[threeten-dev] Possible addition of pattern letters in CLDR

[Stephen Colebourne]

On 14 December 2012 04:00, Dan Chiba <dan.chiba at oracle.com> wrote:
> Thank you for filing the CLDR ticket. Your proposal sounds great. May I ask
> the status of the shortest GMT format? When could it be implemented by
> vendors?
>
> As for punctuations, I think comma and dot are already locale sensitive for
> number formatting, so it would be easy for people to understand how the
> locale sensitive punctuations for date time formatting work. Because the
> predefined formatting patterns for locales have the separators for date and
> time fields and they are commonly used, it doesn't seem to be an issue that
> there is no locale sensitive pattern letter for them. So I think I am only
> interested in the decimal separator for fractional seconds. Alternatively,
> if CLDR had predefined locale sensitive patterns with fractional seconds,
> that could also be a solution. For instance, a predefined common pattern to
> print hour, minute, second and millisecond for the US locale may look like
> this:
>
> <dateFormatItem id="HmsS">HH:mm:ss.SSS</dateFormatItem>

For everyones info, we previously had a letter "f", which meant output
a fraction with a localized decimal point

 HH:mm:ss.SSS - always use dot
 HH:mm:ssfSSS - use localized decimal point (old JSR-310)
 HH:mm:ssfff - possible localized decimal point alternative

in JSR-310 we used "f" for exact length and "ff" for up to nanos length:
 HH:mm:ssfSSS - print 3 digit fraction
 HH:mm:ssfSS - print 2 digit fraction
 HH:mm:ssffSSS - print at least 3 digits and a maximum of 9

We don't have "f" right now, but there is the germ of a good idea in there.

> Would you elaborate what "p" (prefix for padding) does? Does it make sense
> to have it defined in LDML as well?

Some examples:

 MMM-dd -> "Dec-07"
 MMM-d -> "Dec-7"
 MMM-ppd -> "Dec-*7"
 MMM-pppd -> "Dec-**7"

(using * instead of space for clarity in this email)

So, the "p" pattern letter means "pad the next field with spaces on
the left to a width determined by the number of p characters". Thus
"pp" means "pad the next field to a width of 2.

I can't think how a pad width of 1 would be useful however, so it
would be clearer to reduce the "p" level by one:

 MMM-pd -> "Dec-*7"
 MMM-ppd -> "Dec-**7"

That would make "p" mean "pad the next field with spaces on the left
to a width determined by the total of the number of p and value
characters".

So, "p" now means "pad the next field to a width of 2.

It would be good to see "p" in LDML. We would need to agree on one of
the two definitions above.

> Also, do you think 310 can suppor the shortest GMT format if its status is
> ready for implementation?

If the data is available in Java, we can find a way to support it,
time permitting.

Stephen