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Re: [SG16-Unicode] NL 029 : Disallow zero-width and control characters

From: Zach Laine <whatwasthataddress_at_[hidden]>
Date: Thu, 24 Oct 2019 19:18:07 -0500
Is this a real problem that is biting people right now? Are people using
these characters in identifiers and causing great upheaval? This seems of
the lowest possible priority to me, and not at all C++20-related.


On Thu, Oct 24, 2019 at 5:25 PM Steve Downey <sdowney_at_[hidden]> wrote:

> SG16 has an NB comment to deal with! Tom has already scheduled it for
> Belfast. It's basically that the list of allowed code points have some
> interesting control characters like zero width joiners and RTL modifiers.
> https://github.com/cplusplus/nbballot/issues/28
> There's also an issue that JF raised earlier:
> https://github.com/sg16-unicode/sg16/issues/48
> Improve support for Unicode characters in identifiers
> Relevant unicode standard:
> https://unicode.org/reports/tr31/ UNICODE IDENTIFIER AND PATTERN SYNTAX
> Which is complicated because it allows things like identifiers written in
> Farsi which requires zwj for disambiguation, and suggests regex to detect
> particular allowed identifiers. It's fairly dense, and I haven't digested
> it yet, but it looks like there might be allowed ways to exclude that.
> Plus tailoring would be needed because C++ disallows some characters such
> as '$' which might otherwise be allowed. This is also discussed in TR31.
> My feeling on the comment is that it's not a new issue for C++20, so it's
> not clear that it has to be fixed for C++20. I believe it should be fixed,
> but it ought to be fixed in a principled manner, and that likely means
> TR31.
> We would also have to discuss if emoji are allowed in identifiers. TR31
> does not strictly disallow them. The TonyTable shall be interesting.
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Received on 2019-10-25 02:18:19