From: Matthew Lipper <matt@...>
Date: 2004-01-04T06:24:05+09:00
Subject: Problems Extending DateTime

Howdy,

I'm writing my first Ruby application and have a few super-newbie
questions, so bear with me...I'm trying to add date precision to the
existing Date and DateTime classes.

My first attempt involves a module with a simple nested value class and
a standalone subclass of DateTime:

require 'date'

module Runt
module DatePrecision

  YEAR=0
    ...
  HOUR_OF_DAY=3
    ...etc.

  HOUR_OF_DAY_PREC = Precision.new(HOUR_OF_DAY)
    
  def to_hour_of_day(arg)
    #DateTimes are immutable
    HOUR_OF_DAY_PREC.to_p(
                          DateTime,
                  *[arg.year,arg.mon,arg.day,arg.hour,0,0])
  end
 
  class Precision       
    include Comparable
    attr :precision 

    def initialize(prec)
      @precision = prec 
    end
        
    def <=>(other)
      self.precision <=> other.precision
    end
  
    def to_p(klass, *args) 
      klass.new(*args)  
    end                 
  end
end
end
--
require 'date'

class DateWithPrecision < DateTime 
     
  include Runt::DatePrecision 
     
  attr :precision  
 
  def initialize(*args)
    @precision = args.pop
    super(*args)
  end

  #This doesn't work either?!
  def initialize(yr=1,mon=1,day=1,hr=0,min=0,sec=0) 
    super(yr,mon,day,hr,min,sec) 
  end 
end

However when I do something like this:

day_precise
= DateWithPrecision.new(1998,12,12,14,58,32,HOUR_OF_DAY_PREC)

or even this

day_precise = DateWithPrecision.new(1998,12,12,14,58,32)

I get errors like the following:

ArgumentError: wrong number of arguments(6 for 3)
    dateprecisiontest.rb:116:in `initialize'
    dateprecisiontest.rb:116:in `initialize'
    /usr/lib/ruby/1.8/date.rb:1175:in `new0'
    /usr/lib/ruby/1.8/date.rb:1175:in `new'
    dateprecisiontest.rb:56:in `test_to_precision'

4 tests, 16 assertions, 0 failures, 1 errors

I can't seem to call Date/DateTime's constructor from my subclass; even
when I don't add or change arguments.

Is it, in fact, a bad idea to have a module create instance variables?
Is there another, simpler/better way of doing this?

I'm running Ruby 1.8.1 on RedHat 9.
 
Any feedback is greatly appreciated.

Thanks! 

Matt