Why does Date.new not call initialize? - ruby

Question

I want to create a subclass of Date.
A normal, healthy, young rubyist, unscarred by the idiosyncrasy of Date's implementation would go about this in the following manner:
require 'date'
class MyDate < Date
def initialize(year, month, day)
#original_month = month
#original_day = day
# Christmas comes early!
super(year, 12, 25)
end
end
And proceed to use it in the most expected manner...
require 'my_date'
mdt = MyDate.new(2012, 1, 28)
puts mdt.to_s
... only to be double-crossed by the fact, that the Date::new method is actually an alias to Date::civil, which doesn't ever call initialize. In this case, the last piece of code prints "2012-01-28" instead of the expected "2012-12-25".
Dear Ruby-community, wtf is this?
Is there some very good reason for aliasing new, so that it ignores initialize, and as a result, any common sense and regard for the client's programmer's mental health?

Answer 1

You define initialize, but you create the new instance with new. new returns a new instance of the class, not the result of initialize.
You may do:
require 'date'
class MyDate < Date
def self.new(year, month, day)
#original_month = month
#original_day = day
# Christmas comes early!
super(year, 12, 25)
end
end
mdt = MyDate.new(2012, 1, 28)
puts mdt.to_s
Remark:
#original_month and #original_day are not available in this solution. The following solution extends Date, so you can access the original month and day. For normal dates, the values will be nil.
require 'date'
class Date
attr_accessor :original_month
attr_accessor :original_day
end
class MyDate < Date
def self.new(year, month, day)
# Christmas comes early!
date = super(year, 12, 25)
date.original_month = month
date.original_day = day
date
end
end
mdt = MyDate.new(2012, 1, 28)
puts mdt.to_s
puts mdt.original_month
But I would recommend:
require 'date'
class MyDate < Date
def self.create(year, month, day)
#original_month = month
#original_day = day
# Christmas comes early!
new(year, 12, 25)
end
end
mdt = MyDate.create(2012, 1, 28)
puts mdt.to_s
or
require 'date'
class Date
def this_year_christmas
# Christmas comes early!
self.class.new(year, 12, 28)
end
end
mdt = Date.new(2012, 1, 28).this_year_christmas
puts mdt.to_s