The polls that were taken before this one indicated that both languages are headed towards distinct types that behave similarly in certain ways, but distinctly in other ways, and yet it was repeated that the goal was that if a program using those types compiles in both C and C++, then the runtime semantics should be the same. And that wasn't happening. Consequently, pretending that the types in C++ were aliases to the types in C was just plain misleading and wrong. If we are concerned about economic harms because of differences, there subtle differences should dissuade us to purse an "type aliasing" semantics.

-- Gaby

-----Original Message-----
From: Aaron Ballman <aaron_at_[hidden]>
Sent: Thursday, October 7, 2021 8:55 AM
To: WG14/WG21 liaison mailing list <liaison_at_[hidden]>
Cc: Tom Honermann <tom_at_[hidden]>
Subject: Re: [wg14/wg21 liaison] C and C++ Compatibility SG meeting summary for Oct 06, 2021

On Thu, Oct 7, 2021 at 11:39 AM Tom Honermann via Liaison
<liaison_at_[hidden]> wrote:
>
> Thank you for hosting the meeting yesterday, Aaron!

My pleasure, I'm glad it was a productive meeting, thank you for participating!

> With regard to this poll: Should the _Float* C names be available
> (through some means) in C++ and be used as the types behind the
> std::float* aliases?
>
> The SA vote rationale was "My reasons against were that similar but
> slightly incompatible types is not good for the same names. ...."
>
> Previous polls had consensus to align the usual arithmetic conversions
> between C and C++, but did not have consensus for applying the C++
> implicit conversion rules to C. With regard to the SA rationale above,
> is the "slightly incompatible types" concern directed at those
> differences in the implicit conversion rules? Or is the concern over
> other differences? If the latter, a list of notable differences would be
> useful.

I'll leave it to the person who made the comments to explain further,
but my personal interpretation of the comment was that there was
unease with exposing the C names in C++ unless the semantics were
identical and there are cases where the semantics are compatible for a
well-formed program in both languages but not identical across
languages. If I have this wrong, hopefully I'll be corrected.

> My understanding is that the intent of P1467R4, and as stated by the
> author yesterday, is that these types would have the same semantics in
> each language with the only exception being that, in some cases, a use
> may be ill-formed in one language and not the other (e.g., the
> differences in the implicit conversion rules).

This matches my understanding of the authors' intent with P1467.

~Aaron

>
> Tom.
>
> On 10/7/21 8:57 AM, Aaron Ballman via Liaison wrote:
> > The meeting minutes from the Oct 2021 special session on
> > floating-point types can be found at:
> > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki.edg.com%2Fbin%2Fview%2FWg21telecons2021%2FTeleconference2021-10-06&amp;data=04%7C01%7Cgdr%40microsoft.com%7Ca30052ddbd7c405d2fb508d989aacfc1%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637692189018702310%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=LlvJC6uabn09HKOQ5C7koIWueB8SPAuz2d5Sht%2BOnfU%3D&amp;reserved=0.
> > The WG14 minutes will be posted to the document log in the near
> > future.
> >
> > Big thanks to Rajan Bhakta for taking minutes, and to all the
> > attendees for having such a productive special session!
> >
> > ~Aaron
> > _______________________________________________
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