libc++ is using #define _LIBCPP_AUTO_CAST(expr) static_cast<typename decay <decltype((expr))>::type>(expr)
which has equivalent-ish semantics and inferior throughput. I suspect they would like to replace that with auto(expr) when possible. On Tue, Jan 4, 2022 at 11:47 AM Jonathan Wakely via SG10 < [email protected]> wrote: > > > On Tue, 4 Jan 2022 at 19:27, Barry Revzin via SG10 <[email protected]> > 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 <[email protected]> >> Date: Tue, Jan 4, 2022 at 1:25 PM >> Subject: Fwd: New issue: auto(x) should have a feature-testing macro >> To: Barry Revzin <[email protected]> >> Cc: Zhihao Yuan <[email protected]>, <[email protected]> >> >> >> 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 <[email protected]> >> Reply-To: Zhihao Yuan <[email protected]> >> To: William M. \(Mike\) Miller <[email protected]> >> CC: 'Arthur O'Dwyer' <[email protected]> >> >> 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. >> >> _______________________________________________ >> -- >> SG10 mailing list >> [email protected] >> https://lists.isocpp.org/mailman/listinfo.cgi/sg10 >> > -- > SG10 mailing list > [email protected] > https://lists.isocpp.org/mailman/listinfo.cgi/sg10 >
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