How to get the number of days in a given month in Ruby, accounting for year?

Question

I'm sure there's a good simple elegant one-liner in Ruby to give you the number of days in a given month, accounting for year, such as "February 1997". What is it?

Answer 1

This is the implementation from ActiveSupport (a little adapted):

COMMON_YEAR_DAYS_IN_MONTH = [nil, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

def days_in_month(month, year = Time.now.year)
   return 29 if month == 2 && Date.gregorian_leap?(year)
   COMMON_YEAR_DAYS_IN_MONTH[month]
end

Answer 2

How about:

require 'date'

def days_in_month(year, month)
  (Date.new(year, 12, 31) << (12-month)).day
end

# print number of days in Feburary 2009
puts days_in_month(2009, 2)

You may also want to look at Time::days_in_month in Ruby on Rails.