addeable_extender.rb

module AddableExtender
  def define_adder(*keys)
    define_method :+ do |other|
      result = keys.map { |key| send(key) + other.send(key) }
      self.class.new(*result)
    end
  end
end

Point = Struct.new(:x, :y) do
  extend AddableExtender

  define_adder(:x, :y)

  # オーバーライドして定義ができない
  def +(other)
    puts ":+ called"
    super(other) #=> `+': super: no superclass method `+' for #<struct Point x=42, y=4> (NoMethodError)
  end
end

p Point.new(42, 4) + Point.new(10, 1)