Interesting. I was in the room too and came out with a different impression :-)

Anyway, if include translation is mandatory the we do have serious deployment and usability problem...

— Gaby

> On Jul 10, 2019, at 3:23 PM, Bryce Adelstein Lelbach aka wash <brycelelbach_at_gmail.com> wrote:
>
> FWIW my impression was that LEWG understood that P1502R0 implies that
> standard library includes will always get translated.
>
> (While I did raise concerns about the implications of this, I
> wholeheartedly support P1502R0)
>
>> On Wed, Jul 10, 2019 at 3:15 PM Michael Spencer <bigcheesegs_at_gmail.com> wrote:
>>
>>> On Wed, Jul 10, 2019 at 2:51 PM Gabriel Dos Reis via SG15 <sg15_at_lists.isocpp.org> wrote:
>>>
>>>
>>>
>>> | -----Original Message-----
>>> | From: Bryce Adelstein Lelbach aka wash <brycelelbach_at_gmail.com>
>>> | Sent: Wednesday, July 10, 2019 2:37 PM
>>> | To: Gabriel Dos Reis <gdr_at_microsoft.com>
>>> | Cc: Tom Honermann <tom_at_honermann.net>; modules_at_lists.isocpp.org;
>>> | sg15_at_lists.isocpp.org
>>> | Subject: Re: [isocpp-modules] [SG15] Determining identity like #pragma once
>>> |
>>> | On Wed, Jul 10, 2019 at 11:02 AM Gabriel Dos Reis <gdr_at_microsoft.com>
>>> | wrote:
>>> | >
>>> | > You are implying that the include translation is mandatory. Is that your
>>> | argument?
>>> |
>>> | It is my belief that include translation is mandatory.
>>> |
>>> | "If the header identified by the header-name denotes an importable
>>> | header ([module.import]), the preprocessing directive is instead
>>> | replaced by the preprocessing-tokens: import header-name ;"
>>> | http://eel.is
>>> | %2Fc%2B%2Bdraft%2Fcpp.include%237&amp;data=02%7C01%7Cgdr%40mic
>>> | rosoft.com%7C57adb75b608743ebf6e208d7057ed5d4%7C72f988bf86f141af
>>> | 91ab2d7cd011db47%7C1%7C0%7C636983914618863287&amp;sdata=JsvGf
>>> | 0RfvcjOSMF6q%2FfsW60hhKx5TI%2F1K42M8PdRbOU%3D&amp;reserved=0
>>> |
>>> | To me, that reads as "including an importable header must be
>>> | translated to an import".
>>> |
>>> | Was that the original design intent?
>>>
>>> The original intent, as I understood it, was to *permit* include translation.
>>>
>>> A mandatory include translation is practically unworkable for the MSVC audience. I wouldn't be surprised at all if that is the case of other compilers too.
>>>
>>> A permission, as opposed to a requirement, would allow adoption of header import as better and principled replacement of PCH. Otherwise, it would create more problems than it solves.
>>>
>>> -- Gaby
>>>
>>
>> I was there for most of the LEWG discussion on D1502R0 (Standard library header units for C++20), and I can not say with confidence that the room understood the implication that this would require include translation. There don't seem to be any minutes of the discussion on the wiki.
>>
>> However, the paper does explicitly point this out:
>>
>>> This has a number of consequences, such as:
>>> * ...
>>> * Existing #includes of standard library headers transparently turn into module imports in C++20
>>
>> It also in the wording explicitly adds the headers to the set of implementation-defined importable headers.
>>
>>> An importable header is a member of an implementation-defined set of headers that includes all importable C++ library headers (16.5.1.2 [headers])
>>
>> So I believe the author's intent was to require that include translation occurs.
>>
>> + Richard so we can ask them :)
>>
>> - Michael Spencer
>
>
>
> --
> Bryce Adelstein Lelbach aka wash
> CUDA Core C++ Libraries Lead @ NVIDIA
> ISO C++ Library Evolution Incubator Chair
> ISO C++ Tooling Chair
> CppCon and C++Now Program Chair
> CUDA Convert and Reformed AVX Junkie
>
> Sleep is for the weak
> --