On Mon, Mar 24, 2025 at 11:20 AM Filip via Std-Proposals <std-proposals_at_[hidden]> wrote:

P.S.

Maybe worth mentioning is the fact that I never want to include a file more than once.

I do occasionally use X-macros that only work with repeated includes. Also, Boost has some weird macro stuff that relies on it. But, you are right that 99.99% of the time I just want to include the header once.

P.S.S.

Should we not standardize include once since we have a non standard option available everywhere?

Shouldn’t we standardize everything that’s useful and thus lower the chance for bugs?

If we have a good solution I'd agree. Just standardizing how #pragma once currently works just with a different keyword is slightly different. Yes, it is useful and yes, it generally lowers the chance for bugs. However, the implementations themselves have (incompatible) "bugs" in the sense that it will not always work. If you run into this problem there is no way to fix it yourself (especially when it occurs because of 3rd party libraries). So, if this feature will be standardized, it needs to be better than #pragma once and it needs to work 100% of the time. Nobody has solved this problem so far, so I'd rather advocate for keeping the status quo. (I personally don't trust #pragma once and always use include guards. I also spend less than 1% of my time writing include guards. Chance of undetected bugs in include guards is really low (copy'n'paste???).)

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