| -----Original Message-----
| From: Bryce Adelstein Lelbach aka wash <brycelelbach@gmail.com>
| Sent: Wednesday, July 10, 2019 2:37 PM
| To: Gabriel Dos Reis <gdr@microsoft.com>
| Cc: Tom Honermann <tom@honermann.net>; modules@lists.isocpp.org;
| sg15@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@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 ;"
| https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Feel.is
| %2Fc%2B%2Bdraft%2Fcpp.include%237&data=02%7C01%7Cgdr%40mic
| rosoft.com%7C57adb75b608743ebf6e208d7057ed5d4%7C72f988bf86f141af
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|
| 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