support L in dayOfMonth field

[graingert]

This is to match the Last day in a month,

currently you have to use

Cron("55 23 30 4,6,9,11 ?")
Cron("55 23 31 1,3,5,7,8,10,12 ?")
Cron("55 23 28 2               ?")

but this still doesn't handle leap days properly

I'd like to be able to use:

Cron("55 23 L * ?")

[alonsodomin]

This is (unfortunately) not supported yet in 0.4, although I would really like to have it. Problem is that it might take a bit of time to get it working. The implementation itself is not trivial as I just wouldn't like to support L in day of month, the L itself represents additional constraints to the specific expression and, looking a more complete CRON implementations, we have a wide variety of thos type of constraints:

• L alone in day of month meaning the last day of the month
• nL in day of week, being n a number between 0 and 6 meaning the last day of week of a month
• nW in day of month, being n a number between 0 and 31 meaning the nearest weekday (Monday-Friday) to the given month day.
• n#m in day of week, being n a number between 0 and 6 and m a number between 0 and 5 meaning the mth day of the month.

Of course all of this needs to be implemented individually, the first part would be tackling the first two points (people would find it weird that L is supported in day of month but not supported in _day of week) and should put the ground work needed to implement the rest of the constraints.

Additionally, the documentation is missing mentioning the fact that not the whole cron standard (if there is one) is supported so this should be included ASAP.

As an end note, I believe that, providing that in cron4s there is a seconds field, the correct expression should be:

Cron("0 55 23 L * ?")