[Issue 20069] New: std.format digit grouping separator (aka thousands separator) needs to be revisited

d-bugmail at puremagic.com d-bugmail at puremagic.com
Sun Jul 21 16:33:00 UTC 2019


          Issue ID: 20069
           Summary: std.format digit grouping separator (aka thousands
                    separator) needs to be revisited
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: asumface at gmail.com

Currently the default separator used by std.format is always ','.
With the C locale (default) the number 123456.789 is thus formatted as
If another locale is activated, the output does not match the locale and
sometimes even becomes a mess:
writefln("%,f", 123456.789)
de_DE.UTF-8: "1,234,56,,789,000"
fr_FR.UTF-8: "1,234,56,,789,000"
fr_CH.UTF-8: "123,456.789,000"
en_IN.UTF-8: "123,456.789,000"
nl_NL.UTF-8: "1,234,56,,789,000"
hak_TW:      "123,456.789,000"
ps_AF:       "12,345,6٫,789,000"
unm_US:      "123,456.789,000"

The printf as defined by POSIX formats the same case as follows (I'd regard
this as the generally correct formatting):
printf("%'f", 123456.789)
C: "123456.789000"
de_DE.UTF-8: "123.456,789000"
fr_FR.UTF-8: "123 456,789000"
fr_CH.UTF-8: "123'456.789000"
en_IN.UTF-8: "1,23,456.789000" (non-uniform group size!)
nl_NL.UTF-8: "123456,789000"
hak_TW:      "12,3456.789000"
ps_AF:       "123٬456٫789000"
unm_US:      "12 34 56.789000"

Grouping after the decimal separator should probably be made optional as it
kind of is nonstandard behavior (scanf doesn't appear to handle such grouping,
for example) yet useful for human interfacing nonetheless. 
Grouping should, unless overridden, behave according to the active locale, for
the C locale, which is active by default, this means no grouping at all. This
is useful because a formatted number such as 100000 is otherwise ambiguous for
comma-decimal-users by default ("100,000").


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