Generate an array of dates on mday (the day-of-month, 1-31). For months in which the mday is not present, no date will be generated.

The period is a year, unless month is non-nil, in which case it is just that month.

Compare to Date.new(), which allows a single Date to be created with similar criteria.

Generate an array of dates on wday (the day-of-week, 0-6, where 0 is Sunday).

If n is specified, only the nth occurrence of wday within the period will be generated. If n is positive, the nth occurrence from the beginning of the period will be returned, if negative, the nth occurrence from the end of the period will be returned.

The period is a year, unless month is non-nil, in which case it is just that month.

Examples:

• DateGen.bywday(2004, nil, 1, 9) => the ninth Sunday in 2004
• DateGen.bywday(2004, nil, 1) => all Sundays in 2004
• DateGen.bywday(2004, nil, 1, -2) => second last Sunday in 2004
• DateGen.bywday(2004, 12, 1) => all sundays in December 2004
• DateGen.bywday(2004, 2, 2, -1) => last Tuesday in February in 2004
• DateGen.bywday(2004, -2, 3, -2) => second last Wednesday in November of 2004

Compare to Date.bywday(), which allows a single Date to be created with similar criteria.

Generate an array of a week‘s dates, where week is specified by year, mon, day, and the weekstart (the day-of-week that is considered the "first" day of that week, 0-6, where 0 is sunday).