Today’s Ruby Tuesday is on Date#leap?.

Date#leap? operates on a Date object, and returns true if the year is a leap year in the Gregorian calender, or false if not.

Date.new(2015, 1, 4).leap?
=> false
Date.new(2012, 1, 1).leap?
# => true
Date.new(2017, 1, 1).leap?
# => false
Date.new(2000, 1, 1).leap?
# => true
Date.new(1900, 1, 1).leap?
# => false

By using Date#leap?, you don’t have to code the rules to check if a year is a leap year, or even have to double check the rules about when the century is a leap year.

There is also a class level version Date::leap?, that will take a integer value for the year, and return a true or false value.

Date.leap? 2015
# => false
Date.leap? 2012
# => true
Date.leap? 2017
# => false
Date.leap? 2000
# => true
Date.leap? 1900
# => false

Both the instance and class level versions of ‘leap?` can handle Year Zero, and negative years.

Date.leap? -1
# => false
Date.leap? -4
# => true
Date.leap? 0
# => true
Date.new(-4, 1, 1).leap?
# => true

I wouldn’t know if that is valid myself, but that is why it is useful to have this a built in method on Date instead of having to code it up myself.

–Proctor