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<div class="moz-cite-prefix">On 9/7/19 9:11 PM, Zach Laine wrote:<br>
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<div dir="ltr">On Sat, Sep 7, 2019 at 7:31 PM Tom Honermann via
Lib <<a href="mailto:lib@lists.isocpp.org"
moz-do-not-send="true">lib@lists.isocpp.org</a>> wrote:<br>
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<div class="gmail-m_8939139310385341323moz-cite-prefix">On
9/7/19 8:27 PM, Tony V E wrote:<br>
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Pro",sans-serif,sans-serif;color:rgb(31,73,125);text-align:initial;background-color:rgb(255,255,255)">I
think we would want it to be measured in glyphs. </div>
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I agree that would be ideal, but...<br>
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<div>Stop right there. If that's ideal, let's do that. Or at
least, let's leave room for it to be done at some point.
Specifying CUs now prevents the ideal from ever being
realized. <br>
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There are other options. For example, a future extension could
allow specifying what units are to be used for field width.<br>
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Pro",sans-serif,sans-serif;color:rgb(31,73,125);text-align:initial;background-color:rgb(255,255,255)">Are
you suggesting code points because glyphs are too
hard?</div>
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I don't know how to achieve that. Field width doesn't
really work for alignment unless one assumes a monospace
font. We could measure in terms of extended grapheme
clusters, but EGCS width has changed over time (e.g.,
family emoji). That makes alignment dependent on both
display properties and Unicode version. And, of course,
this would drag in locale dependence as well.</div>
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<div>If you just count N=EGCs, you get the "right" answer. if
your terminal shows more or less than N characters, get a
new terminal. What I mean by this is that there should be
no consideration of fonts.</div>
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I see field width as either indicating storage (number of code
units) or alignment. The number of user perceived characters is not
useful for aligning text unless a monospace font is assumed.
Therefore, storage seems like the more useful measurement. This
also aligns with <tt>format_to_n</tt> and <tt>formatted_size</tt>
which, unless I'm mistaken, work in code units. (It would be nice
to clarify the wording for these as well; what is meant by "number
of characters in the character representation"?)
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<div>As for the need for a locale, I don't get that. Grapheme
breaking is simple, and requires no locale info. Do you
mean Unicode data? Picking a version and sticking with it
should be sufficient. No system that I know of has multiple
Unicode versions to pick from programatically.</div>
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For char and wchar_t, encoding is locale dependent. Think POSIX
LANG=C (probably ASCII or ISO-8859-1) vs LANG=C.UTF-8.<br>
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<div>Zach</div>
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