(), value() and operator*() need to
return T&, which would not be possible.=