Ruby: intersection between two ranges

require 'date'

class Range
  def intersection(other)
    return nil if (self.max < other.begin or other.max < self.begin) 
    [self.begin, other.begin].max..[self.max, other.max].min
  end
  alias_method :&, :intersection
end

p (Date.new(2011,1,1)..Date.new(2011,1,15)) & (Date.new(2011,1,10)..Date.new(2011,2,15))
#<Date: 2011-01-10 ((2455572j,0s,0n),+0s,2299161j)>..#<Date: 2011-01-15 ((2455577j,0s,0n),+0s,2299161j)>

You can try this to get a range representing intersection

range1 = Date.new(2011,12,1)..Date.new(2011,12,10)
range2 = Date.new(2011,12,4)..Date.new(2011,12,12)

inters = range1.to_a & range2.to_a

intersected_range = inters.min..inters.max

Converting your example:

class Range  
  def intersection(other)  
    raise ArgumentError, 'value must be a Range' unless other.kind_of?(Range)  

    inters = self.to_a & other.to_a

    inters.empty? ? nil : inters.min..inters.max 
  end  

  alias_method :&, :intersection  
end