Expand a two-element array by an interval

array_expand.rb

class Array
  def expand(interval=1)
    raise "Can only expand two-element arrays" if self.size != 2
    raise "Can only expand numeric arrays" unless self.first.kind_of?(Numeric) && self.last.kind_of?(Numeric)

    result = [self.first]

    while result.last < self.last do
      next_value = result.last + interval

      if next_value < self.last
        result << next_value
      else
        result << self.last
      end
    end

    result
  end
end