With a one-line function you can retrieve the number of days in a given month. Month must be passed as a number (1 to 12.)

def DaysIn(MonthNum)
  (Date.new(Time.now.year, 12, 31).to_date << (12 - MonthNum)).day
end

1. def DaysIn(MonthNum): This line defines a function named DaysIn that takes one parameter, MonthNum, representing the month number (1 for January, 2 for February, etc.).
2. Date.new(Time.now.year, 12, 31).to_date << (12 - MonthNum): This line creates a Date object for the last day of the current year (Date.new(Time.now.year, 12, 31)) and then uses the << operator to subtract months from this date. (12 - MonthNum) calculates how many months to subtract to get to the desired month.
3. .day: This returns the day of the month, which, since the date has been adjusted to the last day of the desired month, will be the number of days in that month.

However, there’s a more straightforward way to achieve this in Ruby:

def DaysIn(month_num)
  Date.new(Time.now.year, month_num, -1).day
end

This revised function directly calculates the last day of the given month by setting the day parameter to -1, which Ruby interprets as the last day of the previous month. Thus, this yields the last day of month_num in the current year. This method is clearer and more idiomatic in Ruby.