RE: Empty export {}

[Gabriel Dos Reis]

Sending a second time as the mailer on my phone decided to send the message not to the list.

-------- Original message --------

From: Gabriel Dos Reis <g...@microsoft.com>

Date: 11/2/16 5:08 PM (GMT-08:00)

To: Dwayne Robinson <dwa...@microsoft.com>

Subject: RE: Empty export {}

The compiler error is consistent with the spec. The notation  "export {}" does not introduce any form of scope and shouldn't be tought of as empty namespace or empty blocks or any scope construct.

It is purely a convenience to group non-empty collection of export declarations.

In the scenario below, the code is more readable if you put the export with the declaration being conditionally exported.

-------- Original message --------

From: Dwayne Robinson <dwa...@microsoft.com>

Date: 11/2/16 5:01 PM (GMT-08:00)

To: Gabriel Dos Reis <g...@microsoft.com>

Subject: Empty export {}

Any empty export clause should be a nop rather than a compile error, which would be consistent with {namespaces, local scope, void functions} which all allow empty braces. Depending on project configuration, you may end up with an empty clause.

 

error C2059: syntax error: '}'

 

e.g.:

…   export { #ifndef _DEBUG     class DebugHelper ... #endif   #if PROJECT_CONFIG_USE_CAT     class Cat ... #endif   #if PROJECT_CONFIG_USE_DOG     class Dog ... #endif }   …

 

(yes, I’m merrily mixing the preprocessor with modules, but these are global defines for the whole project.)

[Gabriel Dos Reis]

Arg, wrong mailing list. Please, ignore.

[Jens Maurer]

On 11/03/2016 01:17 AM, 'Gabriel Dos Reis' via SG2 - Modules wrote:
> The compiler error is consistent with the spec. The notation "export {}" does not introduce any form of scope and shouldn't be tought of as empty namespace or empty blocks or any scope construct.
>
> It is purely a convenience to group non-empty collection of export declarations.

That seems inconsistent with what we do for linkage-specifications,
i.e. language linkage such as 'extern "C" { ... }'.

There's no new scope here, either, yet we do allow empty contents
as per the grammar in 7.5p2.

Please open an issue so that this can be discussed in a wider
audience.

Jens

> In the scenario below, the code is more readable if you put the export with the declaration being conditionally exported.
>
>
> -------- Original message --------
> From: Dwayne Robinson <dwa...@microsoft.com>
> Date: 11/2/16 5:01 PM (GMT-08:00)
> To: Gabriel Dos Reis <g...@microsoft.com>
> Subject: Empty export {}
>
> Any empty export clause should be a nop rather than a compile error, which would be consistent with {namespaces, local scope, void functions} which all allow empty braces. Depending on project configuration, you may end up with an empty clause.
>
>
>
> error C2059: syntax error: '}'
>
>
>
> e.g.:
>
> …
>
>
>
> export
>
> {
>
> #ifndef_DEBUG
>
> classDebugHelper ...
>
> #endif
>
>
>
> #ifPROJECT_CONFIG_USE_CAT
>
> classCat ...
>
> #endif
>
>
>
> #ifPROJECT_CONFIG_USE_DOG
>

> classDog ...

>
> #endif
>
> }
>
>
>
> …
>
>
>
> (yes, I’m merrily mixing the preprocessor with modules, but these are global defines for the whole project.)
>

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