While I'm not sure it's a great idea to #define _, I think we should generally err on the side of providing macros for features than not - since we've missed a few over the years in ways that have mattered. 

Looks like the latest revision of the paper has one already.

Thanks!

Barry

On Thu, Jun 15, 2023 at 12:33 AM Corentin via Core <core@lists.isocpp.org> wrote:

+ SG10

This pattern is principally used for global variables, for which placeholders are not allowed, so I doubt this would be useful.

That being said, I defer to SG10 call, I'm happy to add one if people think it would have use cases.

Thanks!

On Wed, Jun 14, 2023 at 10:33 PM Christof Meerwald <cmeerw@cmeerw.org> wrote:

Not sure how widespread these workarounds are, but there are
stackoverflow questions related to this:

https://stackoverflow.com/questions/10379691/creating-macro-using-line-for-different-variable-names
https://stackoverflow.com/questions/1082192/how-to-generate-random-variable-names-in-c-using-macros
https://stackoverflow.com/questions/461062/c-anonymous-variables

(and I think I have seen real-world code using these workarounds)

So I think the use case for a feature-test macro would be something
like this:

#ifndef __unnamed_placeholder
#define CONCAT2(a, b) a ## b
#define CONCAT(a, b) CONCAT2(a, b)
#ifdef __COUNTER__
#define _ CONCAT(placeholder, __COUNTER__)
#else
#define _ CONCAT(placeholder, __LINE__)
#endif
#endif

void f()
{
    int _ = 1;
    int _ = 2;
}


Christof

--

https://cmeerw.org                             sip:cmeerw at cmeerw.org
mailto:cmeerw at cmeerw.org                   xmpp:cmeerw at cmeerw.org

_______________________________________________
Core mailing list
Core@lists.isocpp.org
Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/core
Link to this post: http://lists.isocpp.org/core/2023/06/14395.php

_______________________________________________
Core mailing list
Core@lists.isocpp.org
Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/core
Link to this post: http://lists.isocpp.org/core/2023/06/14397.php