On Sep 14, 2022, at 4:28 AM, Corentin via SG16 <sg16@lists.isocpp.org> wrote:

Hey folks.

How was the table of width in [format] derived? 

http://eel.is/c++draft/format#string.std-12.sentence-3

We have 2 issues here: Lack of explanation in the standard makes it hard to evolve that table,

and it does require maintenance as the Unicode standard evolves.

Reading the intent of https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1868r2.html,

We do want: 

• To treat 0-width codepoint as 1
• To treat emojis as 2
• To treat full width east asian as 2.  

https://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c 

I think a better specification would be given that we have a floating reference to UAX44,

to say that codepoints that have the Unicode property "Emoji_Presentation" or 

East_Asian_Width="W"  have a width of 2.

This ensures implementation remains coherent as Unicode evolves.

Thanks, 

Corentin

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