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### 3818. Exposition-only concepts are not described in library intro

Section: 16.3.3 [conventions] Status: WP Submitter: Tim Song Opened: 2022-11-08 Last modified: 2022-11-17

Priority: Not Prioritized

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Discussion:

This is the resolution for GB-074.

The comment is:

> 16.3.3.2 [expos.only.func] introduces exposition-only function templates. 16.3.3.3.2 [expos.only.types] introduces exposition-only types. 16.3.3.5 [objects.within.classes] introduces exposition-only private members.

> There is nothing about exposition-only concepts, despite them being used extensively in the library clauses.

> The same problem exists for exposition-only variable templates.

[Kona 2022-11-08; Move to Immediate status]

Previous resolution [SUPERSEDED]:

> 1. Modify 16.3.3.2 [expos.only.func] as indicated, changing the stable name:

>    > 16.3.3.2 Exposition-only functions entities [expos.only.func entity]

>    > -1- Several function templates entities defined in 17 [support] through 33 [thread] and D [depr] are only defined for the purpose of exposition. The declaration of such a function an entity is followed by a comment ending in exposition only.

> 2. Strike 16.3.3.3.2 [expos.only.types] as redundant:

>    > 16.3.3.3.2 Exposition-only types [expos.only.types]

>    > -1- Several types defined in 17 [support] through 33 [thread] and D [depr] are defined for the purpose of exposition. The declaration of such a type is followed by a comment ending in exposition only.

>    > [Example 1:

>    > >     namespace std {
>    > >       extern "C" using some-handler = int(int, void*, double);  // exposition only
>    > >     }

>    > The type placeholder `some-handler` can now be used to specify a function that takes a callback parameter with C language linkage. — end example]

[2022-11-09 Tim reopens]

During LWG review of 3753, it was pointed out that typedef-names are not necessarily entities.

[Kona 2022-11-11; Move to Immediate]

[2022-11-12 Approved at November 2022 meeting in Kona. Status changed: Immediate → WP.]

Proposed resolution:

This wording is relative to N4917.

1. Modify 16.3.3.2 [expos.only.func] as indicated, changing the stable name:

   > 16.3.3.2 Exposition-only functions entities, etc. [expos.only.func entity]

   > -1- Several function templates entities and typedef-names defined in 17 [support] through 33 [thread] and D [depr] are only defined for the purpose of exposition. The declaration of such a function an entity or typedef-name is followed by a comment ending in exposition only.

2. Strike 16.3.3.3.2 [expos.only.types] as redundant:

   > 16.3.3.3.2 Exposition-only types [expos.only.types]

   > -1- Several types defined in 17 [support] through 33 [thread] and D [depr] are defined for the purpose of exposition. The declaration of such a type is followed by a comment ending in exposition only.

   > [Example 1:

   > >     namespace std {
   > >       extern "C" using some-handler = int(int, void*, double);  // exposition only
   > >     }

   > The type placeholder `some-handler` can now be used to specify a function that takes a callback parameter with C language linkage. — end example]