From: Brian Candler <B.Candler@...>
Date: 2007-03-16T15:15:06+09:00
Subject: Re: Calculating the age given DOB

On Fri, Mar 16, 2007 at 04:28:16AM +0900, Rick DeNatale wrote:
> rick@frodo:/public/rubyscripts$ cat datemath.rb
> #!/usr/math/bin/ruby
> 
> 
> require 'date'
> class Date
> 
>  # return the number of days since the beginning of the year
>  def years_since(date)
>    # The parens in the expression below aren't strictly necessary, but
>    # I think it makes what's going on a little bit clearer.
>    first, last = *(self >= date ? [date, self] : [self, date])
>    (self <=> date) * ((last.year - first.year) - (first.yday >
> last.yday ? 1 : 0))
>  end
> end

I guess the most generic solution would return the number of [years, months,
days] between two dates - so you can say "You are 31 years, 3 months and 4
days old"

Anyone can work out their own age in this format, so the algorithm should be
clear, albeit probably messy to implement.