I wrote a little cron expression parser in Fantom. https://bitbucket.org/saltnlight5/fan-examples/src/c2baba25527d/scripts/cron.fan

Is there a better way to handle DateTime when I need to reset a field value? I have to use "make" and refill original values, and I have to check for overflow to next field. It would be nice if DateTime would have a set(FiedType, fieldValue) method.

~Zemian

For adding fields you typically use + some duration. It handles overflow, and can get be especially nice if you switch to Date for managing dates. I do an extreme amount of time manipulation, but never actually wanted to set a specific field. Seems useful, but at the same time I don't want to add a constant or method for every field - that would be a ton of clutter for marginal value.

So I think it is really just figuring out a nice API that is only one (or a couple) of methods. Maybe something like using a Locale pattern:

DateTime setField(Str fieldPattern, Obj val)

dt.setField("Y", 2010)

How about a minor change to that proposal:

enum class DateTimeField { // Yes - this needs a better name
  year,
  month,
  day,
  ...
}

class DateTime {
  ...
  @Operator
  DateTime setField(DateTimeField fld, Obj val) {}
  ...
}

So you could then do:

dt[DateTimeField.year] = 2010

I tend to like enum more than free text for type. In any case, a method is better than no better though. :)