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From: "bspencer at blackberry dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/99058] New: Consider adding a note about
 std::optional ABI break to the C++17 status table
Date: Wed, 10 Feb 2021 13:07:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99058

            Bug ID: 99058
           Summary: Consider adding a note about std::optional ABI break
                    to the C++17 status table
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bspencer at blackberry dot com
  Target Milestone: ---

In this table

https://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2017

the row labelled "Library Fundamentals V1 TS Components: optional" says it's
supported since "7.1" and references Note 1, but there's no mention of the =
ABI
break between 7.x and 8.x.

Perhaps I was misusing this table, but I interpreted "supported since 7.1" =
to
mean that if I compile against 7.1 headers, my code will remain ABI compati=
ble
against future versions of the library _and_ other code compiled against fu=
ture
versions of the headers.  This ABI break caught me by surprise, and even th=
ough
these versions are older now, it seems worthwhile to at least mention the b=
reak
in a note to help others.

BTW, this particular example also happens to come up as a question in Marsh=
all
Clow's recent talk on the topic of standard library ABIs.  See
https://youtu.be/7RoTDjLLXJQ?t=3D3191

Thanks.=