On Tue, 4 Jan 2022 at 19:27, Barry Revzin via SG10 <sg10_at_[hidden]>
wrote:

> Do you have an example of code that would benefit from such detection?
>

And what is the alternative code that you'd use in the #else branch?

If the alternative has equivalent semantics and performance, we don't need
a macro.




>
> ---------- Forwarded message ---------
> From: William M. (Mike) Miller <wmm_at_[hidden]>
> Date: Tue, Jan 4, 2022 at 1:25 PM
> Subject: Fwd: New issue: auto(x) should have a feature-testing macro
> To: Barry Revzin <barry.revzin_at_[hidden]>
> Cc: Zhihao Yuan <zy_at_[hidden]>, <arthur.j.odwyer_at_[hidden]>
>
>
> This suggestion should be decided by SG10 rather than being
> handled as a core language issue, so I'm forwarding it to the
> SG10 chair for consideration. Thanks.
>
>
> -------- Forwarded Message --------
> Subject: New issue: auto(x) should have a feature-testing macro
> Date: Tue, 14 Dec 2021 02:48:12 +0000
> From: Zhihao Yuan <zy_at_[hidden]>
> Reply-To: Zhihao Yuan <zy_at_[hidden]>
> To: William M. \(Mike\) Miller <wmm_at_[hidden]>
> CC: 'Arthur O'Dwyer' <arthur.j.odwyer_at_[hidden]>
>
> It's hard to detect whether it is legal to
> do auto(expr) after adopting P0849R8;
> A feature testing macro would help.
>
> There was no __cpp_auto (unlike
> __cpp_decltype_auto), but the direction
> of evolving auto(x) is probably not
> necessarily tied to `auto` in a
> declaration.
>
> Proposed resolution:
>
> This wording is relative to N4901.
>
> Add an entry to [tab:cpp.predefined.ft]
>
> Table 21: Feature-test macros
>
> | Macro name | Value |
> | -------- | ------- || <ins>__cpp_auto_cast</ins> | 202110L |
>
> --
> Zhihao Yuan, ID lichray
>
> The best way to predict the future is to invent it.
>
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