A Ruby Triangle Class.

triangle.rb

class Triangle
  InvalidTriangleError = Class.new ArgumentError
  
  attr_accessor :a, :b, :c
  
  def initialize a, b, c
    @a, @b, @c = [a, b, c].sort
    raise InvalidTriangleError unless valid_triangle?
    @type = triangle_type
  end
  
  private
  
  def valid_triangle?
    !!(@a > 0 && @a + @b > @c)
  end
  
  def triangle_type
    [:equilateral, :isosceles, :scalene][[@a, @b, @c].uniq.size - 1]
  end
end