Operator Overloading in ruby

custom_object.rb

class CustomObject
  attr_reader :a, :b
  def initialize(a, b)
    @a = a
    @b = b
  end
  
  def ==(other)
    (@a + other.a) == (@b + other.b)
  end
  
  def +(other)
    if other.class == self.class
      return CustomObject.new(@a + other.a, @b + other.b)
    elsif other.class == 1.class
      @a += other
      @b -+ other
      self
    end
  end
end

object1 = CustomObject.new(2, 3)
object2 = CustomObject.new(4, 3)
object1 == object2 # true

object1 == object1 # false

object3 = object1 + object2 # create new object
object3 + 1

# point_2d.rb
class Point2D
  attr_reader :x, :y
  def initialize(x, y)
    @x = x
    @y = y
  end

  def ==(other)
    (@x - other.x) == 0 && (@y - other.y) == 0
  end

  def +(other)
    Point2D.new(@x + other.x, @y + other.y)
  end
end

p1 = Point2D.new(1, 1)
p2 = Point2D.new(1, 1)

p1 == p2
p1 + p2

Another usefull tip is to override spaceship operator to be able to sort an array of objects.

def CustomObject
#...
  def <=>(other)
    return nil unless other.is_a?(self.class)
    other.a <=> @a
  end

end

object1 = CustomObject.new(2, 3)
object2 = CustomObject.new(4, 3)
object3 = object1 + object2

[object1, object2, object3].sort
# => [
#          [0] #<CustomObject:0x007f92ae511600 @a=6, @b=6>,
#          [1] #<CustomObject:0x007f92ae579bb0 @a=4, @b=3>,
#          [2] #<CustomObject:0x007f92ae599ed8 @a=2, @b=3>
#      ]